see soluble VAT dye general methods namely: (a) in the presence of Pyridine , with Chlorosulfonic acid treatment VAT dye (C.I. 5905) leuco; (b) VAT dye (C.I. 5905) in Pyridine with metal (such as copper, iron or cast) and Sulfur trioxide source (such as Sulfur trioxide, Chlorosulfonic acid or Methyl chlorosulfonate, etc.) processing. Above two kinds of circumstances are alkaline, filter out insolubles, remove Pyridine and salting out.
