Synthesis and characterization of green menthol-based low transition temperature mixture with tunable thermophysical properties as hydrophobic low viscosity solvent

Abstract

Abstract The liquid transition temperature mixture (LTTM) is a new type of tunable solvent analogous to deep eutectic solvent (DES). LTTMs have been favorable choice of researchers as they are green solvents, having potential to be an alternate to ionic liquids (ILs) and the traditional solvents, as they can be formulated from natural and biodegradable resources. The aim of this work is to design low viscosity, cheap, biodegradable and hydrophobic LTTMs from natural resources. In this study, LTTMs based on DL-menthol as hydrogen bond accepter (HBA) with naturally occurring hydrogen bond donor (HBD), namely thymol, sesamol, and 3-hydroxybenzoic acid were synthesized and characterized. The formation of LTTMs was monitored by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The functional group and purity of LTTMs were studied by Fourier transform infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR), respectively. Density, viscosity and water content of LTTMs were determined to analyse its solvent characteristics. Thermogravimetric analysis (TGA) was investigated to identify the thermal stability and working temperature range of LTTMs. The tuneability, the physicochemical properties of LTTMs at various temperature by changing the HBDs revealed that these LTTMs have the potential for a wide range of applications. Taking the advantage of their hydrophobic and low viscosity properties, these LTTMs have been applied as green extraction solvent in vortex-assisted dispersive liquid-liquid microextraction (VA-DLLME) for the extraction of pyrethroid pesticides (bifenthrin, deltamethrin, fenpropathrin permethrin and tetramethrin) from aqueous solution.