SYNTHESIS OF THE PHOSPHORUS–NITROGEN SKELETON

Chapter 4 SYNTHESIS OF THE

PHOSPHORUS-NITROGEN

SKELETON

A . General Survey of Synthetic Routes A l a r g e n u m b e r of p h o s p h o r u s - n i t r o g e n c o m p o u n d s h a v e b e e n d e s c r i b e d in the literature. S o m e are prepared by direct synthesis, a n d others are obtained by substitution reactions performed o n suitable precursors. In this chapter w e will c o n s i d e r t h e d i r e c t s y n t h e s i s r o u t e s , a n d s u b s t i t u t i o n p r o c e s s e s will b e d i s c u s s e d in C h a p t e r s 5 t h r o u g h 1 4 . A l t h o u g h m a n y d i r e c t s y n t h e t i c r o u t e s t o p h o s p h o r u s - n i t r o g e n c o m p o u n d s h a v e b e e n d e s c r i b e d , m o s t of t h e s e m e t h o d s fall i n t o a few g e n e r a l c a t e g o r i e s , a n d t h e s e a r e c o n s i d e r e d b e l o w in t u r n . O n e reaction, the t r e a t m e n t of h a l o p h o s p h o r a n e s with a m m o n i u m halides, h a s b e e n s t u d i e d so extensively t h a t , in a d d i t i o n t o b e i n g m e n t i o n e d in t h e g e n e r a l s u r v e y , it is c o n s i d e r e d in g r e a t e r d e t a i l in S e c t i o n B .

1. S y n t h e s i s o f C y c l o - a n d

a. Interaction

Polyphosphazenes

of Halophosphoranes

with Ammonium

H a l o p h o s p h o r a n e s react with a m m o n i u m phazenes, according to the general e q u a t i o n

Halides

h a l i d e s t o yield

cyclophos-

1 - 7 1

η R P X + η N H X -> (NPR )„ + An HX 2

3

4

2

T h e g r o u p R can be chloro, b r o m o , or an organic unit, and the halogen atom, X , c a n b e c h l o r o o r b r o m o . T y p i c a l l y , t h e r e a c t i o n t a k e s p l a c e in a b o i l i n g h a l o genated solvent such as s-tetrachloroethane or chlorobenzene. Cyclic trimers a n d t e t r a m e r s a r e u s u a l l y f o r m e d in t h e g r e a t e s t yields, a l t h o u g h s m a l l e r 97

98

4.

SYNTHESIS OF THE P H O S P H O R U S - N I T R O G E N SKELETON

a m o u n t s o f cyclic p e n t a m e r s , h e x a m e r s , e t c . , a n d l i n e a r species c a n a l s o b e isolated. T h e m o s t extensively s t u d i e d r e a c t i o n is t h e o n e b e t w e e n p h o s p h o r u s p e n t a c h l o r i d e a n d a m m o n i u m c h l o r i d e t o yield t h e s t a b l e , w h i t e , c r y s t a l l i n e h e x a chlorocyclotriphosphazene, (NPC1 ) , and octachlorocyclotetraphosphazene, ( N P C 1 ) 4 . ~ T h e o v e r a l l r e a c t i o n s c h e m e is 2

1

3

3 5

2

η PC1 + η NH C1 5

^ > (NPC1 ) + (NPCI ) + · · ·

4

2

3

2

4

T h i s is o n e of t h e m o s t i m p o r t a n t r e a c t i o n s in p h o s p h a z e n e c h e m i s t r y , since it c o m p r i s e s t h e c h e a p e s t a n d m o s t c o n v e n i e n t first s t e p t o t h e s y n t h e s i s of t h e m a j o r i t y of c y c l o - a n d p o l y p h o s p h a z e n e s . I t is a l s o t h e b a s i s o f a m a n u f a c t u r i n g p r o c e s s for c h l o r o c y c l o p h o s p h a z e n e s . 1 3 - 2 2

A s i m i l a r r e a c t i o n is e m p l o y e d for t h e p r e p a r a t i o n of zenes. T h e g e n e r a l e q u a t i o n is

bromophospha-

4 0 - 5 1

η PBr + η Br + η NH Br 3

2

4

~~ " > (NPBr ) + (NPBr ) + · · · 4

HBr

2

3

2

4

T h e l o w e r b r o m o c y c l o p h o s p h a z e n e s a r e s t a b l e , w h i t e , c r y s t a l l i n e solids. T h e y a r e m o r e sensitive t o a t m o s p h e r i c m o i s t u r e t h a n a r e t h e c h l o r o d e r i v a t i v e s . A l t h o u g h fewer cyclic b r o m o p h o s p h a z e n e h o m o l o g u e s h a v e b e e n r e p o r t e d t h a n for t h e ( N P C 1 ) „ o r ( N P F ) „ series, species u p t o t h e cyclic h e x a m e r h a v e been d e s c r i b e d a n d h i g h e r cyclic h o m o l o g u e s u n d o u b t e d l y c a n b e i s o l a t e d . 2

2

4 8 , 4 9

M i x e d c h l o r o - b r o m o c y c l o p h o s p h a z e n e s a r e p r e p a r e d b y t h e u s e of a n a p p r o p r i a t e m i x t u r e of p h o s p h o r u s h a l i d e a n d a m m o n i u m h a l i d e , a s i l l u s t r a t e d by the following e q u a t i o n : 4 3

3 PC1 + 3 Br + 3 NH Br 3

2

4

^ " ^ " ^ S

N P C l B r + 12 HX 3

110°C

3

2

4

Phosphorus tribromide, phosphorus pentachloride, and a m m o n i u m chloride give N P C l B r , w h i l e p h o s p h o r u s t r i c h l o r i d e , b r o m i n e , a n d a m m o n i u m b r o ­ m i d e yield N P C l B r . 3

3

4

2

4 3

3

3

2

4

O r g a n o c y c l o p h o s p h a z e n e s are synthesized by similar m e t h o d s . For e x a m p l e , l , 3 , 5 - t r i p h e n y l - l , 3 , 5 - t r i c h l o r o c y c l o t r i p h o s p h a z e n e is p r e p a r e d f r o m phenyltetrachlorophosphorane and a m m o n i u m chloride, according to the reaction 5 3 - 6 9

Ph 3 PhPCl + 3 NH C1 4

4

>

CL I P\ Ph' ^

x

/

C1 l| / P h Ρ C1 X

+ 12 HC1 (Refs. 57, 60, 65)

99

A. GENERAL S U R V E Y OF SYNTHETIC R O U T E S

S i m i l a r l y , d i p h e n y l t r i c h l o r o p h o s p h o r a n e a n d a m m o n i u m c h l o r i d e yield fully phenylated cyclophosphazenes by the overall process η Ph PCl + η NH C1 2

3

An

> (NPPh ) + (NPPh ) +

H C l

4

2

3

2

4

(Refs. 54, 55) O t h e r related reactions are η PhPBr + η Br 4- η NH Br 2

2

4

4

"

H B r

>

(NPBrPh) + (NPBrPh) 3

4

(Refs. 63, 64) η Me PCl + η NH C1 2

3

η Et PCl + 4n N H 2

*" ' > (NPMe ) + (NPMe ) 4 (Ref. 67) H C

4

3

2

3

2

4

(NPEt ) + 3/i NH C1

3

2

n

4

(Ref. 68) 3 M e N P C l + 12 N H 2

4

> [NP(CI)NMe ] + 9 NH C1

3

2

7

2

3

(Ref. 39)

4

-4/7HC1

"(C F ) PC1 + «NH C1 3

3

> [NP(C F ) ] + [NP(C F ) ]

4

3

7

2

3

3

7

2

(Ref. 69a)

4

A m o r e d e t a i l e d c o n s i d e r a t i o n of t h i s r e a c t i o n is given in S e c t i o n Β of t h i s chapter. b . Cyclization

of Linear

Phosphorus-Nitrogen

Compounds

Cyclophosphazenes are formed when a linear p h o s p h a z e n e with terminal a m i n o groups reacts with a h a l o p h o s p h o r a n e . " 7 2

T h e r e a r e a n u m b e r of

7 7

v a r i a t i o n s t o t h i s t y p e of s y n t h e s i s , b u t t y p i c a l e x a m p l e s a r e s h o w n in t h e following scheme: Ph P.^N.-^PPh 2

I

'C1 2

G

pels

Ph P^^PPh 2

-HCl

I

I NH

NH

2

2

2

(Ref. 73)

II

cK

x

ci

I Me PCl 2

3

— — — >

Ph.P^^PPh, I II Ν Me^

x

(Ref. 76)

Me

In o n e e x p e r i m e n t , r e p o r t e d by H e r r i n g a n d D o u g l a s , p h a z e n e salt, I, w a s p r e p a r e d

by t h e r e a c t i o n

of

7 4

p h o r a n e , P h P C l , w i t h a m m o n i a in c h l o r o f o r m s o l u t i o n . 2

3

the d i a m i n o p h o s -

diphenyltrichlorophos­ 5 9

C o m p o u n d 1 is

a w h i t e , c r y s t a l l i n e solid, w h i c h m e l t s at 2 4 5 ° - 2 4 6 C . It is s u r p r i s i n g l y s t a b l e c

100

4.

SYNTHESIS OF THE P H O S P H O R U S - N I T R O G E N SKELETON

in t h e a t m o s p h e r e . A 1:1 m o l a r m i x t u r e o f I a n d p h o s p h o r u s p e n t a c h l o r i d e w a s h e a t e d i n v a c u u m a t 135°C f o r 16 h o u r s . T h e p r o d u c t w a s r e c r y s t a l l i z e d f r o m p e t r o l e u m e t h e r t o give a 2 5 % yield o f w h i t e c r y s t a l s o f 1,1-dichloro3,3,5,5-tetraphenylcyclotriphosphazene, II. Interestingly enough, the reactions of I w i t h d i p h e n y l t r i c h l o r o p h o s p h o r a n e , P h P C l , 2

phenyltetrachlorophos-

3

p h o r a n e , P h P C l , o r p h o s p h o r u s p e n t a c h l o r i d e yield significant q u a n t i t i e s o f 4

the appropriate cyclote/raphosphazene. Ph P^Nr^PPh 2

I

' C l + 2 Ph PCl

NH ci 4

e

2

2

3

-HCl

I

NH

NH

2

•>

(NPPh ) 2

(Ref. 74)

4

2

T h e a m m o n i u m c h l o r i d e r e q u i r e d f o r t h e s y n t h e s i s is t h o u g h t t o b e f o r m e d d u r i n g side r e a c t i o n s . O n e of the c o m p o u n d s prepared by this route, l,l-dichloro-/m/?5 -3,5-bis,

( 4 - m e t h y l p h e n y l ) - 3 , 5 - d i p h e n y l c y c l o t r i p h o s p h a z e n e , is t h e first r e p o r t e d o p t i c ­ ally active c y c l o t r i p h o s p h a z e n e . T h e c o m p o u n d w a s s y n t h e s i z e d f r o m t h e o p t i c a l l y a c t i v e p h o s p h a z e n e salt s h o w n . Ph

6

NH

NH

2

6

4

4

/Ph

MeC H

C H Me

MeC H » - P — Ν — P — Ph 6

7 2

Cl

e

PCI5

pir I

4HC1

cr

2

C H Me 6

4

(Ref. 72)

ci


I

II

NH

2

Ph P^ ^PPh N

2

RP(OPh)

2PhOH

2

2

2

NH

Ph

I

PPh

II

2

.N

(Ref. 75) w h e r e R is O P h , M e , o r E t . If c o m p o u n d I r e a c t s w i t h t h e h a l i d e o f a n e l e m e n t o t h e r t h a n p h o s p h o r u s , mixed h e t e r o a r o m a t i c rings c a n b e p r e p a r e d . F o r example, with b o r o n tri­ chloride, t h e following reaction takes place: [ + BCI3

Ph F

'PPh

2

II

HN CI

2

+ 3 HCl

(Ref. 77)

A.

c. Thermal

101

G E N E R A L S U R V E Y OF S Y N T H E T I C R O U T E S

Decomposition

of

Azidophosphines

T h i s r e a c t i o n r o u t e utilizes t h e m e t a t h e t i c a l e x c h a n g e b e t w e e n a h a l o p h o s p h i n e a n d a m e t a l a z i d e , f o l l o w e d b y careful d e c o m p o s i t i o n o f t h e r e s u l t a n t azidophosphine. T h e o v e r a l l r e a c t i o n s c h e m e is a s f o l l o w s : 7 8 - 8 5

R PCl + N a N 2

~

3

N a C 1

>

R PN 2

>

3

(R PN)„ + / i N 2

2

This reaction can b e used t o p r e p a r e a variety of cyclo- and p o l y p h o s p h a z e n e s , as illustrated b y t h e following e q u a t i o n s : -LiCl

(CF ) PC1 4- LiN 3

2

PBr + N a N 3

50°-60°C

> (CF ) PN

3

3

-NaBr

3

1A

^

>

0t

2

— NaCl

2

3

n

o

o

_

1

7

5

—

3

JO m m

[Br PN ]

IOJ —loi C

PhPCl + N a N

2

o

> [(CF ) PN]„ + « N

>

3

3

2

(Br PN)„ + / i N 2

[PhClPN ] -> (PhClPN) + η N

>

3

C

n

2

(Ref. 79) (Ref. 78)

2

(Ref. 78)

2

-NaCl

Ph PCl + N a N 2

> [Ph PN ] -> (Ph PN) + 4 N

165°-167°C

3

2

3

2

4

(Ref. 78)

2

Cl Ph P=N—P—Ph 2

2 Ph PCl + 2 PhPCl + 4 N a N 2

2

>

3

I Ν

II

+4N

II Ν

(Ref. 81)

2

I

Ph—Ρ—N=P Ph I

2

Cl Ph PCl + Me SiN 2

3

3

Me SiCl 3

> Ph PN 2

25°C

3

-> (Ph PN) + 3 N 2

3

(Ref. 83)

2

S o m e idea of the required reaction conditions can b e obtained from the p r o ­ cedure reported by Tesi, H a b e r , a n d D o u g l a s . Bis(trifluoromethyl)chlorophosphine, ( C F ) P C 1 , w a s treated with lithium azide a t 0 ° C for 24 hours. D i s t i l l a t i o n in vacuo t h e n yielded a b o u t 7 0 % o f t h e highly e x p l o s i v e bis(trifluoromethyl)azidophosphine, ( C F ) P N . T h i s m a t e r i a l is a v i o l e n t d e t o n a t o r even a t l i q u i d n i t r o g e n t e m p e r a t u r e s . H o w e v e r , s l o w d e c o m p o s i t i o n of t h e a z i d e a t 5 0 ° - 6 0 ° C a t 37 m m p r e s s u r e c a u s e d e l i m i n a t i o n o f n i t r o g e n a n d formation of a white, waxy p o l y p h o s p h a z e n e of formula [ ( C F ) P N ] . A s shown by Herring, i s o l a t i o n o f t h e i n t e r m e d i a t e a z i d o p h o s p h i n e is u n ­ n e c e s s a r y i n o t h e r r e a c t i o n s since, f o r e x a m p l e , d i r e c t a d d i t i o n o f s m a l l q u a n ­ tities o f s o d i u m a z i d e t o m o l t e n d i p h e n y l c h l o r o p h o s p h i n e gives a m i x t u r e o f d i p h e n y l p h o s p h a z e n e s directly. 7 9

3

2

3

2

3

3

2

n

7 8

d. Dehydrohalogenation

of

Aminochlorophosphoranes

A m i n o d i c h l o r o p h o s p h o r a n e s , R P ( C 1 ) N H , can be dehydrohalogenated in t h e p r e s e n c e o f a t e r t i a r y a m i n e t o yield a c y c l o - o r p o l y p h o s p h a z e n e . 2

2

2

8 6 - 9 0

102

4.

