212 ALKYNES (e) The first task is to convert ethyl alcohol to acetylene. Once acetylene is prepared it can be alkylated with a methyl halide CH CHOH H2 SO4 L NaNH,, NH3 1NNH2NH,CH3C≡CH 2. CH, Br Ethyl alcohol 1. 2-Dibromoethane Propyne 9.9 The first 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 BrCH,(CH,), CH HC≡CH HC≡CNa HCECCH,(CH2)4CH3-Pt CH_ CH2CH_(CH2)4CH lene I-Octyne Octane Alternatively, two successive alkylations of acetylene with CH CH, CH, Br could be carried out to ive 4-octyne(CH3 CH,CH, C=CCH,CH, CH3), 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 H, (CH,).CO,H CHa(CH,)7CEC(CH,)7CO,H Lindlar P Stearolic acid Oleic acid Hydrogenation of alkynes over platinum leads to alkanes CHa(CH2)7CEC(CH2),CO,H CH3(CH,),6CO,H Stearolic acid Stearic acid 9.11 Alkynes are converted to trans alkenes on reduction with sodium in liquid ammonia. CH(CH,)7CEC(CH2)7CO,H 2.H2O (CH,,CO,H Stearolic acid Elaidic acid 9.12 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 alky lation of propyne to H,C CH,CH,CH, CH 1. NaNH2. NH, (E)-2-Heptenc CHC≡CH 2. CH,CH2CH2CH, Br CH, CECCH, CH,CH,CH Propyne 2-Heptyne HC CH,CH, CH,CH Lindlar pd (Z)-2-Heptene Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website(e) The first task is to convert ethyl alcohol to acetylene. Once acetylene is prepared it can be alkylated with a methyl halide. 9.9 The first 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 CH3CH2CH2Br could be carried out to give 4-octyne (CH3CH2CH2C>CCH2CH2CH3), 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 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. 1. NaNH2, NH3 2. CH3CH2CH2CH2Br 2-Heptyne CH3C CH CH3C CCH2CH2CH2CH3 Propyne C C H H3C H CH2CH2CH2CH3 (E)-2-Heptene CH2CH2CH2CH3 C C H H3C H (Z)-2-Heptene H2 Lindlar Pd Li, NH3 1. Na, NH3 2. H3O C(CH2 ) CH3(CH2)7C 7CO2H Stearolic acid C C H CH3(CH2)7 H (CH2)7CO2H Elaidic acid 2H2 Pt C(CH2) CH3(CH2)7C 7CO2H Stearolic acid Stearic acid CH3(CH2)16CO2H H2 Lindlar Pd C(CH2) CH3(CH2)7C 7CO2H Stearolic acid C C H CH3(CH2)7 H (CH2)7CO2H Oleic acid NaNH2 NH3 H2 Pt BrCH2(CH2)4CH3 HC CH Acetylene HC CNa Sodium acetylide HC CCH2(CH2)4CH3 1-Octyne CH3CH2CH2(CH2)4CH3 Octane 1. NaNH2, NH3 2. H2O 1. NaNH2, NH3 2. CH3Br H2SO4 heat Br2 CH3CH2OH Ethyl alcohol BrCH2CH2Br 1,2-Dibromoethane HC CH Acetylene CH3C CH Ethylene Propyne H2C CH2 212 ALKYNES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website