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.

Updated On: Sep 26, 2023
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Solution and Explanation

In an aqueous solution, KOH almost completely ionizes to give OH ions. OH ion is a strong nucleophile, which leads the alkyl chloride to undergo a substitution reaction to form alcohol. R-Cl(Alkyl chloride)+KOH(aq)→R-OH(Alcohol)+KCl On the other hand, an alcoholic solution of KOH contains an alkoxide(RO)ion, which is a strong base. Thus, it can abstract hydrogen from the β-carbon of the alkyl chloride and form an alkene by eliminating a molecule of HCl.R-C(β)H2-C(α)H2-Cl+KOH(alc)→R-CH(Alkene)=CH2+KCl+H2O 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 hydrogen from the β-carbon.

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