SYNTHESIS OF THE P H O S P H O R U S - N I T R O G E N SKELETON

A p p r o p r i a t e a m i n o d i c h l o r o p h o s p h o r a n e s for t h i s r e a c t i o n c a n b e s y n t h e s i z e d either by oxidative chlorination of a m i n o p h o s p h i n e s (phosphinamides o r p h o s p h i n o u s amides), o r b y chlorination of p h o s p h i n i c amides. T h e general r e a c t i o n s e q u e n c e is R PNH 2

2

\ci

2

V

-2HC1

Ο

R P(C1 )NH 2

R PNH 2

2

2

>

E t a N

(R PN)„ 2

2

In this reaction, t h e a m i n o d i c h l o r o p h o s p h o r a n e apparently functions as a phosphinimine hydrochloride with t h e structure [ R P ( C 1 ) N H ] C R T h e s c o p e o f this s y n t h e t i c r o u t e is i l l u s t r a t e d b y t h e f o l l o w i n g r e a c t i o n s e q u e n c e s : @

2

2

- 2 HCl

(CF ) PNH + Cl -> (CF ) P(C1 )NH 3

2

2

2

3

2

2

•

2

[(CF ) PN] , ,„ 3

2

3

4

(Refs. 86, 87)

- 2 HCl

( C F ) P N H + Cl 3

7

2

2

2

(C F ) P(C1 )NH 3

7

2

2

( C F ) P N H + Cl -> (C F ) P(C1 )NH 6

5

2

2

2

6

5

2

2

2

> [(C F ) PN]

3

> [(C F ) PN]

3

3

- 2 HCl 2

7

2

(Refs. 86, 87) 6

5

2

(Ref. 90) -POCI3

-2

Ph P(0)NH + PCI5 2

> Ph P(Cl )NH

2

2

2

HCl

> (Ph PN)

2

2

3 a n d 4

(Ref. 89) D e h y d r o h a l o g e n a t i o n c a n b e effected w i t h a s t r o n g b a s e s u c h as t r i e t h y l a m i n e , or, as in t h e latter reaction, simply b y heating in v a c u u m . e. Interaction amine

of Chlorophosphines

with Chloramine

or Ammonia

and Chlor-

Sisler a n d c o - w o r k e r s have shown that diarylchlorophosphines can b e converted t o cyclophosphazenes by treatment with chloramine (scheme l ) , o r w i t h a m m o n i a a n d c h l o r a m i n e ( s c h e m e 2 ) . T w o different r e a c t i o n p a t h 9 1 - 9 3

9 2

9 1

R P(C1 )NH 2

NH C1 "(1)

2

2

^

2

R PC1 2

NH.Cl

R PNH 2

2

[R P(NH ) ]®C1 2

2

G

2

w a y s a p p a r e n t l y exist. B o t h r o u t e s h a v e b e e n u s e d t o p r e p a r e t h e p h e n y l c y c l o phosphazenes, ( N P P h ) . Reaction scheme 1 resembles that discussed a b o v e i n S e c t i o n d. H o w e v e r , t h e s e c o n d s t e p o f r o u t e 1 p r o c e e d s t h r o u g h t h e 2

3 a n d 4

103

A. G E N E R A L S U R V E Y OF S Y N T H E T I C R O U T E S

intermediate f o r m a t i o n of linear p h o s p h a z a n e s , such as P h P ( N H ) ( C l ) N H P 2

2

( C l ) P h , a n d a m m o n o l y s i s leads t o t h e f o r m a t i o n of [ P h P ( N H ) N P ( N H ) 2

2

2

2

2

P h ] C l . T h i s l a t t e r c o m p o u n d w a s a l s o i s o l a t e d f r o m r e a c t i o n 2. T h u s , t h e r e @

G

2

is a s t r o n g r e l a t i o n s h i p b e t w e e n s e q u e n c e 2 a n d t h e r e a c t i o n s d i s c u s s e d i n Section b a b o v e . T h e c h l o r a m i n e - a m m o n i a m i x t u r e used in r o u t e 2 w a s pre­ p a r e d b y t h e g a s - p h a s e r e a c t i o n o f c h l o r i n e w i t h excess a m m o n i a , a n d t h i s m i x t u r e w a s b u b b l e d t h r o u g h a solution of d i p h e n y l c h l o r o p h o s p h i n e in tetrachloroethane. f. Pyrolysis

of a Diorganophosphonium

Halide

T h i s r o u t e utilizes p a r t of t h e s e q u e n c e o u t l i n e d i n r o u t e 2 o f S e c t i o n e a b o v e . Thus, intermediate molecular weight poly(dimethylphosphazenes) containing ~ 1 2 0 repeating units have been p r e p a r e d by the pyrolysis of d i m e t h y l d i a m i n o phosphonium chloride.

T h e o v e r a l l r e a c t i o n s c h e m e is

9 4

200°C

Az[Me P(NH ) ]®Cl 2

2

> (Me PN)„ + η NH C1

0

2

2

4

T h e m e c h a n i s m p r o b a b l y proceeds t h r o u g h t h e p r i o r f o r m a t i o n of [ M e P ( N H ) - - ^ N - - ^ P ( N H ) M e ] © C l followed by cyclization t o cyclophosphazenes and subsequent polymerization. 0

2

2

2

g. Dehydrohalogenation

2

of a

Cyclophosphazane

Cyclouf/phosphazanes (prepared by m e t h o d s t o be described later) c a n be d e h y d r o h a l o g e n a t e d t o yield c y c l o t r i - o r h i g h e r c y c l o p h o s p h a z e n e s , a s s h o w n in t h e f o l l o w i n g e x a m p l e s . T h e d e g r e e o f p o l y m e r i z a t i o n o f t h e l a t t e r p r o d u c t was not reported. 9 5

F

Ph

I

H Ν—PPh

2

Ph P—NH

2

-HF (CsF in benzene)

2

F

2

I

HN-PPh p

h . Miscellaneous

n

ρ

-HP

(

P

H

P

P

N

(CsF in dimethyl sulfoxide)

Syntheses

It h a s b e e n r e p o r t e d t h a t c h l o r o c y c l o p h o s p h a z e n e s c a n a l s o b e p r e p a r e d b y the t r e a t m e n t of p h o s p h o r u s p e n t a c h l o r i d e with a m m o n o b a s i c mercuric

104

4 . SYNTHESIS OF T H E P H O S P H O R U S - N I T R O G E N SKELETON

chloride, N H H g C l , a n d by t h e reaction of phosphoryl nitride with chlorine 2

at temperatures above 8 0 0 ° C .

Poly(chlorofluorophosphazene) (III) c a n

9 6 - 9 9

be prepared by ammonolysis of F P ( 0 ) — Ο — P ( 0 ) F 2

thesis r o u t e Ο

Ο II -NH40PF2

Ο

Il I I

F P—O—PF 2

2

via t h e following syn­

:

9 9 a

+ 2NH

2

o >

3

O

I

H NPF 2

pcis Γϊϊϊά*

II CI P=NPF 3

2

2

-P(0)F C1 200°C -P(0)C1 N 2

3

2

(NPFC1)„ III

2. SYNTHESIS OF CYCLOPHOSPHAZANES A N D M O N O P H O S P H A Z A N E S

a. By Rearrangement

of Hydroxy-

or

Alkoxyphosphazenes

T h e hydrolysis of halocyclotri- a n d t e t r a p h o s p h a z e n e s results in the forma­ t i o n o f h y d r o x y p h o s p h a z e n e s (see C h a p t e r 5). S u c h c o m p o u n d s c a n r e a r r a n g e spontaneously to cyclophosphazanes (IV and V ) ,

Cl

/ C I

x

11 X I

CkJ c

,

ΗΟ HCX

X

-

P

^

C1

S

Χ

I

below.

Ο

ΗΝ

NH

O H OH

HO

as shown

HO

/ O H

II /

1 0 0 - 1 1 5

HO^

X

N Η

P

V

IV

CI

I

OH

CI

I

I

II

II

Ν

I

Cl—Ρ—N=P—Cl

Cl

CI

I

HO—P=N—P—OH

CI—P=N—P—CI Ν

OH

H 0 2

N

N

OH

H 0=P—N—P—OH

I

OH

I

I

ΗΝ

NH

I

HO—P—N=P—OH

I

O

II

I

I

HO—Ρ—N—P=0

OH

II

O

S t a b l e salts o f t h e h y d r o x y p h o s p h a z a n e s c a n a l s o b e i s o l a t e d .

H

1 OH

A.

GENERAL SURVEY OF SYNTHETIC

105

ROUTES

Similarly, alkyl g r o u p m i g r a t i o n occurs from oxygen to nitrogen when alkoxycyclophosphazenes are heated at 160°-200°C. Alkyl halides are catalysts for t h i s r e a c t i o n . RO

/ O R

X

R

Heat

R O

X

R N T

•

Π / O R

RO^| 1 N

X

\ ^ °

O

OR

P

V

N R


I Ν

.OR %

Q

T h e r e a r r a n g e m e n t t a k e s p l a c e w h e n R is M e , Et, «-Pr, /-Pr, o r b e n z y l , b u t it d o e s n o t o c c u r w h e n R is p h e n y l o r t r i f l u o r o e t h y l . T h e r e a c t i o n is c o n ­ s i d e r e d in m o r e d e t a i l in C h a p t e r 13. 116

b . Reactions

of Halophosphorus

Compounds

with

Amines

B o t h t h e cyclic d i m e r i c p h o s p h a z a n e , V I , a n d t h e t r i p l e r i n g s t r u c t u r e , V I I , h a v e b e e n i s o l a t e d f r o m t h e r e a c t i o n of p h o s p h o r u s p e n t a c h l o r i d e w i t h m e t h y l ammonium chloride. Triple ring c o m p o u n d s similar to VII, b u t with 1 1 7 , 1 1 8

®

PC1 + MeNH Cl° 5

-HCl

χ

>

3

Me Me 9 Me Me / Ν Nv I . N . /NL α 3 ΡΓ / P C 1 ! C1 P^ ^ P ^ ^ P ^ > C 1 3

3

Me

Me

VI C O or S 0 described.

2

3

Me VII

u n i t s in p l a c e of t h e t e r m i n a l P C 1

3

groups, have also been

1 1 9 , 1 1 9 a

I n t h e p r e s e n c e of t r a c e s of w a t e r , p h o s p h o r u s p e n t a c h l o r i d e r e a c t s w i t h m e t h y l a m m o n i u m c h l o r i d e t o yield a c o m p o u n d w h i c h is believed t o h a v e a cage structure ( V I I I ) .

1 2 0

The

3 1

P N M R s p e c t r u m s h o w e d a singlet a t + 7 4 . 3

p p m , w h i c h is c o n s i s t e n t w i t h t h e c a g e s t r u c t u r e . C o m p o u n d V I c a n a l s o b e

MeN

Ρ Cl

NMe 2

VIII

106

4.

SYNTHESIS OF THE P H O S P H O R U S - N I T R O G E N

SKELETON

o b t a i n e d f r o m t h e r e a c t i o n of p h o s p h o r u s p e n t a c h l o r i d e w i t h m e t h y l a m i n e . It is a c r y s t a l l i n e solid w h i c h m e l t s a t 178°C. T h e s a m e t y p e o f r e a c t i o n o c c u r s w i t h a r y l c h l o r o p h o s p h o r a n e s . F o r ex­ ample, p h e n y l t e t r a c h l o r o p h o s p h o r a n e reacts with an alkylammonium c h l o r i d e t o yield a c y c l o d i p h o s p h a z a n e ( I X ) . These materials are colorless, 1 2 1

Ph

I

-HCl

2 PhPCI + 2 AlkNH Cl 4

3

C1 P—NAlk "I I AlkN—PC1 -P( 2

•

2

I

Ph IX crystalline substances which are readily hydrolyzed by a t m o s p h e r i c moisture. T h e y c a n n o t b e d e p o l y m e r i z e d t o t h e m o n o p h o s p h a z e n e in b o i l i n g b e n z e n e . H o w e v e r , d i p h e n y l t r i c h l o r o p h o s p h o r a n e r e a c t s w i t h a m i n e s t o f o r m saltlike c o m p o u n d s of f o r m u l a [ P h P ( C l ) — N H R ] © C l . e

1 2 1 a

2

P h o s p h o r u s p e n t a f l u o r i d e r e a c t s w i t h s e c o n d a r y a m i n e s t o yield first a n adduct and then a m o n o p h o s p h a z a n e . 1 2 2

PF + H N R 5

F PNHR

2

5

A m o n o p h o s p h a z a n e is a l s o f o r m e d i n t e r a c t s with a p r i m a r y a m i n e .

