Checked by Cliff S. Hamilton and David B. Capps.
1. Procedure
To a suspension of
38.3 g. (31.5 ml., 0.30 mole) of o-chloroaniline in 300 ml. of warm water is added, with stirring,
27.5 ml. (0.33 mole) of concentrated hydrochloric acid (12N). The resulting solution is placed in a
500-ml. porcelain evaporating dish,
25 g. (0.33 mole) of ammonium thiocyanate is added (Note
1), and the mixture is heated on the
steam bath for 1 hour (Note
2). The liquid, from which a mass of large needles of
o-chloroaniline thiocyanate separates, is allowed to cool, set aside at room temperature for 1 hour (Note
3), and then evaporated slowly to dryness over a period of 2–3 hours. The crystalline residue is crushed finely, 300 ml. of water is added, and again the mixture is evaporated slowly. The dry grayish white residual powder is heated finally on the steam bath for 4–5 hours.
The resulting mixture of crude
o-chlorophenylthiourea and
ammonium chloride (58–62 g.) is powdered finely and suspended in 300 ml. of water. The mixture is warmed slowly to 70° with mechanical stirring, then allowed to cool to 35°, and the solid is filtered with suction. The yield of crude
o-chlorophenylthiourea, melting at
140–144°, is
30–35 g. (
54–63%).
The crude material is dissolved in
60 ml. of absolute ethanol, the solution boiled with
decolorizing carbon for a few minutes, and the clear, nearly colorless filtrate (Note
4) diluted with
100 ml. of hot benzene and
20 ml. of light petroleum ether (b.p.
60–80°). The white crystalline mass of
o-chlorophenylthiourea, which separates gradually on cooling and standing, is separated by filtration under reduced pressure, washed with light
petroleum ether, and dried, m.p.
144–146°. The yield of purified material is
20–24 g. (
36–43%). Evaporation of the mother liquors and crystallization of the residue from a proportionally smaller volume of solvents yields a second crop (
6–8 g.) (Note
5).
2. Notes
2. Comparable results are obtained when three times the quantities specified are used.
3. Uninterrupted evaporation of the initial reaction mixture sometimes tends to give a partly oily product from which only smaller yields can be obtained.
4. The filtration is best effected by the use of reduced pressure employing a
preheated Büchner funnel and
filter flask.
5. According to the submitter the method is generally applicable to the synthesis of aromatic thioureas. For example,
phenylthiourea may be prepared in yields of
37–42%.
3. Discussion
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved