Experiment 109

Objective

To prepare methylamine through the Hoffmann degradation of acetamide.

Introduction

In the Hoffmann degradation reaction, acetamide reacts with bromine and potassium hydroxide under heat, resulting in the formation of methylamine. This reaction is characterized by the loss of a carbon atom from acetamide, transforming it into methylamine.

Reaction:

CH3CONH2 ​+ Br2 ​+ 4KOH → CH3​NH2 ​+ 2KBr + K2​CO3 ​+ 2H2​O

Materials

Chemicals:

●      Acetamide

●      Bromine

●      Potassium hydroxide (KOH)

Apparatus:

●      Flask

●      Bunsen burner

●      Stand

●      Water bath

●      Beaker for bromine collection

●      Thermometer

●      Collecting glass tube

Reagents

●      6 ml of acetamide

●      Bromine (added dropwise)

●      8–10 ml of KOH

Procedure

1.    Place acetamide and KOH in the flask.

2.    Add bromine dropwise to the mixture.

3.    Secure the flask on the stand and place it in a water bath.

4.    Heat the water bath with the Bunsen burner.

5.    Connect the collecting glass tube to the flask, with the other end submerged in a water-filled beaker.

6.    As methylamine forms, it collects in the glass tube.

7.    Mix the collected product with hydrochloric acid (HCl); methylamine will dissolve in HCl.

8.    Concentrate the solution to allow methylamine hydrochloride crystals to separate.

9.    Add KOH to the sample to yield pure methylamine.

Observation

Methylamine has a distinct smell, which is released when HCl is added.

Questions

1.    What is the Hoffmann degradation reaction?

2.    Why is bromine used in the Hoffmann degradation reaction?

3.    Why is the reaction to prepare methylamine called Hoffmann degradation?