A compound HOOC-CH2-CH(OH)-CH2-C#CH (3-hydroxyhex-5-ynoic acid) is treated with excess CH3MgBr. Considering only acid-base reactions, how many moles of CH4 are evolved per mole of compound?

JEE Advanced levelSingle correct optionDifficulty 3 of 3g2133

A compound $HOOC - CH X_{2} - CH (OH) - CH X_{2} - C \equiv CH$ (3-hydroxyhex-5-ynoic acid) is treated with excess $CH X_{3} MgBr$ . Considering only acid-base reactions, how many moles of $CH X_{4}$ are evolved per mole of compound?

Three hydrogens are acidic enough (

p K_{a}

well below that of methane, about 48): the carboxylic

O - H

(about 4.8), the alcoholic

O - H

(about 16) and the terminal alkyne

C - H

(about 25). Each consumes one

CH X_{3} X^{-}

to give one

CH X_{4}

. The

C - H

bonds of the

CH X_{2}

groups are not acidic enough. Hence 3 moles.