Reactions of phenylium ions with gaseous hydrocarbons. 1. methane, ethane, and propane

oom4ozo/u4 s3.oo+.w Rrpmoa Ra Ltd.

nir&&al. VOL40. No. 23, pp. 4865 to 171. m4. RinledinorulBliuin.

REACTIONS

OF

PHENYLIUM

IONS

WITH

GASEOUS

HYDROCARBONS.

1.

FIETHANE,

ETHANE,

AND

PROPANE.

G.

lstituto

di

ANGELINI,

Chimica

C.

Nucleare

SPARAPANI,

del

and

C.N.R.,

H.

Area

SPERANZA.*

della

Ricerca,

Rome,

Italy.

(Received in UK 5 Jme 1984)

Abstract

The

-

generated presence

of

t 17 e

simple

pressure:

reaction

its

CH

bonds

ionic

!>ee;l

isome: (lo-100

torr)

carried

at

R decay

and

recently

to of

-benzene

(eq.

relevant

data

11,

distinct

affinity

been

now

the

decay

study

hydrocarbons

phenylium

for

the

n-centre

to

establish

ion

the

hydrocarbons will to

allow

toward

study

us

to

electrophilic

the

the

been i

1,

highly

gather

ion

toward

to

into a 4865

studies,

affords

the

defined

and

any

1

The

about

from

in

acceptors. ion

Our site

simplest propane.

sensitivity carbocation

system

of was

uninolecular

phenylium

the

convenient

method

decay

n-type

exclusively the

a

into

molecule. and

ethane,

insight

phase gas with previous

generated

containing

of

ium

phenyl the

reactive

restricted

attack

RH

of

information

substrate

methane,

the

with

techniques.

reactivity

substrates

has

class,

of

the

of

and

structure

tracer

ion

a

for

ion

compounds

properties

with

ion

sp ctrometric -3 torr).

inaccessible

reactivity

consistent

phenyliun

aliphatic

its

U-

site

(10

defined by

:!E

pure

fragmentat in

tritiated

of

otherwise

extended

level,

in

reactions

gaseous

and

are

has

their

gather a

atom

of

i ,“,”

features

compared

mass

pressures

carbocations

study

applied

lower

ICR

CZH], tnant 9

toward

phenylium

tho ir

and

from

tritium

free

to

automeriration

this

of

much

I ity

hydrocarbons

discussed

the

effects

%“.“,l

behav i our

The

aliphatic is

as

well

y.

preference

stabi of

CH

considerable

distinct

addition

=

The

even

its

The

as

hypotheses

out

the

ion, in

predo

i’,at31

as

by

from

mechanistic

produce

well

mechan i sms.

simple

to

present

ization

i L:z:t reactivity

substrate.

eva I uated,

toward

Spontaneous

interest

the

intermediates

have

means

of

yields

products.

65

high

substrates, as -type selectivity, demonstrated C-H

torr),

also

were

4

exceedingly

f?H4- (R

‘6 ons

C H R

acceptors

phenylium benzene

1,4-T

hydrocar

tritiated

with

confirms

of

lo-100

nucleophilic

itiate

free

decay

gaseous

corresponding

gaseous

of

nuclear

partial

CH;

reaction

from

p, 21The

with

a

investigation selectivity

g bonds. members We expect of

these

(the

of At of

the the that

simple

phenyliun

G. ANOBLINI et al.

4866 ion)

in

the

effects

gas

phase,

under

(solvation,

reactivity scale

ion-pairing,

model

for

the

conditions

for

etc.).

phenylium

ensuing

ionic

excluding

ion

It

i nterference is

thereby

toward

simple

under

different

adducts,

-.-

0-decay

-

+RH

of

environmental

hoped

hydrocarbons

to and

experimental

Tr it iated

provide a

a

stability

conditions.

Products

(1)

-3He

R = CH3,

C2Hg,

C3H7.

