Synthesis, characterization and application of novel ionic liquids
Authors:   , Arumugam Vasanthakumar 
Published: July 2021

Ionic liquids (ILs) or molten salts at room temperature presently experience significant attention in many areas of chemistry. The most attractive property is the “tenability” of the physical and chemical properties of ILs by varying structure. The use of ILs in solvents demands information about their behaviour in the presence of other compounds including organic solvents such as alcohols or carboxylic acids or water, commonly used for products extraction. In addition, the efficiency of chemical processes (synthesis, extractions and separations) is strongly influenced by the nature of ILs. In this study describes the synthesis and characterization of novel epoxy propyl substituted ionic liquids (ILs). The thermophysical properties of ILs and their binary mixtures with either water, alcohol or carboxylic acids were investigated and the results are discussed in terms of interactions through thermodynamic properties. Furthermore, 2-oxopyrrolidine (Pyr), 2-aminopicoline (Apic) and 1,4-diazabicyclo [2.2.2] octane (DABCO)-based dihydroxypropyl substituted ILs are synthesised and characterised successfully. These ILs were then used to synthesize and characterize a novel 4 th -generation multi-ionic IL. A significant application of this IL is the synthesis of a unique nanomaterial using magnetic iron nanoparticles, h-boron nitride and titanium dioxide. The nanomaterial was strategically used to reduce selected dyes and series of nitroanilines (NAs). The chapter 1 to 4 explains about the introduction, literature review, synthesis and thermophysical properties of ILs as well as thermodynamic properties of ILs. The fifth chapter of this study describe the synthesis, characterization and thermophysical properties of a novel 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium chloride IL and its binary mixtures, with either water or ethanol. The density (ρ), and speed of sound (u), were measured for the above IL and its corresponding binary systems with either water or ethanol at different temperatures ranging from (293.15 to 313.15) K. The derived thermodynamic properties for instance excess molar volumes (V mE ), isentropic compressibility (k s ) deviation in isentropic compressibility (∆k s ) and intermolecular free length (L f ) were investigated from the ρ and u data, respectively. It is noted that V mE , k s ∆k s and L f values increase with increasing temperature. Derived properties such as V mE , and ∆k s data were fitted to the Redlich-Kister polynomial equation. The measured and calculated data were interpreted in terms of intermolecular interfaces and structural effects between similar and dissimilar molecules upon mixing (Paper: I) The chapter six describes the synthesis and characterization of 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium salicylate and 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium acetate ILs. These ILs and their binary mixtures with either water or methanol were then studied to determine their thermophysical properties. The temperature dependent ρ and u for IL, methanol, water, and their corresponding binary mixtures of {IL (1) + methanol or water (2)} were measured over the entire range of mole fractions at temperatures from T = (293.15 to 313.15) K in intervals of 5 K, under atmospheric pressure. The calculated thermodynamic properties such as V mE , k s ∆k s andL f , were derived from the investigated ρ and u data. The resulting experimental data for V mE , L f , and ∆k s , were well fitted to the Redlich-Kister polynomial equation. (Paper: II & III) The chapter seven reports the thermophysical properties of binary mixtures for the combination of 2′, 3′- epoxypropyl-N-methyl-2-oxopyrrolidinium chloride with carboxylic acids either ethanoic or propionic acids. The novel IL [EPMpyr] + [Cl] − was synthesized, and it has been mixed with ethanoic or propanoic acids. The influence of an epoxy group in this IL was more strongly affected with the acids, and their thermophysical properties at varied temperatures are discussed in term of density (ρ), viscosity (η), speed of sound (u), and refractive index (n) measurements. The ρ, u, η, and n of the IL, ethanoic acid, propanoic acid, and their corresponding binary mixtures {[EPMpyr] + [Cl] − (1) + ethanoic or propanoic acid (2)} were measured at T = (293.15-313.15) K and at P = 0.1 MPa. The theoretical thermodynamic properties of V mE , k s , ∆k s , and L f are