question_answer

       Ethyne reacts with dil. \[{{H}_{2}}S{{O}_{4}}\] in presence of mercury salts to give acetaldehyde but with dil. \[HCl\] under similar conditions, it gives vinyl chloride. Explain why?

Answer:

                First of all, mercury ions form a complex \[(I)\]with acetylene. Since, \[{{H}_{2}}O\] is more nucleophilic than \[SO_{4}^{2-}\] ion it attacks the complex \[(I)\] to form first vinyl alcohol which then tautomerises to given acetaldehyde In case of dil. \[HCl\], since, \[C{{l}^{-}}\] ion is more nucleophilic than \[{{H}_{2}}O,\] it reacts with complex \[(I)\] to form vinyl chloride.