(a) in the presence of Pyridine , with Chlorosulfonic acid treatment C.I. Vat Orange 9 leuco ; (b) used in Pyridine metal (such as copper, iron, zinc, etc) and Sulfur trioxide source (such as Sulfur trioxide formation, chlorosulfonic or methyl chlorosulfonic etc) processing C.I. Vat Orange 9. The above two kinds of circumstances are through with alkali, filter out the insoluble,, remove Pyridine and salting-out.
