CBSE Class 12 Chemistry: Organic Conversions Marking Scheme

(a) Benzoic acid to Benzaldehyde

• Step 1 (Reagent Selection): [0.5 Mark] Convert Benzoic acid to Benzoyl chloride using $SOCl_2$.
• Step 2 (Reaction Mechanism): [0.5 Mark] Perform Rosenmund reduction using $H_2 / Pd-BaSO_4$.
• Step 3 (Final Answer): [0.0 Mark] $$C_6H_5COOH \xrightarrow{SOCl_2} C_6H_5COCl \xrightarrow{H_2, Pd-BaSO_4} C_6H_5CHO$$

(b) Ethanal to Propanone

• Step 1 (Grignard Addition): [0.5 Mark] React Ethanal with $CH_3MgBr$ followed by hydrolysis to form Propan-2-ol.
• Step 2 (Oxidation): [0.5 Mark] Oxidize Propan-2-ol using $CrO_3$ or $KMnO_4$ to obtain Propanone.
• Step 3 (Final Answer): [0.0 Mark] $$CH_3CHO \xrightarrow{1. CH_3MgBr, 2. H_3O^+} CH_3CH(OH)CH_3 \xrightarrow{[O]} CH_3COCH_3$$

(c) Acetophenone to Benzoic acid

• Step 1 (Haloform Reaction): [0.5 Mark] Treat Acetophenone with $I_2 / NaOH$ (Iodoform test conditions).
• Step 2 (Acidification): [0.5 Mark] The resulting sodium benzoate is acidified with $HCl$ to yield Benzoic acid.
• Step 3 (Final Answer): [0.0 Mark] $$C_6H_5COCH_3 \xrightarrow{I_2 / NaOH} C_6H_5COO^-Na^+ \xrightarrow{H^+} C_6H_5COOH$$

(d) Bromobenzene to 1-Phenylethanol

• Step 1 (Grignard Formation): [0.5 Mark] Convert Bromobenzene to Phenylmagnesium bromide using $Mg$ in dry ether.
• Step 2 (Nucleophilic Addition): [0.5 Mark] React with Acetaldehyde followed by acidic hydrolysis.
• Step 3 (Final Answer): [0.0 Mark] $$C_6H_5Br \xrightarrow{Mg, \text{dry ether}} C_6H_5MgBr \xrightarrow{CH_3CHO, H_3O^+} C_6H_5CH(OH)CH_3$$