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JEE Advanced levelSingle correct optionDifficulty 3 of 3co098

Benzaldehyde is heated with propanedioic acid (malonic acid) in pyridine with a trace of piperidine (Knoevenagel-Doebner condensation). Which option correctly gives the organic product and the small molecules lost per mole of product?

A3-phenylprop-2-enoic acid; 2 mol $CO X_{2}$ and 2 mol $H X_{2} O$
B2-benzylidenepropanedioic acid; 1 mol $H X_{2} O$ and no $CO X_{2}$
C3-phenylpropanoic acid; 1 mol $CO X_{2}$ and 1 mol $H X_{2} O$
D3-phenylprop-2-enoic acid; 1 mol $CO X_{2}$ and 1 mol $H X_{2} O$

Answer: D

Condensation of

C X_{6} H X_{5} CHO

with

CH X_{2} (COOH) X_{2}

loses 1 mol

H X_{2} O

and gives

C X_{6} H X_{5} CH = C (COOH) X_{2}

. In hot pyridine this alkylidene malonic acid decarboxylates, losing 1 mol

CO X_{2}

. The product is

C X_{6} H X_{5} CH = CHCOOH

, cinnamic acid.

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