Q46P - Organic Chemistry (Mcmurry)

Question

How would you prepare the following compounds from benzene? More than one step is required in each case.

1. m-Chlorobenzoic acid
2. p-Bromobenzoic acid
3. Phenylacetic acid, C₆H₅CH₂CO₂H

Step-by-Step Solution

Answer

a. The steps involved in preparing m-chlorobenzoic acid from benzene are

b. The steps involved in preparing p-bromobenzoic acid from benzene are

c. The steps involved in preparing phenylacetic acid from benzene are  

Step 1: Definition of compounds

Any substance composed of identical molecules consisting of atoms of two or more chemical elements is defined as a chemical compound.

Step 2: Explanations

a. Friedel-crafts alkylation of benzene in the presence of anhydrous $AlC{l}_3$ yields toluene. Toluene is oxidized to benzoic acid by oxidation with acidified $KMn{O}_4$. When benzoic acid is chlorinated using $C{l}_2$ in the presence of $FeC{l}_3$, m-chlorobenzoic acid is produced, since –COOH group is meta-directing in nature.

The steps involved in preparing m-chlorobenzoic acid from benzene are

b. Friedel-crafts alkylation of benzene in the presence of anhydrous $AlC{l}_3$ yields toluene. When toluene is brominated using $B{r}_2$ in the presence of $FeB{r}_3$, p-bromotoluene is produced, since Br is ortho-para directing in nature. P-Bromotolueneis oxidized to p-bromobenzoic acid by oxidation with acidified $KMn{O}_4$.

The steps involved in preparing p-bromobenzoic acid from benzene are 

c. Friedel-crafts alkylation of benzene in the presence of anhydrous $AlC{l}_3$ yields toluene. When toluene is brominated using NBS bromine gets substituted in the side chain to yield benzyl bromide. Benzyl bromide gets converted into benzyl nitrile when treated with NaCN and the nitrile yields phenylacetic acid when hydrolysed using aqueous acids.

The steps involved in preparing phenylacetic acid from benzene are