Heat

——>

2

F P—NR 4

— Hr

when

2

phenyltetrafluorophosphorane

1 2 3

®

PhPF + 2 MeNH 4

PhF P—NHMe + MeNH Cl

2

3

Q

3

P h o s p h o r u s p e n t a c h l o r i d e r e a c t s w i t h a m i n o m e t h a n e s u l f o n i c acid t o give a solid cyclic d i m e r i c p h o s p h a z a n e ( X ) by t h e p r o c e s s 1 2 4

PC1 + H N C H S 0 H 5

2

2

-S0

2

3

>

2

C1 P—NCHoCl | | C1CH N—PC1 3 3

2

3

X T h i s p r o d u c t is a c o l o r l e s s , c r y s t a l l i n e c o m p o u n d , m . p . 1 4 0 ° - 1 4 1 ° C , w h i c h is r a p i d l y d e c o m p o s e d by t r a c e s of m o i s t u r e . C o m p o u n d V I is f o r m e d by t h e i n t e r a c t i o n of p h o s p h o r u s p e n t a c h l o r i d e w i t h 7V,7V'-dimethylsulfamide. T h e cyclohexyl ester of d i c h l o r o p h o s p h o r i c acid r e a c t s w i t h c y c l o h e x y l a m i n e Ο

II

ο Il RO—PC1 + H N R 2

2

_

H C 1

>

ROP-NR I I RN—POR XI

I

o

A.

GENERAL SURVEY OF SYNTHETIC

t o yield a c y c l o d i p h o s p h a z a n e w i t h s t r u c t u r e X I .

Similarly, t h i o p h o s p h o r y l

1 2 5

c h l o r i d e i n t e r a c t s w i t h a n i l i n e h y d r o c h l o r i d e t o yield X I I .

1 2 6

Finally, phos-

PhHNP—NPh | | + 10 HCl PhN—PNHPh

4[PhNH ]®Cl + 2 S=PC1 -> Q

3

107

ROUTES

3

S XII

p h o r u s t r i c h l o r i d e r e a c t s w i t h p r i m a r y a m i n e s , s u c h as a n i l i n e , t o yield c y c l o d i p h o s p h a z a n e s s u c h as X I I I a n d X I V . 2PhNH + 2PCl 2

_HCI

'

1 2 7

It s h o u l d be n o t e d t h a t s i m i l a r

1 2 8

C1P—NPh , I I ^ > PhN—PCI

RHNP—NPh | | PhN—PNHR

R N H

3

c

XIII

XIV

r e a c t i o n s a r e e m p l o y e d for t h e s y n t h e s i s of c y c l o d i p h o s p h a z a n e s a n d m o n o p h o s p h a z e n e s ( p h o s p h i n i m i n e s ) . W h e t h e r d i m e r i z a t i o n of t h e

monophos-

p h a z e n e o c c u r s a p p e a r s t o d e p e n d p a r t l y o n steric f a c t o r s . c. Reactions

of Phosphorus

Halides

with Silicon-Nitrogen

Compounds

128-133

S c h m u t z l e r a n d M a c D i a r m i d h a v e s h o w n t h a t t h e s i l i c o n - n i t r o g e n b o n d in s i l y l a m i n e s o r s i l a z a n e s c a n b e cleaved by f l u o r o p h o s p h o r a n e s t o yield m o n o p h o s p h a z a n e s or cyclodiphosphazanes. T h e following e q u a t i o n s illustrate this method. PF + Me NSiMe 5

2

3

-> F P—NMe + Me SiF 4

2

(Ref. 129)

3

PF + Et NSiMe -> F P—NEt + Me SiF 5

2

3

4

PhPF + Me NSiMe 4

2

2

(Refs. 95, 130)

3

PhF P—NMe + Me SiF

3

3

2

3

(Ref. 130)

F P—NMe \ \ + 4 Me SiF (Refs. 129, 131) MeN—PF 3

2 PF + 2 MeN(SiMe ) 5

3

>

2

3

3

2 PhPF + 2 MeN(SiMe ) 4

3

>

2

PhF P—NMe \ \ + 4 Me SiF (Ref. 131) MeN—PF Ph 2

3

2

T h e f o u r - m e m b e r e d r i n g s y s t e m s a r e sufficiently s t a b l e t o b e distilled o r s u b ­ limed. T h e y are also hydrolytically s t a b l e . However, cyclization does not o c c u r if t w o p h e n y l g r o u p s a r e p r e s e n t o n p h o s p h o r u s , a n d a m o n o p h o s p h a z e n e is f o r m e d i n s t e a d . 1 3 1

Ph PF + MeN(SiMe ) 2

3

2

2

P h F P = N M e + 2 Me SiF 2

3

(Ref. 95)

108 *Η,

4.

3 1

P , and

1 9

SYNTHESIS OF THE P H O S P H O R U S - N I T R O G E N SKELETON

F N M R spectroscopy have been used to confirm the structures

of m o s t of t h e a b o v e c o m p o u n d s . A r e l a t e d c y c l o t r i p h o s p h a z a n e s y n t h e s i s i n v o l v e s t h e i n t e r a c t i o n of p h o s ­ phorus trichloride with a disilazane,

1 3 1

as in t h e e q u a t i o n CI

3 PC1 + 3 EtN(SiMe ) 3

3

EtN 2

NEt

6 Me SiCl 3

C1P . / P C 1 N

Et T h i s c o m p o u n d is u n s t a b l e i n m o i s t a i r . I n a closely r e l a t e d p r o c e s s , d i c h l o r o t r i f l u o r o p h o s p h o r a n e r e a c t s w i t h t h e b i s ( t r i m e t h y l s i l y l ) d e r i v a t i v e o f Ν,,/V'-dimethylsulfamide ( X V ) t o yield t h e m o n o c y c l i c a n d bicyclic p h o s p h a z a n e c o m p o u n d s X V I a n d X V I I b y t h e following s e q u e n c e : 1 3 3

Me Me Si—Nk C1 PF + ^S0 Me Si—Ν Me

Me -Me SiCl

3

2

3

F P^

3

S0

3

2

3

2

Me

XV

XVI -Me SiF 3

Me ^N /P: ^N" ; s o 2 Me F Me Me

o s; 2

v

XVII d. Pyrolysis

of Amino-Phosphorus

Compounds

S o m e very e a r l y p h o s p h a z a n e s y n t h e s e s fall i n t o t h i s c a t e g o r y . F o r e x a m p l e , t h e p y r o l y t i c c o n d e n s a t i o n of C l P ( 0 ) N H P h t o t h e c y c l o d i p h o s p h a z a n e X V I I I was reported by Stokes in 1 8 9 3 . F u r t h e r r e a c t i o n of t h i s p r o d u c t w i t h a m i n e 2

1 3 4

CI

CI

I

2 0=P—CI I

- 2 HCl

i

*

0=P—NPh

I I

PhN—P=0

NHPh

I

CI XVIII h y d r o c h l o r i d e results in t h e replacement of t h e halogen a t o m s a n d t h e forma­ t i o n o f species s u c h a s [ R ' N H ( 0 ) P — N P h ] . « M o r e r e c e n t l y , it h a s b e e n r e p o r t e d t h a t t h e p y r o l y s i s o f p e n t a f l u o r o p h e n y l 1 3 5

2

1 3 6

109

A. GENERAL SURVEY OF SYNTHETIC ROUTES

d i a m i n o p h o s p h i n e s results in t h e elimination of pentafluorobenzene a n d t h e formation

of a

possible

C F P. 6

cyclodiphosphazane

-NHCH Ph

2

2

5

NHCH Ph

0

0

o

However,

1 3 7

this

PhCH NHP—NCH Ph 2

C

~ 6F H C

2

(ΧΓΧ).

2

PhCH N—PNHCH Ph

5

2

2

XIX m a t e r i a l is u n s t a b l e in s o l u t i o n . T h e t h e r m a l d e c o m p o s i t i o n o f o r g a n o p h o s p h o r u s triamides also results in t h e formation of c y c l o p h o s p h a z a n e dimers. 1 3 8 , 1 3 8 a

Ο 2 0=P(NHR)

Heat 3

I

RHNP—NR I I 4-2 R N H RN—PNHR

2

Ο Ο NR

2

Heat

I

2 0=P(NHR)

2

RHNP—NR I I 4-2 R N H RN—PNHR 2

I

ο e. Miscellaneous

Phosphazane

Syntheses

B i s ( t r i f l u o r o m e t h y l ) c h l o r a m i n e o r t h e b r o m o a n a l o g u e r e a c t w i t h tris( t r i f l u o r o m e t h y l ) p h o s p h i n e t o yield a m o n o p h o s p h a z a n e b y t h e p r o c e s s 1 3 9

(CF ) NC1 + (CF ) P -> (CF ) N—P(CF ) + CF C1 3

2

3

3

3

2

3

2

3

A m o n o p h o s p h a z a n e is a l s o f o r m e d b y t h e f o l l o w i n g r e a c t i o n ^S0 C1 PC1 V H N ^ 2

5

^so ci

1 4 0

:

_HCI ^S0 C1 — C I P — N ^ 2

4

so ci

2

2

T h i s is a m o i s t u r e - s e n s i t i v e c o m p o u n d . F i n a l l y , t r i s ( d i e t h y l a m i n o ) p h o s p h i n e i n t e r a c t s w i t h a n i l i n e o r t o l u i d i n e t o give t h e c y c l o d i p h o s p h a z a n e (PhHNP—NPh) . 1 4 1

2

3. S y n t h e s i s o f M o n o p h o s p h a z e n e s ( P h o s p h i n i m i n e s ) a n d H i g h e r L i n e a r Phosphazenes

M a n y different r e a c t i o n s h a v e b e e n d e s c r i b e d f o r t h e p r e p a r a t i o n o f m o n o ­ phosphazenes a n d related linear c o m p o u n d s . " T h e following sections s e p a r a t e t h e s e a p p r o a c h e s i n t o b r o a d r e a c t i o n classes, a l t h o u g h it s h o u l d b e 1 4 2

2 0 8

110

4.

SYNTHESIS OF THE P H O S P H O R U S - N I T R O G E N SKELETON

e m p h a s i z e d t h a t c e r t a i n m o n o p h o s p h a z e n e s y n t h e s e s follow p r o c e s s e s s i m i l a r t o t h o s e m e n t i o n e d p r e v i o u s l y for t h e p r e p a r a t i o n of c y c l o p h o s p h a z e n e s o r cyclophosphazanes. a. Reaction

of Chlorophosphoranes

with Ammonium

Chloride

T h e i n t e r a c t i o n of p h o s p h o r u s p e n t a c h l o r i d e w i t h a m m o n i u m c h l o r i d e u s u a l l y yields l i n e a r p h o s p h a z e n e s a s well as c y c l o p h o s p h a z e n e s . The m e c h a n i s t i c significance of t h i s fact will b e d i s c u s s e d later. Several l i n e a r species have been isolated by Becke-Goehring a n d c o - w o r k e r s , but the p r i m a r y r e a c t i o n is a s f o l l o w s : 2 5 , 1 4 2 - 1 5 0

2 5 , 1 4 2 - 1 4 7

3

[CI P=N—ρα ] [ρα ] + 4 φ

P C I + NH4C1 - >

3

5

θ

3

HCI

6

T h e s y n t h e s i s is c a r r i e d o u t in a s j y r a - t e t r a c h l o r o e t h a n e - n i t r o b e n z e n e s o l v e n t system a t 8 0 ° - 1 4 0 ° C , a n d t h e p h o s p h a z e n e salt crystallizes f r o m t h e s o l v e n t as w h i t e n e e d l e s w h i c h m e l t a t 3 1 0 ° - 3 1 5 ° C . T h e c o m p o u n d is e x c e p t i o n a l l y sensitive t o h y d r o l y s i s . T h e P N M R s p e c t r u m s h o w s t w o p e a k s (at —21.4 a n d + 3 0 5 . 0 p p m relative t o 8 5 % H P 0 ) w i t h a n i n t e n s i t y r a t i o of 2 : 1 . L o n g e r - c h a i n species, s u c h as [ C 1 P = N — P C 1 = N — P C 1 ] ® [ P C 1 P , a r e f o r m e d b y successive c h a i n - b u i l d i n g steps w i t h a m m o n i u m c h l o r i d e a n d phosphorus pentachloride, a n d t h e s e c o m p o u n d s c a n a l s o b e identified b y P N M R s p e c t r a . F o r e x a m p l e , t h e t r i p h o s p h a z e n e salt s h o w n a b o v e yields a triplet s p e c t r u m ; o n e - o f t h e s e lines is r e s o l v a b l e t o a d o u b l e t ( P C 1 ) , o n e t o a triplet ( P C 1 ) , a n d o n e is u n r e s o l v e d ( P C 1 ) . A s d i s c u s s e d l a t e r ( S e c t i o n B ) , l i n e a r c h l o r o p h o s p h a z e n e s of t h i s t y p e a r e believed t o b e i n t e r m e d i a t e s f o r m e d d u r i n g t h e s y n t h e s i s of c y c l o p h o s p h a z e n e s , since a m m o n o l y s i s of t h e l i n e a r c o m p o u n d s r e s u l t s in t h e f o r m a t i o n of c y c l o p h o s p h a z e n e s . I t is a l s o k n o w n t h a t liquid a m m o n i a r e a c t s w i t h p h o s p h o r u s p e n t a c h l o r i d e t o yield t h e l i n e a r aminophosphazene X X by the p r o c e s s 3 1

3

4

3

2

3

6

1 4 5

3 1

3

0

2

2 5

6

5 9 , 1 4 2 , 1 4 7

2 PCI5 + 16 N H

-> [ ( N H ) P — N — P ( N H ) l C l e

3

2

3

2

3

e

+ 9 NH C1 4

XX

O n e of t h e p r o d u c t s i s o l a t e d f r o m t h e r e a c t i o n b e t w e e n p h o s p h o r u s p e n t a ­ c h l o r i d e a n d a m m o n i a is t e t r a a m i n o p h o s p h o n i u m c h l o r i d e ( X X I ) . This p r o d u c t c a n b e c o n d e n s e d w i t h p h o s p h o r u s p e n t a c h l o r i d e t o yield a b r a n c h e d c h l o r o p h o s p h a z e n e salt. 1 5 1

A m o d i f i c a t i o n of t h e p h o s p h o r u s p e n t a c h l o r i d e - a m m o n i u m c h l o r i d e r e ­ a c t i o n t a k e s p l a c e w h e n m e t a l h a l i d e s s u c h as S b C l , S b C l , A1C1 , A l B r , B C 1 , B F , T i C l , Z n C l , F e C l , C u C l , o r T1C1 a r e p r e s e n t . Linear phos­ phazenes are obtained which are end-capped by the metal halide component. F o r e x a m p l e , c o m p o u n d s of c o m p o s i t i o n ( N = P C l ) „ S b C l a r e f o r m e d w h e n antimony trichloride, p h o s p h o r u s pentachloride, a n d a m m o n i u m chloride 3

5

1 5 2 ,

3

3

4

2

3

2

3

1 5 3

3

3

A .

