Principle of the Homologation Reaction

In general, homologation is defined as a reaction by which a member of a chemical class is converted by the introduction of an additional carbon atom at the site of the functional group of the compound  

In a mure specific definition, the carbon atom introduced originates from synthesis gas (CO/Hj) in a homogeneously-catalyzed liquid phase reaction. Substrates accessible for homologation are, in particular, alcohols but can also be ethers, esters.acids, aldehydes, and ketones [1 6]. 

The substituent R may be alkyl, cydoalkyt. or benzyl. Catalysts are selected from transition metals which can form carbonyl complexes. Ruthenium and especially cobalt form active catalysts, although other metals like Rh. Pd. Ft. Os, Ir, Cr, Mn, Fe, and Nt have also been examined. If metals like ruthenium or iron catalysis are used, carbon dioxide is formed instead of water as the by-product. 

Considering the homologation of alcohols, the reaction can be directed to the selective formation of the homologous aldehyde. 

In general, the corresponding aldehydes are thought to be the primary products of alcohols homologation. They easily undergo secondary reactions such as hydrogenation and aldol condensation. 

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