JEE Main 2016 · Chemistry · Carbonyl Compounds, Carboxylic Acids and Amines · medium

10.6 g of benzaldehyde and 2.9 g of acetone are stirred with dilute aqueous NaOH and ethanol, giving dibenzalacetone (C17H14O) in 80% yield. Taking…

Single correct option

10.6\ \mathrm{g}

of benzaldehyde and

2.9\ \mathrm{g}

of acetone are stirred with dilute aqueous

\mathrm{NaOH}

and ethanol, giving dibenzalacetone (

\mathrm{C_{17}H_{14}O}

) in

80\%

yield. Taking

\mathrm{C}=12

\mathrm{H}=1

\mathrm{O}=16

, the mass of dibenzalacetone isolated is

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Answer: (B) $9.36\ \mathrm{g}$

Benzaldehyde

=10.6/106=0.100

mol; acetone

=2.9/58=0.050

mol. Claisen-Schmidt condensation uses two benzaldehyde per acetone,

\mathrm{C_6H_5CHO\,(2)+CH_3COCH_3\to C_6H_5CH{=}CHCOCH{=}CHC_6H_5+2H_2O}

, so the reagents are in exact stoichiometric ratio and the theoretical yield is

0.050

mol.

M(\mathrm{C_{17}H_{14}O})=204+14+16=234

. Theoretical mass

=11.7

80\%

gives

9.36

g. The option

11.7

g ignores yield, and

4.68

g would correspond to using acetone as a

1{:}1

partner at

40\%

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