Organic Chemistry - "Change", Part 10: Catalytic Hydrogenation of an Alkene

 Greetings,

This post covers catalytic hydrogenation of alkenes. This is a controlled lower energy reaction and therefore occurs in a safer manner. A higher percent yield is also obtained by use of the catalyst. The catalyst here is a heavier transition metal, such as palladium. This surface catalyst reaction uses fewer reagents than other addition methods because the metal surface is, essentially, the medium by which the reaction occurs. The alkene and hydrogen reactants are both attracted to the metal surface by van der waals forces. Alkene and hydrogen molecules are held in place within a very thin 2-dimensional layer at the metal surface. It is at the metal surface where the reactant molecules exist at a relatively high concentration and with the proper orientation to react. The metal surface presents more properly-orientated hydrogen and alkene molecules "to each other" than can occur in the more random 3-D environment of a solution within the same time period. The result is that there is a greater probability that a reaction will occur for a certain number of hydrogen-alkene interactions: A lower activation energy state exists which increases the reaction rate without requiring a greater energy input, such as increasing the temperature. Use of a catalyst also provides control of optical isomer production for heterolytic alkene addition reactions, such as hydration: This happens because the species being added to the double bond always add to the same side of the alkene. The reaction-pathway mechanism for the metal-catalyst addition method consists of fewer fundamental steps than other alkene addition reaction methods.

That's all for this post.

As always, thank you for reading!