G E N E R A L

S U R V E Y

NH PC1 + 8 N H 5

-4NH Cl

O F

3

111

R O U T E S

2

H N—Ρ—NH

4

S Y N T H E T I C

2

NH

2

Cl

4 PCI5

e

- 8 HCl

2

Cl

XXI

I

Cl—P—Cl Cl

N

1

1

Cl 1

Cl—P=N—P=N—P—Cl I

I

Cl

N

,

Cl

0

I

Cl

Cl—P—Cl I

Cl r e a c t in t r i c h l o r o b e n z e n e . C o m p o u n d s of t h i s t y p e a r e t h e r m a l l y s t a b l e oils which are apparently resistant to polymerization a b o v e 500°C. T h e y are very easily h y d r o l y z e d , h o w e v e r . Linear, phenyl-substituted phosphazenes can be isolated from the reactions of p h e n y l c h l o r o p h o s p h o r a n e s w i t h a m m o n i u m c h l o r i d e . T h u s , t h e f o l l o w i n g reactions are k n o w n to occur: 2 Ph PCl + NH4CI -> [Ph ClP=N—PClPh ]®Cl + 4 HCl

(Refs. 58, 154)

2 PhPCl + NH4CI -> [PhCl P=N—PCl Ph]®Cl + 4 HCl

(Ref. 155)

e

2

3

2

2

e

4

2

2

T h e i n t e r a c t i o n of d i p h e n y l t r i c h l o r o p h o s p h o r a n e w i t h a m m o n i u m c h l o r i d e t a k e s p l a c e in t e t r a c h l o r o e t h a n e a t 130°C. T h e t e t r a p h e n y l d i p h o s p h a z e n e salt f o r m s c o l o r l e s s c r y s t a l s in 9 0 % yield. T h e r e a c t i o n of p h e n y l t e t r a c h l o r o p h o s p h o r a n e w i t h a m m o n i u m c h l o r i d e a l s o t a k e s p l a c e in h o t t e t r a c h l o r o e t h a n e , a n d t h e l i n e a r d i p h e n y l p h o s p h a z e n e salt c a n b e o b t a i n e d in 60 % yield a s w h i t e crystals, m . p . 210°C. Similar p r o d u c t s are obtained w h e n phenyldichlorophosphine interacts with nitrogen trichloride. 1 5 5

PhPCl

NCI3 2

[PhCl P=N—PCl Ph]®Cl 4- [PhCl P=N—P(ClPh) =N—PCl Ph]®Cl + e

2

e

2

2

2

[PhCl P=N—P(ClPh)=N—P(ClPh)=N—PCl Ph]®Cl 2

2

e

etc.

Related linear phosphazenes are formed when tetraphenyldiphosphine re­ a c t s w i t h a g a s e o u s m i x t u r e of a m m o n i a a n d c h l o r a m i n e according to the following reaction s c h e m e : 1 5 6

Ph P—PPh 2

NH C1 + NH 2

2

3

[PH (NH )P=N—Ρ(ΝΗ )ΡΗ ] α φ

2

2

2

2

θ

+ Ph (NH ) P®Cl 2

2

2

Q

112

4.

S Y N T H E S I S

O F

T H E

P H O S P H O R U S - N I T R O G E N

S K E L E T O N

or when diphenylchlorophosphine interacts with hydrazine h y d r o c h l o r i d e .

1 5 7

H NNH HCI 2

2

Ph PCl

•

2

[Ph (NH )P=N—PPh =N—P(NH )Ph]®Cl 2

2

2

e

2

T h i s l a t t e r p r o d u c t is a w h i t e s o l i d , m . p . 2 8 5 ° C . W h e n h e a t e d i n v a c u u m a t 2 8 0 ° - 3 0 5 ° C a t r e d u c e d p r e s s u r e it f o r m s

hexaphenylcyclotriphosphazene,

(NPPh ) . 2

3

b . Treatment

of Cyclophosphazenes

with Inorganic

Halides

P h o s p h o r u s pentachloride reacts with hexachlorocyclotriphosphazene

or

o c t a c h l o r o c y c l o t e t r a p h o s p h a z e n e t o yield l i n e a r p h o s p h a z e n e s b y t h e p r o r P

o 1 3 , 18, 158, 159 R

Cl

2

PC1

C1 P^ /PC1 2

F o r example, M o r a n Cl

e

1 5 9

N

5

->

[Cl(Cl P==N) PCl ]®Cl 2

n

e

3

2

has reported that the c o m p o u n d [C1(C1 P=N) PC1 ]®2

3

3

c a n b e p r e p a r e d b y h e a t i n g ( N P C 1 ) w i t h P C 1 in a n a p p r o x i m a t e l y 1.0 t o 2

3

5

1.9 m o l a r r a t i o a t 2 5 0 ° C for 11 h o u r s . T h e y e l l o w p r o d u c t is i n s o l u b l e in b e n ­ z e n e a n d h e x a n e a n d it m e l t s a t 9 5 ° - 9 6 ° C . A n o t h e r y e l l o w solid c o m p o u n d , [ C 1 ( C 1 P = N ) P C 1 ] ® C 1 , is o b t a i n e d after 0

2

4

3

100 h o u r s r e a c t i o n . W h e n

the

( N P C 1 ) t o PCI5 r a t i o is 5 : 1 , oily h i g h e r l i n e a r p o l y m e r s a r e f o r m e d , a n d t h e s e 2

3

polymerize to high polymers when heated above 300°C. A mechanism p r o ­ p o s e d for t h e i n i t i a l a t t a c k b y P C 1

5

on (NPC1 ) 2

3

includes an electrophilic

a t t a c k at nitrogen by the [ P C 1 ] c o m p o n e n t of the [PC1 ] [PC1 ]~ complex, +

+

4

followed

by ring cleavage

4

of the resultant Cl

2 PC1 + (NPC1 ) 5

2

3

I

6

cyclophosphazene

cation.

1 5 9

2

©

2

PC1

PCl e

II

C1 P^PC1 4

6

2

J

[C1 P=N—PC1 =N—PC1 =N—PCl ]®[PCl ] 3

2

2

3

e

6

T r e a t m e n t of t h e s e l i n e a r species w i t h a l u m i n u m t r i c h l o r i d e o r b o r o n t r i ­ c h l o r i d e r e s u l t s in t h e r e p l a c e m e n t of t h e [ P C 1 ] ~ a n i o n b y [A1C1 ]~ o r [BC1 ]~ 6

4

4

a n i o n s . T h i s t r e a t m e n t e n h a n c e s t h e t h e r m a l s t a b i l i t y of t h e l i n e a r p h o s p h a ­ zenes.

1 5 9

I t is a l s o w o r t h w h i l e t o n o t e t h a t c h l o r o c y c l o p h o s p h a z e n e s

apparently

u n d e r g o ring cleavage with a l u m i n u m chloride a n d other metal h a l i d e s , and that ( N P F ) 2

3

a p p e a r s to be cleaved by cesium f l u o r i d e .

1 6 0 3

1 8 , 1 6 0

Octaphenyl-

A .

G E N E R A L

S U R V E Y

O F

S Y N T H E T I C

113

R O U T E S

cyclotriphosphazene, ( N P P h ) , also reacts with p h o s p h o r u s pentachloride to 2

give l i n e a r d e r i v a t i v e s . c. Reaction

of Amino

4

1 6 1

Compounds

with Phosphorus

Pentachloride ' * 162 1

4

T h i s s y n t h e s i s r o u t e , g e n e r a l l y k n o w n a s t h e K i r s a n o v r e a c t i o n , c a n b e for­ m u l a t e d in g e n e r a l t e r m s b y t h e e q u a t i o n PC1 + R N H 5

C1 P=NR + 2 HCl

2

(Ref. 162)

3

T h e g r o u p R can be varied over a considerable range, as illustrated by the following e q u a t i o n s : PCI5 + PhNH -> C l P = N P h + 2 HCl 2

(Refs. 166, 167)

3

PCI5 + RCONH -> C l P = N C O R + 2 HCl 2

PCI5 + P h S 0 N H 2

(Ref. 168)

3

-> C1 P=N—S0 —Ph + 2 HCl

2

3

PCI5 + NH OH

C l P = N O H + 2 HCl

2

(Ref. 170)

3

2 PC1 + N H S 0 H -> C1 P=N—S0 C1 + 3 HCl + POCl 5

2

3

3

PCI5 + H NP(0)(OPh) 2

(Ref. 169)

2

2

(Refs. 171, 172)

3

CI P=N—P(0)(OPh) + 2 HCl

2

3

(Ref. 173)

2

PCI5 + H NP(S)(OPh) -> C1 P=N—P(S)(OPh) + 2 HCl 2

2

2 PCI5 + S 0 ( N H ) 2

2

3 PCI5 + H NP(0)(OH) 2

(Ref. 173)

2

-> C 1 P = N — S 0 — N = P C 1 + 4 HCl

2

2

3

3

2

(Ref. 174)

3

-> C1 P=N—P(0)C1 + 4 HCl + 2 POCl 3

2

3

(Ref. 175)

2 PCI5 + RP(0)(OAlk)NH -> C1 P=NP(0)C1R + 2 HCl + POCl + AlkCl 2

3

3

(Ref. 176) F PC1 + H N S 0 F -> F P = N S 0 F + 2 HCl

(Ref. 177)

F PC1 + H NPOF

(Ref. 177)

3

2

3

2

2

2

3

2

F P-=NPOF + 2 HCl

2

3

F PC1 + H NP(S)F -> F P = N P ( S ) F + 2 HCl 3

2

2

2

3

(Ref. 177)

2

Ph PCl + H NPh -> P h P = N P h + 2 HCl 3

2

2

(Refs. 178-180)

3

Ph PCl + H N — S 0 — C H M e -> P h C l P = N — S 0 — C H M e + 2 HCl (Ref. 181) 2

3

2

2

6

4

Ph PCl + H NOSC H N0 -
2

2

6

4

2

2

2

6

4

P h P = N S O C H N 0 + POPh + 2 HCl 3

6

4

2

3

(Ref. 182) Ph PCl + H NC(S)NHPh -> Ph P=NC(S)NPhH + 2 HCl 3

2

2

(Ref. 183)

3

I n a closely r e l a t e d p r o c e s s , p h o s p h o r u s p e n t a c h l o r i d e , p h o s p h o r u s tri­ chloride, and hydroxylamine hydrochloride react according to the s c h e m e 1 8 4

2 PC1 + PCI5 + 2[H NOHl®Cl 3

3

Q

-> C1 P=NP(0)C1 + 4 HCl + 4 NH C1 + POCl 3

2

4

3

I t s h o u l d b e n o t e d t h a t t h e m a j o r i t y of a r o m a t i c a m i n e s r e a c t w i t h p h o s ­ p h o r u s p e n t a c h l o r i d e t o f o r m d i m e r s of s t r u c t u r e ( C 1 P — N A r ) (i.e., c y c l o diphosphazanes) rather than m o n o m e r s . Only weakly basic amines form stable 3

2

114

4.

S Y N T H E S I S

O F

T H E

P H O S P H O R U S - N I T R O G E N

S K E L E T O N

monophosphazenes. H o w e v e r , r e p l a c e m e n t of o n e c h l o r i n e a t o m in C l P = N A r b y a n o r g a n i c u n i t s h a r p l y r e d u c e s t h e t e n d e n c y for d i m e r i z a t i o n . A n u m b e r of p h o s p h a z e n e s t h a t w e r e o r i g i n a l l y t h o u g h t t o b e m o n o m e r i c h a v e s u b s e q u e n t l y b e e n s h o w n t o b e cyclic d i m e r s . 1 6 7

3

d. Interaction

of a Tertiary

Phosphine

or a Halophosphine

with an

Azide

T h i s r e a c t i o n r o u t e w a s u s e d b y S t a u d i n g e r for t h e e a r l y s y n t h e s i s of m o n o ­ phosphazenes. I t r e q u i r e s t h e r e a c t i o n of a t e r t i a r y p h o s p h i n e w i t h a n o r g a n i c a z i d e in e t h e r , a c c o r d i n g t o t h e f o l l o w i n g g e n e r a l s e q u e n c e : 1 8 5 ,

1 8 6

R P + R'N 3

3

-> R P N — N = N — N R ' -> R P = N R ' + N 3

3

2

R and R' can be aromatic or aliphatic. W h e n aliphatic groups are present on n i t r o g e n , t h e c o m p o u n d s a r e v e r y sensitive t o m o i s t u r e , a n d t h e a p p r o p r i a t e phosphine oxide and amine are formed by hydrolysis. However, when a r o m a t i c g r o u p s a r e a t t a c h e d t o n i t r o g e n , t h e d e r i v a t i v e s s h o w m o r e stability t o w a t e r b u t c a n still b e h y d r o l y z e d b y d i l u t e a c i d . It is of i n t e r e s t t h a t P h P = N P h is p a l e yellow in c o l o r , w h e r e a s P h P = N H , P h P = N E t , P h P = N C O P h , a n d m a n y other m o n o p h o s p h a z e n e s are colorless. 1 8 7

3

3

3

3

P h o s p h o r u s ylides a l s o r e a c t w i t h o r g a n i c a z i d e s t o yield m o n o p h o s p h a z e n e s according to the p r o c e s s 1 8 8

P h P = C H R + 2 PhN -> P h P = N P h + P h N = C H R + 2 N 3

3

3

2

It h a s r e c e n t l y b e e n s h o w n t h a t silyl a z i d e s c a n a l s o b e e m p l o y e d for s y n t h e s e s of t h i s t y p e .

