Reductive and oxidative activation of oxygen for selective oxygenation of hydrocarbons

Abstract

In this chapter, a simple method for reductive activation of dioxygen by applying electrochemical O 2 –H 2 cell reactions is discussed for the oxygenation of alkanes and aromatics at cathodes. In contrast to the reductive activation of O 2 during the O 2 –H 2 cell reaction, the electrolysis of acidic water should oxidatively activate the oxygen of water at the anode. The reductive activation of oxygen at the cathode, in the presence of a suitable catalyst, is similar to the concept described for the O 2 –H 2 cell system. The active oxygen species for most of the cathodes with and without metal compounds has been suggested to be OH radicals. However, the active oxygen species in the case of a SmCl 3 /graphite cathode has not been found to be an OH radical. Among various metal oxides, metal salts and metal blacks tested the most active and selective anode catalyst for the formation of 1,2-epoxyhexane has been Pt black. The electrolysis of water forms oxidatively activated O 2- that causes the epoxidation of various alkenes, including propene to propene oxide, on a PtO 2 phase for a Pt black anode. Based on the zinc-air battery, a new catalytic system design has been composed of metal chlorides, carboxylic acids, and zinc powder for oxygenation of alkenes to epoxides and partial oxidation of light alkanes (CH 4 , C 2 H 6 , C 3 H 8 ) into alcohols and aldehydes. These catalytic systems are likely to activate oxygen. Among the many metal salts, Eu Salts has showed catalytic activity for the oxygenation of hydrocarbons at room temperature. The reductively activated oxygen generated in this catalytic system showed strong electrophilicy as well as radical character.