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Counter-Electrode Reactions for One-Compartment Cell Electro-Reductions in Aprotic Media.

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Dieses Manuskript ist
zu zitieren als
Angew. Chem. Suppl.
This manuscript is
to be cited as
Angew. Chem. Suppi.
7983,691 -702
1983,691 -702
Y
a
a
G Verlag Chemie GmbH, D-6940 Weinheim,1983
0721 4227/83/06060691
B 02.50/0
ounter-Electrode Reactions
for O n e - C o m p a r t m e n t C e l l E l e c t r o - R e d u c t i o n s
i n Aprotic Media
by
Rainer Engelst, Cornelis J. Smit
and Wim J . M . van Tilborg
Cathodic syntheses in aprotic media are normally carried Out
in
divided
W
electrolytic cells to avoid reoxidation of the (primary) products at the
0
c
anode. The use of such a two-compartment cell provides
a
simple and
W
W
rl
strai.ghtforward solution to a very general electrochemical problem.
%L
t.
W
However, in aprotic media a c e l l divider Can only be used on laboratory
3
"
4
--
W
*
2
Dr. R. Engels+, Ing. C.J. Smxt+, Dr. W.J.M.
van
m a
Tilborg+,
K o n i n k l i j k e f S h e l l - L a b o r a t o r i u m , Amsterdam (Shell Research B.V.):
Hol1and
+
Present address: Billiton Research H.V., P.O. Box 3 8 ,
NL-6800 LH Arnhem
-
691
-
-
693
-
scale. The complicated and expensive cell constructions, the high ohrnlc
electrode reactions listed in Table 1 is by no means restricted to
resistance and especially the short lifetime o f the ion-exchange membranes
carboxylations (compare Table 3 ) . Tne other onalic and acetic acid
normally used have excluded reactions in aprotic solvents from technical
derivatives shown (Table I, entrles 2-4) can be used as well. The fate
realisation [ I ] , although very interesting cathodic transformations can
of the (primary) oxidation products, shown formally
be carried out in these media "21. We report a generally applicable
has not been studied; however, none of these or possible subsequent
method for solving this problem for cathodic syntheses, viz. by the use
products were found to interfere with the cathodic reaction.
of
a
as
the Kolbe radicals,
suitable counter-electrode reaction. Using a substrate that has a
The broad applicability of these counter-electrode reactions for one-
sufficiently low oxidation potential, one can control the anode potential
compartment cell electro-reductions is demonstrated in Tables 2 and 3 .
and thus prevent rhe cathodic products from being destroyed a t the
Some of the reactions had been carried
ouc
earlier in divided cells; for
counter-electrode.
these we obtained comparable results in undivided cells.
Table 1 shows the foot potentials for the oxidation of a number of salts
The results compiled
I"
Table 2 show that the selectivity of the cathodic
of oxalic and formic acids and substituted acetic acids at a platinum
reaction can depend strongly on the type of counter-electrode reaction.
anode. Graphite
can
be used as an electrode material at equally low
The reductive eiectrocarboxyiation of dimethylmaleate [ 5 1 in Lhe presence
anodic potentials. The one-electron oxidation of ditetraethylammonimum
of DTEAOx as the conducting-salt/counter-electrode
substrate yields a
oxalate I31 (Table 1, entry 1) yields carbon dioxide plus its radical
mixture of the mono- and dicarboxylated monomers (1, 2 ) and dimers
=
anion. The carbon-dioxide radical anion is a strong reducing agent and
is oxidized immediately to carbon dioxide before it can be trapped by an
P
(i,
5-),
whereas the hydrodimer 2 could not be detected. However, the protons
that are formed during the anodic oxidation of TEAForm shift the selectivity
acceptor ( 4 1 . Upon oxidation of tetraethylamnonium formate (Table 1,
Of the electrocarboxylation reaction towards the monocarboxylated
entry 5) carbon dioxide plvs
a
proton are formed. As anodic and cathodic
monomer
reactions are electrochemically coupled, this allows strict control of
-
(1) plus the hydrodimer 2. whereas
2, 4 and 2
are no longer
formed. A similar change in product distribution is found in the reductive
the supply of prorons in an otherwise aprotic medium to the reaction
electro-carboxylation of I,3-butadiene. A change in the counter-electrode
proceeding at the working electrode (vide infra).
reactzon from the oxidation of DTEAOx to the oxidation of TEAForm
The anodreally evolved carbon dioxide can be used in reductive electro-
strongly favours the formation of the three isomeric C10-dicarbonylic
carboxylations ( s e e Table 2 ) ; however, the application of the counter-
acids
2-E. Presumably, protonation of
at least one of the intermediate
ally1 radical anions facilitates radical dirnerisacion 161. Recent
results by P a r k e r 1 9 1 support this aeeumptwn.
