Preparation
(a) in the presence of Pyridine , with Chlorosulfonic acid treatment C.I. 73405 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. 73405. The above two kinds of situation after alkaline, filter out insolubles, remove Pyridine and salting out.
