Reduction of Alkenes Hydrogenation

Alkenes react with H2 in the presence of a metal catalyst such as palladium or platinum to yield the corresponding saturated alkane addition products. We describe the result by saying that the double bond has been hydrogenated, or reduced. Note that the word reduction is used somewhat differently 

Platinum and palladium are the most common laboratory catalysts for alkene hydrogenations. Palladium is normally used as a very fine powder supported on an inert material such as charcoal (Pd/C) to maximize surface area. Platinum is normally used as Pt02, a reagent known as Adams catalyst after its discoverer, Roger Adams. 

Mechanism of alkene hydrogenation. The reaction takes piace with syn stereochemistry on the surface of insoiubie cataiyst particies. 

Molecular hydrogen adsorbs to the catalyst surface and dissociates into hydrogen atoms. 

The alkene adsorbs to the catalyst surface, using its tt bond to complex to the metal atoms. 

Roger Adams (1889-1971) was born in Boston, Massachusetts, and received his Ph.O, in 1912 at Harvard. He taught at the University of (iiinois from 1916 until his retirement in 1957, during which time he had an enormous influence on the development of organic chemistry in the United States. Among many other accomplishments, he established the structure of tetrahydrocannabinol, the active ingredient in marijuana. 

An interesting stereochemical feature of catalytic hydrogenation is that the reaction is extremely sensitive to the steric environment around the double bond. As a result, the catalyst often approaches only one face of an 

Insertion of hydrogen into carbon-carbon double bond 

4-Methylhex-2-ene has a disubstituted double bond, RCH=CHR, and would probably give a mixture of two alcohols with either hydration method since Markovnikov s rule does not apply to symmetrically substituted alkenes. 3-Methylhex-3-ene, however, has a trisubstituted double bond and would give only the desired product on non-Markovnikov hydration using the hydrohoration/oxidation method. 

What products would you expect from oxymercuration of the following alkenes From hydrohoration/oxidation  

What alkenes might the following alcohols have been prepared from  

The following cycloalkene gives a mixture of two alcohols on hydrohoration/ oxidation. Draw the structures of both, and explain the result. 

Interactive to use a web-based palette to predict products from the reduction of alkenes. 

Top side ol double bond blocked by methyl group 

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Addition of Water to Alkenes Oxymercuration 239 Addition of Water to Alkenes Hydroboration 242 Addition of Carbenes to Alkenes Cyclopropane Synthesis Reduction of Alkenes Hydrogenation 249... 

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