EXPERIMENTAL. The key substrate purified,

and analyzed

by introducing activity:

sealed

together

capillaries

with

torr),

into

and thoroughly

vessels

mixtures

were a C.

detector,

fror

then

then

opened

of

columns:

authentic (i)

550 10% on 80/100

RESULTS

aromatic maximum

rate

of

products

specimens

months

chromatograph

were

under

in

could

the

equipped

proportional

identified

identical

that

benzene

connected

be formed

at

content with

counter

chromatographic

ranging

(4

passage mixture.

temperature.

The

by radio

glc,

hot-wire

kept at 1800~.

their

retention

conditions,

Supelcoport,

by the

analyzed

a

oxygen

the gaseous room

to

introduced,

a high-sensitivity

tube,

by comparing

1.75%:5% on loo/l20

then

(specific

was then

through

dark

and their

Chromosorb W-AU, 5m, at temperatures

composition

products products theoretical

calculated

tritiated

gas

species

conditions

benzene

(NuH = NH3 or CH30H) and of

tritiated

12-14

were

substrate

was prepared, were prepared

on

volumes two

5m, at 800~3 (ii)

with

different

Silicone

Oil

from 100 to 2OOV.

AND DISCUSSION. The

tritiated

for

with a Berthold

Rentone 34-SP 1200,

hydrocarbon

additive

the

tritiated

The ampoules

ampoules.

of

airtight

4200

in series

The tritiated those

stored

under

Erba Fractovap

coupled

decay

1 mCi of

-ca.

of the radical

the nuclear

were

Pyrex

The gaseous

a nucleophilic

which was used as a scavenger

The decay

be

300-x&

1,4-T2 -benzene, [ The decay samples

procedure.3

described containing

degassed.

minor amounts of

of the D-particle

using

glass

1

experiments,

the nuclear-decay

a previously

90 mCi mmol-l)

vacuum line

for

using

from

benzene the

tritium,

are

of

the

reported

were

in

obtained

activity the sample the

decay

by

that

initial (54%

the

systems Table.

comparing

may be activity

[1,4-T2

abundance

and The

incorporated the

]-benzene of

the

yields

of

in isotopic

and

46%

the

yields

overall

their

and

(72%)

the

absolute

the

of

identified the

activity

with

products.

This

can

of

the

composition T-benrene),3

C H + structure 6 5

listed

the

retained

the

decay after

Reactions of phcnylium ions with -US TABLE.

Product

Alkaneo

in

the

Gy*tem

Alkane,

Yields Gas

from

the

Reaction

of

Tritiatsd

4861

I

Phenyliua

Ions

with

a)

(tow)

Absolute

Yields

of

Products

(%I

12.3

15

R = CH3,

20

NH3 (2.0)

10.0

c)

co.5

R = CH3,

35

NH3

(2.0)

23.5

c)

co.5

R = CH3,

25

NH3

(4.0)

55.2

cl

co.5

R = CH

20

CH30H

(2.6)

22.3

22.4

to.5

R = CH3,

20

CH30H

(5.3)

12.3

34.4

(0.5

R = CH

100

-

58.3

3’

R = C2H5,

10

-

15.6

R = C2H5,

100

-

22.7

R = C3H7,

10

-

R = C3H7,

a)

The

100

systems

average

of

aniline

yields

at

exchangeable

nuclear

systems. products, of

the

adducts,

contained, least are

besides

three not

the

reported,

being

and

the

Analysis

of

the

Table

of

following

whose tritiated

(R=

nPr)

18.2

(R=

iPr)

13.1

(R=

nPr)

phenylium

formed

other

ion

variable

ic

be

because

that from

directly

1 on

CH4

labeled

products

the

-ca.

of

lO$, of

exclusively stability

the of

the c)

The

readily

detector

toluene

respectively,

recovered to

(s

represent

presence

yields

C2H6, are

the

data

efficiency

and

data

formed.

restricted

to

The of

appreciable

and

RH and

b)

of

ethylbenzene

counting

be

02g

-

deviation

propylbenrenes will

d)

of

Standard

tritiated

reveals

isomer

can

4 torr

largely

discussion

formation

neglecting

3.8

absolute

exclusively

proportions The

iPr)

analyses.

d) Also 2.4% of

4

are

(R=

substrates,

independent

transition,

ethylbenzene variable

-

d)

15.4

I I

NH2 hydrogens,

employed.

b)

6 6 $“”

NuH

R = CH3,

3'

Simple

Phaas.

