The treatment of alkyl chloride with aqueous KOH leads to the formation of alcohols but in the presence of alcoholic KOH, alkenes are the major products. Explain why?
Answer : In aqueous solution, KOH is ionised into K+ and OH−. OH− being a nucleophile leads to nucleophilic substitution reaction with alkyl chlorides to form alcohols. Moreover, the OH− ions in aqueous solution are highly hydrated. This reduces the basic character of OH− ions which, therefore, fail to remove hydrogen from β-carbon to form an alkene.
An alcoholic solution of KOH, on the other hand, contains alkoxide (RO−) ions that are much stronger base than OH− ions; hence, alcoholic solution of KOH preferentially eliminates a molecule of HCl from an alkyl chloride to form an alkene.