Question

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

Answer 1

In an aqueous solution, KOH almost completely ionises to give OH^– ions. OH^– ions is a strong nucleophile, which leads the alkyl chloride to undergo a substitution reaction to form alcohol.

On the other hand, an alcoholic soln of KOH contains alkoxide (RO^–) ion, which is a strong base. Thus, it can abstract a hydrogen from the β – carbon of the alkyl chloride and form an alkene by eliminating a molecule of HCl.

OH^– ion is a much weaker base than RO^– ion. Also, OH^– ion is highly solvated in an aqueous solution and as a result the basic character of OH’ ion decreases. Therefore, it cannot abstract a hydrogen from β - carbon.