See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Concept: CrO3 in aqueous H2SO4 (Jones-type oxidation) oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones. For decarboxylation to occur readily on heating, the oxidation product must be a beta-keto acid (a carboxylic acid with a ketone at the beta-carbon, i.e., 3-oxo acid), which undergoes facile decarboxylation via a cyclic six-membered transition state. Step 1 - Identify what structure gives a beta-keto acid upon oxidation: A diol that, when oxidized by CrO3/H2SO4, produces a beta-keto acid must have: one primary OH (oxidized to COOH) and one secondary OH at the beta-position (oxidized to C=O), i.e., the two OH groups are separated by one carbon (1,3-diol pattern with appropriate substitution), OR one OH is secondary and adjacent positioning gives a beta-keto acid. Actually, the key requirement: oxidation of a 1,3-diol where one OH is primary gives a 3-hydroxy acid intermediate, but further oxidation of the secondary OH in a 1,3-diol gives a beta-keto acid (3-oxoacid), which decarboxylates readily. Step 2 - Analyze each diol: (I) 1,5-pentanediol (or similar long-chain primary diol): oxidation gives a dicarboxylic acid (glutaric acid type), not a beta-keto acid. Does not readily decarboxylate. (II) A branched diol - from the structure, it appears to be 3-methyl-1,3-butanediol or 2-methyl-1,3-propanediol. If it is a 1,3-diol with one primary and one tertiary OH: oxidation gives a beta-keto acid (the tertiary OH becomes a ketone, primary OH becomes COOH, giving a 3-oxo acid). Beta-keto acids decarboxylate readily on heating. This qualifies. (III) 1,2-butanediol (vicinal diol): oxidation gives an alpha-keto acid (2-oxo acid), not a beta-keto acid. Alpha-keto acids do not decarboxylate as readily under simple heating conditions (they require different conditions). Does not qualify. (IV) From the structure (appears to be a 1,3-diol with secondary OH): one OH is secondary (becomes ketone on oxidation) and one is primary (becomes COOH), with beta relationship, giving a beta-keto acid that readily decarboxylates. This qualifies. Step 3 - Why other options fail: (a) I and II: Compound I gives a dicarboxylic acid, not a beta-keto acid, so it does not readily decarboxylate. Eliminated. (b) II and III: Compound III gives an alpha-keto acid, not suitable. Eliminated. (d) I and IV: Compound I does not give a beta-keto acid. Eliminated. Only compounds II and IV produce beta-keto acids upon oxidation with CrO3/H2SO4, and these beta-keto acids readily undergo decarboxylation on heating. Therefore, the correct answer is C.