An improved method for the preparation of 2-hydrazinylbenzo[d]thiazoles from benzo[d]thiazol-2-amines

Abstract

Hydrazinylbenzo[d]thiazoles are promising bio-active heterocycles known for their use in pharmaceutical and agrochemical industries1-4. This class of compounds namely hydrazinylbenzo[d]thiazoletriapine was identified as anti-cancer agents5. Further, 2-(2-(4-aryloxybenzylidene) hydrazinyl)benzothiazole derivatives were reported as anti-tubercular agents6-8. Benzothiazole based pyrene receptors9-12 displayed fluorescent properties for the recognition of Zn2+3. Consequently, the synthesis of hydrazinylbenzo[d] thiazoles and their derivatives have attracted considerable attention. The 2-hydrazinylbenzo[d]thiazole was prepared by reacting benzo[d]thiazol-2-amines with hydrazine hydrate in presence of ethylene glycol as the solvent at 140°C13. To the best of our knowledge, ethylene glycol is the only solvent used for the preparation of 2-hydrazinylbenzo[d]thiazole14. Ethylene glycol is not a good solvent when handling the large scale preparation of pharmaceutically important compounds. Exposure of ethylene glycol can be extremely dangerous, with significant morbidity and mortality if left untreated. Therefore, there is a need to develop the method by replacing the ethylene glycol solvent with other enviro friendly solvent like water. In the course of our research on heterocyclic compounds, we have reported various heterocycles15-17 includingbenzohydrazides18. As part of our research work on development of benzothiazole heterocycles; we have conducted the reactions between benzo[d]thiazol-2-amines and hydrazine hydrate in water provided hydrazinylbenzo[d]thiazoles and the results are discussed below.