3,4'-dicarboxy-4-hydroxy azo benzene.

it is a coupling reaction...........it forms a azo dye.

when salicylic acid reacts with amino benzoinc acid.. initially amino benzoinc acid

reacts with nitrous acid and hydrochloric acid to form azo group....

azo group: -N=N-

then that azo compound react with salicylic acid to form an azo dye

(3,4'-dicarboxy-4-hydroxy azo benzene).

C6H4COOH(OH)-salicylic acid

C

H2NC6H4CO2H- amino benzoinc acid.

H2NC6H4CO2H+HNO2+HCL-->CL-N=N-C6H4COOH

(AZO COMPOUND)

3,4'-dicarboxy-4-hydroxy azo benzene.

(AZO DYE)