Question

Show how to convert toluene to (a) 2,4-dinitrobenzoic acid and (b) 3,5 -dinitrobenzoic acid.

Short answer

Answer: The conversion of toluene to 2,4-dinitrobenzoic acid and 3,5-dinitrobenzoic acid involves the following steps: 1. Nitration of toluene using a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) to form ortho-nitrotoluene and para-nitrotoluene. 2. Oxidation of nitrotoluene derivatives using potassium permanganate (KMnO4) in alkaline conditions to form ortho-nitrobenzoic acid and para-nitrobenzoic acid. 3(A). Nitration of ortho-nitrobenzoic acid using a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) to form 2,4-dinitrobenzoic acid. 3(B). Nitration of para-nitrobenzoic acid using a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) to form 3,5-dinitrobenzoic acid.

Step-by-step solution

Nitration of toluene (common for both products)

In the first step, we need to introduce nitro groups (-NO2) to the toluene molecule through electrophilic aromatic substitution. Toluene consists of a benzene ring and a methyl group (-CH3). By treating toluene with a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4), one nitro group can be added to the benzene ring. Toluene + HNO3 --> ortho-nitrotoluene + para-nitrotoluene

Oxidation of nitrotoluene derivatives (common for both products)

In this step, we need to oxidize the methyl group in the nitrotoluene derivatives to a carboxylic acid group (-COOH). We can use potassium permanganate (KMnO4) in alkaline conditions to carry out this transformation: ortho-nitrotoluene + KMnO4 --> ortho-nitrobenzoic acid para-nitrotoluene + KMnO4 --> para-nitrobenzoic acid

Step 3(A): Nitration of ortho-nitrobenzoic acid (for 2,4-dinitrobenzoic acid)

To achieve the desired product (2,4-dinitrobenzoic acid), we need to add a second nitro group to the ortho-nitrobenzoic acid molecule. We use a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) for this purpose: ortho-nitrobenzoic acid + HNO3 --> 2,4-dinitrobenzoic acid

Step 3(B): Nitration of para-nitrobenzoic acid (for 3,5-dinitrobenzoic acid)

In this case, our desired product is 3,5-dinitrobenzoic acid. We need to add a second nitro group to the para-nitrobenzoic acid molecule. We once again use a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) for this purpose: para-nitrobenzoic acid + HNO3 --> 3,5-dinitrobenzoic acid As a result, we have shown two different reaction pathways to convert toluene to 2,4-dinitrobenzoic acid and 3,5-dinitrobenzoic acid, respectively.