Composition

RH

hydrocarbons-

these

in labeled

related of

the

low-boiling

to

and while

the

C H

3 8

aromatic the

attack

ensuing

ionic

compounds,

G.

4868 T-benzene,

etc.)

eccounting

the

whose

format

Table,

ion

fragmentation

or

Direct (R

=

CH3,

aromatic

addition and

pro’ducts

of

2

case

the

(eq.

of

most

is

due

hydride-ion

C2H5,

intermediate In

for

ion

the 21,

the

to

-via

excited

by

the the

reaction

2

the to

activity

processes,

between

suggested

Table,

residual

secondary

phenylium is

RH = CH 4’

of

to

transfer

of

C3H,)

ANOELINI et al.

1 and

C-H

be

a

bonds

of

exothermicity is

1

reported

as

unimolecu

of

the

in lar

hydrocarbon. hydrocarbon

the

channel

of

only

the

the

major

formation

not

such

leading

corresponding

their

the

arenium

formation

energetically

RH

to

process.

allowed

channel

(2)

+ RH -

exe 2

available C2H6

to

or

transfer C6H5R

C3H8, to

is

propane,

the

decay

process

give

in

Ihe

species. pressure the

the In of

excited the

fact, the

(

R = CH3)

3L7

As a matter

of

le

be

(AH“

methane

mixtures (-

by

of

2

of

tritiated

as

well

as

sequence

fact,

loss previous

absolute

=

to

100

undergo

that

of

with

increases NH or 3

of

RH =

tritiated

with

the

ethane

or

hydrocarbon

fragmentation

aromatics with

yield those

when

hydride-ion

torr).

collisions may

whereas

with CH OH, 3

to

simpler

the

partial

which

favours

2.

fragmentation

involves

-1) , 5

corresponding

respect

PtRHI

unreactive

mol

the

higher

with at

keel

by

a

Accordingly,

conditions

yield

= -60

accompanied

intermediates

step

A plausib CH4

6

hydrocarbon,

neutralization

from

the

same

ion

may

stabilized

Unless molecules,

2

T-benzene.

observed under

phenylium

pathway of

available

molecule a H 2

low-pressure

to to

ICR

+H

2

give

the

excited

benzyl

investigation

species

cation indicated

(3)

3

2 (eq. that

4869

Reactionsof pbenylium ioos with g&o118 hydrccarbons- I

a

C,H7+’fragment

phenylium

ion

species occurrence

of

excluded. among

In

the

least is

from

Owing 10

to

It

give

that,

the be

benryl

under

Leading

attack a ‘6”7

on

+ fragment

4

3 as

those

is

as

11

other

the

rate

of

alternative

the

from

and

CH30H, am i nes9

eq.

C,H7+

2

do

ion

not

or

isomers,

fragmentat

fission

safmly

recovered

toward

C7H,+

aromatic

be

be

NH3

ions

of C,H7+

experiments, can

containing of

the

at

process

reactions

(-

that

additional

3

ring

products.

available

4).

decay

could

arenium

attack

of

extent

reactivity

well

from

structure

present

systems

excited

8

investigation to

established

the

ionic

involving

loss

of

Although

occurrence

that

(eq.

