Question

How will you prepare benzoic acid from benzene, with the help of Friedel-Craft reaction? Also write any two chemical properties of Benzoic acid?

Answer 1

Hint: To prepare benzoic acid we refer to the definition and property of Friedel-Craft reaction and observe what happens when performed with benzene. And we use the properties of benzoic acid.

Complete step by step answer:
To prepare, benzoic acid from benzene:
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution.
We know the chemical formula of benzene is ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{6}}}$and benzoic acid is${{\text{C}}_{\text{6}}}{{\text{H}}_5}{\text{COOH}}$.

Using the Friedel-Craft reaction, we obtain benzoic acid as follows:
${{\text{C}}_6}{{\text{H}}_6}{\text{ + COC}}{{\text{l}}_2}{\text{ }}\xrightarrow[{{\text{Anhydrous}}}]{{{\text{AlC}}{{\text{l}}_3}}}{\text{ }}{{\text{C}}_6}{{\text{H}}_5}{\text{COCl }}\xrightarrow[{ - {\text{HCl}}}]{{{{\text{H}}_2}{\text{O}}}}{\text{ }}{{\text{C}}_6}{{\text{H}}_5}{\text{COOH}}$.
Benzene is reacted with Carbon Dichloride (${\text{COC}}{{\text{l}}_2}$) in presence of anhydrous Aluminum Chloride (meaning a molecule of aluminum chloride which is attached with water molecules) undergoes Friedel–Crafts Alkylation to form Benzoyl Chloride (${{\text{C}}_6}{{\text{H}}_5}{\text{COCl}}$). Further this compound is reacted with water (derived from the anhydrous aluminum chloride molecule), it releases Hydrochloric acid and forms Benzoic Acid.

Chemical Properties of Benzoic Acid are:
Benzoic Acid is converted into Benzyl Alcohol (${{\text{C}}_6}{{\text{H}}_5}{\text{ - C}}{{\text{H}}_2}{\text{ - OH}}$) by reacting it with Lithium Aluminum Hydride (${\text{LiAl}}{{\text{H}}_4}$).
${{\text{C}}_6}{{\text{H}}_5}{\text{ - COOH }}\xrightarrow{{{\text{LiAl}}{{\text{H}}_4}}}{\text{ }}{{\text{C}}_6}{{\text{H}}_5}{\text{ - C}}{{\text{H}}_2}{\text{ - OH}}$.

Benzoic Acid reacts with thionyl chloride (${\text{SOC}}{{\text{l}}_2}$) (in presence of pyridine) to form benzoyl chloride (${{\text{C}}_6}{{\text{H}}_5}{\text{ - COCl}}$) along with Sulphur dioxide (${\text{S}}{{\text{O}}_2}$) and hydrochloric acid (HCl).

${{\text{C}}_6}{{\text{H}}_5}{\text{ - COOH + SOC}}{{\text{l}}_2}\xrightarrow{{{\text{Pyridine}}}}{\text{ }}{{\text{C}}_6}{{\text{H}}_5}{\text{ - COCl + S}}{{\text{O}}_2}{\text{ + HCl}}$.

Note: In order to answer this type of questions the key is to know what output benzene and benzoic acid gives when reacted with respective substances.
Benzene molecule is a six carbon atom structure joined in the form of a ring with one hydrogen atom attached to each vertex. As it contains only carbon and hydrogen atoms, benzene is classed into a type of compound in chemistry called hydrocarbon.
Benzoic acid consists of a carboxyl group attached to a benzene ring. Therefore, benzoic acid is said to be an aromatic carboxylic acid. This compound exists as a crystalline, colorless solid under normal conditions.