A compound (X) containing C, H and O does not react with sodium. It also does not reduce Tollens’ reagent. On heating with an excess of hydroiodic acid (HI), (X) gives only one organic product (Y). On hydrolysis, (Y) gives a new compound (Z), which can be converted back into (Y) by reaction with red phosphorus and iodine. On oxidation with potassium permanganate, (Z) gives a monocarboxylic acid whose molar mass is 60 g mol−1.
In the passage, the alcohol (Z) is converted back into the alkyl halide (Y). Consider the following statements about the conversion of alcohols into alkyl halides.
(A) In the Lucas test, alcohols are soluble in the reagent, while the alkyl halides formed from them are immiscible and produce turbidity.
(B) In the Lucas test, primary alcohols produce turbidity immediately at room temperature.
(C) In the Lucas test, the difference in the reactivity of primary, secondary and tertiary alcohols with HCl is used to distinguish them.
(D) Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (C) and (D) only
In these reactions the C–O bond of the alcohol breaks and a halogen takes the place of the –OH group. With a hydrogen halide:
\( \displaystyle \ce{R-OH + HX -> R-X + H2O} \)
(A) In the Lucas test, alcohols are soluble in the reagent, while the alkyl halides formed from them are immiscible and produce turbidity. — True. Lucas reagent is conc. HCl and ZnCl2. The alcohol dissolves in it; the alkyl chloride does not, so the solution turns turbid once the halide forms.
(B) In the Lucas test, primary alcohols produce turbidity immediately at room temperature. — False. It is tertiary alcohols that give turbidity at once, as they form the halides easily. Primary alcohols give no turbidity at room temperature.
(C) In the Lucas test, the difference in the reactivity of primary, secondary and tertiary alcohols with HCl is used to distinguish them. — True. This difference in reactivity is the basis of the test.
(D) Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide. — True. PBr3 replaces the –OH group by bromine:
\( \displaystyle \ce{3R-OH + PBr3 -> 3R-Br + H3PO3} \)
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “The difference in reactivity of three classes of alcohols with HCl distinguishes them from one another (Lucas test). Alcohols are soluble in Lucas reagent (conc. HCl and ZnCl2) while their halides are immiscible and produce turbidity in solution. In case of tertiary alcohols, turbidity is produced immediately as they form the halides easily. Primary alcohols do not produce turbidity at room temperature.”
“2. Reaction with phosphorus trihalides: Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide (Refer Unit 6, Class XII).”