Palladium Lindlar

Hydrogenation of alkynes may be halted at the alkene stage by using special catalysts Lindlar palladium is the metal catalyst employed most often Hydrogenation occurs with syn stereochemistry and yields a cis alkene... 

The alkane formed by hydrogenation of (S) 4 methyl 1 hexyne is optically active but the one formed by hydrogenation of (S) 3 methyl 1 pentyne is not Explain Would you expect the products of hydrogenation of these two compounds in the presence of Lindlar palladium to be optically active" ... 

Hydrogenation over Lindlar palladium converts an alkyne to a cis alkene. Oleic acid therefore has the structure indicated in the following equation ... 

The proper double-bond stereochemistry may be achieved by using 2-heptyne as a reactant in the final step. Lithium-ammonia reduction of 2-heptyne gives the trans alkene hydrogenation over Lindlar palladium gives the cis isomer. The first task is therefore the alkylation of propyne to 2-heptyne. 

Apply the technique of reasoning backward to gain a clue to how to attack this synthesis problem. A reasonable final step is the formation of the Z double bond by hydrogenation of an alkyne over Lindlar palladium. 

Once 1-hexyne is prepared, it can be converted to 1-hexene by hydrogenation over Lindlar palladium or by sodium-ammonia reduction. 

Hydrogenation of compound B over Lindlar palladium yields d.v-cyclotctradecene (compound C). 

Tlie product of tliis reaction can be reduced to an alkane with hydrogen and a platinum or rhodium catalyst, or an alkene with Lindlar palladium. 

In subsequent equations, we will not specify the components of the Lindlar palladium catalyst in detail but will simply write Lindlar Pd over the reaction arrow. 

PROBLEM 9.10 Oleic acid and stearic acid are naturally occurring compounds, which can be isolated from various fats and oils. In the laboratory, each can be prepared by hydrogenation of a compound known as stearolic acid, which has the formula CH3(CH2)7C=C(CH2)7C02H. Oleic acid is obtained by hydrogenation of stearolic acid over Lindlar palladium stearic acid is obtained by hydrogenation over platinum. What are the structures of oleic acid and stearic acid ... 

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