Question

Methylparaben is used as a preservative in foods, beverages, and cosmetics. Provide a synthesis of this compound from toluene.

Short answer

Question: Outline the synthesis of methylparaben from toluene. Answer: The synthesis of methylparaben from toluene involves the following steps: 1. Nitration of toluene to form para-nitrotoluene. 2. Reduction of para-nitrotoluene to produce para-toluidine. 3. Diazotization of para-toluidine to generate para-toluidine diazonium chloride. 4. Hydrolysis of para-toluidine diazonium chloride to create para-cresol. 5. Esterification of para-cresol with methanol to yield methylparaben.

Step-by-step solution

Nitration of toluene

To introduce a nitro group at the para position of toluene, nitrate the toluene using a mixture of concentrated nitric acid (HNO_3) and concentrated sulfuric acid (H_2SO_4) as nitrating agents. This reaction will produce para-nitrotoluene as the major product. Toluene + HNO_3 → para-Nitrotoluene + H_2O

Reduction of para-nitrotoluene

To convert the nitro group into an amino group, reduce para-nitrotoluene using a suitable reducing agent such as tin (Sn) and hydrochloric acid (HCl) or catalytic hydrogenation with a palladium on carbon (Pd/C) catalyst and hydrogen gas (H_2). This reaction will produce para-toluidine. para-Nitrotoluene + Sn/HCl or H_2/Pd/C → para-Toluidine

Diazotization of para-toluidine

To convert the amino group of para-toluidine into a diazonium group, diazotize it with sodium nitrite (NaNO_2) and hydrochloric acid (HCl) in an ice bath to produce para-toluidine diazonium chloride. para-Toluidine + NaNO_2 + HCl → para-Toluidine diazonium chloride

Hydrolysis of para-toluidine diazonium chloride

The diazonium group needs to be replaced with a hydroxyl group. To achieve this, hydrolyze para-toluidine diazonium chloride using water (H_2O) and heat to form para-cresol. para-Toluidine diazonium chloride + H_2O → para-Cresol

Esterification of para-cresol

Finally, to convert para-cresol into methylparaben, perform an esterification reaction by treating it with methanol (CH_3OH) in the presence of a strong acid catalyst, such as concentrated sulfuric acid (H_2SO_4), to produce methylparaben. para-Cresol + CH_3OH → Methylparaben + H_2O By following these steps, methylparaben can be synthesized from toluene.