the

that

of

C,H9+

the

benzylmethylether

CH 4

conditions,

aromatic

namely

the

of

on

significant

any nor

well-established

ICR

process ethane,

In

to

concluded

than to

Low-pressure fragmentation

3

from

decay

lower

not

ion

cation

the

substantially

opening),

to can

ion

study.

benzylamine

products

formation

informat

no

that

fragmentat neither

tr itiated

alcohols,

fragment

the fact,

respectively. and

However,

available

was

accompanies

invariably CH4.8

on

adduct

a

2

an

from

phenylium-ion

moiety with formation of C H 24 of such fragmentation channel

(4)

+ C2H4 exe 2

cannot

be

tritiated

demonstrated benzene

-benzene, y ie Ids

of

those

samples

the

the

reasonable

the

apparent

CH4/CH30H The

selected Format xylenes

are

of

it

is

supported

recovered methane high

high

ethy

is

is

I benzene

completely

of

in

absent,

labeled

and

first ratio

of

the

leads

starting

C H 38

to

1.4-T2

lower

\a solu j e

systems,

than

with

of

sequence

for

the

formation

to

range

around

C2H6

ion a

systems, that

the

in

the

decay

ion

even

that

for

n-electrons,

In

fact,

systems.

step

by

recovered

phenylium lower

phenylium

indicates

C6H5R

CH4/CH30H

accompanied in

undecayed

C2H6

it

since

comparatively

RH -

of

the

calculated

reactivity

the

the

the

affinity

constant

systems

by

appreciably

data the

from

in

yields

appears

that

experiments,

samples.

distinct

rate

hydrocarbons ion

discernible

competition

assumption

the

decay

not

relatively

this

present

is

the

although

by

the

products from

demonstrate

electrons,

in

which

aromatic

to

The

step,

by

nevertheless

respect

shown

4

2

is

of 8.6

toward

the

while phenylating

the

pure

u as

with

the

rate-limiting

toluene i

significant

toward

and

anisole

0.9. B

bonds

site toluene

of

the

selectivity. and

reactant

isomeric 1 attacks

4870

G. ANOELW et al,

exclusively (eq.

the

UC H bonds

of

the

substrate,

wh i le

ignoring

the

UC-C

bond

5).

+

0

(5) + ‘zH6

1

5

A similar preference

of

demonstrated over the

that

the by

of

direct

extensible

a

matter

n-propyl 1.0

torr).

side-chain with

the

the

is

to

relatively

1

primary

and

of

fact,

This of

trend

intermediate

lifetime

of

the

in

2n

C-H

may

C H 3 8’ of bonds

i-propylbenzene at to

an

(n-propyl

2”

of

pressures

ion

v+ 2i

(eq.

1

in

to

that

= 0.33. that

100

of

extent

same

(6)

As the

torr,4.0

isomerization

The

be

formation from

exceed at

to

might

case

different

(1.4

is

attributable

ion

whose 6).

distinct

(19.2%)

n-propylbenzene

i-propyl),

arenium

the

hydrocarbon

be

propane,

unimalecular

-

part

phenylium

appears

low

where the

propylbenzenes

largely

:Ki-6 v+

in

i-propylbenzene:

support

excited

isomeric

proportions

increasing

lends

of

selectivity

i of

a factor

of

formation

bond

secondary

basis

formation by

the

whose

occurs

C H systems, 3 a 6C_H bonds of

the

yields

a C-C

site

a statistical

isomer,

high

into

propylbenzenes

on

in for

(2.4%),

of

significant the

obtained

electrophile

ethylbenzene

isomeric

expected

ionic

insertion The

of

picture

at

of

the

increases

energet

ical

ly

Reactions of phenyhum ions with gaseous hydrocarbons-

condensation

of In

phenylium only

phenylium

ion

reactant of

with

excited

the

the

our

toward

the

ion

conclusion,

extended

pure

a-type

formed the

present

simple

the

the

intermediates

dilute

has

the

the

gas

state

from

gas-phase C2H5,

also

reaction

and

C3H7) of

allowed

to

of

has

the

direct

opened

the

2d

reactivity

pathways

dilute

gas

the

R = CH3,

and

but

exe i ted

in

methylpropylether. of

RH (

nature

isomerization

in

the

investigation

hydrocarbons of

in

appropriate

substrates,

and

ion

addition

1 with

knowledge

fragmentat

when

ions,

methylpropylphenyloxonium

observed

been

has

process

isomeriration

favoured

4871

1

not

ionic

evaluation the

ensuing

del la

Ricerca

state.

