Some effects of trifluoromethanesulphonic acid on mercuration in trifluoroacetic acid

C60

Journal of Organometallic Chemistry. 194 (1980) C6O-C62 0 Elsevier SequoiaS.A.,Lausanne-PrintedinTheNetherlands

Preliminary

Communication

SOME EFFECTS OF TRIFLUOROEIETHANESLJLPHONICACID ON >IERCURATION

IN TRIFLUOROACETIC

G. 5. Deacon

Chemistry

and

M. F. O'Donoghue

Department,

(Received

June

With

3rd,

suitzble

University,

Clayton,

choice

acid

of

with

conditions,

mercuration

added

2,5-dimercuration,

tetramercurated acid

Monash

alone

anisole

gives

Victoria

3168

(Australia)

1980)

in trifluoroacetic predominant

ACID

of

2,3,5_trimercuration,

in short

3-mercuration,

I-methoxybenzoic

trifluoromethanesulphonic

reaction

times,

or

acid formation

whereas

3.5~dimercuration

or,

can

use

with

of

acid give

2,3,4,5-

of trifluoroacetic

long

reaction

times,

2,3,Strimercuration.

Addition

of

fluoroacetate sulphonate proceeds

trifluoromethanesulphonic

in trifluoroacetic Cl].

Mercwation

far more

readily

though

this

compound

report

that

use

benzoic

acid

hanced

leads

1:4)

2).

(cF~sO~H:

of

By

and

of the with main

3).

The

expected

mercurating

ipso

trifluoroacetic

(scheme

when

2,5-dimercurated kinetically ions

acid.

after

favolured 5 min

Presumably,

acid

species

gave

121.

We

of

now

4-methoxy-

product,

to en-

(decarboxylation).

15 min

yielded,

of unchanged

appears

for

acid 15 min

as the

was

gave,

principal

to result

3.5~dimercurated

from

isomer,

after

(mole bromc-

anisic

of a carboxyl

group

acid, acid

added after

brorm-

product rearrangement

since

3,5-dibromo-4-methoxybenzoic

coordination

reagent

3,5-dibromo-4-methoxybenzoic

reaction

tri-

111, even

trifluoroacetate

trifluoromethanesulphonic a similar

3:5,v/v),

agent

mercuric

for

this

alone

dimercuration

a mixture

1) and

with

in mercuration

mercuration

with

acid

product,

acid

contrast,

compounds

the preferred

acid

of mercuric

trifluoromethane-

trifluoroacetate

acid

2,5-dibromo-4-methoxybenzoic

tribromide dibromo

excellent

to enhanced

the mercuration

cf3c02H=

demercuration, (scheme

an

mercuric

of 4-methoxybenzoic

3-bromo-4-methoxybenzoic (scheme

with

to a change.in

in refluxing

to a solution merEuric

of polyfluoroaromatic than

is itself

polymarcuration

demercuration

acid generates

of trifluoromethanesulphonic

Mercuration ratio

acid

cleavage acid

as the i-. 1s

to CF3.S03Hg

C61

more

thermodynamically

second

CF,SO3Eig+

Scheme

than

C02H

=OP

1.

R1,

2.

1 2 R,R,R,

3.

R1,

R2,

R3,

R3,

R4,

acid

R=,

R6=H;

R6=Br;

X=cF3C02

R4,

R6=H;

R2=HgX;

R5=Br;

X=CF3S03

R

2

15 min

gave,

benzoic

acid

some reactions

6~1,

followed

by

after

treatment

5 min.

with

acid

after

was

:CE3C02H

acid

indicative

decarboxylation not ratio

mercuration

bromodemercuration

(ipso

of major to

lrl

became

was

ratio

tribromide

acid (scheme

of 6:l

ions

v/v),

mercuration)

was

(v/v)

with

substantial

a mercuric the

2,3,4,5-tetqbromoanisole

OMe

C02H

following

(scheme after

1).

180

min.

of trifluororeaction

for

of polymercuration.

observed

However,

and

the

tri-

2,3,5-tribromo-4-methoxy-

enhancement

significance.

and

addition

a similar

predominantly of major

21,

With

3

in boiling

gave

acid

(scheme

4).

(CF3S03H:CF3C02H=3:5,

41,

mole

2 or CF3S0

3-bromo-4-methoxybenzoic

bromodemercuration,

(scheme

or CF3S03

X=CFaCO

:.nrene

trifluoroacetate

3.5-dibromo-4-methoxybenzoic

but

ipso

R4 , R6=Br;

, R5=H;

2,3,5-tribromo-4-methoxybenzoic methanesulphonic

to a

X=CF3C02

R3=HgX:

products:

15 min.

group

C02H

R5,R;

R1 , R3=HgX:

fluoroacetic

n&zboxy

4

of a mercuric

principal

of the

group.

OMe

Use

CF3S03H

coordination

OMe

4.

after

stable

in all

on

salt:

arene

predominant (scheme

the

increasing mole

foregoing the rati0

product

of

after

5).

0Me

OMe

Ggx

EL

X=CF3S03 At

this

to the

stage, methoxy

4-methoxybenzoic in mercurating

it is difficult group. acid both

to see

Certainly, (scheme

positions

the

why

4) suggests or&o

the

ready

one

vacant

formation

that

to methoxy.

there

of

position

should

be

or%

2,3,5_trimercurated

is no

intrinsic

difficulty

C62 A complicating substantial predominantly this

is in the

solution

Cur

show

in trifluoroacetic

ation

reactions

is the

polymercurated

4-methoxybenzoic

insoluble

fraction,

occurrence

acid

though

of partial

In the

arenes.

(scheme

it is also

reaction

31,

the

bulk

the main

or giving of

component

phase.

results

sulphonic

in all of the

2.5-dimercurated

product

of the

factor

precipitation

acid.

that

acid This

of mercuric

the

scope

is greatly

differing

and

of mercuration

enhanced

by

increased

trifluoromethanesulphonate

by mercuric

addition

trifluoroacetate

of trifluoromethane-

reactivity,

resulting

Cl], is to be

further

from

form-

explored.

A&nowledgement We Bristol

are

grateful

to Dr.

for

an authentic

J.F.W.

sample

of

McCXnie,

School

of Chemistry,

University

2,3,4,5-tetrabromoanisole.

References l_

G-B.

Deacon

2.

H.C.

Brown

see

also

Roberts,

and and

C.W.

D. Tunaley, R.A.

Fung,

J. Chem.

Wirkkala,

J. Organometal. J. Amer.

M. Khorramdel-Vahed,

Sot.

Perkin

Trans.

Chem.,

Chem.

Sot.,

R.J.

II, (1980)

156 88

Ranson, 267.

(1978) (1966) and

403_ 1447;

R.M.G.

of