Studies on photochemistry of aromatic hydrocarbons IV

Chemosphere ~]o. 6, pp 371 - 376, 1977.

STUDIES

Pergamon Press.

ON P H O T O C H E M I S T R Y

Printed in Great Britain.

OF AROMATIC

HYDROCARBONS

IV

M e c h a n i s m of formation of n i t r o p h e n o l s by the p h o t o c h e m i c a l r e a c t i o n of benzene and toluene with n i t r o g e n oxides in a~r Kazuhiro

Nojima

and Saburo

Kanno

Faculty of P h a r m a c e u t i c a l Sciences, Josai U n i v e r s i t y Keyakidal, Sakado, Saitama Pref., Japan (Received in Japan ~ M ~

1977; received in UK for publication i0 Maj 1977) Introduction

In the previous as benzene

and toluene

ult r a v i o l e t

ene,

paperl'2it

rays

were

was r e p o r t e d

converted

in the presence

of n i t r o g e n

paper

m-nitrotoluene

and p - n i t r o t o l u e n e

aromatic

and cresols nitrite

finally

the p h o t o c h e m i c a l

compounds

respectively

rearrangement,

orcduced

were

by the

followed

by the o x i d a t i o n

reaction

converted

liberation

oC n i t r o b e n z e n e ,

described.

at first

with

monoxide

exposed

to

o-nltrotolu-

It has been

to the

shown

correspondin~

monoxide

nitrogen

with

when

such

in air.

of n i t r o v e n

by n i t r a t i o n

of n i t r o g e n

derivatives

monoxide

has been

hydrocarbons

through

d~oxide,

the excess

that

ohenol

the nitro-

w h i c h was

of oxygen

in air,

to give nitrophenols.

The

experimental

nitrophenols oxides

nitro

the aromatic

to n i t r o p h e n o l

In the present

these

that

results

might

by the p h o t o c h e m i c a l

be related

r e a c ti o n

to the m e c h a n i s m

of aromatic

of formation

hydrocarbons

with

of

nitrogen

in air. Experimental

Irradiation

condition

erie, m - n i t r o t o l u e n e en r e s p e c t i v e l ~ re~oval ides. sel,

The which

5 hours

and p - n i t r o t o l u e n e

in the

of n - h e x a n e residual

nitrobenzene

a xenon

to I000 ~ I

lamp

solution

in n-hexane

i liter r e a c t i o n

and s u b s t i t u t i o n

corresponds

with

One ml of each

vessel

made

of Pyrex

deposited

if vaoorized,

(cut off below

900 nm)

371

o-nitrotolu-

(~1.46 x 10-5moles/ml)

with air or n i t r o < e n

or n i t r o t o l u e n e £as

of nitrobenzene,

was

slass,

free

followed

from n i t r o < e n

Dartiall>I

irradiated

described

was

takby ox-

in the ves-

at 25-30~C

in the previous

for

paper}

]72

No. 6

Test reaction solid

solution vessel

c omb i n e d text

in methanol,

was w a s h e d with

together

solution

irradiation

flask,

described

solution

twice

was

shaken

injected

until

transferred

and the m e t h a n o l

up to 20 ml with m e t h a n o l by the

at 0 - i 0 ~

sure,

made

and n i t r o t o l u e n e s was

directly

irradiation

into the

the y e l l o w i s h into

a flask.

solutions

and served

were as the

in air and B by the

after

However,

in the

the m e t h y l a t e d

excess

chromatograph

The m i x t u r e

diazomethane

The r e s u l t i n g

could not be s e p a r a t e d

of the two compounds,

equipped

with

aliquot

directly

was

was removed

case of 3 - m e t h y l - 6 - n i t r o p h e n o l

to i ml and a n a l y z e d

each

A was added

by gas c h r o m a t o g r a p h y - m a s s

compounds

identification

solution

mg CH2N2/ml).

up to i ml with methanol.

of n i t r o p h e n o l s

injected

of u n r e a c t e d

of the test

spectrometer

so-

under

I paper.

