Experiment 104

Objective

To prepare benzaldehyde by the oxidation of benzyl chloride using cupric nitrate.

Introduction

Benzaldehyde is synthesized by heating benzyl chloride with aqueous cupric nitrate. Initially, benzyl chloride is hydrolyzed to benzyl alcohol and hydrochloric acid (HCl). This HCl reacts with cupric nitrate (Cu(NO₃)₂) to form CuCl₂ and nitric acid (HNO₃), which generates oxygen free radicals that oxidize benzyl alcohol to benzaldehyde.

Reactions:

1.    Hydrolysis: C₆H₅CH₂Cl + H₂O → C₆H₅CH₂OH + HCl

2.    Oxidation: C₆H₅CH₂OH + [O] → C₆H₅CHO

Materials

Chemicals

●      Benzyl chloride

●      Copper nitrate

●      Distilled water

●      Calcium chloride (CaCl₂)

●      2,4-Dinitrophenyl hydrazine

Apparatus

●      Test tube

●      Test tube holder

●      Thermometer

●      Bunsen burner

Reagents

●      30 ml of copper nitrate solution

●      3.659 g of benzyl chloride

●      2,4-Dinitrophenyl hydrazine for purification

Procedure

1.    Place the benzyl chloride and copper nitrate solution in a test tube.

2.    Secure the test tube in a holder and heat it in a sand bath using the Bunsen burner, maintaining a constant temperature.

3.    Stop heating when benzaldehyde is produced.

4.    Add 2,4-dinitrophenyl hydrazine to the test tube to purify; observe the formation of benzaldehyde 2,4-dinitrophenylhydrazine crystals.

5.    Add calcium chloride for further purification to obtain pure benzaldehyde.

Observation

Upon adding 2,4-dinitrophenyl hydrazine, an orange precipitate forms, confirming the presence of benzaldehyde.

Questions

1.    What is 2,4-dinitrophenyl hydrazine?

2.    What color precipitate is observed with 2,4-dinitrophenyl hydrazine?

3.    How is benzaldehyde purified in this process?