Question

When cis-2-methylcyclohexanol reacts with the Lucas reagent, the major product is 1-chloro-1-methylcyclohexane. Propose a mechanism to explain the formation of this product.

Short answer

Lucas reagent is the chemical solution of zinc chloride ( ZnCl₂ ) and concentrated hydrochloric acid (HCl), which as a chlorinating agent replaces the hydroxyl group in alcohol with a chlorine atom.

Alcohol is soluble in the Lucas reagent, while the alkyl chloride formed is not soluble in the Lucas reagent.

Step-by-step solution

Lucas reagent

Lucas reagent is the chemical solution of zinc chloride ( ZnCl₂ ) and concentrated hydrochloric acid (HCl), which as a chlorinating agent replaces the hydroxyl group in alcohol with a chlorine atom.

Alcohol is soluble in the Lucas reagent, while the alkyl chloride formed is not soluble in the Lucas reagent.

Step 2: Mechanism of formation of 1-chloro-1-methylcyclohexane

Cis -2-methyl-cyclohexanol When reacted with Lucas reagent converts the hydroxy group to a good leaving group.

Good leaving group leaves, forming a 2⁰ carbocation which rearranges by hydride shift forming a stable 3⁰ carbocation

Chloride ion attacks the carbocation to form the product 1-chloro-1-methylcyclohexane.

Mechanism of forming 1-chloro-1-methylcyclohexane