: To i0 ml of the test

and,

: For the analysis

LKB 9000 gas c h r o m a t o g r a p h - m a s s

in the previous

of d i a z o m e t h a n e 4 ( 1 0

night

trated

made

A was o b t a in e d

and n i t r o t o l u e n e s

condition

nalysis

the vessel

and the r e s u l t i n g

A and B into a S h i m a d z u

solution

respectively,

(I) N i t r o b e n z e n e

(2) N i t r o p h e n o l s

and

into the

i0 ml of m e t h a n o l

in nitrogen.

nitrobenzene

the

irradiation,

5 ml of m e t h a n o l

A and B, where

Analysis

lution

the

with a syringe

dissolved

The vessel

After

under

solution

to stand over-

diminished

was used

pres-

for the a-

spectrometry(GC-MASS). and

3-methyl-4-nitrophenol,

I0 ml of the test

a UV detector

allowed

by GC-MASS.

using a Jasco

5 ml of an e t h e r e a l

For the solution

TRI ROTOR

separation A was

concen-

high pressure

of 254 nm in w a v e l e n g t h

liquid

and a SS-05

col-

umn of 250 mm in length. (3) Phenols used

: Ten ml of the test

for the analysis

of phenols

solution

The

nitrotoluene yields

irradiation

of the p r o d u c t s

are

nitrophenol shown

to I ml, w h i c h was

and D i s c u s s i o n

of nitrobenzene,

in air y i e l d e d

concentrated

by GC-MASS.

Results I.

B was

o-nitrotoluene,

derivatives

in Table

I.

m-nitrotoluene

as shown

in Scheme

I.

and pThe

No. 6

373

~2

~N02

OH

002

in air Nitrobenzene

~

N02

OH

~ in air

2-Methyl-4-nitrophenol

2-Methyl-6nitrophenol

CH 3

CH~

I%1# 02

CH 3

~N02

in air

~

m-Nitrotoluene

v

~

+

"OH

in a i r

CH 3 H ÷

02N~H

NO2 3-Methyl-6nitrophenol

3-Methyl-2nitrophenol

3-Methyl-4nitrophenol

@2

NO2

OH 4-Methyl-2-nitrophenol

p-Nitrotoluene i.

+

2

o-Nitrot oluene

Scheme

p-Nitrophenol

o-Nitrophenol

P h o t o c h e m i c a l r e a c t i o n of n i t r o b e n z e n e

Through these experiments

and n i t r o t o l u e n e s

it is noticed that the r e a c t i o n did never afford

the directly h y d r o x y l a t e d derivatives of the original nitrotoluenes. in the case of o - n i t r o t o l u e n e toluene, sidered

in air

For example,

the r e a c t i o n did not give the h v d r o x y ! a t e d o-nltro-

but 2 - m e t h y l - 6 - n i t r o p h e n o l 5 a n d

2-methyl-~!-nitrophenol~

It might be con-

from these results that the p h o t o - e x c i t e d nitro compounds turned at first

into the c o r r e s o o n d i n g phenols,

followed by n i t r a t i o n as d i s c u s s e d later.

Hastings and M a t s e n 6 r e p o r t e d on the vapor phase p h o t o c h e m i s t r y of n i t r o b e n zene, which r e s u l t e d in n i t r o s o b e n z e n e

and p - n i t r o p h e n o l

ing mechanism.

O~ 0 +

6

&V (26oo~)

6N

+0

62 OH

a c c o r d i n ~ to the follow-

374

No. 6

However,

c o n s i d e r i n g the structures of the r e a c t i o n products

in our experi-

merits, it seems difficult to apply this m e c h a n i s m to the Formation of n i t r o p h e n o l derivatives m e n t i o n e d above. 2.

W h e n nitrobenzene,

i r r a d i a t e d in nitrogen,

o-nitrotoluene,

m-nitrotoluene

and p - n i t r o t o l u e n e were

the nitro group of each compound turned into the hydroxyl

group. In r e l a t i o n to the p h o t o c h e m i s t r y of the substituted nitrobenzene

derivatives,

Ki~aura and M a t s u u r a 7 s h o w e d that a nitro group was converted to a hydroxyl group only in the h i n d e r e d n i t r o b e n z e n e ni~robenzene

derivative such as 2,6-dimethyl-

in isopropyl alcohol,

or 2,6-dichloro-

the reason of which was based on the m e c h a n i s m

that the nitro group might be subject to the n i t r o - n i t r i t e r e a r r a n g e m e n t ~ However,

it was c l a r i f i e d that the n o t - h i n d e r e d n i t r o b e n z e n e

plDyed in our experiments were also subject to the n i t r o - n i t r i t e the vapor phase,

since the vibrational

by the irradiation. as shown in Scheme

6'

2.

2.

state of the nitro group might be enhanced

do

in n i t r o g e n

+

NO

OH

ONO

, ~]-C%

, [~]}-CH~ ÷

NO

in n i t r o g e n

P h o t o c h e m i c a l reaction of n i t r o b e n z e n e and n i t r o t o l u e n e s Table I.

Materials

in

The yields of the products are shown in Table i.