1 8 9 , 1 9 0

T h u s , tertiary phosphines react with trimethylsilyl azide to

yield m o n o p h o s p h a z e n e s by t h e p r o c e s s Me0H-H S0

_ N,

R P + Me SiN 3

3

2 3

2

-> R P = N S i M e 3

4

•

3

3

R P = N H + MeOSiMe 3

3

-20°C

iV-Silylated a m i n o p h o s p h a z e n e s a r e f o r m e d w h e n t r i m e t h y l s i l y l a z i d e r e a c t s with a m i n o p h o s p h i n e s . Phenyl azide interacts with p h o s p h o r u s trichloride o r w i t h p h e n y l c h l o r o p h o s p h i n e s t o give 7V-phenyl m o n o p h o s p h a z e n e s , 1 9 1

1 9 2

PC1 + PhN -> C l P = N P h + N 3

3

3

2

PhPCl + PhN -> PhCl P=NPh + N

2

Ph PCl + PhN -> Ph ClP=NPh + N

2

2

2

3

2

3

2

and diphenylphosphinyl azide undergoes a reaction with diphenylchlorop h o s p h i n e t o f o r m a l i n e a r p h o s p h a z e n e of s t r u c t u r e P h ( 0 ) P [ N = P P h ] C l . T h i s is a w h i t e , c r y s t a l l i n e s u b s t a n c e , m . p . 1 4 5 ° - 1 4 6 ° C . D i p h e n y l p h o s p h i n y l a z i d e also r e a c t s w i t h d i p h e n y l p h o s p h i n e a c c o r d i n g t o t h e s e q u e n c e 1 9 3

2

2

3

1 9 4

Ph PH + Ph P(0)N 2

2

~ "> N

3

Ph P(0)NHPPh 2

p h 2 P ( Q ) N 3 2

>

Ph P(0)NHPPh =NP(0)Ph 2

2

2

A .

G E N E R A L

S U R V E Y

O F

S Y N T H E T I C

115

R O U T E S

T h e p r o d u c t of t h i s r e a c t i o n t a u t o m e r i z e s t o P h P ( 0 ) [ N = P P h ] — O H . A n a d d i t i o n a l m o d i f i c a t i o n of t h e a r y l a z i d e r o u t e i n v o l v e s t h e r e a c t i o n o f this reagent with a bis(dialkylamino)chlorophosphine ( X X I I ) . T h e p h o s 2

ArN

2

^NAr

3

Et NHN

U> ( R N ) P ^ , Cl

(R N) PC1 2

2

XXII

2

—

2

3

,

3

^

2

2

I

I

I

N

3

XXIV

OR

2

I

(RO) PNHAr' 2

ArN=P—N=P—NHAr' < NR

^NAr

TX

(R N) P:f

XXIII NR

2

'

OR

2

XXV p h o r o d i a m i d a m i d i c c h l o r i d e ( X X I I I ) is t h e n c o n v e r t e d t o t h e a z i d e ( X X I V ) with t r i e t h y l a m m o n i u m azide, and subsequent treatment with a dialkylarylp h o s p h o r a m i d i t e yields t h e l i n e a r d i p h o s p h a z e n e X X V . A z i d e s of t y p e X X I V a r e r e p o r t e d t o b e light y e l l o w l i q u i d s w h i c h a r e sufficiently s t a b l e t o b e v a c u u m - d i s t i l l e d o r h e a t e d a t 100°C for 3 h o u r s w i t h o u t d e c o m p o s i t i o n . 1 9 5

e. The Reaction

of Tertiary

Phosphines

with Other

Reagents

C h l o r a m i n e T , 0 , 7 V - d i b e n z o y l h y d r o x y l a m i n e , 2- o r 4 - b r o m o a n i l i n e , a n d chloramine followed by «-butyllithium, react with ter/-phosphines t o give phosphazenes according to the following e q u a t i o n s : R P 4 Na C l N S 0 C H M e -> R P = N — S 0 C H Me 4 NaCl

(Ref. 196)

Ph P + PhCON(H)OCOPh

(Ref. 197)

3

2

6

4

3

2

3

2

6

3

[Ph P—NHPh]®Br

4

2 5

2

2

25

N a Q H

>

Ph P=NPh 3

— NaBr

[C H PMe NH ]®Cl 12

25

2

C H PMe =NHLiCl 12

e

3

C, H PMe 4NH Cl 2

4

Ph P=NCOPh 4 PhCOOH

3

Ph P 4- H N C H B r

6

n-BuLi

e

2

> C H PMe =NH

2

(Ref. 198)

1 2

2 5

2

(Ref. 191)

T h e d i m e t h y l d o d e c y l p h o s p h a z e n e f o r m e d in t h e l a t t e r r e a c t i o n d e c o m p o s e s w i t h w a t e r t o give a m m o n i a a n d t h e p h o s p h i n e o x i d e . f. Miscellaneous

Routes

to Linear

Phosphazenes

T h e f o l l o w i n g a r e a n u m b e r of r e a c t i o n s w h i c h d o n o t fall r e a d i l y i n t o t h e above categories. (1) P h o s p h a z e n e s a r e f o r m e d q u a n t i t a t i v e l y w h e n 7 V - a c y l a m i d o t r i p h e n y l phosphiniminium bromides are d e h y d r o h a l o g e n a t e d . 1 9 9

[Ph PNHNHC(0)R]®Br® 3

~

H B r

Et N 3

>

Ph P=NNHC(0)R 3

116

4.

SYNTHESIS OF T H E P H O S P H O R U S - N I T R O G E N

SKELETON

(2) T e t r a s u l f u r t e t r a n i t r i d e r e a c t s w i t h p h e n y l d i c h l o r o p h o s p h i n e t o yield a linear d i p h o s p h a z e n e

t o g e t h e r w i t h l o n g e r - c h a i n species.

2 0 0

S N + PhPCl -> [PhCl P=N—PCl Ph]®[PCl ] + PhP(S)Cl + PhCl P=N—P(S)ClPh e

4

4

2

2

2

6

2

2

(3) P h o s p h o r u s t r i c h l o r i d e a n d d i n i t r o g e n t e t r o x i d e r e a c t t o f o r m a p h o s ­ phazene.

2 0 1

PCI3 + N 0 2

-> C 1 P = N — P ( 0 ) C 1

4

3

(4) M o n o t h i o p h o s p h o r i c

acid

+ PCI5 + N O C 1

2

triamide reacts with

c h l o r i d e t o yield p h o s p h a z e n e s a l t s , a s in t h e e q u a t i o n

5SP(NH ) 2

C1 P=N\

Ν—PCI

3

phosphorus

3

[PCl ]

3

CI

^N=PC1

penta­

2 0 2

e

6

3

(5) O r g a n o m e t a l l i c p h o s p h a z e n e s c a n b e p r e p a r e d b y t h e f o l l o w i n g syn­ thetic s e q u e n c e ,

2 0 3 - 2 0 5

-NH4CI

(Me C) PCl + 2 N H 3

2

(Me C) PNHLi 3

—> (Me C) P—NH

3

3

M e 3 M C I

2

(Me C) P—NH—MMe 3

2

n-BuLi

>

3

'

•

2

(Me C) P—NH—MMe n

3

2

2

(Me C) PNHLi 3

2

(Me C) P—NLi—MMe M'Me

B u L l >

3

2

2

3

3

Me^M'Cl

(Me C) P—NLi—MMe 3

2

1

y

3

(Me C) P=N—MMe 3

2

3

w h e r e M is Si o r G e , a n d M ' is Si, G e , o r S n . (6) A m o n o p h o s p h a z e n e is f o r m e d w h e n reacts with 7V-methyl-hexamethyldisilazane.

diphenyltrifluorophosphorane

95

Ph PF + MeN(SiMe ) -* P h F P = N M e + 2 Me SiF 2

3

3

2

2

3

(7) M o n o p h o s p h a z e n e s c a n a l s o b e i s o l a t e d f r o m t h e r e a c t i o n o f p h o s ­ p h o r u s pentachloride with a n aryl-7V-dichlorosulfonamide.

206

P C 1 + C l N S 0 A r -> 2 Cl + C l P = N S 0 A r 5

2

2

2

3

2

(8) T r i a r y l p h o s p h i t e s a r e c o n v e r t e d t o m o n o p h o s p h a z e n e s b y t h e f o l l o w i n g process

2 0 7

:

NCI

NP(OAr)

il

Cl* - i î Î U

li

AlkC—NH + P(OAr) 2

AlkC—NH 3

N=P(OAr)

9 3

2

-HCl

I AlkC=NH

3

117

A. GENERAL S U R V E Y OF SYNTHETIC R O U T E S

(9) I t h a s b e e n s h o w n t h a t t h e r e a c t i o n b e t w e e n t h i o p h o s p h o r i c t r i s ( i s o t h i o c y a n a t e ) a n d c h l o r i n e l e a d s t o t h e f o r m a t i o n of 7 V - t r i c h l o r o m e t h y l t r i c h l o r o phosphazene.

2 0 8

S = P ( N C S ) + Cl -> C1 P=N—CC1 + SC1 + S C1 + Cl—S—CC1 3

2

3

3

2

2

2

3

(10) Sulfur o x i d e ( f l u o r o s u l f o n y l ) i m i d e r e a c t s w i t h p h o s p h o r u s p e n t a b r o m i d e t o yield P - t r i b r o m o - 7 V - f l u o r o s u l f o n y l m o n o p h o s p h a z e n e . 208a

F S 0 N = S = 0 + PBr -> F S 0 N = P B r + SOBr 2

5

2

3

2

(11) F i n a l l y , a m i n o p h o s p h i n e s of f o r m u l a R P — N H R ' ( w h e r e R = P h o r 2

O E t , a n d R ' = P h o r Pr") r e a c t r a p i d l y w i t h c a r b o n t e t r a c h l o r i d e o r b r o m o t r i c h l o r o m e t h a n e t o give m o n o p h o s p h a z e n e s . R P—NHR' + CCI4 -> Ph P(Cl)NHPh-CCl 2

4.

2

2

2 0 9

-> Ph P(Cl)=NPh + CHC1 2

2

S Y N T H E S I S OF S O M E M I S C E L L A N E O U S P H O S P H O R U S - N I T R O G E N C O M P O U N D S

P h o s p h o r u s p e n t a c h l o r i d e r e a c t s w i t h A ^ W - d i m e t h y l u r e a t o yield a h e t e r o ­ cyclic m o l e c u l e w h i c h c o n t a i n s p h o s p h o r u s , n i t r o g e n , a n d c a r b o n . 2 1 0

.Cl

Ο

PCI5 + OC(NHMe)

MeN"

s

C1^®^C1

NMe

MeN

I

2

+

c^

NMe

P s

I

ci-

I

X

Me

Me

XXVI

XXVII

A n o t h e r i n t e r e s t i n g series of h e t e r o c y c l i c s y s t e m s is f o r m e d w h e n p h o s p h o r i c dichlorides interact with Λ^Ν'-dimethylalkylenediamines. 211

Me

Me

Ο

II ^ C l

RP.

XI

ΗΝ

+

χ

HN'

.(CH )„

2Et N

2

3

„ 1 >•

HCl

CK

.N.

^ P ^ >CH )„ R N^ 2

I

I

Me (λ =

1

Me

or 2).

B i s ( d i p h e n y l p h o s p h i n o ) a m i n e s r e a c t w i t h c h l o r a m i n e a n d a m m o n i a in t h e m a n n e r shown by the e q u a t i o n

2 1 2

NH /PPh RN. ^PPh

2

+2NH C1 + NH 2

2

3

RN.

.PPh

2

"PPh

2

C l + NH4CI e

NH

2

118

4.

SYNTHESIS OF THE P H O S P H O R U S - N I T R O G E N SKELETON

It is a l s o w o r t h w h i l e t o n o t e t h a t t h e l i n e a r p h o s p h a z e n e f o r m e d b y t h e i n t e r a c t i o n of p h o s p h o r u s p e n t a c h l o r i d e w i t h sulfuryl a m i d e c a n b e cyclized w i t h h e x a m e t h y l d i s i l a z a n e o r a m m o n i a t o yield t w o n o v e l h e t e r o a r o m a t i c systems, X X V I I I and X X I X 2 1 3

PC1 + H N — S 0 — N H 5

2

2

o

-> C I P = N — S 0 — N = P C 1

2

3

2

3

o

2

N ^ N C1 P^ /PC1 2

2

N ^ N

N

I

2

NH4

II

(NH ) P^

2

P(NH )

2

2

2

Me XXVIII

XXIX

A n u m b e r of o t h e r i n t e r a c t i o n s w h i c h i n v o l v e t h e s y n t h e s i s of p h o s p h o r u s nitrogen-sulfur ring systems have been r e p o r t e d .

Ph / NBr P^ Me S^ + ^CH Ν Br Ρ Ph

Ph Ν—Ρ / \ Me S CH W / Ν—Ρ Ph . 2

2

2

2 1 4

2

2

2

2ΒΓ

2

2

120°C hv

Ph Ν—Ρ // "\\ Me—S ;CH 2

Ν—Ρ Ph

NH,

/

Ph N =Ρ

2

\

S CH / W N - -P Ph

-NH Br 4

2

2

Ph ^N—Br Me S:^ + NH ^N—Br Ρ Ph

Ph Ν—Ρ

2

2

2

-HBr

//

Br

2

J

2

N\

Me S ΪΝ W Ν—Ρ Ph 2

2

Br-

Θ

A.

119

GENERAL SURVEY OF SYNTHETIC ROUTES

S c h m i d p e t e r a n d c o - w o r k e r s h a v e r e p o r t e d a series of s y n t h e s e s w h i c h give rise t o d i p h o s p h a - s - t r i a z i n e s

(XXX).

2 1 5

2 2 1

These reactions are

outlined

below. R I

[C1 P=N—C=NPCl ]®SbCl ® 3

3

6

NH4CI

R

I

R

2

P^ /PR N

2

XXX R

RNHCH=NR

I

H NC=NH/or 1 [H NC—NH ] C1

,-RNH

2

+

2

R' R [CI—P--=N—P—C11 CI2

2

2

2

NH

+

3

-HCl

R' R H NP=N—P=NH 2

2

2

R = P h or Cl A r e l a t e d e i g h t - m e m b e r e d r i n g s y s t e m ( X X X I ) is f o r m e d b y t h e f o l l o w i n g 222.

reaction s e q u e n c e ^ : NP(OAr)

NX

I

I!

