Question

The reaction of alkyl chloride with aqueous KOH leads to the formation of alcohols but in presence of alcoholic KOH, alkenes are major products. Explain. 

Answer 1

In aqueous medium, KOH ionises readily to form OH^– ions which behave as a powerful nucleophile and cause nucleophilic substitution. These OH^– ions being highly hydrated in aqueous medium, cannot abstract a proton (H⁺) form β-carbon. Hence elimination does not take place. But in alcoholic medium the ionisation of the base (KOH) is poor. So OH^– ions behave as weak nucleophile and the substitution is chacked. Actually KOH in presence of alcoholic medium gives E₂ elimination reaction to form alkene.