Ionic liquids have a varieties of applications in chemical processes as solvents as well as catalysts. Dimethyl carbonate (DMC) is considered to be a green and sustainable reagent for many processes. In this work selective O-methylation of mono-, di- and tri-hydroxy benzenes has been studied with DMC as the alkylating agent and ionic liquids as catalyst at 200 oC in an autoclave. Various phosphonium based ionic liquids such as trihexyl (tetradecyl) phosphonium chloride, trihexyl (tetradecyl) phosphonium bromide, trihexyl (tetradecyl) phosphonium decanoate, trihexyl (tetradecyl) phosphonium hexafluoro phosphate and tetrabutyl phosphonium bromide were screened. Different process parameters were studied including catalyst concentration, reactant concentration, temperature and ionic liquid reusability. The process developed gives maximum conversion and selectivity at 200 °C, 1:6 mole ratio of reactant to DMC with trihexyl (tetradecyl) phosphonium bromide as catalyst. Reaction mechanisms are proposed and discussed to deduce kinetics.
Key words: Phenol, Catechol, Pyrogallol, Hydroxy benzene, Dimethyl carbonate, Ionic liquids, O-Methylation.