the alcohol that gives turbid mixture when mixed with lucas reagent after warming at 60c after 5 minutes in

Question

a) 2-methylpropanol

b) 2,2-dimethylpropanol

c) Propanol

D) ethylene glycol

Answer 1

Lucas' reagent is a useful tool for differentiating substituted alcohols. The reagent itself is composed of ZnCl2 and concentrated HCl, and performs the following Sn1 Reaction.

ROH + HCl --> RCl + H2O

This reaction proceeds by protonating the alcohol group, forming a water leaving group that leaves a reactive carbocation behind. This reaction is driven forward by excess Cl- nucleophile, and proceeds fastest with more stable carbocations.

Therefore, the most stable carbocation formed from the options listed will react the fastest to produce an alkyl chloride, causing the solution to become turbid due to decreased solubility. Therefore, propanol cannot react this quickly or at this temperature due to forming at best a secondary carbocation after a hydride shift. Ethylene glycol also forms a primary carbocation at first, that will prefer instead to eliminate forming an enol over an alkyl halide.

Finally, the other two propanols can form tertiary carbocations after a hydride shift for 2-methylpropanol, or a methyl shift for 2,2-dimethylpropanol. Because of the increased inductive stability of the more substituted 2,2-dimethylpropanol, given its ethyl substitution over a methyl, I believe 2,2-dimethylpropanol is the reagent that will quickly form the turbid solution.