Question

How will you bring about the following conversions? (any three)
Benzoic acid to Benzaldehyde
Ethanal to Propanone
(c) Acetophenone to Benzoic acid
(d) Bromobenzene to 1-Phenylethanol

Hint:

For organic conversions, selective reagents such as LiAlH\(_4\), KMnO\(_4\), and Grignard reagents play a crucial role in controlling the specific transformation of functional groups.

Answer 1

(a) Benzoic acid to Benzaldehyde:
This can be achieved by the reduction of benzoic acid using a selective reducing agent like diborane (B\(_2\)H\(_6\)) or Lithium aluminum hydride (LiAlH\(_4\)). This will reduce the carboxyl group (-COOH) to an aldehyde group (-CHO), forming benzaldehyde. \[ \text{C}_6\text{H}_5\text{COOH} \xrightarrow{\text{LiAlH}_4} \text{C}_6\text{H}_5\text{CHO} \] (b) Ethanal to Propanone:
Ethanal (acetaldehyde) can be oxidized to propanone (acetone) using a mild oxidizing agent like Chromium(VI) oxide (CrO\(_3\)). This oxidation introduces a second methyl group, forming propanone. \[ \text{CH}_3\text{CHO} \xrightarrow{\text{CrO}_3} \text{CH}_3\text{COCH}_3 \] (c) Acetophenone to Benzoic acid:
Acetophenone can be oxidized to benzoic acid using an oxidizing agent like potassium permanganate (KMnO\(_4\)). The methyl group (-CH\(_3\)) is oxidized to a carboxyl group (-COOH), forming benzoic acid. \[ \text{C}_6\text{H}_5\text{COCH}_3 \xrightarrow{\text{KMnO}_4} \text{C}_6\text{H}_5\text{COOH} \] (d) Bromobenzene to 1-Phenylethanol:
Bromobenzene can be converted to 1-phenylethanol via the Grignard reaction. First, magnesium is added to bromobenzene to form a phenylmagnesium bromide (Grignard reagent), which then reacts with ethyl formate followed by hydrolysis to form 1-phenylethanol. \[ \text{C}_6\text{H}_5\text{Br} \xrightarrow{\text{Mg}} \text{C}_6\text{H}_5\text{MgBr} \xrightarrow{\text{C}_2\text{H}_5\text{COO}^-, \text{H}_2\text{O}} \text{C}_6\text{H}_5\text{CH}_2\text{OH} \]