Question

Find the product B in the reaction.
$PhCHO + {\left( {C{H_3}CO} \right)_2}O\xrightarrow{{C{H_3}COONa}}A\xrightarrow{{HBr}}B$
A. $PhCH = CHC{H_2}Br$
B. $PhCH\left( {Br} \right)C{H_2}COOH$
C. $PhC{H_2}CH\left( {Br} \right)COOH$
D. $PhCH = CH = COBr$

Answer 1

Hint: We must remember that the Perkin reaction is a chemical reaction that gives -unsaturated aromatic acid. A reaction between aromatic aldehydes, the aliphatic acid anhydride, and the alkali salt of the acid to give cinnamic acid derivatives is called Perkin reaction.

Complete step by step answer: Now, we see the Perkin reaction.
The condensation of a carboxylic acid anhydride and an Aldehyde in the presence of a weak base, to give unsaturated carboxylic acid is called the Perkin reaction. Synthesis of coumarin by heating the sodium salt of Salicylaldehyde with acetic anhydride is an example of Perkin's reaction.
Now, we see the given reaction,
$PhCHO + {\left( {C{H_3}CO} \right)_2}O\xrightarrow{{C{H_3}COONa}}A\xrightarrow{{HBr}}B$
Benzaldehyde and acetic anhydride condense in the presence of sodium acetate to form is cinnamic acid and then it undergoes Markovnikov's addition of \[HBr\]to form\[3 - bromo - 3 - phenylpropanoic\;acid\].
Therefore, the option B is correct.

Additional Information:
-The alkali salt of the acid anhydride is used as a catalyst.
-The reaction is used for the synthesis of phytoestrogenic stilbene resveratrol in the laboratory.
-The first synthesized compound is cinnamic acid.

Note: We must remember that Markovnikov's rule is employed to predict regioselectivity of electrophilic addition reactions of alkenes and alkynes. It states that, in hydrohalogenation of an unsymmetrical alkene, the atom within the hydrogen halide forms a bond with the doubly bonded atom within the alkene, bearing the greater number of hydrogen atoms.
Cinnamic acid is also prepared by Knoevenagel condensation. In the presence of base Benzaldehyde and malonic acid reactants to give cinnamic acid is a Knoevenagel condensation reaction.