Ultrasound assisted synthesis of benzohydrazides catalysed by silica sulphuric acid: Multivariate optimisation and green metric evaluation

Abstract

This work presents a simple, environmentally friendly, and straightforward method for the synthesis of benzohydrazide via a one-pot, solvent-free tandem reaction. Using silica sulphuric acid (SSA) and ultrasound-assisted irradiation, the procedure combines the esterification of benzoic acid with methanol, followed immediately by hydrazinolysis. With this method, the lengthy reaction times, isolation of the intermediate methyl benzoate, and volatile organic solvents required for traditional stepwise synthesis are all avoided. The initial esterification was facilitated by the solid acid catalyst, which also prepared the carbonyl for hydrazine hydrate's nucleophilic attack. A multivariate statistical modelling response surface methodology (RSM) was used to analyse the effects of several parameters on the reaction performance, including temperature, catalyst loading, and sonication time. The catalyst demonstrated robust stability and could be reused for several consecutive cycles without a significant loss in catalytic activity. Green metrics evaluation of the benzhydrazide synthesis was carried out using DOZN™ 3.0, and an aggregate value of 2 was obtained, indicating that the synthesis process was environmentally friendly. The result indicated that the ultrasound method was better than the traditional method. This one-pot protocol offers a green and economically viable alternative for the production of benzohydrazide and potentially other hydrazide derivatives, characterised by its operational simplicity, minimal waste generation, and exceptional energy efficiency. • Benzohydrazides were synthesized via a one-pot ultrasonication, solvent-free tandem reaction. • Silica sulphuric acid efficiently catalysed the synthesis of benzohydrazide. • The optimum conditions were achieved using the RSM BBD model. • DOZN™ 3.0 confirmed that the benzhydrazide synthesis followed green processes.

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