Question

An organic compound \(P\) of molecular formula \( \mathrm{C_6H_{12}O_3} \) gives positive iodoform test but negative Tollens’ test. When \(P\) is treated with dilute acid, it produces \(Q\). \(Q\) gives positive Tollens’ test and also iodoform test. Identify compound \(P\).

• A. \( \mathrm{CH_3COCH(OCH_3)CH_2OCH_3} \)
• B. \( \mathrm{CH_3COCH_2CH(OCH_3)_2} \)
• C. \( \mathrm{HCOCH_2CH_2CH(OCH_3)_2} \)
• D. \( \mathrm{CH_3COC(OCH_3)_2CH_3} \)

Hint:

Remember:

• Iodoform test detects: \[ \mathrm{CH_3CO-} \] group.
• Tollens’ reagent detects aldehydes.
• Ketals/acetals hydrolyse back to carbonyl compounds in acidic medium.

Answer 1

The Correct Option is D

Concept: Iodoform test is given by compounds containing: \[ \mathrm{CH_3CO-} \] group or compounds oxidisable to it. Tollens’ reagent gives positive test mainly with aldehydes. Acetals and ketals on hydrolysis with dilute acid regenerate carbonyl compounds.

Step 1: Analysing properties of compound \(P\). Compound \(P\):

• Gives positive iodoform test
• Gives negative Tollens’ test

Therefore:

• \(P\) must contain methyl ketone functionality or masked methyl ketone.
• It should not contain free aldehyde group.

Step 2: Analysing compound \(Q\). On hydrolysis with dilute acid: \[ P \rightarrow Q \] and \(Q\):

• Gives positive Tollens’ test
• Gives positive iodoform test

A compound giving both tests is: \[ \mathrm{CH_3CHO} \] that is ethanal. Ethanal:

• Gives Tollens’ test because it is an aldehyde.
• Gives iodoform test because it contains: \[ \mathrm{CH_3CHO} \]

Step 3: Identifying the structure of \(P\). Option (4): \[ \mathrm{CH_3COC(OCH_3)_2CH_3} \] is a ketal derivative. On acidic hydrolysis: \[ \mathrm{CH_3COC(OCH_3)_2CH_3} \] regenerates: \[ \mathrm{CH_3CHO} \] which satisfies both:

• Positive Tollens’ test
• Positive iodoform test

Hence, option (4) is correct. \[ \boxed{(4)} \]