Describe three common reactions of ethyne, including reaction equations and products.

Ethyne undergoes addition reactions with halogens like bromine. It can add two molecules of bromine across the triple bond.

$$\text{HC}\equiv\text{CH}(\text{g}) + 2\text{Br}_2(\text{aq}) \longrightarrow \text{Br}_2\text{CH}-\text{CHBr}_2(\text{l})$$

Ethyne + Bromine $\longrightarrow$ 1,1,2,2-Tetrabromoethane

Ethyne can be fully hydrogenated to an alkane by adding two molecules of hydrogen in the presence of a metal catalyst (e.g., Nickel, Platinum, or Palladium).

$$\text{HC}\equiv\text{CH}(\text{g}) + 2\text{H}_2(\text{g}) \xrightarrow{\text{Ni or Pt or Pd}} \text{CH}_3-\text{CH}_3(\text{g})$$

Ethyne + Hydrogen $\longrightarrow$ Ethane

Ethyne reacts with water in the presence of mercury(II) sulfate ($\text{HgSO}_4$) and sulfuric acid ($\text{H}_2\text{SO}_4$) to form an enol, which immediately tautomerizes to acetaldehyde.

$$\text{HC}\equiv\text{CH}(\text{g}) + \text{H}_2\text{O}(\text{l}) \xrightarrow{\text{HgSO}_4, \text{H}_2\text{SO}_4} \text{CH}_3\text{CHO}(\text{l})$$

Ethyne + Water $\longrightarrow$ Acetaldehyde