Ethanol to c2h5cl then wurtz reaction by Na dry ether . butane is formed . add Br2 light and then excess NaNH2 butyne would be formed .

To convert ethanol to but-1-yne, follow these steps:

1. Dehydration of Ethanol: Ethanol needs to be dehydrated to remove water molecules from the molecule. This is done by reacting ethanol with a dehydrating agent such as concentrated sulfuric acid or phosphoric acid. The reaction is as follows:
C2H5OH → H2SO4, 180°C → C2H4 + H2O

2. Conversion of Ethylene to Acetylene: Ethylene produced from the first step is then converted to acetylene by reacting it with calcium carbide. The reaction is as follows:
C2H4 + CaC2 → HC≡CH + Ca(OH)2

3. Hydrogenation of Acetylene: Acetylene is then hydrogenated to form but-1-yne by reacting it with hydrogen in the presence of a catalyst such as palladium. The reaction is as follows:
HC≡CH + H2 → CH3CH2C≡CH

Overall Reaction: C2H5OH → H2SO4, 180°C → C2H4 + H2O → C2H4 + CaC2 → HC≡CH + Ca(OH)2 → HC≡CH + H2 → CH3CH2C≡CH

In summary, ethanol is converted to but-1-yne by first dehydrating it to ethylene, converting ethylene to acetylene, and then hydrogenating acetylene to form but-1-yne.