Diazo reagent composed of diazo A and diazo B, as above described, combines with bilirubin to give a reddish purple compound known as azobilin. The intensity of this color can be measured in a colorimeter for a determination of the bilirubin present in the serum.

Diazo compounds are used as precursors to carbenes, which are generated by thermolysis or photolysis, for example in the Wolff rearrangement. As such they are used in cyclopropanation for example in the reaction of ethyl diazoacetate with styrene.

The diazotization reaction mechanism begins with the reaction of nitrous acid with the other acid to give water and nitrosonium ion. Thus, the required nitrosonium ion is formed.

DIAZO REAGENT A For bilirubin determination