Match the entries of column I with appropriate entries of column II and choose the correct option out of the four options given.
| Column I | Column II |
| (a) Lucas Reagent | (i) No change |
| (b) 1o alcohol + Lucas reagent | (ii) Cloudy mixture immediately |
| (c) 2o alcohol + Lucas reagent | (iii) Anhydrous ZnCl2 + Conc. HCl |
| (d) 3o alcohol + Lucas reagent | (iv) Cloudy mixture within 20 minutes |
Answer & explanation
Correct answer: option 4
The correct answer is option 4. (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii).
| Column I | Column II |
| (a) Lucas Reagent | (iii) Anhydrous ZnCl2 + Conc. HCl |
| (b) 1o alcohol + Lucas reagent | (i) No change |
| (c) 2o alcohol + Lucas reagent | (iv) Cloudy mixture within 20 minutes |
| (d) 3o alcohol + Lucas reagent | (ii) Cloudy mixture immediately |
Let us go through each part in detail to understand why the Lucas reagent reacts differently with primary, secondary, and tertiary alcohols, and how these reactions help us match the given pairs correctly.
The Lucas reagent is composed of anhydrous zinc chloride (\( \text{ZnCl}_2 \)) and concentrated hydrochloric acid (\( \text{HCl} \)). This reagent is used to test for the presence of alcohols by converting them into alkyl chlorides.
Reactions with Lucas Reagent:
a. Lucas Reagent : (iii) Anhydrous ZnCl\(_2\) + Conc. HCl
The Lucas reagent is specifically a combination of anhydrous zinc chloride and concentrated hydrochloric acid.
b. Primary Alcohol + Lucas Reagent : (i) No change at room temperature
Primary alcohols react very slowly with the Lucas reagent because the formation of a carbocation intermediate in primary alcohols is highly unfavorable. As a result, no visible change (no cloudiness) occurs at room temperature. It might take a very long time for any reaction to be observed, if at all.
c. Secondary Alcohol + Lucas Reagent: (iv) Cloudy mixture within 20 minutes
Secondary alcohols react with the Lucas reagent at a moderate rate. The reaction proceeds via the formation of a secondary carbocation, which is more stable than a primary carbocation but less stable than a tertiary carbocation. This reaction typically produces a cloudy mixture within about 5 to 20 minutes.
d. Tertiary Alcohol + Lucas Reagent: (ii) Cloudy mixture immediately
Tertiary alcohols react almost instantly with the Lucas reagent because the formation of a tertiary carbocation is highly favorable and occurs rapidly. The reaction results in the immediate formation of a cloudy mixture as the alkyl chloride forms quickly.
The correct option is: (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)