An efficient and chemical oxidants-free protocol of synthesizing carboxylic acids from aldehydes catalyzed by the betaine-fatty acids ionic liquid derived from vegetable oil

Abstract

Oxidation is a fundamental process in the manufacturing of explosives, plastics and pharmaceuticals. Numerous techniques to produce carboxylic acids from benzaldehydes in the presence of chemical oxidants have been developed. However, these approaches are complex and limited by catalytic system constraints, which include the use of costly and toxic chemicals. In addition, recent literature has revealed that these processes are also reliant on the use of rare metals, which will become harder to source in 20 years’ time. As a result, chemists are seeking feasible alternatives that are environmental-friendly and sustainable. In this study, a simple, effective and chemical oxidant-free approach of preparing carboxylic acids from benzaldehydes is proposed using betaine-fatty acids ionic liquid ([Bet][FA] IL) derived from vegetable oil. [Bet][FA] IL itself is found to be catalytically active in the synthesis of the targeted product. Additionally, good yield (76–97 %) of the desired product may be obtained using the precipitation method. [Bet][FA] IL is characterized using 1H nuclear magnetic resonance spectroscopy analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Experiments showed that [Bet][FA] IL has a melting point below 100 °C and is thermally stable at high temperatures. Surface-active properties of [Bet][FA] IL measured by surface tension and conductivity at 25 °C found that its critical micelle concentration is lower than traditional surfactants. This environment-friendly approach is in line with green principles since it supports the use of sustainable catalysts. Finally, it is expected to be beneficial in future production of chemical intermediates via oxidant-free methods.