Green Synthesis of Oximes Using Low-Melting Sugar Mixtures

Oximes (R₂C=N-OH) are nitrogen-containing organic compounds formed by condensing aldehydes or ketones with hydroxylamine. They are versatile scaffolds in organic synthesis, serving as precursors to amides via the Beckmann rearrangement, as protecting groups for carbonyls, and as key intermediates in the pharmaceutical, agrochemical, and coordination-chemistry industries. However, conventional oxime synthesis employ toxic solvents, prolonged reflux, resulting in chemical waste and poor alignment with twelve principles of green chemistry.

This study presents a green method for oxime synthesis using a biodegradable, sugar-based deep eutectic solvent (DES) as an alternative to conventional organic solvents. The sugar-melt medium, composed of common, inexpensive, non-toxic, recyclable sugars and requires no added catalyst, providing a homogeneous, environmentally benign reaction environment. Two complementary variants were developed and compared: conventional heating in a water bath at 80–90 °C, and microwave-assisted synthesis within the identical sugar-melt medium. Both conventional heating and microwave-assisted methods efficiently produced aldoximes and ketoximes in good yields, with the microwave approach significantly reducing reaction time and energy consumption.

Because the reagents and sugar-melt medium are inexpensive, non-hazardous, and require no specialized apparatus, this protocol is well suited for an undergraduate green chemistry laboratories. It enables students directly compare conventional and green methods while demonstrating how safer solvents and efficient heating can make a classical synthesis more sustainable. Thus, it provides both a practical synthetic approach and an effective teaching model for green chemistry.