FORMATION OF CYCLIC CARBONATES FROM ALKENES AND CO2 USING GOLD NANOPARTICLE CATALYSTS STABILIZED IN TETRAALKYLPHOSPHONIUM IONIC LIQUIDS
Cyclic carbonates have found extensive uses in numerous industrial applications. Conventional methods for cyclic carbonate formation, however, often employ toxic phosgene precursors in which hydrochloric acid is being produced as a by‑product. In recent years, routes for the direct synthesis of cyclic carbonates from alkenes instead of epoxides have been sought due to the lower cost and greater availability of alkenes as the starting materials. Among the investigated catalysts, gold nanoparticles (Au NPs) have shown excellent catalytic activity for alkene epoxidation as they allow rapid chemical transformations, and are less prone to over-oxidation and self-poisoning during selective oxidation reactions. Highly stable Au NPs were synthesized in the trihexyl(tetradecyl)phosphonium chloride ionic liquid ([P66614][Cl] IL), a greener alternative to traditional volatile organic solvents. This composite system is novel as the Au NPs act as the catalyst for the epoxidation of alkenes, whereas the IL functions as a solvent for CO2 and a catalyst for the ring-opening of the intermediate epoxides and CO2 (via the chloride nucleophile). The focus of this thesis is to optimize the conditions needed for the one-pot activation of alkenes and CO2 to form cyclic carbonates via studying the required conditions for each reaction. It was found that while epoxidation of alkenes such as propylene and styrene by tert-butyl hydroperoxide can be catalyzed by Au NPs stabilized in the IL solvent, care has to be taken to ensure that the NPs do not get oxidized during the reaction. The cyclic carbonate reaction was found to be effectively catalyzed by the IL chloride anion and has pseudo-first order kinetics with respect to CO2. Increased rates and conversions were further seen at elevated CO2 pressures (i.e. 2.4 MPa), and stirring the system at 600 rpm helped to take the reaction out of the mass-transfer limited range. The established reaction conditions were then being examined for the direct synthesis of cyclic carbonates from alkenes and CO2. Moderate conversion and selectivity were observed. A non-halide tetraalkylphosphonium IL, trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P66614][NTf2]), was also tested to compare with [P66614][Cl] for the same reaction.
Ionic Liquids, Cyclic Carbonates, Gold Nanoparticles
Master of Science (M.Sc.)