Catalysis in environmentally friendly solvents
Room temperature ionic liquids (RTILs) are attracting increasing interest as environmentally benign reaction media for chemical synthesis and catalysis. This thesis describes the use of the RTILs (BMIM[OTf], BMIM[PF6], BMIM[NTf2], BMIM[BF4]) as solvents for a variety of non-catalysed and metal-catalysed reactions, and some copper-catalysed asymmetric reactions. Chapter one provides an overview of the principles of Green Chemistry, biphasic catalysis, the physiochemical properties of RTILs and an introduction to chemistry in RTILs. Chapter two describes nucleophilic aromatic substitution reactions of dinitrochlorobenzene and explores the potential to reuse the IL. The employment of RTILs in alkylation reactions and the Biginelli condensation is also discussed. Chapter three reports the synthesis and use of BMIM[C1]-ZnC12 as a catalyst and reaction medium for Diels-Alder reactions and the Fisher-Indole synthesis. The effect of the composition of the IL on yield and selectivity is examined. Further applications of BMIM[C1]-ZnC12 in the synthesis of coumarins by the Pechmann reaction, and as a catalyst for the one pot Pictet-Spengler reaction are described. Chapter four concerns the use of chiral copper oxazoline complexes as catalysts for several reactions including Diels-Alder, cyclopropanation, aziridination, and allylic oxidation. These reactions have been investigated in RTILs, and the affect of anion on yield and enantioselectivity is discussed. In all cases a comparison is made to conventional organic solvents and attempts are made to correlate the results against known solvent parameters. The possibility of recovery and reuse of the catalyst ionic liquid solution is discussed in selected cases, as is the effect of impurities in the RTILs on the reactions.