Question

$\left(D\right)+Benzaldehyde\underset{\left(ii\right)H_2{O}^{+}}{\overset{\left(i\right)Pyridine,\Delta }{\to }}MajorProduct\left(E\right)$
The major product $\left(E\right)$ is

• A. Crotomic acid
• B. Cinnamic acid
• C. Benzoic acid
• D. Mandelic acid

Answer 1

The correct option is B Cinnamic acid

The organic compound (A) is 1,3-dichloropropane. On reduction with red $P$ and $Hl$, it gives propane.

(A) on hydrolysis by an alkali followed by oxidation gives malonic acid (B). The $-Cl$ groups of 1,3-dichloropropane are replaced with $-OH$ groups to give propylene glycol. Primary alcoholic groups are then oxidized to carboxylic groups to give malonic acid. Malonic acid on heating gives acetic acid (C) by thermal decarboxylation of beta keto acid.

Both (B) and (C) give effervescence with $NaHC{O}_3$. This indicates presence of $-COOH$ groups.

Malonic acid (B) on reacting with ethyl alcohol gives diethyl malonate (D) which is a well known synthetic agent. The next step is the condensation between benzaldehyde and diethyl malonate (D). A molecule of water is lost during condensation. In the next step, the ester groups are hydrolyzed. The final step is the thermal decarboxylation of beta keto acid to form cinnamic acid (E).