Solid base catalysts: fundamentals and their applications in organic reactions

Solid base catalysis studied over the last a half of century is reviewed briefly including mainly those performed in our laboratories. The review begins with advantages of solid base catalysts over homogeneous base catalyst in industrial use followed by definition of Brϕnsted base and Lewis base. The materials known as solid base catalysts are listed, and four reasons for which these materials are recognized as solid base catalyst are explained. For all solid base catalysts, variations in activity as a function of pretreatment temperature show a volcano shape; an incline with the temperature results from an appearance of basic sites by removal of water and carbon dioxide from the surface and a decline results from an elimination of basic sites by rearrangement of surface atoms. The reactions catalyzed by solid base catalysts can be classified into three types: double bond isomerization, addition of anion and proton to various double bonds, and alcohol decomposition. These are represented by 1-butene isomerization, hydrogenation of conjugated 1,3-butadiene and dehydration of 2-butanol. Their mechanisms are explained. In addition, bifunctional base-catalyzed reactions in which basic sites participate in one step of successive steps are exemplified for methyl isobutyl ketome synthesis, metathesis, Tishchenko reaction and side-chain alkylation of toluene. Some industrial processes and future perspectives are briefly described.