A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1959, 39, 77
DOI: 10.15227/orgsyn.039.0077
[Carbonic acid, trithio-, bis[carboxymethyl] ester]
Submitted by R. E. Strube1
Checked by John D. Roberts and Stanley L. Manatt.
1. Procedure
In a 300-ml. three-necked, round-bottomed flask equipped with a magnetic stirrer and a gas-inlet tube reaching below the surface of the liquid is placed a solution of 63 g. (0.96 mole) of potassium hydroxide (Note 1) in 100 ml. of water. The solution is cooled in ice, and hydrogen sulfide is bubbled through (Note 2) with stirring until the gain of weight is 33–34 g. (Note 3). The solution is then poured into a 3-l. three-necked, round-bottomed flask provided with a stirrer, a gas-inlet tube, a reflux condenser, and a thermometer reaching into the liquid. The small flask is rinsed with 25 ml. of ice water and the rinsings added to the rest of the solution. Then 63 g. (0.96 mole) of potassium hydroxide is added and allowed to dissolve. The 3-l. flask is then well flushed with nitrogen and, at a temperature of about 30°, 76.0 g. (1.0 mole) of carbon disulfide (Note 4) is added at once. The mixture is stirred vigorously for 2 hours (Note 5) while nitrogen is passed through at a rate of about one bubble per second (Note 6) and the temperature is kept at 35–38° (Note 7). Then the gas supply is disconnected and the dark-red solution is cooled in an ice bath.
A solution of 189 g. (2.0 moles) of chloroacetic acid (Note 8) in 300 ml. of water is neutralized to litmus with a solution containing approximately 135 g. (2.1 moles) of potassium hydroxide in 300 ml. of water. The resulting potassium chloroacetate solution is placed in a dropping funnel and added to the stirred potassium thiocarbonate solution obtained above at such a rate that the temperature does not go above 40°. After the addition is complete, the stirring is continued for 1 hour at room temperature. Then 200 ml. of concentrated hydrochloric acid is added while the temperature is kept below 20° by cooling in an ice bath. Finally, the reaction mixture is stirred for 30 minutes at room temperature. The yellow precipitate is filtered and washed twice with 150-ml. portions of ice water. The crude material is dried under reduced pressure in a vacuum desiccator over calcium chloride to constant weight (about 2 days). The drying is expedited if the lumps are occasionally broken up. The yield of yellow product having m.p. 169–174° (uncor.) (Note 9) is 152–160 g. (67–71%).
2. Notes
1. Potassium hydroxide pellets, Mallinckrodt, 85% minimum KOH assay, were used.
2. A bubbler filled with mercury was placed between the gas cylinder and the gas-inlet tube. A good hood should be used throughout the procedure because hydrogen sulfide is toxic in minute concentrations.
3. Two to three hours is required to saturate the solution. The submitter used the same 3-l. flask to prepare the potassium sulfide and to carry out the subsequent reaction. The checkers found the smaller flask more convenient for following the hydrogen sulfide uptake.
4. Carbon disulfide, Mallinckrodt, analytical grade reagent, was used.
5. The carbon disulfide layer usually disappears in about 45 minutes, but longer times may be required if the stirring is not effective.
6. Contact of the reaction mixture with atmospheric oxygen is to be avoided, but the gas flow should be kept slow enough to minimize loss of carbon disulfide. A bubbler filled with water was placed between the gas cylinder and the gas-inlet tube.
7. A water bath kept at 40–43°, or an electrically heated mantle may be used.
8. Chloroacetic acid, m.p. 62–64°, Eastman Kodak, was used.
9. The submitter reports yields of 160–175 g. (71–77%) of product melting at 166–172°. Recrystallization from water gives 150–165 g. (66–73%) of material melting at 174–176° (cor.).
3. Discussion
Trithiocarbodiglycolic acid can be prepared by heating an aqueous solution of the alkali salts of thiocarbonylethoxythioglycolic acid,2,3 by heating an aqueous solution of potassium methylxanthate and sodium monochloroacetate,3 and by heating an aqueous solution of potassium thiocarbonate and sodium monochloroacetate.3 The compound is also formed by heating an aqueous solution of potassium ethyltrithiocarbonate and sodium monochloroacetate,4 and by heating an aqueous solution of thiocarbonylglycolic acid-thioglycolic acid with ammonia5 or aniline.6 The procedure described is adapted from that of Holmberg.7
This preparation is referenced from:

References and Notes
  1. Research Division, The Upjohn Company, Kalamazoo, Michigan.
  2. Holmberg, J. prakt. Chem., 71, 271 (1905).
  3. Biilmann, Ann., 348, 134 (1906).
  4. Holmberg, J. prakt. Chem., 75, 182 (1907).
  5. Ahlqvist, J. prakt. Chem., 99, 55 (1919).
  6. Holmberg, J. prakt. Chem., 84, 645 (1911).
  7. Holmberg, J. prakt. Chem., 71, 279 (1905).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

trithiocarbodiglycolic acid

calcium chloride (10043-52-4)

hydrochloric acid (7647-01-0)

ammonia (7664-41-7)

aniline (62-53-3)

hydrogen sulfide (7783-06-4)

oxygen (7782-44-7)

nitrogen (7727-37-9)

mercury (7439-97-6)

chloroacetic acid (79-11-8)

sodium monochloroacetate (3926-62-3)

potassium hydroxide (1310-58-3)

carbon disulfide (75-15-0)

potassium sulfide (1312-73-8)

potassium chloroacetate

Carbonic acid, trithio-, bis[carboxymethyl] ester (6326-83-6)

potassium thiocarbonate

thiocarbonylethoxythioglycolic acid

potassium methylxanthate

potassium ethyltrithiocarbonate

thiocarbonylglycolic acid-thioglycolic acid