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%.