calculated using experimental ρ and u data. The V mE and ∆k s values for both binary mixtures were found to be negative over the entire mole fraction range of compositions at all the investigated temperatures. These results suggest the existence of specific interactions between components in the molecules. The experimental data could be helpful to understand the molecular interactions between the IL and carboxylic acid combinations. The experimental data were fitted to the Redlich-Kister polynomial equation. This study is very important for industries because most of the ILs are viscous and have high pH values, so making their applications in industries are difficult. Hence these main disadvantages could be addressed and rectified simultaneously without drastically altering the nature of the IL by using various carboxylic acid combinations. Moreover, the thermophysical data and information about acid and IL mixtures will provide insight into the use of these ILs in acidic conditions, thereby enabling the development of processes for future industries. Additionally, the measurements of thermophysical properties were used to calculate thermodynamic properties, which lead to a better understanding of the interactions amongst unlike molecules and hydrogen bonds in binary mixtures. (Paper: IV) In summary, the first four publications describes the synthesis, characterization and thermophysical properties of 2′,3′-epoxypropyl substituted 2-oxopyrrolidinium cation-based novel ILs with various anions such as chloride, acetate and salicylate. These ILs were characterized by FTIR, 1 H NMR, 13 C NMR and elemental analysis to confirm the chemical structure of the ILs. The binary mixtures of ILs with either water or methanol or ethanol were carefully prepared. Experimental measurements of the thermophysical properties of ρ, u, η and n, selected solvents, and their binary mixtures at various temperatures, across the entire mole fraction ranges of ILs, were determine. Thermodynamic properties of V mE , k s , ∆k s and L f were calculated from ρ, and u data. These thermodynamic properties were correlated using the Redlich-Kister polynomial equation. Molecular interactions, especially H-bonding and other interaction effects that occur between ILs and molecular solvents were discussed. The chapter eight discusses the synthesis and characterization of novel 4 th generation amino trismethyl phosphonate (ATMP) based IL such as [DABCO, PYR, APIC-PDO] + [ATMP] - and their application to the synthesis and characterization of partially oxidized h-boron nitride modified nanomaterial with copper ferrite magnetic nanoparticles (NPs). This nanomaterial was characterized through various spectroscopic, microscopic and surface morphological techniques. Thereafter it was used as environmentally friendly heterogeneous catalyst for the reduction of a series of NAs and dyes such as 2-nitroaniline (2-NA), 3-nitroaniline (3-NA), 4-nitroaniline (4-NA), 4-nitro-1,2-phenylenediamine (4-NPD), methylene blue and allura red to their corresponding amino analogues. The rate constant, order of reaction, activation energy and constant ratio were calculated for each substrate. The order of reduction, was 4-NPD > 4-NA > 3-NA > 2-NA. Kinetic studies indicated either zero or pseudo-first order reactions. Furthermore, kinetic studies at various temperatures such as 25, 30, 40, 50 and 60 o C as well as the range of various quantities of catalyst such as 0.015, 0.030 and 0.045 ml (0.2mg/ml concentration) showed that either an increase in temperature or the amount of catalyst increased the rate of the reaction. It was found that the nanomaterial is an efficient catalyst in aqueous solution at ambient temperature, and the processes for recovery were simple. It was re-used more than seven times with negligible loss of its catalytic activity. It is envisaged that new industrial applications of the ILs and their nanomaterials will emanate in the future. (Paper: V) The chapter nine describes the synthesis, characterization and application to the reduction of NAs which were made using 2′,3′- epoxypropyl-N-methyl-2-oxopyrrolidinium salicylate IL, NiFe 2 O 4 NPs and titanium dioxide (TiO 2 ). Here IL was used as a bonding or capping agent to synthesize NiFe 2 O 4 NPs doped TiO 2 nanocomposite. This nanocomposite was characterized by various microscopic and surface morphological studies. The nanocomposite displayed a good catalytic activity for the reduction of 2-NA to 2-aminoaniline and can be recovered as well as recycled easily. (Paper: VI)