Physical properties of benzyl tri-methyl ammonium chloride based deep eutectic solvents and employment as catalyst

Abstract

Deep eutectic solvents (DES) are a type of ionic solvents composed of two components and that have a melting point lower than either of the individual components. DES's can be prepared combining a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA). In this study, benzyl tri-methyl ammonium chloride (BTMAC) is used as the hydrogen bond acceptor, and p-toluene sulfonic acid (PTSA), citric acid (CA), and oxalic acid (OX) are used as the HBD. The physical properties of DES 1 (BTMAC-PTSA), DES 2 (BTMAC-CA), and DES 3 (BTMAC-OX) were investigated at their respective eutectic points. The refractive index, conductivity, density, viscosity, and pH values were measured for the three DES between 293.15 and 333.15K. As expected, the density, refractive index, and viscosity decreased and the ionic conductivity increased with increasing temperature, whereas, the pH values remained constant. The catalytic activities of the DES were tested in the esterification reaction between acetic acid and butanol. The results showed the superiority of DES 1 (BTMAC: PTSA) which gave the highest conversion of acetic acid and a further parametric study including the effects of catalyst loading, mole ratio, alcohol type, and reusability were conducted using DES 1. The obtained results showed a high applicability of DES for catalytic applications.