91Ó°ÊÓ

Alkynes get converted to alkenes in the presence of hydrogen and Lindlar’s catalyst. The alkenes are further converted to alcohols by treating with ozone, zinc and ${\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$ .

(a)The given reaction shows the conversion of 1-pentyne to butanal. The reactant, 1-pentyne can be treated with${\mathrm{H}}_2$ and Lindlar’s catalyst to produce 1-pentene. This further reacts with${\mathrm{O}}_3$ , zinc and acetic acid to produce butanal. The reaction can be given as:

Alkynes are treated with ${\mathbf{NaNH}}_{\mathbf{2}}\mathbf{,}{\mathbf{NH}}_{\mathbf{3}}$ in the presence of alkyl bromide to give a higher alkyne. This further reacts with Li in ammonia to form the alkene.

(b)The reaction shows the conversion of 4-methyl-1-pentyne to trans-6-methyl-3-heptene.In the first step, the lower alkyne, 4-methyl-1-pentyne is converted to a higher alkyne, 6-methyl-hept-3-yne by reacting with${\mathrm{NaNH}}_2$ in liquid ammonia and${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}$ . The resultant alkyne further reacts with Li in ammonia to produce trans-6-methyl-3-heptene. The reaction can be given as: