Chapter 2 - Hydrogenations

Abstract

A great deal of industrial heterogeneous organic chemistry involves the use of hydrogen. Making bonds between hydrogen and other atoms is a primary method for converting one functional group into another. This is typically called hydrogenation if hydrogen is added across a π-bond, but it is called hydrogenolysis if hydrogen is added across σ-bond. Hydrogenation of alkynes is important in the chemical reactions for several reasons. First, it is important for the removal of traces of alkynes from alkene feed stocks in the polymer industry, and second, it is important for synthesizing cis-alkenes. Both of these processes involve the hydrogenation of only one of the two π-bonds of the alkyne. Hydrogenation of dienes resembles hydrogenation of both monoenes and alkynes. Allenes, 1,2-dienes, generally undergo first cis addition of hydrogen to the least-hindered side of the least-hindered double bond and then isomerization and/or hydrogenation of the second. Hydrogenation of carbon–carbon double bonds is frequently performed in laboratory and industrial organic syntheses. Usually it can be accomplished with little difficulty over a wide variety of catalysts.