Choline Chloride Based Deep Eutectic Solvents as a Tuneable Medium for Synthesis of Coumarinyl 1,2,4-Triazoles: Effect of Solvent Type and Temperature

Article abstract of DOI:10.1002/ejoc.201900249

A study of 1,2,4-triazole synthesis from 2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide (1) or 2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetohydrazide (2) and various isothiocyanates, in deep eutectic solvents, was performed. In order to find the best conditions for 1,2,4-triazole formation, a model reaction on 1 and phenylisothiocyanate was performed in 14 different choline chloride based deep eutectic solvents, at two different temperatures (40 °C and 80 °C). Pure 1,2,4-triazoles were obtained in choline chloride/urea (1:2) and choline chloride/N-methyl urea (1:3) deep eutectic solvents at 80 °C. Pure thiosemicarbazides were obtained in choline chloride/ethane-1,2-diol (1:2), choline chloride/malic acid (1:1), choline chloride/malonic acid (1:1), choline chloride/butane-1,4-diol (1:3) and choline chloride/glycerole (1:2) at 40 °C. The ratio of 1,2,4-triazoles and thiosemicarbazides in reaction mixtures was determined by HPLC and ¹H NMR. After the best conditions for 1,2,4-triazole synthesis were found, some coumarinyl 1,2,4-triazoles were synthesized from two different coumarinyl hydrazides (1 and 2) and various alkyl and aryl isothiocyanates in one step reaction.