Phenyl iso-thiocyanate from aniline

Phenyl iso- thiocyanate may be prepared in quantity directly from aniline. Aniline, carbon disulphide and concentrated aqueous ammonia react to form the sparingly soluble ammonium phenyldithiocarbamate this is decomposed by lead nitrate to produce phenyl iso-thiocyanate  

Equip a 500 ml. tliree-necked flask with a powerful mechanical stirrer and a separatory funnel leave the third neck open or loosely stoppered. Introduce, while the flask is cooled in a freezing mixture of ice and salt, 90 ml. of concentrated ammonia solution (sp. gr. 0-88) and 54 g. (43 ml.) of pure (e.g., A.R.) carbon disulphide. Stir the mixture and run in 56 g. (55ml.)of pure aniline from the separatory funnel during about 20minutes stir for a further 30 minutes, and allow to stand for another 30 minutes. A heavy precipitate of ammonium phenyldithiocarbamate separates. Transfer the salt to a 5 litre round-bottomed flask by four extractions with 200 ml. portions of water. Add to the resulting solution, with 

In this modified procedure the presence of alcohol is essential otherwise no iso-thiocyanate is obtained. The process may be applied to other substituted anilines. 

Salts of primary aromatic amines react with solutions of alkali cyanates to yield first the amine cyanate, which then undergoes molecular rearrangement to the arylurea, for example  

The monoarylurea may be prepared directly from the amine by heating it in aqueous solution with an equivalent quantity of alkali cyanate and excess of acetic acid, for example  

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