A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1947, 27, 73
DOI: 10.15227/orgsyn.027.0073
Submitted by C. Ernst Redemann, Roland N. Icke, and Gordon A. Alles.
Checked by H. R. Snyder and John H. Johnson.
1. Procedure
A. Ammonium dithiocarbamate. Gaseous ammonia is passed into 250 ml. of 95% ethanol (Note 1) contained in a 1-l. Erlenmeyer flask immersed in an ice bath until the gain in weight is 39 g. (2.3 moles). To this solution, still cooled by the ice bath, is added a well-cooled mixture of 76 g. (60 ml., 1 mole) of carbon disulfide and 200 ml. of ether. The flask is stoppered loosely (Note 2) and allowed to remain in the ice bath for 2–3 hours and then at room temperature overnight (Note 3). The mixture is again cooled in an ice bath or refrigerator, and the crystals are collected by filtration (hood), sucked dry, and washed on the filter with two 50-ml. portions of ether. Air is drawn through the crystals for 5 minutes (Note 4) to effect removal of most of the ether. The product is used promptly without further treatment; the weight of the lemon-yellow solid varies between 80 and 90 g., depending principally on the completeness of the removal of the solvent.
B. Rhodanine. Just before the filtration of the ammonium dithiocarbamate, a solution of sodium chloroacetate is prepared by dissolving 71 g. (0.75 mole) of chloroacetic acid in 150 ml. of water contained in a 1-l. wide-mouthed round-bottomed flask and neutralizing the acid with 40 g. (0.38 mole) of anhydrous sodium carbonate (or an equivalent amount of the hydrate) while stirring the solution mechanically. This solution is cooled in an ice bath, and the ammonium dithiocarbamate from the preceding preparation is added during 5 minutes with continual stirring. As soon as the first portion of ammonium dithiocarbamate is added the solution becomes very dark in color. After all the dithiocarbamate has been added the ice bath is removed and stirring is discontinued. The solution is allowed to stand for 20–30 minutes longer, during which time the color changes to a clear yellow. In a 1-l. beaker 400 ml. of 6 N hydrochloric acid is heated to boiling, and the above solution (Note 5) is poured slowly with stirring into the hot acid. Heating is continued until the solution has attained a temperature of 90–95°, after which the solution is allowed to cool slowly to room temperature. The rhodanine separates as nearly colorless long blades which are collected by filtration, washed well with water, and dried. The product weighs 83–89 g. (83–89% based on the chloroacetic acid), and melts at 167–168°. Recrystallization from boiling glacial acetic acid (2 ml. per gram) raises the melting point to 168–168.5° (Note 6); the recovery, without reworking of the mother liquor, is 87%.
2. Notes
1. Absolute ethanol is satisfactory. Methanol may be used, but ammonium dithiocarbamate is much more soluble in methanol than in ethanol and the recovery will be lower.
2. The flask should be stoppered loosely to retard the escape of ammonia. It is not wise to stopper it tightly, as some gas is evolved and pressure may develop. Hydrogen sulfide is present in the gases evolved.
3. The success of the preparation depends upon securing ammonium dithiocarbamate of good quality. Although much solid sometimes separates within 1–2 hours, it contains a large amount of the very unstable ammonium trithiocarbamate.1 After prolonged standing, the solid is nearly pure ammonium dithiocarbamate.
4. Ammonium dithiocarbamate is relatively unstable, and no attempt should be made to dry the compound thoroughly before use.
5. If this solution is not clear and free from solid impurities it should be filtered before addition to the acid.
6. The melting points observed with the aid of a hot-stage microscope are slightly higher—170–170.5° for the unrecrystallized material, and 170.5–171° for the purified product. Although rhodanine usually is described in the literature as melting with decomposition, the checkers observed no evidence of decomposition during melting under the microscope and found the melting point unchanged when molten samples in ordinary melting-point tubes were cooled and remelted.
3. Discussion
Rhodanine has been prepared by the reaction of chloroacetic acid with ammonium thiocyanate;2 by the action of ethyl chloroacetate upon ammonium dithiocarbamate in the presence of alcohol and hydrogen chloride;3 by saturating a solution of thioglycolic acid and potassium thiocyanate in absolute ethanol with hydrogen chloride;4 by ring closure of thiocarbamylthioglycolic acid in various ways.5,6,7 The present method of preparation is adapted from that of Julian and Sturgis.7

References and Notes
  1. Miller, Contrib. Boyce Thompson Inst., 5, 31 (1933).
  2. Nencki, J. prakt. Chem., (2) 16, 2 (1877).
  3. Miolati, Ann., 262, 85 (1891).
  4. Fredyl, Monatsh., 10, 82 (1889).
  5. Holmberg, Ber., 39, 3069 (1906); J. prakt. Chem., (2) 79, 261, 265 (1909).
  6. Granacher, Helv. Chim. Acta, 5, 610 (1920).
  7. Julian and Sturgis, J. Am. Chem. Soc., 57, 1126 (1935).

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

ethanol (64-17-5)

hydrogen chloride,
hydrochloric acid (7647-01-0)

acetic acid (64-19-7)

ammonia (7664-41-7)

methanol (67-56-1)

ether (60-29-7)

ammonium thiocyanate (1762-95-4)

hydrogen sulfide (7783-06-4)

sodium carbonate (497-19-8)

chloroacetic acid (79-11-8)

sodium chloroacetate (3926-62-3)

carbon disulfide (75-15-0)

Ethyl chloroacetate (105-39-5)

potassium thiocyanate (333-20-0)

Rhodanine (141-84-4)

ammonium dithiocarbamate

ammonium trithiocarbamate

thioglycolic acid (68-11-1)

thiocarbamylthioglycolic acid