From the primary amines are derived the diazo compounds and azo compounds; closely related are the hydrazines (q.v.).
Selenophene gives the series: selenazole, diazoselenide and piaselenole, corresponding to oxazole, diazo-oxides and furazane.
The simplest aliphatic compounds, such as diazo-methane, diazoethane, and azo-formic acid, are yellow; the diamide of the latter acid is orange-red.
The acid finds considerable use in organic chemistry, being employed to discriminate between the different types of alcohols and of amines, and also in the production of diazo, azo and diazo-amino compounds.