(e)The first task is to convert ethyl alcohol to acetylene. Once acetylene is prepared it can bealkylated with a methyl halide.9.9The first task is to assemble a carbon chain containing eight carbons. Acetylene has two carbonatoms and can be alkylated via its sodium salt to 1-octyne. Hydrogenation over platinum converts1-octyne to octane.Alternatively, two successive alkylations of acetylene with CH3CH2CH2Br could be carried out togive 4-octyne (CH3CH2CH2C>CCH2CH2CH3), which could then be hydrogenated to octane.9.10Hydrogenation over Lindlar palladium converts an alkyne to a cis alkene. Oleic acid therefore hasthe structure indicated in the following equation:Hydrogenation of alkynes over platinum leads to alkanes.9.11Alkynes are converted to trans alkenes on reduction with sodium in liquid ammonia.9.12The proper double-bond stereochemistry may be achieved by using 2-heptyne as a reactant in thefinal step. Lithium–ammonia reduction of 2-heptyne gives the trans alkene; hydrogenation overLindlar palladium gives the cis isomer. The
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