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501*‘ 24;, 1946-
c.‘ R. BOE1TGE_R, JR, ErAL
I
ELECTROLYTIC PINACOL PRODUCTION
Filed Jul-y 11,_ 1942
2,408,036
- retested septa, 1946
2,408,036 '
.1
‘r
' accents
ELEGTRGLYTIC PINACWL ERUQUUEIIQN
rice lit. oettger, .llrn, Roselle, Thomas S.
(?bers, Newark, andiwber G. ?ictterbech,
mahway, N. St, assignors to Standard (iii He
veiopment @ompany, a corporation oi Deiaware
Application July 11, 19%, Serial No. 450,513
' c easy (oi. soc-tr)
3
The present invention pertains to a method of
preparing vicinal glycols by electrolytic reduc
tion'of iretones and generaly to all types of carbon
to carbon reductive condensation reactions.
Speci?cally, this invention is concerned with
the reduction of acetone electrolytically to
tetrame'thylethylene glycol. i,
It is the object of the present invention to pro-,
2%.
converting acetone to pinacol have been unsatis
factory either because pinaool current e?ciency
in‘ the overall current e?cienclv or both were too
ow.
'
.
It has now been found that the formation or‘
toxic lead alkyls which diminish the e?ectiveness
of the cathode can be minimized and the reduc
tion of iretones to vicinal glycols e'?ected with
good current e?clency and high ratio otglycols
method of electrolytically forming vicinal glycols 10 to other reduction products hy utilizing cathodes,
and especially pinacols from the corresponding . the surfaces of which contain about 30-80% of
vide the art with a novel and highly advantageous '
iretones, and also to provide the art with novel
electrodes for effecting the reduction of organic
copper or other metal of similar low hydrogen
over-voltage and about 70-20% of lead.
'
The‘ cathodes in accordance ‘with the present
The electrolytic reduction of ketones can take 15 invention may he'prepared in various ways. The
simplest procedure would involve merely mixing
place at the cathode surface according to‘any
?nely
divided lead and copper in the desired pr0-‘
.one of the followingireactionsz
‘
compounds.
‘
.
.
R:
C
C/
m/ \013 (69s.
R1
\CHOH
portion and compressing the mixture into sheets
of the desired dimensions. Alternatively the
cathodes could be prepared by coating lead par~
.20 ticles with copper and subjecting a mass of such
coated particles to high pressure and possibly to
a heating or sintering treatment. This procedure
yields a copper matrix in which lead particles are
evenly distributed. By" reversing the procedure
25 and using copper particles coated with lead it is.
possible to obtain ‘a lead matrix with copper par
ticles uniformly distributed therein.
Substantially the same results are obtained if
Other side reactions result in the formation of
metal alky1s,. especially when the reduction is
effected in acid medium with lead cathodes.
An electrolytic method for effecting the reduc
tive condensation reaction whereby acetone is
30 only the surface of the cathode corresponds to
the above composition.
Such cathodes can be
made simply by forcing metal powder, wire
strands, screening or the like of low hydrogen
overvoltage metals into the surface of a lead
sheet under heavy pressure. Instead of copper
converted to pinacol (tetramethylethylene glycol) 35 powder, screening, or the like, one may also use ,using a lead cathode and an acid catholyte is
other metals of low hydrogen overvoltage‘ or al
described in German Patent 113,719 (1899).
loys such as nickel, brass or Monel metal.
Several German patents pertaining to the elec
The ketones which may be treated in accordtrolytic reduction of acetone to tetramethylethyl
40 ance ‘with the present invention correspond to
enie glycol were issued in the period 1912-1920.
Among these patents were D. R. P. 306,304 (1917),
the general formula
R
306,523 (1918) and 324,919 (1920). ‘ The principal
developments made in this period appear to have
R.
been the use of mixed metal and alloy cathodes,
such as 4 to 10% copper-96 to 90% lead mixtures 45
and 10% tin-90% lead alloy and the use of hori- ’ wherein the R stands for a member of the group
zontally suspended cathodes to prevent the metal
9 ' alkyls formed from accumulating on and decreas
ing the activity of the electrode surface.
All of (the prior, processes for electrolytically
consisting of alkyl and aryl radicals and alkyl
and aryl radicals substituted by a group which is
not reducible under the conditions employed 1.. e.,
50 halogen, carboxyl, etc. Such ketones include, for
. 2,408,036
4
example, acetone, methyl ethyl ketone, diethyl
ketone, methyl propyl ketone, ethyl propyl ketone,
acetophenone, and benzophenone.
'
. By using mixtures of di?’erent ketones. it is
possible to prepare certain mixed glycols. For
example, acetone may be condensed with methyl
about 40 per cent.
ethyl ketone to form the glycol corresponding to“
the formula
cm
on.
“
The anolyte may be a sulfuric acid solution of
about 10' to'40 per centstrength. The electrolyte
is preferably maintained at temperatures between
about 0° C. and about 25° C. The current density
.10 applied may vary between about 0.1 and about
\C__,c/
. (ls/tn it...
