(a) in the presence of Pyridine , with Chlorosulfonic acid treatment C.I. Vat Violet 9 leuco; (b) in the Pyridine with metal (such as copper, iron, zinc, etc) and Sulfur trioxide source (such as Sulfur trioxide, Chlorosulfonic acid or Methyl chlorosulfonate, etc.) processing ?C.I. Vat Violet 9. The above two kinds of situation after alkaline, filter out insolubles, remove Pyridine and salting out.
