Q47P - Organic Chemistry (Mcmurry)

Question

Predict the product of the reaction of p-methyl benzoic acid with each of the following

1.  $\mathit{L}\mathit{i}\mathit{A}\mathit{l}{\mathit{H}}_{\mathbf{4}}\mathbf{,}\mathbf{ }\mathbf{then}\mathbf{ }\mathbf{ }{\mathit{H}}_{\mathbf{3}}{\mathit{O}}^{\mathbf{+}}$
2. N-Bromosuccinimide in $\mathit{C}\mathit{C}{\mathit{l}}_{\mathbf{4}}$
3. $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{M}\mathit{g}\mathit{B}\mathit{r}\mathit{ }\mathbf{ }\mathbf{in}\mathbf{ }\mathbf{ }\mathbf{ether}\mathbf{,}\mathbf{ }\mathbf{ }\mathbf{then}\mathbf{ }\mathbf{ }{\mathit{H}}_{\mathbf{3}}{\mathit{O}}^{\mathbf{+}}$
   
4.  $\mathit{K}\mathit{M}\mathit{n}{\mathit{O}}_{\mathbf{4}}\mathbf{,}\mathbf{ }\mathbf{ }{\mathit{H}}_{\mathbf{3}}{\mathit{O}}^{\mathbf{+}}$

Step-by-Step Solution

Answer

1. The product obtained is p-methyl-benzyl alcohol
2. The product obtained is p-bromomethylbenzoic acid.
3. The product obtained is methane
4. The product obtained is benzene-1,4-dicarboxylic acid.

Step 1: Definition of product

A substance that is formed as the result of a chemical reaction is defined as a product.

Step 2: Explanations

(a) When p-methyl benzoic acid is treated with $LiA{H}_4 \mathrm{and} \mathrm{then} \mathrm{with}\mathit{ } H_3{O}^{+}$ the carboxyl group is reduced to a primary alcohol group. The product obtained is p-methyl-benzyl alcohol.

(b) When p-methyl benzoic acid is treated with N-bromosuccinimide in $CC{l}_4$, a bromine atom gets substituted in the benzyl carbon. The product obtained is p-bromomethylbenzoic acid.

(c) When p-methyl benzoic acid is treated with $C{H}_{3}MgBr\mathit{ } \mathrm{and} \mathrm{then} \mathrm{with} H_3{O}^{+}$ the methyl anion in the Grignard reagent picks up a proton from the acid to obtain a product called methane.

(d) When p-methyl benzoic acid is treated with $KMn{O}_4$ in the presence of $H_3{O}^{+}$the methyl group in the p-position is oxidized to acid. The product obtained is benzene-1,4-dicarboxylic acid.