Phenylamine & Azo Compounds (CIE A Level Chemistry)

Organic molecules are an important source of colour both in the natural world and in a wide range of industrial applications.

Azo dyes are synthetic compounds that do not occur naturally. They can be used to colour textiles such as cotton.

The acid‐base indicator methyl red is an azo dye that can be produced from 2‐nitrobenzaldehyde and phenylamine as shown in Fig. 1.1.

Fig. 1.1

When heated, phenylamine can react with iodomethane to form compounds B and C. 

Suggest why the temperature used in steps 2 and 3 should be kept as close to 5 °C as possible. 

Indigotin, shown in Fig. 1.2 is a naturally occurring compound that is used to dye denim a blue colour.

Fig. 1.2

It can be synthesised from 2‐nitrobenzaldehyde and propanone in aqueous sodium hydroxide.

Coumarin 440 is a dye that occurs naturally in plants but can be synthesised in the laboratory. It is used to generate blue light in lasers.

Coumarin 440 is hydrolysed with excess sodium hydroxide to form the organic compound D in Fig.1.4.

Coumarin 440 is condensed with ethanol chloride to form the organic compound E in Fig.1.4.

Fig. 1.4

Draw the structures of compounds D and E in the boxes.