3

[ArCNH l®X® 2

ArCNH + P(OAr') 2

-HCl

3

Et N 3

- Ar'OH

X = Cl or Br

Ar

Ar

I

A r

O

ι ^OAr'

Ι

Ο -

P

Ν'

- N = C I

Ar XXXI

N

H

.C=N. ^P(OAr)

I

II

(ArO) P " N = C " Ν 2

I

Ar

2

120

4.

S Y N T H E S I S

O F

T H E

P H O S P H O R U S - N I T R O G E N

S K E L E T O N

F i n a l l y , a t t e n t i o n is d i r e c t e d t o t h e " p h o s p h a m s " w h i c h a r e p h o s p h o r u s n i t r o g e n c o m p o u n d s of c o m p o s i t i o n P N H . 2

2 2 3

They are formed during the

a m m o n o l y s i s of p h o s p h o r u s p e n t a c h l o r i d e , o r b y p y r o l y s i s o f a m i n o c y c l o phosphazenes. [(NH ) P-N] 2

2

-> [(NPNH) L, + 3 N H

3

3

3

P h o s p h a m s can be decomposed thermally to triphosphorus

pentanitride,

( P N ) „ , a n d p h o s p h o r u s nitride, (PN)„. 3

5

B . The Reaction between Halophosphoranes and Ammonium H a l i d e s

1.

E X P E R I M E N T A L

A

N

D

M A N U F A C T U R I N G

C O N S I D E R A T I O N S

It w a s m e n t i o n e d e a r l i e r t h a t t h e r e a c t i o n b e t w e e n p h o s p h o r u s p e n t a ­ c h l o r i d e a n d a m m o n i u m c h l o r i d e t o yield c h l o r o p h o s p h a z e n e s c o m p r i s e s o n e o f t h e m o s t i m p o r t a n t s y n t h e t i c r e a c t i o n s in t h i s field. F o r t h i s r e a s o n , t h e f o l l o w i n g d e t a i l e d e x p e r i m e n t a l o u t l i n e is given. a. Synthesis of (7VTC/ ) , ( 7 V P C / ) , and Higher Homologues t o r y p r o c e d u r e b a s e d o n ref. 13) 2

3

2

(Standard labora­

4

A 2-liter flask is fitted w i t h a reflux c o n d e n s e r a n d is c h a r g e d w i t h p h o s p h o r u s p e n t a c h l o r i d e (625.5 g, 3.0 m o l e s ) , a m m o n i u m c h l o r i d e (176.5 g, 3.3 m o l e s ) , a n d ^ m - t e t r a c h l o r o e t h a n e (1.0 liter). T h e m i x t u r e is h e a t e d a t t h e reflux t e m p e r a t u r e of t h e s o l v e n t for 7.5 h o u r s , d u r i n g w h i c h t i m e h y d r o g e n c h l o r i d e (12.0 m o l e s ) is e v o l v e d . H y d r o g e n c h l o r i d e f u m e s c a n b e r e m o v e d b y a w a t e r s c r u b b e r device c o n n e c t e d t o t h e c o n d e n s e r o u t l e t . A f t e r c o m p l e t i o n o f t h e r e a c t i o n , t h e w a r m s o l u t i o n is filtered t o r e m o v e a m m o n i u m c h l o r i d e (20.0 g ) , a n d t h e s o l v e n t is r e m o v e d b y d i s t i l l a t i o n a t r e d u c e d p r e s s u r e . T h e r e s i d u e after d i s t i l l a t i o n is a b r o w n " b u t t e r y " m i x t u r e of oil a n d c r y s t a l s (326.5 g, 9 3 . 9 % ) . R e p e a t e d e x t r a c t i o n of t h i s m i x t u r e w i t h p e t r o l e u m ( b . p . 4 0 ° - 6 0 ° C ) yields a m i x t u r e of cyclic ( N P C 1 ) „ o l i g o m e r s (235.5 g, 66.9 % ) , a n d t h e r e s i d u e is a light b r o w n m i x t u r e of oily l i n e a r species (88.0 g, 2 7 % ) . T h e l o w e r cyclic c h l o r o ­ phosphazenes are quite stable to atmospheric moisture, whereas the linear a n a l o g u e s h y d r o l y z e slowly. 2

I n a t y p i c a l p r e p a r a t i o n , t h e cyclic o l i g o m e r f r a c t i o n c o n s i s t s of a b o u t 37 % ( N P C 1 ) , 2 8 % ( N P C 1 ) , a n d 3 5 % h i g h e r cyclic ( N P C 1 ) „ species. S e v e r a l m e t h o d s a r e a v a i l a b l e for t h e s e p a r a t i o n of t h i s m i x t u r e . F r a c t i o n a l s u b l i m a ­ t i o n o r d i s t i l l a t i o n p e r m i t s a facile s e p a r a t i o n of t r i m e r f r o m h i g h e r h o m o ­ l o g u e s . F r a c t i o n a l c r y s t a l l i z a t i o n f r o m light p e t r o l e u m o r ^ - h e p t a n e p r o v i d e s a l a b o r i o u s b u t effective m e a n s of s e p a r a t i o n of t h e l o w e r h o m o l o g u e s . A n a d d i ­ t i o n a l s e p a r a t i o n m e t h o d r e p o r t e d b y P a d d o c k a n d c o - w o r k e r s is a s f o l l o w s . 2

3

2

4

2

1 3

Β .

T H E

R E A C T I O N

B E T W E E N

H A L O P H O S P H O R A N E S

A

N

D

A M M O N I U M

H A L I D E S

121

A m i x t u r e o f p r e d o m i n a n t l y cyclic c h l o r o p h o s p h a z e n e s ( 7 7 5 0 g) is e x t r a c t e d w i t h 16.5 liters o f 4 0 ° - 6 0 ° C b . p . p e t r o l e u m t o o b t a i n 19.5 liters o f a s o l u ­ t i o n o f cyclic species ( 5 7 0 0 g c o n s i s t i n g o f 35 % t r i m e r a n d 22 % t e t r a m e r ) a n d i n s o l u b l e l i n e a r species (2050 g). T h e p e t r o l e u m s o l u t i o n is e x t r a c t e d b a t c h e s w i t h 9 8 . 7 % sulfuric a c i d (2300 m l ) i n a t h r e e - s t a g e

in

fractionation

s c h e m e . T r i m e r is d i s s o l v e d p r e f e r e n t i a l l y b y t h e a c i d a n d is r e c o v e r e d f r o m it b y d i l u t i n g t h e a c i d s o l u t i o n t o a p p r o x i m a t e l y 6 0 % sulfuric a c i d a n d b a c k e x t r a c t i n g t h e p r e c i p i t a t e d t r i m e r w i t h fresh p e t r o l e u m .

Fractional

crys­

t a l l i z a t i o n f r o m t h i s s o l u t i o n t h e n gives t r i m e r (1060 g ) , m . p . 112°, a n d a m i x e d p o l y m e r f r a c t i o n (690 g ) . C r y s t a l l i z a t i o n of t h e sulfuric a c i d - i n s o l u b l e p o r t i o n yields t e t r a m e r (712 g ) , m . p . 122°, 515 g o f a 6 9 % t r i m e r , 2 0 % t e t r a m e r m i x ­ t u r e , 808 g of a m i x t u r e o f oil a n d c r y s t a l s , a n d 1915 g of a l i g h t y e l l o w oil. T h e oily f r a c t i o n s a r e distilled a t r e d u c e d p r e s s u r e t o yield p e n t a m e r , h e x a m e r , h e p t a m e r , a n d octamer. After

final

recrystallizations from

petroleum

or

Η - h e p t a n e , t h e t r i m e r m e l t s a t 112.8° a n d t h e t e t r a m e r a t 122.8°.

b . Modified

Synthesis for Optimization

Paddock and co-workers

1 3

of Cyclic Chlorophosphazene

Formation

h a v e a l s o s h o w n t h a t t h e yield o f cyclic c h l o r o ­

p h o s p h a z e n e s c a n b e i m p r o v e d d r a m a t i c a l l y a t t h e e x p e n s e of t h e oily l i n e a r species b y m a i n t a i n i n g a n excess o f a m m o n i u m c h l o r i d e i n t h e

reaction

m i x t u r e . F o r e x a m p l e , p h o s p h o r u s p e n t a c h l o r i d e (62.5 g, 0.3 m o l e ) a n d a m m o ­ n i u m c h l o r i d e (176.5 g, 3.3 m o l e s ) w e r e h e a t e d in b o i l i n g .yyra-tetrachloroe t h a n e , 1.0 liter). T h e refluxing s o l v e n t w a s r e t u r n e d t o t h e r e a c t i o n vessel t h r o u g h a b e d o f p h o s p h o r u s p e n t a c h l o r i d e (563 g, 2.7 m o l e s ) w h i c h w a s slowly e x t r a c t e d i n t o t h e r e a c t i o n m i x t u r e d u r i n g a p e r i o d of 6 h o u r s . A f t e r a t o t a l r e a c t i o n t i m e of 7.5 h o u r s , 11 m o l e s (92 % ) of h y d r o g e n c h l o r i d e h a d b e e n e v o l v e d a n d a 21.7 g excess o f a m m o n i u m c h l o r i d e r e m a i n e d . T h e s o l u t i o n yielded 322.3 g ( 9 2 . 6 % ) o f cyclic species w h i c h c o n s i s t e d of a p p r o x i m a t e l y 5 4 % of t r i m e r , 1 1 . 4 % of t e t r a m e r , a n d 2 9 % o f h i g h e r cyclic species. S i m i l a r results were obtained w h e n w a r m p h o s p h o r u s pentachloride solution was a d d e d slowly t o t h e r e a c t i o n m i x t u r e . I t s h o u l d b e n o t e d t h a t a n excess o f p h o s p h o r u s p e n t a c h l o r i d e in t h e r e a c t i o n m i x t u r e f a v o r s t h e f o r m a t i o n

of

l i n e a r species r a t h e r t h a n cyclic c o m p o u n d s a n d t h a t t r e a t m e n t o f cyclic c h l o r o ­ p h o s p h a z e n e s w i t h p h o s p h o r u s p e n t a c h l o r i d e gives l i n e a r c o m p o u n d s

of

formula ( N P C l ) P C l . 2

n

Emsley a n d U d y

5

2 2 4

have pointed out that the a m m o n i u m chloride particle

size h a s a g r e a t e r influence o n t h e c o u r s e of t h e r e a c t i o n t h a n t h e r a t e of a d d i ­ t i o n of p h o s p h o r u s

pentachloride. T h e use of

finely

divided

ammonium

c h l o r i d e i n c r e a s e s t h e r e a c t i o n r a t e a n d f a v o r s t h e f o r m a t i o n of cyclic c h l o r o ­ p h o s p h a z e n e s . R e a c t i o n t i m e s a s s h o r t as 2.5 h o u r s h a v e b e e n

reported.

T h i s influence is a r e s u l t of t h e fact t h a t a m m o n i u m c h l o r i d e is v i r t u a l l y

122

4.

S Y N T H E S I S

O F

T H E

P H O S P H O R U S — N I T R O G E N

S K E L E T O N

i n s o l u b l e in s - t e t r a c h l o r o e t h a n e a n d s u r f a c e effects a r e i m p o r t a n t . R e a c t i o n s carried o u t at high dilutions favor the f o r m a t i o n of ( N P C 1 ) at the expense of l i n e a r p r o d u c t s . 2

c. Solvents

and

3

Catalysts

.sym-Tetrachloroethane h a s been used as a solvent for the p h o s p h o r u s p e n t a c h l o r i d e - a m m o n i u m c h l o r i d e r e a c t i o n since t h e p i o n e e r i n g w o r k of S c h e n k a n d R o m e r in 1 9 2 4 . T h e a d v a n t a g e s o f t h i s m a t e r i a l a s a r e a c t i o n m e d i u m i n c l u d e its h i g h b o i l i n g p o i n t , its r e l a t i v e i n e r t n e s s t o r e a c t a n t s a n d p r o d u c t s , a n d t h e fact t h a t it is a s o l v e n t for p h o s p h o r u s p e n t a c h l o r i d e a n d c h l o r o p h o s p h a z e n e s . H o w e v e r , . y y r a - t e t r a c h l o r o e t h a n e is relatively e x p e n s i v e , highly toxic, a n d inconvenient to r e m o v e by distillation. F o r these reasons, a t t e m p t s h a v e b e e n m a d e t o find m o r e s u i t a b l e r e a c t i o n m e d i a a n d t o d i s c o v e r c a t a l y s t s for t h e s y n t h e s i s . 8

M o n o c h l o r o b e n z e n e is less t o x i c t h a n t e t r a c h l o r o e t h a n e , it is c h e a p e r , a n d it h a s a l o w e r b o i l i n g p o i n t . H o w e v e r , a t least 2 5 t o 30 h o u r s a r e r e q u i r e d b e f o r e t h e r e a c t i o n is c o m p l e t e a t t h e b o i l i n g p o i n t o f t h i s s o l v e n t . It h a s b e e n shown that the addition of 1-10% of a n h y d r o u s metal chlorides reduces the r e a c t i o n t i m e t o 5 t o 10 h o u r s in c h l o r o b e n z e n e o r 2 t o 4 h o u r s in .syra-tetrachloroethane. Suitable chlorides include stannic chloride, magnesium chloride, zinc chloride, and titanium t e t r a c h l o r i d e . ' Molybdenum pentachloride h a s a m a r k e d c a t a l y t i c e f f e c t . Q u i n o l i n e a l s o a c t s a s a c a t a l y s t in c h l o r o ­ b e n z e n e , a n d r e a c t i o n t i m e s o f 8 h o u r s h a v e b e e n r e p o r t e d . It h a s a l s o b e e n r e p o r t e d t h a t p h o s p h o r u s o x y c h l o r i d e ( o r r e a g e n t s s u c h a s w a t e r , w h i c h will give rise t o P O C l in t h e r e a c t i o n m i x t u r e ) r e d u c e t h e r e a c t i o n t i m e in symt e t r a c h l o r o e t h a n e t o 3.5 h o u r s . N i t r o b e n z e n e c a n a l s o b e u s e d a s a m e d i u m for t h e s y n t h e s i s a t t e m p e r a t u r e s in t h e 1 4 0 ° - 1 5 0 ° C r e g i o n . T h e r e a c t i o n a p p a r e n t l y r e q u i r e s 5 - 6 h o u r s for c o m p l e t i o n u n d e r t h e s e c o n d i t i o n s . 1 4

1 4

3 1

38

3 6

3

3 2

3 5

d. Solid-State

Reactions

I n 1942 S t e i n m a n , S c h i r m e r , a n d A u d r i e t h r e p o r t e d a c o n v e n i e n t s y n t h e s i s of chlorophosphazenes using n o solvent at a l l . T h e technique involved the heating of an intimate mixture of p h o s p h o r u s pentachloride a n d a m m o n i u m c h l o r i d e in a l a r g e d i a m e t e r ( 3 5 - 5 0 m m ) P y r e x glass test t u b e . T h e o u t e r s e c t i o n of the t u b e contained a m m o n i u m chloride only. After 4 - 6 h o u r s at 145°160°C, a 9 0 - 9 5 % c o n v e r s i o n t o cyclic c h l o r o p h o s p h a z e n e s w a s o b t a i n e d . T h i s r e a c t i o n h a s b e e n r e i n v e s t i g a t e d m o r e r e c e n t l y in t h e U S S R , w h e r e yields of u p t o 85 % w e r e r e p o r t e d . I n view of t h e s e r e p o r t s , s o l i d - s t a t e r e a c t i o n s w o u l d a p p e a r t o p r o v i d e a c o n v e n i e n t s m a l l - s c a l e r o u t e for t h e p r e p a r a t i o n of chlorophosphazenes. 1 0

3 4 , 3 7

Β .

