Abstract
In this work, we have explored the thermophysical properties of tetraalkylammonium hydroxide ionic liquids (ILs) such as tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) with isomers of butanol (1-butanol, 2-butanol and 2-methyl-2-propanol) within the temperature range 293.15–313.15 K, with interval of 5 K and over the varied concentration range of ILs. The molecular interactions between ILs and butanol isomers are essential for understanding the function of ILs in related measures and excess functions are sensitive probe for the molecular interactions. Therefore, we calculated the excess molar volume (VE) and the deviation in isentropic compressibility (Δκs) using the experimental values such as densities (ρ) and ultrasonic sound velocities (u) that are measured over the whole compositions range at five different temperatures (293.15, 298.15, 303.15, 308.15 and 313.15 K) and atmospheric pressure. These excess functions were adequately correlated by using the Redlich–Kister polynomial equation. It was observed that for all studied systems, the VE and Δκs values are negative for the whole composition range at 293.15 K. And, the excess function follows the sequence: 2-butanol>1-butanol>2-methyl-2-propanol, which reveals that (primary or secondary or tertiary) position of hydroxyl group influence the magnitude of interactions with ILs. The negative values of excess functions are contributions from the ion-dipole interaction, hydrogen bonding and packing efficiency between the ILs and butanol isomers. Hence, the position of hydroxyl group plays an important role in the interactions with ILs. The hydrogen bonding features between ILs and alcohols were analysed using molecular modelling program by using HyperChem 7.
Highlights
Till date numerous research groups have focused their work on the study of fascinating physical properties of ionic liquids (ILs), due to their wide variety of applications in industries and applied chemistry [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
In order to have the better understanding of the molecular interactions between tetraalkylammonium hydroxide ILs with polar solvents such as 1-butanol, 2-butanol and 2-methyl-2propanol, we have measured r and u properties over the whole composition range at various temperatures such as 293.15, 298.15, 303.15, 308.15 and 313.15 K under atmospheric pressure
This shows that the density values of the tetrapropylammonium hydroxide (TPAH)+alcohol mixtures are not affected much due to change in the position of hydroxyl group in different isomers
Summary
Till date numerous research groups have focused their work on the study of fascinating physical properties of ionic liquids (ILs), due to their wide variety of applications in industries and applied chemistry [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. For the applications in chemical and industrial processes, the knowledge of the thermophysical properties of IL is essential, as they represent the basis for the chemical and biological process [17,18,19,20,21,22,23,24,25,26,27,28]. Many of these studies have led to new possible applications for ILs [18,19,20,21]. The variations in thermophysical properties of ILs, such as density (r) and speed of sound (u) are observed to be very sensitive to the change in ion, mainly due to the microscopic level interactions between solvent molecules [12,13,14,15,16]
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