Step 1: Understanding the Concept:
Lucas reagent is a mixture of concentrated hydrochloric acid (\(HCl\)) and anhydrous zinc chloride (\(ZnCl_{2}\)).
It is a standard laboratory test used to distinguish between primary (\(1^{\circ}\)), secondary (\(2^{\circ}\)), and tertiary (\(3^{\circ}\)) alcohols.
The reaction involves the substitution of the hydroxyl group (\(-OH\)) with a chloride ion (\(-Cl\)) to produce an alkyl chloride (\(R-Cl\)).
Alkyl chlorides are insoluble in the aqueous Lucas reagent, so they form a separate phase that appears as cloudiness or turbidity.
Step 2: Detailed Explanation:
The reaction of alcohols with Lucas reagent generally proceeds via an \(S_{N}1\) mechanism, especially for secondary and tertiary alcohols.
The mechanism involves:
1. Protonation of the alcohol oxygen to form a good leaving group (\(-OH_{2}^{+}\)).
2. Departure of the water molecule to form a carbocation intermediate (\(R^{+}\)).
3. Nucleophilic attack by the chloride ion on the carbocation to form the alkyl chloride.
The rate of the reaction is determined by the stability of the carbocation intermediate.
- Tertiary ($3^{\circ}$) Alcohols: These form tertiary carbocations, which are the most stable due to inductive effects and hyperconjugation from three surrounding alkyl groups. Consequently, the reaction is extremely fast.
Turbidity appears immediately at room temperature.
- Secondary ($2^{\circ}$) Alcohols: These form secondary carbocations, which have moderate stability. The reaction is slower.
Turbidity usually appears within 5 to 10 minutes at room temperature.
- Primary ($1^{\circ}$) Alcohols: These would form primary carbocations, which are very unstable. Therefore, primary alcohols do not react with Lucas reagent at room temperature.
Turbidity only appears if the mixture is heated.
Analyzing the options:
(A) Ethanol (\(CH_{3}CH_{2}OH\)) is a primary alcohol.
(B) Propan-1-ol (\(CH_{3}CH_{2}CH_{2}OH\)) is a primary alcohol.
(C) Propan-2-ol (\(CH_{3}CH(OH)CH_{3}\)) is a secondary alcohol.
(D) tert-Butyl alcohol (\((CH_{3})_{3}COH\)) is a tertiary alcohol.
Since tertiary alcohols react fastest, tert-Butyl alcohol will produce immediate turbidity.
Step 3: Final Answer:
The alcohol that reacts immediately with Lucas reagent to produce turbidity is tert-Butyl alcohol.
This corresponds to Option (D).