Synthesis of 5-arylazo-2-thiohydantoins

The methylene group of 2-thiohydantoin reacts with diazonium salts to give azothiohydantoins, whose longwave absorption maximum is shifted hypsochromically as compared with the corresponding azorhodanines, and bathchromically compared with azohydantoins. Introduction of an acetyl group, particularly of benzoyl, at position 1 in the hydantoin ring causes considerable bathochromic displacement of the absorption maximum, while introducing a phenylsulfonyl group leaves the absorption maximum unaffected.