'
- :.
catholyte is one containing about 4 volumes of
acetone for each volume of sulfuric acid of about
20 per cent strength. The acid, however, may
vary in strength between about 10 per cent and‘
4 amperes/sq. dm., the preferred current density
being within the range of about 1.5 to about
2 ampere‘s/sq. dm.
n
or methyl ethyl ketone may be ‘condensed for °
' ‘ The following examples serve to illustrate our
example with~acetophenone to form the glycol 15 invention but it is to be understood that our
invention is not limited thereto.
_ _
7
'
Example 1
576 cc. of a 4/1 acetone-10 per cent sulfuric
The glycols formed in accordance with the"
present . invention correspond to the general‘
-
formula:
‘
20 acid solution were placed in the cathode come '
partment of a cell as shown in the drawing. The
anolyte used was 10 per cent sulfuric acid and -
the‘ anode was lead. The cathodes used, con
tained 60% copper and 40% lead.
‘
Electrolysis was eifected at about 16° C. at a
'- current density of 1.67 amps/sq. dm. and at
, 5.4 volts. The run‘ was continued for 4 hours
and a total ofv 11.2 ampere hours were supplied
I wherein each R. stands for an alkyl or aryl radical
or an alkyl or aryl radical substituted by a sub
stituent such as halogen, carboxyl; ‘etc.
' ’A cell-suitable for carrying out the vreduction
to the cell. Upon conclusion‘ of the electrolysis
30 the catholyte was stripped of isopropyl alcohol
and unreacted acetone and pinacol' (tetramethvl- _
ethylene glycol) was separated as the hexahydrate I
by cooling and ?ltering the stripped catholyte.
of ketones in accordance with the present inven
8.0 grams of pinacolv hydrate and 2 grams of
tion is shown diagrammatically in the accoml 35 isopropyl alcohol were obtained corresponding
panying drawing. The single unit cell shown
to a current e?lciency based upon‘ pinacolof
consists of a rectangular jar or the like 22 ar
17%. The mole ratio of pinacol to isopropyl
ranged in a cooling bath a. An anode e of lead
- or the like is arranged inside an acid‘ resistant
diaphragm d, which divides the cell into ‘an
anode and cathode compartment. As shown, two
cathodes c of the composition indicated above
are arranged in the cell.
The details of the cell are not critical to our
alcohol was 1/1.
"
l
1 Example 2
3430 cc.- of" 4/1 acetone-10 per cent sulfuric
acid solution were placed in the cathode com
partment of a single unit cell as shown in the
drawing. .The anolyte'used was 10 per cent sul
furic acid and the anode was lead. The cathodes
invention and the cell may be altered in numerous 45
used were prepared by rolling copper gauze under
ways. For example, anumber of cells could be
pressure onto lead sheets. Rough measurement
combined in a single tank and if desired the
indicated that the surface consisted of about 70%
process could be carried out continuously by
of copper and 30% of lead.
providing a circulating pump, an over?ow means
The electrolysis was effected at about 16° C.
for drawing off the electrolyte from the cell, means so
at a current density of about 0.84 amp/sq. dm.
for‘ separating electrolysis products from the with
and at 6.2 to 7 volts.‘ The run was continued for
drawn catholyte and means for making the elec
8 hours and a total of 40.2 ampere hours were
trolyte up to initial strength for re-introduction
supplied to the cell. Upon conclusion of the elec
into the cell.
.
.
.
.
trolysis the catholyte was treatedas described in
The use of a diaphragm is recommended since
the products formed at the cathode are liable 55 Example 1 to'separate the pinacol hydrate. 42.9
gramsof pinacol hydrate and 11.2v grams of iso
to be oxidized at the anode. The use of a dia
propyl alcohol were obtained corresponding .to a
phragm may be avoided if ‘desired by the use
current e?iciency based upon pinacol of 25.3%
and" a current e?lciency based upon isopropyl
of a high anodic current density or by the use of 60 alcohol of 25%. The mole ratio ,of pinacol to
isopropyl alcohol was 1/1.
anodes having a low oxygen overvoltage, i. e.,
nickel‘ or by a combination of two or more of
Ewample 3
' of anolyte and catholyte of unequal densities in
cells provided with .horizontal electrodes, the use
these expedients.
'
2340 cc. of a 4/1 acetone-25 per cent sulfuric
Aside from the nature of the cathode surface.
the factor which has the greatest effect upon 65 acid solution were treated in a cell similar to that
used in the foregoing examples. The anolyte was
the course of the reaction in the cell is the con
25 per cent sulfuric acid and the anode was lead. 5 ‘
centratlon and type of electrolyte used. Acid
The
cathodes‘ were prepared bycompressing 20
media have given the best results. The ratio of
mesh copper wirescreen into a lead sheet. Rough
ketone to water in the catholyte should be high.
However, a ratio of 4/1 appears to be approxi 70 measurements gave about 40% lead and 60% I
copper on the exposed surface of the cathode.
mately the upper limit economically because of
The electrolysis was effected at about 16° C.
the high resistivity of the solution which would .
and a current density of about 1.67 am./sq. dm.
greatly increase the power cost. In the producand at 5.8 to 6.8 volts. The run was continued
tion of tetramethylethylene glycol the preferred 75 for
5 hours.
'
v
'
.
‘ 2,408,086
5.
duction of an aqueous'sulfuric acid‘ solution of
A comparison run was made in. a similar cell
a ketone of the formula
with the same volume and strength of catholyte
and with a lead anode. The“ cathode used was a
.
B
"
mixture containing 4% copper and 96% lead.
/
_ The electrolysis was effected at about 16° C. at
R
a current density of 2.0 amps/sq. dm. and at
6.3 to ‘7.8 volts.
>
.
wherein It stands for-a member of the group
'
consisting oi’ alkyl' and aryl radicals and alkyl
and aryl radicals substituted by a group which
The results of both of the foregoing runs are
summarized in the following table:
'
‘
Pmmlhydrm
Time,
Amp‘
hrs.
totéi
18° “Wuh-
(grams)
IPinacolO a
)
Iso ro
'
11110 c E
p w 5
,
pinacol/
_
'
Total Intervall Total Intervall Total Interval‘ Total Intervall
50% Cu 40% Pb .......... ..
2
20
21.3
4
40
40.0
56.5
18.5
2
24
0.3
as
4
c
48
i vv12
11.5
28.3
11.2
10.8
5
-
4% Cu96%1’b ___________
'
50
21.3
18.7‘
5.2
:12
25.2
8.9
11.1
23.1
11.5
as
25.2
222
ace
80.4
................. -.
0.2
as
15.8 ......... -.
8.7
as
11.1
10.0
23.5
19.0
20.8
10.5
1101mm
isglpropyl
°°h°
n5
1.08/1
1115
1.2/1
23.2
1
1.3/1
0.41/1
1 Readings and analysis were made at thelstated time intervals given.
is not reducible under the conditions employed
No lead alkyls were ‘stormed with the cathode
having the copper screening rolled thereon but 25 the improvement which comprises effecting‘ said
reduction in a diaphragm cell in contact with a .
large amounts of lead alkyls were formed and
cathode consisting of from 60 to 80% of copper
coated the surface of the 4% copper, 96% lead
and from 40 to 20% of lead at ‘at temperature.‘
cathode.
below about 25° C. and at a current density of
" vWe claim:
’
1. In the process of producing glycols corre 80 between about 0.1‘ and about 4 amperes per sq. dm.‘
3. The process as de?ned in claim 2 wherein
- sponding to the general formula
the ketone and sulfuric acid are used in the ratio
of about 4 volumes of ketone to 1 volume of acid. .
4. In the process of preparing tetramethyl
ethylene glycol by the ‘electrolytic reduction of
an aqueous acid solution of acetone the improve
wherein R stands for a member of the Broup.
consisting of alkyl and aryl radicals and substi
tuted alkyl and aryl radicals by the electrolytic
ment which comprises effecting the reduction in
a diaphragm cell in contact with‘a cathode con
sisting of from about 60 to 80% of copper and
40 to 20% of lead at a temperature below about
reduction of an aqueous acid solution of a ketone
of the formula
R
25° C. and at a current density of between about .
0.1 and about 4 amperes per sq. dm.
-
-
5. .In the process of preparing tetramethy
' \c=o
ethylene glycol by the electrolytic reduction of an '
aqueous sulfuric acid solution of acetone‘ the
3
improvement which comprises e?ecting the re
duction in a diaphragm cell in contact with a
wherein R stands for a member of the group con
sisting of, alkyl and aryl radicals and alkyl and.
aryl radicals substituted by a group which is not
' cathode consisting of from about 60 to 80% 0!
copper and 40 to 20% 0! lead at a temperature
reducible under the reaction conditions employed
the improvement which comprises effecting said 50 below about 25° C. and at a current density of be
tween about 0.1 and about 4 amperes per sq. dm.
reduction in a diaphragm cell in contact with a
6. In the process of preparing tetramethyl
‘cathode consisting of from 60 to 80% of copper
ethylene
glycol by the electrolytic reduction of a
and 40 to 20% of lead at a temperature below
about 25? C. and at a current density of between . solution of about 4 volumes ‘of acetone in about
55 ,one volume of aqueous sulfuric acid of about 20% ‘
about 0.1 and about 4 amperes per sq. dm.
strength the improvement which comprises ef
2. In the process of producing glycols corre
fecting
the reduction in a diaphragm cell in con
sponding to the general formula
'
tact with a cathode consisting'of from about 60
to 80% of copper and 40 to 26% oi lead at a
temperature below about 25° C. and at a current
density of between about 0.1and about 4 ampere:
_
wherein R stands for a member of the group con
sisting of alkyl and aryl radicals and substituted
alkyl and aryl radicals. by the electrolytic re
per sq. dm.
CHARLES R. BOET'I‘GER,_J,R_.
mouse a. CHAMBERS. .
‘03m 0. sto'rrmsox. '
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