Design and Development of Functionalized Ionic Liquids: Synthesis, Temperature-dependent Properties and Applications

Overall this thesis is a combination of synthesis of neutral, acidic and basic ILs; temperature-dependent properties like density, conductivity, viscosity and solvent properties; toxicity and biodegradability; and applications of acidic ILs in order to replace Brønsted acidic ILs in various esterifications and transesterification reactions; and applications of basic ILs in transesterification of dimethyl carbonate. The synthesis, temperature-dependent properties like density, conductivity, viscosity and solvent properties of morpholinium dicyanamides were reported; and toxicity and biodegradability values of morpholinium bromides were also reported in Chapter 2. Then ILs were functionalized using “renewable” compounds, such as 1,3-chloropropanediol, which arises from glycerol (a natural product, which is obtained as byproduct during the production of glycerol). To prepare these functionalized ILs, we have used several nitrogen bases; N-methylimidazole, N-methylpyrrolidine, N-methylmorpholine, dimethyl imidazole, 4-hydroxy-N-methyl piperidine and N-methylpiperidine. The synthesis of these ILs were carried out. Then their temperature-dependent properties such as density, conductivity, viscosity and solvent properties were studied, data are reported in Chapter 3. Also in this chapter, the analysis of the behavior of some properties (viscosity and conductivity) in terms of the Arrhenius and VTF equations have been reported for all the synthesized ILs. Finally, for four ILs also the thermosolvatochromism was investigated. An introduction to a new series of ILs starting from a seven-membered ring amine, namely azepane (hexamethylenimine), has been reported in Chapter 4. The structural effect on the physico-chemical properties of this class of ILs having dicyanamide as counteranion was studied by changing the alkyl chains to butyl, ethanol and glyceryl groups. The properties of this new class of ILs were compared with those of analogously morpholinium (a functionalized ring) and piperidinium (a non-functionalized ring) salts. The temperature-dependent behavior of viscosity and conductivity of these ILs were compared. The polarity values were also compared and the seven-membered ring having a non-functionalized alkyl chain gave high polarity values. Acidic ILs were prepared starting from nitrogen bases and inorganic acids. These acidic ILs were tried to replace few Brønsted acids in three esterification reactions and one transesterification reaction. These Brønsted acidic ILs were used both as solvent and catalyst in the esterification of octanol and acetic acid in which the product recovery was very simple, by just decanting the product, as the product and the IL formed two separate phases. The IL was also recycled easily by just drying in rotary to remove the water formed during the esterification process. Few of these Brønsted acidic ILs were used in esterification of 1,2-propanediol and acetic acid in which multiple product formation was observed and also yields were not so very high. Some Brønsted acidic ILs were also used to study the selectivity of primary hydroxyl group on the C6 position of β-methyl-D-glucopyranoside. Lastly, these Bronsted acidic ILs were used to study the transesterification of ethyl-trans cinnamate using methanol as well as octanol. All these studies are explained in Chapter 5. Some of the ILs studied in this PhD thesis can be classified also as basic ILs by taking into consideration their anionic part. In particular, the dicyanamide-based IL can be included in this category. These basic ILs were used as solvent as well as catalyst to prepare an important compound, namely glycerol carbonate, starting from two cheap compounds i.e. glycerol and dimethyl carbonate. The conversion yields were very high though the product separation was not possible without distillation at reduced pressures. This application is explained in Chapter 6