Synthesis of L-cysteine and L-cysteic acid by paired electrolysis method

Article abstract of DOI:10.1246/cl.2004.332

L-Cysteine and L-cysteic acid were synthesized by paired eletrolysis method. A high purity over 98% and high yield over 90% of both products were gained. When current density was 7 A/dm² and concentration of L-cysteine was 0.6 mol/dm³, the highest current efficiency of anode and cathode was achieved. Total current efficiency was over 180%. The cyclic voltammetry behaviors of hydrobromic acid and cystine showed that a typical EC reaction took place in the anodic cell. The anode reaction and successive chemical reaction accelerated each other to get a high speed and current efficiency.

Full text of DOI:10.1246/cl.2004.332

3
32
Chemistry Letters Vol.33, No.3 (2004)
Synthesis of L-Cysteine and L-Cysteic Acid by Paired Electrolysis Method
ꢀy
Xixin Wang and Jianling Zhao
Department of Chemistry, Nanyang Teachers’ College, Nanyang 473061, P. R. China
Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, P. R. China
y
(Received November 17, 2003; CL-031108)
L-Cysteine and L-cysteic acid were synthesized by paired
eletrolysis method. A high purity over 98% and high yield over
HB-104 signal generator and a YEW3086 X-Y recorder. GM
388 alternating impedance system and M270 cyclic voltammetry
software were used in the study of electrochemical behavior. The
instruments were supplied by Park Cooperation of USA.
9
7
0% of both products were gained. When current density was
2
3
A/dm and concentration of L-cysteine was 0.6 mol/dm , the
2
0
ꢁ
highest current efficiency of anode and cathode was achieved.
Total current efficiency was over 180%. The cyclic voltammetry
behaviors of hydrobromic acid and cystine showed that a typical
EC reaction took place in the anodic cell. The anode reaction and
successive chemical reaction accelerated each other to get a high
speed and current efficiency.
Reactant L-cystine (½ꢀꢂ
¼ ꢃ219 ꢄ 5 ) possess the oppo-
D
2
0
site optical activity from the products L-cysteine (½ꢀꢂ
¼
D
ꢁ
20
ꢁ
þ6:5 ꢄ 1 ) and L-cysteic acid (½ꢀꢂ
¼ þ8:6 ꢄ 1 ). Conse-
D
quently optical activity of both cathodic and anodic electrolytes
changed markedly during the electrolyzing process. Determin-
ing optical activity of the electrolyte could monitor the reaction
course and controll the electrolysis end.
Current efficiency at different current density and reactant
concentration was tested. The results at anode and cathode were
shown in Figures 1 and 2.
Experiments showed that reactions in anode and anodic
electrolytes were almost ideal with high speed. Accordingly fac-
tors such as current density and reactant concentration had little
influence on its current efficiency. The cathodic product was in-
clined to take place side reaction so the cathodic reaction
reached its highest efficiency only when the electrode reaction
L-Cysteine and L-cysteic acid are important biochemical re-
agents that are widely used as additives for medicine, forage and
detergent.1 At present most manufacturers produced L-cysteine
from L-cystine by electrolysis method in which process only
cathodic reaction was utilized while oxygen was given out from
anode. As a result, electricity was not fully used and the product
was single. L-Cysteic acid was often synthesized by oxidizing L-
cystine with hydrogen peroxide, bromine or dimethyl sulphoxide
with a low yield below 80%. In this article, L-cysteic acid and L-
cysteine were simultaneously synthesized from L-cystine in the
electrolytic cell by paired electrolysis method. This kind of
paired electrolysis method can raise current efficiency and yield
per unit volume of electrolytic cell at a fixed time so that produc-
tion cost can be reduced strikingly. It has been adopted in prepar-
ing many useful fine chemicals such as gluconate, mannitol, sor-
–3
a
95
90
85
80
75
b
4
,5
bitol, succinic, and glyoxylic acid.
The experiment was conducted as follows: 0.6 mol/dm L-
cysteine solution dissolved in hydrochloric acid and 0.6 mol/
3
70
65
60
3
dm L-cysteine solution dissolved in hydrobromic acid were
poured into cathodic and anodic cells of the self-made H-style
electrolytic cell, respectively. The cathodic and anodic cells
were connected with magnet pump through plastic pipe so that
cathodic and anodic solutions circulated continuously. Graphite
was adopted as electrodes in the electrolyzing process. Keeping
5.0
5.5
6.0
6.5
7.0
7.5
8.0
2
current density / A/dm
Figure 1. Effect of current density on current efficiency. (a)
anode, (b) cathode.
2
ꢁ
current density to be 7 A/dm and temperature to be 40 C, con-
stant current electrolysis was conducted. The reaction end was
indicated by following changes of optical activity in electrolyte.
After electrolysis the solutions from anodic and cathodic cells
were condensed through vacuum distillation while hydrochloric
and hydrobromic acids were recovered during the process. L-
Cysteine and L-cysteic acid were obtained through washing,
crystallizing, and drying the remainder after vacuum distillation.
Both in the cathodic cell and anodic cells the actual yields were
over 90% while purity over 98%.6,7 Electrochemical experi-
ments were performed in a three-compartment cell with Pt as
the counter electrode. A saturated calomel electrode (SCE)
was the reference electrode while Pt sealed with glass was the
a
9
9
8
5
0
5
b
80
7
5
70
0
.3
0.4
0.5
0.6
0.7
3
concentration of L-cystine / mol/dm
2
study electrode with an area of 0.00785 cm . Cyclic voltammo-
grams were obtained with a model 273 potentisostat/galvaostat,
Figure 2. Effect of concentration of L-cystine on current effi-
ciency. (a) anode, (b) cathode.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.3 (2004)
333
speed matched with experiment condition. Keeping current den-
2
acid and L-cystine were tested on their cyclic voltammetry be-
haviors. Their cyclic voltammetry behaviors under the same
scanning rate and scanning scope were given in Figure 4.
sity to be 7 A/dm , concentration of L-cystine to be 0.6 mol/
3
dm , current efficiency of both anode and cathode was maximum
with an overall current efficiency over 180%.
Electrode reaction and chemical reaction in the electrolytes
were:
5
00
ꢃ
anode: 10Br ꢃ 10e ! 5Br2
400
300
electrolyte of anode: 5Br2 + RSSR + 6H2O ! 2RSO3H +
þ ꢃ
0H + 10Br
1
þ
cathode: RSSR + 2H + 2e ! 2HOOCH(NH2)CH2SH
2
00
00
0
R = HOOCH(NH2)CH2
During the electrolyzing process, Br2 generated from anode
reacted immediately with L-cystine to turn into L-cysteic acid
and HBr. There was no accumulation of Br2 which could be veri-
fied by the colorless electrolyte before reaching the electrolyzing
end. After the complete reaction of L-cystine, Br2 generated
from anode would not be consumed which resulted in the yellow
electrolyte.
1
2
00
400
600
800
1000
1200
1400
E / mv / vs.SCE
Figure 4. Cyclic voltammetry curves. Peak current decrease
3
3
following the series of 10 mmol/dm HBr + 0.1 mol/dm L-cys-
3
3
3
tine, 10 mmol/dm HBr, 0.1 mol/dm L-cystine, 0.5 mol/dm
H2SO4.
a
1
00
As it could be concluded from Figure 4, reducing peak of
bromine was found in HBr solution without L-cystine. After
the addition of L-cystine into hydrobromic acid, oxidation cur-
rent increased strikingly while there was no reducing peak of
bromine during the reverse scans. Conclusion could be drawn
from the cyclic voltammetry behaviors that it was a typical EC
catalytic process. In the reaction system, as an oxidation media,
HBr was first oxidized to Br2 which reacted immediately with L-
cystine to produce L-cysteic acid and bromide ion which would
be oxidized to Br2 once again on the anode. Above process cir-
culated and accelerated reciprocally and resulted in the prompt
and quantitative reaction.
8
6
4
2
0
0
0
0
0
b
0.2
0.4
0.6
0.8
1.0
1.2
1.4
electrolyzing time/times of theoretical time
Figure 3. Effect of electrolyzing time on the yield. (a) anode,
b) cathode.
(
In conclusion, L-cysteine and L-cysteic acid were synthe-
sized by paired electrolysis method. The yields at anode and
cathode were both over 90% while products purity was above
As it was shown in Figure 3 the product yields at anode and
cathode increased linearly before the time of theoretic electro-
lyzing time. Prolonging the electrolyzing time had little influ-
ence on the anodic product but had bad influence on the cathodic
product which resulted in decrease of yield of the cathodic prod-
uct. Accordingly, electrolysis should be terminated at the com-
pletion of cathodic reaction. By adjusting mass concentration
the anodic reaction should be made to reach its terminal before
that of cathode.
In addition we had also studied other factors including the
reaction temperature, flow rate of the electrolyte, and concentra-
tion of HBr and HCl. Higher reaction temperature was in favor
of dissolving the raw materials and the products but would re-
duce the life time of ion-exchanging membrane which was key
part of the electrolytic cell. Higher electrolyte flow rate would
decrease concentration polarization and raise current efficiency
but would also affect the lifetime of ion-exchanging membrane.
Concentration of HBr and HCl had little effect on the reaction so
enough HBr and HCl were used to dissolved L-cystine.
Electrochemical theory of the cathodic reaction has been
well investigated elsewhere. Consequently we only studied the
preliminary electrochemical behavior of the anodic reaction
here. Solution of hydrobromic acid, L-cystine, both hydrobromic
2
98%. Keeping current density to be 7 A/dm , concentration of
3
L-cysteine to be 0.6 mol/dm , current efficiency of both anode
and cathode reached their maximum value with an overall cur-
rent efficiency above 180%. Cyclic voltammetry behaviors
showed that a typical EC catalytic process took place in the an-
odic cell. The anodic reaction and the successive chemical reac-
tion accelerated reciprocally which resulted in rapid reaction and
high current efficiency.
References
1
2
3
Leydetalain, Bioorg. Med. Chem. Lett., 6, 397 (1996).
Ohyong-im, Bioorg. Med. Chem. Lett., 4, 2245 (1994).
E. N. Gutierrez, M. Park, and Wushang-ren, WO97/23450
(1997).
4
H. M. Li, W. Li, and D. P. Gu, Collect. Czech. Chem.
Commun., 60, 928 (1995).
5
6
G. Hilt, Angew. Chem., Int. Ed., 42, 1720 (2003).
J. L. Zhao, Z. J. Zhu, and D. L. Jiang, J. Instr. Anal., 19, 72
(2000).
7
X. X. Wang, J. L. Zhao, D. L. Jiang, D. P. Gu, and R. T.
Tong, Chem. Res. Appl., 14, 467 (2002).
Published on the web (Advance View) February 17, 2004; DOI 10.1246/cl.2004.332