Structural investigation of aroylhydrazones in dimethylsulphoxide/water mixtures

Molecular structures of aroylhydrazones derived from salicylaldehyde, o-vanilin and nicotinic acid hydrazide in DMSO and DMSO/H2O mixtures have been studied by NMR, UV–Vis, ATR and Raman spectroscopy. The addition of water to the system did not induce the tautomeric conversion of the existing form constituted of the ketoamino hydrazide part and the enolimino aldehyde part, but it was involved in the formation of hydrated molecules. Vibrational spectra (ATR and Raman) clearly indicated hydrogen bonding of the studied hydrazones through the carbonyl, amino and hydroxyl groups with water molecules. Increasing the water content conversion from E to Z isomer was not observed.

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► No tautomeric and isomeric conversion of aroylhydrazones was observed.
► The most stable form consisted of: ketoamino (hydrazide part) and enolimino (aldehyde part).
► Vibrational spectra (ATR and Raman) indicated H-bond formation with water.