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Dolbier HW Solutions 218 - 212 ALKYNES(e CH3CH2OH H2SO4 H2C...

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( e ) The fi rst task is to convert ethyl alcohol to acetylene. Once acetylene is prepared it can be alkylated with a methyl halide. 9.9 The fi rst task is to assemble a carbon chain containing eight carbons. Acetylene has two carbon atoms and can be alkylated via its sodium salt to 1-octyne. Hydrogenation over platinum converts 1-octyne to octane. Alternatively, two successive alkylations of acetylene with CH 3 CH 2 CH 2 Br could be carried out to give 4-octyne (CH 3 CH 2 CH 2 C > CCH 2 CH 2 CH 3 ), which could then be hydrogenated to octane. 9.10 Hydrogenation over Lindlar palladium converts an alkyne to a cis alkene. Oleic acid therefore has the structure indicated in the following equation: Hydrogenation of alkynes over platinum leads to alkanes. 9.11 Alkynes are converted to trans alkenes on reduction with sodium in liquid ammonia. 9.12 The proper double-bond stereochemistry may be achieved by using 2-heptyne as a reactant in the fi nal step. Lithium ammonia reduction of 2-heptyne gives the trans alkene; hydrogenation over Lindlar palladium gives the cis isomer. The
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