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

A study of 1,2,4‐triazole synthesis from 2‐((4‐methyl‐2‐oxo‐2 H ‐chromen‐7‐yl)oxy)acetohydrazide ( 1 ) or 2‐(7‐hydroxy‐2‐oxo‐2 H ‐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 1 H 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.