ACKNOWLEDGEMENT. is

Acknowledgement C.N.R.,

di

Roma,

(1)

a) Cacace,

F.,

and Molecules” Ion-Molecule Gate.

Ausloos,

H.,

J. Am. Chem. Sot.,

63775 d) Fornarini, G.,

(4)

Carlson,

T.A.,

(5)

The enthalpy

FT-MS

several

running

Plenum, New York,

Ausloos,

P. Ed.,

M., Tetrahedron

Angelini,

the

S ervice

mass

of

p.

Plenum Press,

Area

spectrometric

Cacace,

1975,

the

F.,

527;

in

c)

New York,

spectra.

“Interaction

Cacace,

1979,

p.

F.,

between in

Ions

“Kinetics

of

1991 d) Speranza,

M.,

1983 -113 37.

a) Speranza,

kcal

P, Ed.,

Reactions”,

Chim. Ital.

(3)

to

Adv. Phys Org. Chem. 1970 8 79% b)

(2)

H.M.,

for

Italy,

due

Lett.

1982 -104 4773,

S.,

Speranza,

Speranza,

1980 z c)

1983~ b) Angelini,

Speranza,

H.,

H., J. Chem. Sot.

M., Segre,

J. Chem. Phys.

A.L.,

Keheyan, Y.,

Perkin

Altman,

G.,

L.J.,

Trans.

Fornarini,

Angelini,

II

S.,

C.,

ibid.

Speranza, 1983 lag

1984 171.

J. Org. Chem. 1980 -45 3291.

1960 32 1234.

change has been calculated

a AHOf = 270 kcal

using

mole1 for

1 (Rosenstock,

Larkins, J.T., Walker, J.A., Int. J. Mass Spectrom. Ion Phys. 1973 -11 309), aARe = 192 f -1 mol for 2 (Devlin, J.L., III, Wolf, J.F., Taft, R.W., Hehre, W.J., J. Am. Chem. Sot.,

1976 98 1990). (6)

The first

step

of eq.

2 can be calculated

to be -ca.

63 kcal

mol

-1

Hydride-ion transfer between 1 and RR is -ca. 15 kcal and C3H8* while it is exothermic when RR = C2H6 ( AHo = - 11 kcal mol-‘) -1 -1 mol , if R+ = n-propyl ion,and - 33 kcal mol , if R+ = i-propyl

when RH = C H 26 mol endothermic for RR = CH 4’ and RH = C H ( AH* = - 17 kcal 38 ion).

(7)

enthalpy

Sequence -1 in01 . (8)

Speranza,

(9)

Bruins,

(10)

1 -

N., A.P.,

2 -

3 is

Sefcik,

M.D.,

Nibbering,

a) Sen Sharma, D.K.,

Sparapani,

C.,

(11)

Sequence

kcal

sol-‘.

Speranza, l-

2 -4

computed

Henis,

involve

J.R.S.,

P.,

Can. J.

Radiochimica is

Acta,

an overall

Gaspar,

N.M.M., Tetrahedron

Kebarle, I!.,

to

Lett.

P.P., 1974 1

exothermic,

-1

change

J. Am. Chem. Sot.

of

-ca.

-36

kcal

1977 99 5583.

2677.

Chem. 1981 59 15921 b)

Cacace,

F.,

Ciranni,

G.,

in press.

computed to involve

an overall

enthalpy

change ranging

around -38