Question 22 of 26advanced🔧 ApplyLong Answer5 marks

How will you bring about the following conversions in not more than two steps? (i) Propanone to Propene (ii) Benzoic acid to Benzaldehyde (iii) Ethanol to 3-Hydroxybutanal (iv) Benzene to m-Nitroacetophenone (v) Benzaldehyde to Benzophenone (vi) Bromobenzene to 1-Phenylethanol (vii) Benzaldehyde to 3-Phenylpropan-1-ol (viii) Benzaldehyde to α-Hydroxyphenylacetic acid (ix) Benzoic acid to m-Nitrobenzyl alcohol

(i)
Answer

Propanone to Propene: Step 1: Propanone is reduced to Propan-2-ol using NaBH₄ or LiAlH₄. Step 2: Propan-2-ol undergoes dehydration using concentrated H₂SO₄ at 443K to form Propene.

(ii)
Answer

Benzoic acid to Benzaldehyde: Step 1: Benzoic acid reacts with SOCl₂ to form Benzoyl chloride. Step 2: Benzoyl chloride undergoes Rosenmund reduction with H₂/Pd-BaSO₄ to give Benzaldehyde.

(iii)
Answer

Ethanol to 3-Hydroxybutanal: Step 1: Ethanol is oxidised to Ethanal using PCC. Step 2: Ethanal undergoes aldol condensation with dilute NaOH to give 3-Hydroxybutanal.

(iv)
Answer

Benzene to m-Nitroacetophenone: Step 1: Benzene undergoes Friedel-Crafts acylation with acetyl chloride/AlCl₃ to form Acetophenone. Step 2: Acetophenone undergoes nitration with HNO₃/H₂SO₄ to give m-Nitroacetophenone.

(v)
Answer

Benzaldehyde to Benzophenone: Step 1: Benzaldehyde reacts with PhMgBr (Grignard reagent) followed by H₃O⁺ to give Diphenylmethanol. Step 2: Diphenylmethanol is oxidised using CrO₃ to form Benzophenone.

(vi)
Answer

Bromobenzene to 1-Phenylethanol: Step 1: Bromobenzene reacts with Mg in ether to form Phenylmagnesium bromide (Grignard reagent). Step 2: Phenylmagnesium bromide reacts with Ethanal followed by H₃O⁺ to give 1-Phenylethanol.

(vii)
Answer

Benzaldehyde to 3-Phenylpropan-1-ol: Step 1: Benzaldehyde undergoes cross aldol condensation with Ethanal to form Cinnamaldehyde. Step 2: Cinnamaldehyde is reduced using H₂/Ni or LiAlH₄ to give 3-Phenylpropan-1-ol.

(viii)
Answer

Benzaldehyde to α-Hydroxyphenylacetic acid: Step 1: Benzaldehyde undergoes benzoin condensation with KCN/NaCN to form Benzoin. Step 2: Benzoin is oxidised with HNO₃ to give α-Hydroxyphenylacetic acid (Mandelic acid).

(ix)
Answer

Benzoic acid to m-Nitrobenzyl alcohol: Step 1: Benzoic acid undergoes nitration with HNO₃/H₂SO₄ to give m-Nitrobenzoic acid. Step 2: m-Nitrobenzoic acid is reduced using LiAlH₄ to give m-Nitrobenzyl alcohol.

Explanation

These conversions require understanding of key reactions: reduction, oxidation, Grignard reactions, aldol condensation, Friedel-Crafts reactions, and functional group interconversions. Each conversion is completed within two steps as required.

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