~'-~ c H3 ~'' Scheme

rearrangement

em-

Accordingly the r e a c t i o n in these experiments might proceed

NO2

v

derivatives

in n i t r o g e n

P h o t o c h e m i c a l reaction of aromatic nitro compounds

Rate of

Products

disappearance

(yield) c)

N i t r o b e n z e n e a)

38 %

o-Nitrophenol(3.1%),

Nitrobenzene b)

25 %

Phenol(5.8

c - N i t r o t o l u e n e a)

79 %

2-Methyl-6-nitrophenol(6.1%) 2 - M e t h y l - 4 - n i t r o p h e n o l ( 7 . 5 %)

o - N i t r o t o l u e n e b)

71%

o-Cresol(8.5

m - N i t r o t o l u e n e a)

20 %

3-Methyl-2-nitrophenol(trace) 3-Methyl-6-nitrophenol(trace) 3 - M e t h y l - 4 - n i t r o p h e n o l ( 4 . 6 %)

m - N i t r o t o l u e n e b)

18 %

m-Cresol(9.8

p - N i t r o t o l u e n e a)

38 %

4-Methyl-2-nitrophenol(6.1%)

p - N i t r o t o l u e n e b)

20 %

p-Cresol(2.9

a) R e a c t e d in air. b) Reacted in nitrogen, ty of d i s a p p e a r e d m a t e r i a l respectively.

c)

p-Nitrophenol(4.6

%)

%)

Z)

%)

%) Yield was based on the quanti-

No. 6

375

3.

In addition to the experiments

that the dark reaction oxides

of phenol,

o-cresol,

in air also yielded respectively

in Scheme

I.

For example,

nitrophenol.

The yields

Table

2.

o-cresol

above,

m-cresol

it has been ascertained

and p-cresol with nitrogen

the same nitrophenol

of the products

are shown in Table

Products

o-Cresol

2-Methyl-6-nitrophenol(30 2-Methyl-4-nitrophenol(36

% %

m-Cresol

3-Methyl-2-nitrophenol(12 3-Methyl-6-nitrophenol(25 3-Methyl-4-nitrophenol(24

% % %

p-Cresol

4-Methyl-2-nitrophenol(52

%

derivatives

ene as an example,

from nitrobenzene

could be rationalized

CH~ No2

k~

,

in air

nitro-nitrite .

in air

%), p-Nitrophenol(20

of original material

On the basis of these experimental

nitrophenol

2.

( y i e l d ) a)

o-Nitrophenol(22

Yield was based on the quantity

as shown

and 2-methyl-4-

Dark reaction of phenols with nitrogen oxides

Phenol

4.

derivatives

gave 2-methyl-6-nitrophenol

Materials

a)

mentioned

results,

respectively.

the formation m e c h a n i s m

and nitrotoluenes, by Scheme

%)

taking o-nitrotolu-

3.

CH3 ~ONO

,

÷

NO

rearrangement

o-Nitrotoluene

~

/ / OH +

NO 2

P

2-Methyl- 6-nit rophenol

o-Cresol CH 3

2-Methyl-4-nitrophenol Scheme

3.

Formation m e c h a n i s m of nitrophenols

of

from o-nltrotoluene

376

IJo. 6

Conclusion It is suggested on the basis of these observations that a photochemical action of aromatic hydrocarbons

re-

such as benzene and toluene with nitrogen oxides

in air might proceed through three steps, that is, first the nitration of the hydrocarbons with nitrogen dioxide,

second the conversion of the nitro group to the

hydroxyl group and third the nitration of phenols with nitrogen dioxide,

to result

in the formation of nitrophenol derivatives. References I.

II : K. Nojima,

2.

III:

K. Fukaya, S. Fukui and S. Kanno, Chemosphere,

K. Nojima, K. Fukaya,

S. Fukui,

S. Kanno,

4, 76 (1975).

S. Nishiyama and Y. Wada,

Chemosphere, 5, 25 (1976~. I : K. Nojlma,

K. Fukaya,

Organic Syntheses,

S. Fukui and S. Kanno, Chemosphere,

3, 247 (1974).

2, 165 (1966).

G. P. Gibson, J. Chem. Soc., 127, 44 (1925). S. Hastings and F. Matsen, J. Am. Chem. Soc., 7_O0, 3514 Y. Kitaura and T. Matsuura,

Tetrahedron,

(1948).

27, 1583 (1971).

H. A. Morrlson in "The Chemistry of the Nitro and Nitroso Groups", Ed., Wiley, New York, N. Y., 1969, p 168 ff.

H. Feuer,