-
692 -
-
694 -
TABLE 2.
KEDUCTIVE ELECTROCARBOXYLATIONS IN UNDIVIDED ELECTROLYTIC CELLSa
Products
Starting compound
1
I
trimethyl ethane-l,l,Z-tricarboxylate (1)
tetramethyl ethane-l,1,2,2-tetracarboxylare (2)
tetramethyl butane-l,2,3,4-tetracarboxylate
(2)
pencamethyl butane-l,l,2,3,4-pentacarboxylate ( 4 )
hexamethyl butane-l,1,2,3,4,4-hexacarboxylate
A4
!
~
methyl 2-butene-1-carboxylat~ (6)
dimethyl 2-butene-l.4-dicarboxylate (L)
dimethyl 2,6-octadiene-I,a-d~carboxylate (8)
dimethyl 5-vinyl-Z-hexene-l,6-dicarboxylace ( 2 )
dimethyl 2 , 3 - d i v i n y l b u t a n e - l , 4 - d i c a r b o x y l a t e
(12)
acrylonitrile
dimethyl cyanosuccinate
u-me t hy 1S L yrene
dimethyl
(11)
methyl a-phenyllactate
arobeneene
N,N-biscarboxymethylhydrazobenzene (16)
N-carboxymethylhydrazobenzene ( I )
1-bromo-2-methylpentane
5
(a)
2,7-diphenylbutanedi01-2,3
5
24
20
12
45
46/51
8/61
18/61
3e
1
l5
i
;
41
56e,f
5/61
41/51
19
(E)
R,S-methyl J-phenylphenylglyein=t
acetophenone
5
59
14e
(g)
benralaniline
1
48
2
3
2-methyl-2-phenylsuccrnate
Counterelectrode reacti,
~~
(2)
1.3-butadiene
Dxvided cel
current efficiency, Z
ntry
(Is)
'
60171
79
6
58
21
7
38
64/81
16
methyl 2-methylpentanecarboxylaee
8
95
__
see experimental.
b) Isolated after esterification with methyliodide D3]
a ) Beaker cell; for details
c ) See Table
I.
d) with counter-electrode reaction 2
3 1s formed in 3n Z current efficiency.
e) Capillary gap cell ( s e e experimdalf, material yield of 5 to '0
based on butadiene 2 95 1 .
f) -8:9:10
= 7-2:l
==
_
-
_
695 -
-
TABLE 3 . NON-CARBOXYLATING HLECTROREDUCTIONS IN UNDIVIDED ELECTROLYSIS CELLSa
TAR1.E 3
697 -
lcontlnved f r o m p a g e 6 9 6 1
Starting compound
dimethyl-p-nitrotolyl s o l f o n i i i m chloride
l,lO-bi.(p-toluenesulph~"yl)-
I,lO-diaro-IS-ciown-6
acetophennnee
9d kl]
d,l-l,2-dibromo-l,2dipheny letnane
85 DO]
2
-
___
a ) See experimental.
b) See Table 1.
c ) Isolated material yield.
d) cisltrans = 38/62.
e ) The same results were obtained with counter-electrode reactions 3 and
-
696 -
44
-
698
-
The electrocarhonylation o t acrylonitrile
in
an undivided cell yields
For the carhoxylation o f 1.3-butadiene a capillary gap cell is used
the cyanosuccinate 11 in the same yield as in a two-compartment cell
(graphite anode, lead cathode; cathode surface 50 cm2; electrode
( 5 1 , vhereas from a-methylstyrene in an analogous reaction only a l o w
distance 0.5 m) incorporated in a cyclic flow system which also contains
-
(12)
yield of Z - m e t h y l - 2 - p h e n y l s u c c l n a t e
IS,
obtained. In a c l e a n reaction
benralaniline gives the corresponding carboxylated product
'3 171.
The
a circulation pump, flowmeter, drylng column (molecular sieves 3
x),
heat exchanger and mixing vessel. After being flushed with carbon dioxide
reduction of acetophenone in an undivided cell ~n the presence of DTEAOx
the System i s filled with 1 1 of electrolyte ( 0 . 2 3 M DTIEAOx o r 0.46 N
and carbon dioxide yields, after esterificatron, methyl-a-phenyllactate
TEAForm rn dry acetonitrile) and pressurized with carbon dioxide up to
(2)in
a
moderate yield and additionally the dimer 15 (vide I n f r a ) .
4 bar. After pumping the electrolyte through rhe system for ten minutes,
the gas mixture is vented. This procedure is repeated once. Blectrolysis
From ambenzene a mixture of the mono- and dicarboxylated products ( 16,
-
-
17)
IS
obtained [&I.
