Electrosynthesis of hydrogen peroxide in room temperature ionic iquids and in situ epoxidation of alkenes

Abstract

Hydrogen peroxide is advocated as green oxidant and widely applied on academic and industrial applications since it only leaves oxygen and water in the reaction stream after reaction. Industrial production (AQ process) and in situ electrogeneration of hydrogen peroxide is the major production route of hydrogen peroxide. The former requires huge amount of organic solvents, metal catalysts and energy input to produce highly concentrated hydrogen peroxide. The latter only needs oxygen, carbon cathode and electricity in aqueous media to give diluted hydrogen peroxide by electroreduction of oxygen. Nevertheless, the electrogeneration of hydrogen peroxide in aqueous media limits its applications in organic synthesis because of the immiscibility between aqueous medium and the organic compounds. Recently, ionic liquids are considered as clean solvents as they are non-volatile, easily recycled and able to dissolve compounds with different polarities. In addition, they have been explored in electrochemistry because they usually possess a wide electrochemical window. We believed that the ionic liquids can act as promising and effective electrolyte for the electrosynthesis of hydrogen peroxide from oxygen electroreduction when compared with the aqueous electrolytes (Chapter 2). Based on the unique properties of ionic liquids, the usefulness of the electrogenerated hydrogen peroxide in the ionic liquids can be enhanced because it can be applied in organic oxidation. In Chapter 3, a simple epoxidation system was developed to epoxidize electrophlic alkenes with electrogenerated hydrogen peroxide in the ionic liquid-water mixtures. The ionic liquid itself can be easily recovered and re-used. The work presented in this thesis aims to develop a simple, environmentally friendly and effective method to electrochemically generate hydrogen peroxide in the recyclable ionic liquids and subsequently in situ to epoxidise alkenes.