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Org. Synth. 1959, 39, 1
DOI: 10.15227/orgsyn.039.0001
N-(p-ACETYLAMINOPHENYL)RHODANINE
[Rhodanine, 3-(p-acetamidophenyl)-]
Submitted by R. E. Strube1
Checked by John D. Roberts and Stanley L. Manatt.
1. Procedure
In a 2-l. round-bottomed flask fitted with a mechanical stirrer and a reflux condenser are placed 30.0 g. (0.20 mole) of p-aminoacetanilide (Note 1) and 400 ml. of water. The mixture is heated on a steam bath with stirring, and to the clear solution is added at once a hot solution of 45.2 g. (0.20 mole) of trithiocarbodiglycolic acid (p. 967) in 500 ml. of water. Heating and stirring are continued for 5 hours (Note 2). The steam bath is then replaced by an ice bath, and the reaction mixture is cooled to 20–25°. The precipitate is removed by suction filtration. The solid is transferred to a 500-ml. Erlenmeyer flask containing 200 ml. of water. The mixture is heated on the steam bath to 70–75° while the lumps are crushed by a glass rod to obtain a homogeneous mixture. The mixture is filtered with suction while hot, and the flask is cleaned by rinsing it with small amounts of hot water. The solid on the filter is sucked as dry as possible and then transferred to a 2-l. round-bottomed flask fitted with a reflux condenser. Glacial acetic acid (1.5 l.) is added and the mixture is heated in an oil bath to vigorous reflux for 5 minutes (Note 3). A small amount of solid does not dissolve, and this is removed by filtration while hot (Note 4). The filtrate is stirred mechanically and cooled to 15–20° by an ice bath and kept at this temperature for 1 hour. The slightly yellow crystals are collected by suction filtration, washed successively with 25 ml. of glacial acetic acid, 100 ml. of ethanol, and 100 ml. of ether. The yield of air-dried material is 26–28 g. (49–53% yield). The compound decomposes on heating above 240° (Note 5).
2. Notes
1. p-Aminoacetanilide (white label) supplied by Eastman Kodak Company was used.
2. Within 10 minutes a precipitate is formed; the greater part of the reaction product is present after 2 hours' heating.
3. The purification should be carried out in a hood, since gas escapes during the heating and hot acetic acid is irritating to the eyes. The checkers used a 2-l. heating mantle instead of an oil bath.
4. The filtration of the hot acetic acid solution should be done with care. The flask was surrounded by a towel and rubber gloves were worn. The filtration can best be done in two steps. Approximately half of the hot acetic acid solution is filtered through a large, fluted filter paper; the other half is heated again to reflux and then filtered through another fluted filter paper. Filtration through a steam-heated Büchner funnel may sometimes be troublesome, since the suction accelerates crystallization causing plugging of the funnel stem.
5. Analytical values: Calcd. for C11H10N2O2S2: C, 49.62; H, 3.78; N, 10.52; S, 24.08. Found: C, 49.76; H, 3.76; N, 10.36; S, 24.07.
3. Discussion
This procedure is based on the method of Holmberg2 for preparing N-substituted rhodanines. The synthesis of N-(p-acetylaminophenyl)rhodanine has not yet been reported in the literature.

References and Notes
  1. The Upjohn Company, Kalamazoo, Michigan.
  2. Holmberg, J. prakt. Chem., 81, 451 (1910).

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

trithiocarbodiglycolic acid

ethanol (64-17-5)

acetic acid (64-19-7)

ether (60-29-7)

N-(p-ACETYLAMINOPHENYL)RHODANINE,
Rhodanine, 3-(p-acetamidophenyl)- (53663-36-8)

p-aminoacetanilide (122-80-5)