CD 13.10 Azo Compounds

An important aspect of the CD topic is the production of dyes. Azo compounds are used as dyes, and are more fast than diazonium salt dyes because they are more stable. The video above is made for the OCR specification, so go take a look and enjoy the jazzy music, check out Ash Z's channel for more revision videos.

Azo compounds contain an -N=N- group. It is highly stable because it becomes part of the delocalised system involving the arenes.

They generally look like this with different groups coming off eg. The OH group would come from reacting a diazonium ion with phenol as a coupling reagent, and the NH2 group would come from reacting with phenylamine.

The first thing we need is a diazonium salt. The book gives the example of the benzenediazonium ion. For the exam we need to know how this is made.

A cold solution of sodium nitrite (sodium nitrate (III)) is added to a solution of an arylamine (an arene with an NH2 group) in dilute acid. It's kept below 5 degrees because it'll decompose at higher temperatures.

First the sodium nitrate reacts with the acid (usually hydrochloric or sulfuric) to form nitrous acid.

The nitrous acid reacts with the arylamine (in this case phenylamine.)

Azo dyes are made in coupling reactions. The diazonium ion acts as an electrophile and reacts with the benzene ring of the coupling agent.
Examples in the book are with phenol and amines.

The different functional groups on the azo compounds causes a slight difference in colour as it affects the chromophore.