T H E

R E A C T I O N

e. Safety

B E T W E E N

H A L O P H O S P H O R A N E S

A

N

D

A M M O N I U M

H A L I D E S

123

Considerations

A l t h o u g h s m a l l - s c a l e l a b o r a t o r y p r e p a r a t i o n s o f c h l o r o p h o s p h a z e n e s offer n o particular hazards, a d e q u a t e care should be taken to prevent inhalation of r e a c t i o n p r o d u c t s a n d s o l v e n t s . ^ m - T e t r a c h l o r o e t h a n e is a p o w e r f u l i n h a l a ­ t i o n p o i s o n a n d a d e q u a t e v e n t i l a t i o n is r e q u i r e d for l a r g e - s c a l e h a n d l i n g o f t h i s m a t e r i a l . T h e c o n s i d e r a b l e q u a n t i t i e s of h y d r o g e n c h l o r i d e e v o l v e d f r o m t h e s e syntheses present a serious problem, and water extractors and scrubbers are n e c e s s a r y t o p r e v e n t d i s c o m f o r t t o p e r s o n n e l a n d severe c o r r o s i o n of f u m e h o o d s , etc. T h e l o w e r c h l o r o p h o s p h a z e n e s ( p a r t i c u l a r l y t h e t r i m e r ) h a v e a relatively h i g h v a p o r p r e s s u r e a t r o o m t e m p e r a t u r e , a n d t h e y c a n b e d e t e c t e d by their rather pleasant " o r g a n i c " odor. However, precautions should be taken t o a v o i d i n h a l a t i o n o f t h e v a p o r , o r e x p o s u r e of t h e eyes t o it. E v e n s m a l l c o n c e n t r a t i o n s c a u s e p r o l o n g e d i r r i t a t i o n o f t h e eye m e m b r a n e s , a n d m a n y r e s e a r c h e r s h a v e c o m p l a i n e d o f " c o n j u n c t i v i t i s " several d a y s after e x p o s u r e to the trimer. T e m p o r a r y t h r o a t and lung irritation has also been reported f o l l o w i n g i n h a l a t i o n o f t h e s e c o m p o u n d s . It follows t h a t c h l o r o p h o s p h a z e n e s s h o u l d n e v e r b e h e a t e d a n d v o l a t i l i z e d in t h e o p e n l a b o r a t o r y . L a r g e q u a n t i t i e s of chlorophosphazenes should be handled with a d e q u a t e ventilation and with t h e u s e of p r o t e c t i v e c l o t h i n g . f. The Manufacture

of

Chlorophosphazenes

Several c o m p a n i e s have u n d e r t a k e n the m a n u f a c t u r e of hexachlorocyclot r i p h o s p h a z e n e , a n d a n u m b e r of p a t e n t s c o v e r i n g c o m m e r c i a l p r o c e s s e s h a v e been i s s u e d . I n g e n e r a l , t h e m a n u f a c t u r i n g p r o c e s s a p p e a r s t o follow t h e s a m e p r o c e d u r e s as the laboratory-scale p r e p a r a t i o n s described above. T h e p a t e n t l i t e r a t u r e stresses t h e n e e d for a s l o w a d d i t i o n of p h o s p h o r u s p e n t a ­ c h l o r i d e t o a n excess o f a m m o n i u m c h l o r i d e in ^ m - t e t r a c h l o r o e t h a n e in o r d e r t o i m p r o v e t h e yield of cyclic r a t h e r t h a n l i n e a r s p e c i e s . T h e u s e of m e t a l h a l i d e s a s c a t a l y s t s a n d t h e u s e of c h l o r o b e n z e n e a s a s o l v e n t h a v e a l s o b e e n d e s c r i b e d in p a t e n t s p e c i f i c a t i o n s . A f u r t h e r m o d i f i c a t i o n i n v o l v e s t h e u s e of c h l o r i n e a n d p h o s p h o r u s t r i c h l o r i d e in p l a c e o f p h o s p h o r u s p e n t a ­ chloride. 1 4 - 2 2

1 4 , 1 5 , 1 6

14

2 0

N o s e r i o u s t e c h n o l o g i c a l p r o b l e m s a r e i n v o l v e d in s c a l i n g u p t h e l a b o r a t o r y r e a c t i o n , a n d l a r g e - s c a l e s y n t h e s e s c a n b e c a r r i e d o u t in t h e l a b o r a t o r y o r p i l o t p l a n t . T h e m o s t s e r i o u s p r o b l e m is c o n n e c t e d w i t h t h e i s o l a t i o n a n d purifica­ t i o n of t h e p r o d u c t s . F o r t h i s r e a s o n , c r u d e m i x t u r e s of c h l o r o p h o s p h a z e n e s c a n b e p r o d u c e d q u i t e c h e a p l y , b u t t h e p u r e cyclic t r i m e r is e x p e n s i v e . O n e p a t e n t h a s s u g g e s t e d t h a t p u r i f i c a t i o n m a y b e effected b y t h e r m a l d e p o l y m e r i z a t i o n o f t h e c r u d e m i x t u r e t o yield d i s t i l l a b l e t r i m e r a n d t e t r a m e r . Dif­ f e r e n t i a l p a r t i t i o n i n g of t h e c h l o r o p h o s p h a z e n e s b e t w e e n a n i n e r t o r g a n i c sol­ v e n t a n d a s t r o n g m i n e r a l acid is a l s o s u g g e s t e d a s a p u r i f i c a t i o n p r o c e s s . 2 1

1 7

124

4.

S Y N T H E S I S

O F

T H E

P H O S P H O R U S - N I T R O G E N

S K E L E T O N

All t h e a b o v e f a c t o r s a r e of s o m e c o n s e q u e n c e in view of t h e c o m m e r c i a l p o t e n t i a l of m a n y of t h e p h o s p h a z e n e d e r i v a t i v e s d e r i v e d f r o m h e x a c h l o r o c y c l o t r i p h o s p h a z e n e . I n fact, t h e l a c k o f a n i n e x p e n s i v e r o u t e f o r t h e m a n u ­ f a c t u r e of c h l o r o p h o s p h a z e n e s h a s b e e n t h e p r i n c i p a l b o t t l e n e c k for a n u m b e r of i m p o r t a n t t e c h n o l o g i c a l p r o c e s s e s . g.

Bromophosphazenes

B r o m o p h o s p h a z e n e s a r e s y n t h e s i z e d w i t h t h e u s e of t h e s a m e g e n e r a l t e c h ­ n i q u e a s d e s c r i b e d a b o v e f o r c h l o r o p h o s p h a z e n e s . H o w e v e r , since p h o s p h o r u s p e n t a b r o m i d e is u n s t a b l e , t h e s y n t h e s i s is u s u a l l y c o n d u c t e d b y a d d i t i o n of b r o m i n e t o a m i x t u r e of p h o s p h o r u s t r i b r o m i d e a n d a m m o n i u m b r o m i d e in a h o t s o l v e n t . L o s s of p h o s p h o r u s b r o m i d e s b y s u b l i m a t i o n is a v o i d e d b y slowly raising the reaction t e m p e r a t u r e to ~140°C. T h e following experimental p r o ­ c e d u r e is b a s e d o n t h e o n e r e p o r t e d b y J o h n a n d M o e l l e r . 4 6

A m i x t u r e of p h o s p h o r u s t r i b r o m i d e (300 g, 1.1 m o l e ) , b r o m i n e (200 g, 1.25 m o l e ) , a n d a m m o n i u m b r o m i d e (300 g, 3.06 m o l e ) in s j r a - t e t r a c h l o r o e t h a n e (600 m l ) is h e a t e d t o 1 4 0 ° - 1 4 2 ° C o v e r a p e r i o d of 5 d a y s . T h e t e m p e r a t u r e is m a i n t a i n e d a t 142°C for 2 d a y s , a n d a d d i t i o n a l b r o m i n e (150 g, 0.94 m o l e ) is a d d e d . A f t e r c o m p l e t i o n o f t h e r e a c t i o n , u n r e a c t e d a m m o n i u m b r o m i d e is filtered off a n d t h e s o l v e n t is r e m o v e d b y d i s t i l l a t i o n t o l e a v e 255.2 g o f c r u d e b r o m o p h o s p h a z e n e s . E x t r a c t i o n w i t h h o t b e n z e n e r e m o v e s cyclic t r i m e r a n d t e t r a m e r , a n d s o l v e n t e v a p o r a t i o n f o l l o w e d b y s u b l i m a t i o n yields 119 g ( 5 2 . 5 % ) of a t r i m e r - t e t r a m e r m i x t u r e . A m o d i f i c a ­ t i o n of t h e r e a c t i o n b y a d d i t i o n of a p h o s p h o r u s t r i b r o m i d e - b r o m i n e m i x t u r e t o a m m o n i u m b r o m i d e a n d t e t r a c h l o r o e t h a n e a t 1 3 2 ° - 1 3 4 ° C yields 89.9 g (36.9 % ) of a t r i m e r - t e t r a m e r m i x t u r e . It s h o u l d b e n o t e d t h a t t h e m o n o p h o s p h a z e n e N P B r P B r is f o r m e d in s u b s t a n t i a l yields in t h e s e r e a c t i o n s . T h e cyclic t r i m e r - t e t r a m e r m i x t u r e c a n b e s e p a r a t e d i n t o its c o m p o n e n t s b y frac­ tional sublimation or recrystallization from petroleum ether. Bromocyclop h o s p h a z e n e s a r e less s t a b l e t o a t m o s p h e r i c m o i s t u r e t h a n t h e c h l o r o - d e r i v a tives, a n d p u r i f i c a t i o n p r o c e d u r e s s h o u l d b e c o n d u c t e d w i t h o u t excessive d e l a y . B r o m o c y c l o p h o s p h a z e n e s a r e u s e d in t h e m a n u f a c t u r e of h a l o g e n l a m p s . 2

5

2 2 4 a

s y m - T e t r a b r o m o e t h a n e c a n b e e m p l o y e d a s a s o l v e n t in p l a c e of t e t r a c h l o r o ­ e t h a n e . I n fact, e v i d e n c e exists t h a t h a l o g e n e x c h a n g e o c c u r s in t h e l a t t e r sol­ v e n t t o give m i x e d c h l o r o b r o m o p h o s p h a z e n e s . A s m e n t i o n e d earlier, h y b r i d halocyclophosphazenes are formed by related reactions. Mixed c h l o r o b r o m o species s u c h a s t h e s e c a n b e s e p a r a t e d effectively b y v a p o r - p h a s e c h r o m a t o ­ g r a p h y u s i n g a silicone oil s u b s t r a t e . 4 6

4 9

h.

Organophosphazenes

T h e p r e p a r a t i o n of o r g a n o c y c l o p h o s p h a z e n e s f r o m o r g a n o h a l o p h o s p h o r anes a n d a m m o n i u m halides follows the s a m e general techniques as outlined

Β. THE REACTION BETWEEN H A L O P H O S P H O R A N E S A N D A M M O N I U M HALIDES

125

a b o v e for h a l o p h o s p h a z e n e s y n t h e s i s . F o r e x a m p l e , t h e f o l l o w i n g p r e p a r a t i o n of ( N P C l P h ) w a s r e p o r t e d by G r u s h k i n , S a n c h e z , a n d R i c e . 6 5

3 a n d 4

A s o l u t i o n of P h P C l (358 g, 210 m o l e s ) in c h l o r o b e n z e n e (2 liters) is c h l o r i n a t e d u n t i l it is b r i g h t yellow in c o l o r , a n d n i t r o g e n is b u b b l e d t h r o u g h u n t i l t h e yellow c o l o r h a s d i s a p p e a r e d . T h i s s o l u t i o n of P h P C l is t h e n a d d e d slowly o v e r 12 h o u r s t o a s u s p e n s i o n of a m m o n i u m c h l o r i d e (214 g, 4.0 m o l e s ) in b o i l i n g c h l o r o b e n z e n e (8 liters). H y d r o g e n c h l o r i d e is t h e n r e m o v e d by a s t r e a m of n i t r o g e n . After a f u r t h e r 12 h o u r s of r e a c t i o n , t h e a m m o n i u m c h l o r i d e is r e m o v e d by filtration. R e m o v a l of a p p r o x i m a t e l y 75 % of t h e s o l v e n t f r o m t h e filtrate c a u s e s a slow p r e c i p i t a t i o n of cyclic t r i m e r s a n d t e t r a m e r s . T h e s e a r e s e p a r a t e d by a r a t h e r a r d u o u s series of crystalliza­ t i o n s f r o m fl-pentane. It s h o u l d b e n o t e d t h a t s u c h p r e p a r a t i o n s a r e c o m p l i ­ c a t e d c o n s i d e r a b l y if g e o m e t r i c i s o m e r s as well a s species w i t h different r i n g sizes a r e p r e s e n t , as in t h e p r e s e n t case. S e p a r a t i o n of cis a n d trans i s o m e r s c a n often b e a c c o m p l i s h e d by careful r e c r y s t a l l i z a t i o n s e q u e n c e s . T h e c o m p o u n d s are quite stable to atmospheric moisture. 2

4

2.

