Use of glycerol, waste glycerol from biodiesel production and other protic solvents in bioactive α,β-unsaturated ketones synthesis

Abstract

Glycerol is the main co-product from biodiesel production and has been recognized as a sustainable solvent. Herein, we used glycerol and waste glycerol in synthesis of two bioactive α,β-unsaturated ketones (E,E)-1,5-diphenylpenta-2,4-dien-1-one (1) and (E,E)-2,6-dibenzylidenecyclohexanone (2), using aldol mono- and di-condensation reactions, respectively. Crude yield values were calculated from product mass after precipitation and drying. Purity was measured by High Performance Liquid Chromatography with Photodiode Array (HPLC-PAD) using analytical curves and reference compounds. Glycerol and waste glycerol were able to furnish 1 and 2 in higher crude yields and HPLC-PAD purities values than other protic solvents (ethanol, methanol, PEG-400 and water). In order to investigate reasons of glycerol efficiency when compared to water efficiency, we performed computational calculations using Density Functional Theory (DFT). Theoretical predictions confirmed the E1cB mechanism, as well as favourable energy barrier using glycerol in comparison to water, corroborating their sustainable properties. In addition, waste glycerol from corn and sunflower oil transesterifications were used in the synthesis of 1 and 2 for four recycles, displaying good crude yields and HPLC-purities.