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JEE Main · 2023 · 30 Jan 2023 · Shift 2 · Alcohols Phenols and Ethers

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Number of compounds from the following which will not dissolve in cold and NaOH solutions but will dissolve in hot NaOH solution is ______.
Structure 1
1
Structure 2
2
Structure 3
3
Structure 4
4
Structure 5
5
Structure 6
6
Structure 7
7

Answer: 3

Solution

The test sorts the compounds by acid strength. A carboxylic acid is strong enough to dissolve even in cold sodium hydrogen carbonate, and an ordinary phenol dissolves in cold sodium hydroxide, so neither answers the description. What is wanted are compounds with no free acidic hydrogen in the cold yet which react on heating with alkali, and these are the esters, insoluble in cold base but hydrolysed by hot sodium hydroxide into soluble products. Among the given structures the three esters, methyl benzoate, 4-methylphenyl acetate and phenyl acetate, meet this requirement, while the carboxylic acid and the phenols dissolve already in the cold and the aryl ether resists even hot alkali. The number of such compounds is three.

JEE Main · 2023 · 30 Jan 2023 · Shift 2 · Integer answer

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