Preparation
(a) in the presence of Pyridine , with Chlorosulfonic acid treatment C.I. Vat Red 34 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 Red 34. The above two kinds of situation after alkaline, filter out insolubles, remove Pyridine and salting out.