REACTION MECHANISMS

T h e s y n t h e s e s o u t l i n e d a b o v e c a n b e s u m m a r i z e d by t h e g e n e r a l e q u a t i o n η R PX + η N H X -* (R PN)„ + 4n HX 2

3

4

2

w h e r e R is h a l o g e n o r a n o r g a n i c g r o u p , a n d X is h a l o g e n . I n t h e s u b s e q u e n t d i s c u s s i o n it will b e a s s u m e d t h a t t h e g e n e r a l r e a c t i o n m e c h a n i s m s a r e s i m i l a r i r r e s p e c t i v e of t h e n a t u r e of R o r X . It m u s t be p o i n t e d o u t , h o w e v e r , t h a t m o s t of t h e m e c h a n i s t i c i n f o r m a t i o n a b o u t t h i s r e a c t i o n h a s b e e n d e r i v e d from s y s t e m s w h e r e R is c h l o r i n e . T h e f o l l o w i n g e x p e r i m e n t a l facts a r e k n o w n a b o u t this r e a c t i o n : (1) A l t h o u g h t h e m a i n r e a c t i o n l e a d s t o t h e f o r m a t i o n of cyclic p h o s p h a ­ z e n e s of s t r u c t u r e ( N P X ) „ , l i n e a r p h o s p h a z e n e species a r e n e a r l y a l w a y s formed at the same time. F o r example, the reaction between PC1 and N H C 1 in ^ m - t e t r a c h l o r o e t h a n e yields identifiable oily l i n e a r species of s t r u c t u r e s C1 P=N—PC1 =N—PC1 , C1 P(NPC1 ). = N — P C 1 , [C1 P=N— PC1 ]©[PC1 P a n d [ C 1 P = N — P C 1 = N — P C l ] ® [ P C I ] . ' ' ' Simi­ larly, t h e r e a c t i o n b e t w e e n p h o s p h o r u s t r i b r o m i d e , b r o m i n e , a n d a m m o n i u m b r o m i d e yields species w h i c h c o r r e s p o n d t o t h e s t r u c t u r e s [ B r P = N — P B r ] ® B r and B r P N P B r . F u r t h e r m o r e , a c o m p o u n d , which may have the structure [ P h B r P = N — P B r P h ] B r w a s i s o l a t e d f r o m t h e r e a c t i o n of p h e n y l d i b r o m o p h o s p h i n e a n d b r o m i n e w i t h a m m o n i u m b r o m i d e , a n d species of t h e t y p e s [Ph ClP=N—PClPh ]©Cl and [ P h C l P = N — P C l P h p C l are formed w h e n a m m o n i u m c h l o r i d e r e a c t s with diphenyltrichlorophosphorane, 2

5

1 4 2

3

2

4

1 3

3

2

1 0

4

e

3

6

3

2

3

2 5

3

2 6

3

5

@

2

G

2

6 4

e

2

2

e

2

1 4 3

1 4 6

6

0

2

4

2

3

126

4.

S Y N T H E S I S

O F

T H E

P H O S P H O R U S - N I T R O G E N

S K E L E T O N

P h P C l , or with phenyltetrachlorophosphorane, P h P C l . 2

3

4

5 8 ,

154

*

1 5 5

Linear

p h o s p h a z e n e s s u c h a s t h e s e a r e believed t o b e i n t e r m e d i a t e s in t h e s y n t h e s i s of cyclophosphazenes. Becke-Goehring and co-workers have provided evidence for t h e i o n i c s t r u c t u r e s o f m a n y o f t h e s e l i n e a r p h o s p h a z e n e s . T h e s e s t r u c t u r e s are comparable to the P C l

@ 4

PCl

f o r m u l a t i o n for p h o s p h o r u s p e n t a c h l o r i d e .

e 6

(2) Cyclic p h o s p h a z e n e s a r e f o r m e d w h e n l i n e a r species of t h e t y p e d e s c r i b e d a b o v e a r e h e a t e d in ^ m - t e t r a c h l o r o e t h a n e , p a r t i c u l a r l y in t h e p r e s e n c e o f a m m o n i u m h a l i d e o r a m m o n i a . F o r e x a m p l e , ( N P C 1 ) c a n b e f o r m e d directly 2

from

3

[C1 P=N—PC1 =N—PC1 P[PC1 P, and (NPC1 ) 3

2

[C1 P=N—PCl ]®Cl 3

3

6

2

and ammonium chloride.

e

3

4

is f o r m e d

from

2 6

(3) A s d i s c u s s e d earlier, if t h e r e a c t i o n b e t w e e n p h o s p h o r u s p e n t a c h l o r i d e a n d a m m o n i u m c h l o r i d e is c o n d u c t e d in s u c h a w a y t h a t a m m o n i u m c h l o r i d e is a l w a y s in excess, cyclic c h l o r o p h o s p h a z e n e s a r e f o r m e d in h i g h yields. If p h o s p h o r u s p e n t a c h l o r i d e is in excess, t h e l i n e a r species a r e f o r m e d in g r e a t e r amounts.

1 3

(4) L i n e a r p h o s p h a z e n e s c a n b e f o r m e d b y t h e t r e a t m e n t o f c y c l o p h o s p h a ­ zenes with p h o s p h o r u s p e n t a c h l o r i d e .

1 3

F o r example, a n intimate mixture of

( N P C 1 ) a n d P C 1 yields a m i x t u r e o f l i n e a r p h o s p h a z e n e s a t 3 5 0 ° C . L i n e a r 2

3

5

species of s t r u c t u r e C 1 P — ( N P C 1 ) „ N H a r e f o r m e d w h e n p h o s p h o r u s p e n t a ­ 3

2

c h l o r i d e a n d a m m o n i u m c h l o r i d e r e a c t in a n a u t o c l a v e in t h e a b s e n c e o f sol­ vent. (5) A m m o n i a c a n r e p l a c e a m m o n i u m c h l o r i d e in several of t h e s y n t h e t i c reactions with h a l o p h o s p h o r a n e s . F o r instance, diphenyltrichlorophosphora n e , P h P C I , r e a c t s w i t h l i q u i d a m m o n i a a t —4 0 ° C t o yield d i p h e n y l c y c l o p h o s p h a z e n e s , ( N P P h ) „ , plus a m m o n i u m c h l o r i d e . Similarly, M e N P C l reacts with a m m o n i a to form ( N P ( C l ) N M e ) . 2 4

2

3

5 4

2

2

4

3 9

2

3

T h e a b o v e facts s t r o n g l y f a v o r a m e c h a n i s m in w h i c h l i n e a r p h o s p h a z e n e s a r e f o r m e d a s i n t e r m e d i a t e s , p r i o r t o f o r m a t i o n of t h e cyclic species. A mechanism which has gained wide acceptance was proposed by BeckeGoehring and co-workers. F o r convenience, three steps c a n be f o r m u l a t e d for t h e o v e r a l l r e a c t i o n . T h e s e a r e m o n o p h o s p h a z e n e f o r m a t i o n , l i n e a r p o l y ­ merization, a n d cyclization. 2 5 , 2 6

a. Monophosphazene

Formation

P h o s p h o r u s pentachloride a n d a m m o n i u m chloride are assumed to function as t h e ionized a n d dissociated forms, respectively. PC1 ^ PC1 + PC1 5

NH4CI ^

4

NH

3

6

+ HCl

Β .

T H E

R E A C T I O N

B E T W E E N

H A L O P H O S P H O R A N E S

A

N

D

A M M O N I U M

H A L I D E S

127

A m m o n i a then reacts with the P C 1 cation according to the sequence 4

[PCl NPCl ] + NH

C1 P=NH + 2 HCl + PC1

e

4

6

3

3

5

P a d d o c k a n d S e a r l e suggested t h a t the t r i c h l o r o m o n o p h o s p h a z e n e could a l s o b e p r o d u c e d t h r o u g h t h e i n t e r m e d i a t e f o r m a t i o n of a m m o n i u m h e x a c h l o r o p h o s p h a t e , [NH ]®[PC1 P, which w o u l d be formed directly from P C 1 a n d NH4CI. 1 2

4

b . Linear

6

5

Polymerization

T h e m o n o p h o s p h a z e n e is t h e n believed t o r e a c t first w i t h [ P C l ] ® [ P C l ] a n d t h e n w i t h a m m o n i a in a c h a i n - l e n g t h e n i n g s e q u e n c e . e

4

6

C1 P=NH + [PCl ]®[PCl ] -> [C1 P=N—PCl ]®[PCl ] + HCl e

3

4

e

6

3

[C1 P=N—PCl ]®[PCl ] + N H 3

6

6

-> C1 P=N—PC1 =NH + 3 HCl + PC1

e

3

3

3

3

2

5

A v a r i e t y of c h a i n - g r o w i n g s t e p s a r e t h e n p o s s i b l e , i n c l u d i n g [C1 P=N—PC1 ]® + C1 P=NH -> [C1 P=N—PC1 =N—PC1 ]® + HCl 3

3

3

3

2

3

C1 P=N—PC1 =NH + [PCl ] "> [C1 P=N—PC1 =N—PC1 ]® + HCl e

3

2

4

3

2

3

C1 P=N—PC1 =NH + [C1 P=N—PC1 ]® -> [C1 P=
2

3

3

3

2

2

3

T h u s , g r o w t h of t h e c h a i n s t o c o n t a i n t h r e e , f o u r , five, six, o r a h i g h e r n u m b e r of p h o s p h o r u s a t o m s can be readily u n d e r s t o o d . In practice, the c o m p o u n d [ C 1 P = N — P C 1 ] [ P C 1 ] is t h e first species d e t e c t e d , ' and Emsley a n d Udy h a v e s h o w n t h a t it is f o r m e d in o v e r 80 % yield w i t h i n 80 m i n u t e s of t h e s t a r t of t h e r e a c t i o n a n d t h a t it is a l m o s t i n s o l u b l e in t h e m e d i u m . B e c a u s e of t h i s h e t e r o g e n e i t y , t h e n e x t h i g h e r m e m b e r s of t h e series, [ C 1 P = N — P C 1 = Ν — P C 1 ] [ P C 1 ] and [ C 1 P = N — P C 1 = N — P C 1 = N — P C 1 ] ® [ P C 1 ] , are f o r m e d o n l y slowly. @

3

0

3

2 2 5

2 2 6

6

2 2 5

3

φ

c.

2

0

3

0

6

3

2

2

3

6

Cyclization

C y c l i z a t i o n of t h e c h a i n is p o s s i b l e w h e n a t e r m i n a l N H g r o u p is p r e s e n t . S u c h a s i t u a t i o n c a n arise w h e n e v e r a c a t i o n - a n i o n c o m p l e x r e a c t s w i t h a m m o n i a or a m m o n i u m chloride. [C1 P=N—PC1 =N—PCl ]®[PCl ] + NH C1 -> e

3

2

3

6

4

C1 P=N—PC1 =N—PC1 =NH + 3 HCl + PC1 3

2

2

Cl C1 P=N—PC1 =N—PC1 =NH 3

2

2

-HCl

•

2

I || ChP^PCl,

5

128

4.

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T h u s , c y c l i z a t i o n w o u l d b e f a v o r e d b y a n excess o f a m m o n i u m h a l i d e a n d r e t a r d e d b y a n excess o f p h o s p h o r u s p e n t a c h l o r i d e . A n a l t e r n a t i v e a n d p r o b a b l y m o r e likely c y c l i z a t i o n m e c h a n i s m is o n e in w h i c h cyclic t r i m e r is f o r m e d f r o m t h e l i n e a r tetramer b y loss o f a P C 1 ® cation. 4

2 2 5

Cl P®—CI

Cl ρ

2

C I

2

P ^ P C I

2

2

CI P^ ^PCI 2

N

2

T h e r e l a t i v e p r o p o r t i o n s o f cyclic t r i m e r , t e t r a m e r , p e n t a m e r , e t c . , in t h e final r e a c t i o n m i x t u r e d e p e n d p a r t l y o n t h e a m o u n t s of l i n e a r p r e c u r s o r s p r e s e n t a n d , in t u r n , o n t h e efficiency of t h e c h a i n g r o w t h . R e m o v a l of s o m e l i n e a r species f r o m t h e r e a c t i o n p h a s e b e c a u s e o f t h e i r i n s o l u b i l i t y m u s t a l s o affect t h e final r a t i o s of cyclic species. F u r t h e r m o r e , t h e r e l a t i v e a m o u n t s of t h e v a r i o u s cyclic c o m p o u n d s will d e p e n d o n t h e steric a n d statistical ease of cycli­ z a t i o n of t h e l i n e a r p r e c u r s o r . T h i s u n d o u b t e d l y p r o v i d e s a n e x p l a n a t i o n for t h e fact t h a t cyclic d i m e r s a r e n o t i s o l a t e d , a n d t h a t t h e cyclic t r i m e r a n d t e t r a m e r a r e u s u a l l y f o r m e d in g r e a t e r a m o u n t s t h a n h i g h e r cyclic c o m p o u n d s . S t e r i c f a c t o r s i n v o l v i n g t h e side g r o u p ( R o r h a l o g e n ) m a y influence t h e rela­ tive e a s e of c y c l i z a t i o n t o t r i m e r s a n d t e t r a m e r s . I t a l s o s e e m s r e a s o n a b l e t o s u p p o s e t h a t c y c l i z a t i o n is f a v o r e d b y t h e p r e s e n c e o f s o l v e n t s in v i e w o f t h e k n o w n effects of d i l u t i o n o n t h e c y c l i z a t i o n c o n s t a n t s of m a n y p o l y m e r s .

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