The last reaction in Table 2 offers
a
very convenient
under
a
COT pressure of 4 bar is started after the required amount of
butadiene ( e . g . 4 to 5 ZV) has been introduced. Samples are taken at
alternative to the Grignard carboxylation: in a very clean reaction
various time intervals and analysed by GLC after acidibase work-up and
1-bromo-2-methylpencane is converted to the 2-methylpentme carboxylate
addition of bis-trimethylsilyl acetamide.
in a one-compartment eletrolytic cell.
Some
applications of the oxidation of DTEAOx and TEAFarm to non-carboxylating
electroreductions in undivided electrolytic cells are s u m a r i z e d i n Table 3.
The reduction of dimethyl p-nitrotolyl-sulfonium chloride g i v e s a
-
fair y i e l d of p-nitrotoluene (19) and additionally a small amount of the
dimer 1,I-bis (p-nitrophenyl) ethane
of sulphonamides i n aprotic media
(0).
- The
821
electrochemical reduction
provides an efficient means f o r
cleaving tosyl-protecting groups from a nitrogen function. The application
of this reaction to a cryptand synthesis g i v e s
bis-deprotected l,lO-diara-18-crom-6
an
(2).If
excellent yield of the
acetophenone is
Literature:
1. F. Beck, Elektroorganische Chemie, Verlag Chemie, Weinheim. 1974
reduced in an undivided cell in methanol as the solvent in the presence
of TEAForm the acetophenone pinacol
- is
formed in excellent material
2 . For a recent compilation see H. J . Schlfer, Angev. Chem.
".The
yield without any detectable amount of the carboxylated product 1
-
(1981); Angev. Chem. Int. Ed. Engl.
g.911
",
978
(1981).
current yield of I r i s somewhat laver, due to hydrogen evolution.
-
699
The reduction of halogen compounds is
a
-
-
borderline
c a s e : Whereas
l-bromo-
701
-
3 . Saveant et al. used the oxidation of DTEAOx 8 s the counterrelectrode
2-methylpentane is reductively carboxylated with a high yield in the
reaction
presence of DTEAOx (Table 2 , entry 8 ) and 1,2-dibromo-1,2-diphenylethane
here: J.C. Gressin, D. Nichelet, L. Nadja, J.N. Savdanc, N o w . 1. C h m .
gives a good yield of stilbene
(11,
- Table
3, entry 4 ) , DTEAOx
IS
3,
-
esterrfied
I"
a divided cell without recognizing the advantages reported
545 (1979).
~n a very fast reaction by 1-bromo-3-chloropropane.
4 . I. Rubinstein, A.J. Bard, J. Am. Chem. Scc.
These examples demonstrate that the oxidations of the o x a l i c and formic
5. D.A. Tyssee, M.M. Baizer, J . O r g . Chem.
x,
512 (1981)
2, 2819
(1Y74).
acid derivatives can be successfully applied as counterrelectrode
reactions to a wide variety o f one-compartment-cell electroreductions in
aprotic media
6.
van Tilborg, C.J. Smit, Recl. Trav. Chim. Pays-Bas
W.J.M.
'00,
437
(1981).
1. N.L. Weinberg, A.K. Hoffmann, T.B. Reddy. Tetrahedron Lett.
19)1,
2211.
8 . R.C.
Hallcher, M.M. Baizer, Liebigs Ann. Chem.
9. V.D. Parker, Acta Chem. Scand.
835, 147,
10. H. Lund. E . Hobolt, Acca Chem. Scand.
Experimental. Typical experimental procedures are
as
(80 mi) containing 0.2 - 0.4 M starting compound plus 0.23 M DTEAOx or
a
149 (1981).
"0, 895
(1976)
follows. A solution
0 . 4 6 M TEAFOrm i n dry acetonitrile i s electrolysed in a beaker equipped
with
1977, 137
platinium anode and a lead cathode, while carbon dioxide is
11. W.J.M. van Tilborg, C.J. Smit, Recl. Trav. C h m . Pays-Bas
z,
532
(1979).
12. R. Kossai, J. Sirnonet, G. Jeminet, Tetrahedron Lett.
1979, 1059
bubbled through the solution. (For non-carboxylating reductions tne cell
is kept under argon instead of carbon dioxide). After the theoretical
amount of electricity has been passed through the cell, the electrolysis
13. J.H. Wsgenknecht, M.H. Baizer, J.L. Chruma, Synth. Commun.
2,
215
(1972).
is stopped. Methyl iodide is added to the reaction mixture and the
carboxylates formed are isolated and analysed as their corresponding
Received May 10. 1982, revised April 1 8 ,
methyl esters.
-
700
-
-
702
-
1983 / Z
37 S I
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