Question

When acetylene is passed into methanol at $160-200ºC$ in the presence of a small amount of potassium methoxide under pressure, the following is formed -

• A. Polyvinyl alcohol
• B. Divinyl ether
• C. Dimethyl ether
• D. Methyl vinyl ether

Answer 1

Answer: (D)

When acetylene is passed into methanol at $160-200^{º}C$ in the presence of a small amount $(1-2\%)$ of potassium methoxide and under pressure just high enough to prevent boiling, methyl vinyl ether is formed.
The mechanism is believed to involve nucleophildic attack in the first step.
$\mathrm{HC}\equiv \mathrm{CH}+\mathrm{CH}{}_3\mathrm{O}{}^{-}\to \mathrm{C}{}^{-}\mathrm{H}=\mathrm{CH}\mathrm{OCH}{}_3\stackrel{\mathrm{CH}{}_3\mathrm{OH}}{\to }\mathrm{CH}{}_2=$ $\underset{\text{Methyl vinyl ether}}{\mathrm{CHO}\mathrm{CH}{}_3+\mathrm{CH}{}_3\mathrm{O}¯}$