Russian Journal of Applied Chemistry, Vol. 75, No. 9, 2002, pp. 1438 1440. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 9,
2002, pp. 1470 1472.
Original Russian Text Copyright
2002 by Islamgulova, Shitova, Akhmerova, Tomilov.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Improvement of a Process for Synthesis of Thioglycolic Acid
V. R. Islamgulova, E. N. Shitova, S. G. Akhmerova, and A. P. Tomilov
Research and Technological Institute of Herbicides and Plant Growth Regulators with Pilot Plant,
Ufa, Bashkortostan, Russia
State Research Institute of Organic Chemistry and Technology, Moscow, Russia
Received November 26, 2001; in final form, June 2002
Abstract An environmentally clean process was proposed for synthesis of thioglycolic acid by condensation
of monochloroacetic acid with sodium disulfide, followed by electrochemical reduction of the resulting
mixture.
Thioglycolic acid (TGA) and its derivatives are
used in production of polymers, drugs, pesticides,
dyes, flotation agents, and perfumes [1].
takes much longer time, and above 80 C by-products
start to form. Under the optimal conditions, the yield
of DTDGA is nearly quantitative.
The known routes to TGA are based on reactions
of monochloroacetic acid (MCAA) in the form of
sodium salt with various sulfur derivatives. MCAA
reacts with sodium hydrosulfide in one stage under
Electrochemical reduction of DTDGA occurs with
the consumption of 2F of electricity per mole:
HOOCCH2SSCH2COOH + 2e + 2H+
2HSCH2COOH.
H S pressure of 5 50 atm; yield of TGA 81.0 90.8%
2
[2 5]. The reaction of MCAA with sodium thiosulfate
yields sodium 5-carboxymethyl thiosulfate; its hydrol-
ysis in the presence of oxidants affords TGA, yield
92 96% [6 8]. The reaction is sensitive to oxidants,
whose presence results ion formation of dithiodigly-
colic acid (DTDGA) as impurity [8]. DTDGA can be
prepared in a reasonable yield by the reaction of sodi-
um disulfide with sodium monochloroacetate [9] and
can be subsequently reduced to TGA (yield 98 99%)
on hydrogenation catalysts at 140 C and hydrogen
pressure of 50 atm [10]. DTDGA can also be reduced
electrochemically (yield 80%) [11].
According to published data, the reaction occurs
with a high yield in a sulfuric acid solution on a lead
anode; however, the process was not optimized.
For the success of the electrochemical synthesis,
TGA should be stable under the electrolysis condi-
tions. We have studied the behavior of pure TGA in
aqueous sulfuric acid at 25 30 C and current density
2
of 200 A m . The amount and purity of TGA re-
mained unchanged after passing 2F of electricity per
mole. Similar results were obtained when a double
amount of electricity was passed in the course of
electroreduction of DTDGA (see figure). The maximal
amount of TGA formed remains unchanged after pass-
ing 200% amount of electricity relative to the stoichi-
ometry, with the optimal amount being 140 150%.
Thus, the known procedures for preparing TGA
either involve the use of high pressures or require
thorough protection of the reaction mixtures from
atmospheric oxygen. Taking into account published
data and the availability of starting compounds for
commercial synthesis, we chose the route based on the
reaction of MCA with sodium disulfide, followed by
electrochemical reduction of the resulting DTDGA.
Y, %
MCA reacts with sodium disulfide as follows:
Na2S2 + 2ClCH2COOH
HOOCCH2SSCH2COOH
q, %
+ 2NaCl.
TGA yield Y as a function of the amount of electricity
First, we determined the optimal conditions for this
reaction: 70 80 C, 30 min. Below 70 C the reaction
passed q (relative to stoichiometry). 20 25 C; current den-
2
sity 200 A m
.
1070-4272/02/7509-1438$27.00 2002 MAIK Nauka/Interperiodica