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.
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see e.g.
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Fleischmann
Olah,
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