A simple method for deoxygenation of amine oxides to amines free from precious metals and undesirable reductants: Photocatalytic reaction in alcohol suspensions of TiO2 under solar light

Abstract

Deoxygenation of amine oxides to corresponding amines is one of the important reactions in the fields of organic chemistry, biochemistry and medical chemistry. Since this reaction generally requires undesired hydrogen sources (reductants) and harsh conditions such as high temperatures and high pressure, a simpler and safe catalytic reaction system working under milder conditions is highly desired. A very simple method for deoxygenation of amine oxides to corresponding amines, i.e., photocatalytic reaction in an alcohol suspension of titanium(IV) oxide (TiO2) without any other elements, is desired in this paper. Photocatalytic deoxygenation of amine oxides occurred at room temperature and under atmospheric pressure with an alcohol acting as a hydrogen donor. We report variations of this reaction system including variation in substrates (amine oxides) and alcohols and the effects of reaction conditions (amine oxide concentration, reaction temperature and light sources) on deoxygenation. The characteristic of this reaction system, i.e., a thermal acceleration effect, is discussed in detail on the basis of results of physicochemical analysis. Finally, we show that this reaction proceeds under solar light even under a static condition (without stirring of the suspension).