Electrooxidation of cyclopentane at cryogenic temperatures

Electrooxidation of cyclopentane at cryogenic temperatures

Tetrahedron Letters No. 36, pp 3221 - 3224, 1976. Pergamon Rese. ELECTROOXIDATION OF CYCLOPENTANE by Shalom *Laboratoire Pitti,Michel de Chimie ...

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Tetrahedron Letters No. 36, pp 3221 - 3224, 1976. Pergamon Rese.

ELECTROOXIDATION

OF CYCLOPENTANE

by Shalom *Laboratoire

Pitti,Michel

de Chimie

++Department

AT CRYOGENIC

Herlem*

Analytique,lO

Jordan+*

rue Vauquelin,75231

Laboratory,University

Pennsylvania

TEMPERATURES

and Joseph

of Chemistry,Pennsylvania

152 Davey

Printed in Great Britain.

16802,

State

Paris-France

University,

Park,

U.S.A.

(Received in UK 16 July 1976; accepted for publication 23 July 1976) The discovery superacid

media

laboratories alkanes

has revolutionized

have

It was concluded

electrogeneration

solvents

transfer

including

is preceded

of carbenium

fluorosulfuric

ions from

acid

(FSA).

by a fast protonation

of the

behaviour

by &he abstraction of a H2 molecule,yielding the 3 we have found a different electrochemical carbenium ion.Recently

of several

not compatible

with

alkanes

including

this reaction

We wish

crucial

to report

the reaction

interest

cyclopentane.Experimental

sequence.Consequently

not be in the form of protonated

of evident

via

that charge

hydrocarbons in Olah*s 1 chemistry . In recent years several

carbonium

the anodic

non aqueous

of aliphatic

and is followed

corresponding

could

reported2

in various

alkane

of the xeactivity

alkane

in the context

the electrogeneration

molecu1es.A

of the cyclopentyl

. + dc; . v I

H

mechanism

ion

(IV) at -6O'C,

111

3221

L +

e

+

H+

+

l

II

fast

u

+H

slow I

IV

spmies

possibilities.

d

v"

. .

were

sequence:

(1) ..,

(3).

relevant

of electrosynthetic

H

(n)...

results

the electroactive

is

3222

No. 36

This

communication

is the first

of a carbenium

ion at cryogenic

recently

that

shown

elucidating reactions have

are

electron

and conclusively

transfers

species

(II) and

The experimental

evidence

experiments

which

viz,,cyclic

voltametry,coulometry

yielded

of the anodic

between

in Figure

zero and

which

consistent

sweep

of a typical

reference Current

1. Typical

the sequence based

principal

that

to all

(l),(Z)

on about methods

and

(3)

fifty

were

used

and.NMI?,A relevant

voltammogram

two peaks

experimental

(V)

electrode:

corrected

of cyclopentane

in a range

is

of potentials

obtained

at--60°C

+ 2M NaF

spectrum

cyclopentene

Hg/Hg

ofdissolved (V).

S 0 F 2262

for residual

curre

The reverse cathodic scan showed 6 revealed the following in the figure,2

results

acid

NMR

volt/see.

tic criteria identified

intermediates.

by the fact

1 .

potential

cyclic

radical

- in contradistinction

are presented

at -60%

of 0.01 M (I) and

rate-O.01

via free

was predicated

results.Three

in fluorosulfuric

scan

steps

that

side

is that we

electron-transfers 5 that multi-

study

at controlled

1,revealing

single postulate

substantiates

findings

of our work

the basic

in the sense

tool for

mechanisms,because

+l.Q volt.

Figure

voltammosram

feature

- they do not isomerize

below.Representative

is a powerful

Haber-Weiss

(I) for a model

is outlined

section

identified

(IV) are unique ions

of the electrogeneration and Van Duyne 4 have

in complex

novel

occur by monoelectronic

alkylcarbenium

illustrated

steps

the classical

of cyclopentane

report

electrochemistry

transfer

to be quenched.The

(3),substantiating

The choice

other

electron

likely

segregated

(1) and

low temperature

primary

known

temperatures.Reilley

denotes

no corresponding (where

sweep

capital

peaks.Well letters

known

refer

rate and 2 cyclopentane

diagnos-

to peaks

concentrations)

No. 36

3223

= A

RT

dlnv2

F RT

u -E d lnp+ZL

0.6

=

+

0.1

0.06

.

=p/2d In c

;

i

=- 0

\ Plot

F

of current

function

d Ep/2 7ln~,/~

i5

=

( ip / c v3

;

0.6

I In v2 is sigmoid

) vs.

d EP/2

=

in shape.

0

d In c

B i

Q2)

d ( Ep-

I?

RT

=

dlnv

The data

indicate

transfer

coupled

mechanism

with

with

;

0.06

d In v

unambiguously

that peak

a fast chemical

an, ~0.6 i 0.1, where

in the rate determining

A correspond

to a one-electron

"follow-upt' reaction,a na=l is the number

step.Coulometry

so called

of electrons

at an appropriate

EC'

involved

controlled

potential

revealed that the overall number of electrons was the same as n viz. (E3/4 p) a' n=l.The reaction sequence (1) and (2) is obviously consistent with these requirements.The

diagnostic

one-electron

transfer

nism).Again

ana=0.6

plus

preceded 2 0.1 and

(3) is evidently The crux

corresponds interposed

to a reasonable between

chemistry.The

absence

and

in the light of converse

of the radical

ion

this paricular

protonate

in FSA

(via reaction

(IV),which

. . .

sequence

the same chemical

transfer

steps.The

mecha(2)

peaks

is that it

reaction

proposed

knowledge

is accounted

conclusively

the prevalence

(Cl) be

sequence

of carbenium

ion

fox the short

of reactions

(l),(2)

Was compared with that of cyclopentene.The type of experiment was that (V) was found to

4) at cryogenic

is identical

with

+ HSO,F

-

temperatures,yielding

the final

product

IV

quantita-

of reaction

+ so,F-

u

V

( "C'E" sequence

results.

of contemporary

cathodic

a slow

of cyclopentane

behind

(4)

equilibrium

n=na=l.Reaction

of the overall

that

with

(II).

to substantiate

(3) the voltametry

species

these

assumption

rationale

tively

with

in favour

B are consistent

chemical

(by coulometry)

the two one-electron

reasonable

In order

for peak

by a rapid

compatible

of the argument

also appears

lifetime

findings

(3):

3224

No.

This right

is documented

side of figure

compound pentyl

ion

indeed

cyclopentene

(IV) ' which to peaks was

obtained

found

should

singlet

A and B in figure experimentally

Consultations

are gratefully

proton

in a sample is known

be non oxidizable

in the figure:peaks

Acknowledgment; Gachet

was

(V) in FSA at -6O'C.The

corresponding This

by the low temperature

1,which

NMR spectrum pxepared

as is apparent

by J. Badoz

from

on the

by dissolving

to be characteristic in the range

l,if the proposed

A and B were

shown

of cyclo-

of potentials

mechanism

is correct.

the voltamogram

conspicuous

by their

and the technical

36

labeled

absence.

assistance

of M.

acknowledged.

References; 1. For a review

: G.A.

see e.g.

2. J. Bertram,M.

Fleischmann

Olah,

M. Fleischmann

and D. Pletcher,

M, Fleischmann

and D. Pletcher,J.

and J.M. Oelderik,Rec. J. tier.

Chem.

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