Tetrazo- or Disazo-dyestuffs

These bodies differ,from the simple azo-compounds by containing the azo-group —N=N— more than once in the molecule. 

According to their method of formation and constitution, these compounds may be divided into different classes. The first of these classes, the type of which is phenolbidiazobenzene discovered by Griess, contain the two azo-groups and the auxochrome amido-or hydroxyl groups in one benzene nucleus. These compounds are obtained by the action of diazo-compounds on oxy- or amido-azo-compounds. 

A second class contains only the azo-groups in one ring, while the auxochrome is in another. They may be prepared by acting upon amines or phenols with diazoazo-compounds (from amido-azo-bodies), or by diazotisation of diamines and subsequent combination with amines or phenols [43,46]. 

A third class of tetrazo-dyestuffs includes those prepared from benzidine and its analogues. These contain two azo-groups in two different rings, which are linked to each other. Tertiary and quaternary azo-compounds, i. e., those containing three and four azo-groups, have also been obtained. 

Is prepared by treating diazobenzene nitrate with carbonate of barium, or by the action of the former on oxyazobenzene. 

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