Alizarine Yellow R

Alizarine Yellow R is a yellow colored azo dye made by the diazo coupling reaction. It is usually commercially available as a sodium salt. In its pure form, it is a rust-colored solid. It is mainly used as a pH indicator.

Preparation
Alizarine Yellow R is produced by azo coupling of salicylic acid and diazonium derivative of 4-Nitroaniline