A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1926, 6, 18
DOI: 10.15227/orgsyn.006.0018
[Isothiocyanic acid, p-chlorophenyl ester]
Submitted by G. Malcolm Dyson
Checked by Frank C. Whitmore and P. L. Cramer.
1. Procedure
In a 5-l. crock or battery jar, provided with a powerful mechanical stirrer, are placed 3.5 l. of water and 249 g. (165 cc., 2.16 moles) of thiophosgene (p. 506) (Note 1). To the vigorously stirred (Note 2) mixture is added slowly 255 g. (2 moles) of p-chloroaniline during about one-half hour. The stirring is continued for about an additional one-half hour. The dark brown oil is separated, washed with 50 cc. of 10 per cent hydrochloric acid, and placed in a flask for steam distillation.
The flask is immersed in an oil bath heated to 120° and dry steam is then passed through the reaction mixture. The first few cubic centimeters of distillate contain the excess of thiophosgene and are discarded. The isothiocyanate passes over with the water as an oil that solidifies on cooling. The steam distillation requires about four hours. The crude material is crystallized from two parts of ethyl alcohol at 50°, from which it separates as white needles melting at 44–45°. The yield is 245–275 g. (72–81 per cent of the theoretical amount) (Note 3).
2. Notes
1. Because of the objectionable properties of thiophosgene, care should be exercised in its use.
2. The stirring at the start must be very vigorous or the yield is decreased.
3. The method is general for alkyl- and halogen-substituted aromatic amines. An alternative procedure which gives lower yields but avoids the use of thiophosgene will be found on p. 447.
3. Discussion
p-Chlorophenyl isothiocyanate can be prepared by treating an alcoholic solution of sym-di-p-chlorophenyl thiourea with iodine;1 from ammonium p-chlorophenyldithiocarbamate and lead nitrate;2 and by the action of thiophosgene on p-chloroaniline.3
This preparation is referenced from:

References and Notes
  1. Losanitsch, Ber. 5, 156 (1872).
  2. Dains, Brewster and Olander, Univ. Kansas Sci. Bull. 13, 1 (1922) [C.A. 17, 543 (1923)].
  3. Dyson and George, J. Chem. Soc. 125, 1702 (1924).

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

ethyl alcohol (64-17-5)

hydrochloric acid (7647-01-0)

iodine (7553-56-2)

lead nitrate (10099-74-8)

Thiophosgene (463-71-8)

isothiocyanate (302-04-5)

p-Chlorophenyl isothiocyanate,
Isothiocyanic acid, p-chlorophenyl ester (2131-55-7)

p-chloroaniline (106-47-8)

di-p-chlorophenyl thiourea

ammonium p-chlorophenyldithiocarbamate