[2,2'-Bi-1H-indole]-3,3'-diol, 5-bromo-, bis(hydrogen sulfate) (ester), disodium salt

(a) in the presence of ?Pyridine?, with Chlorosulfonic acid treatment C.I. Vat Blue 3 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 Blue 3. The above two kinds of situation after alkaline, filter out insolubles, remove Pyridine and salting out.

red light blue. Soluble in water is blue.

Standard	Ironing Fastness	Chlorine bleach	Light Fastness	Mercerized	Oxygen bleach	Soaping
						Fading	Stain
ISO	4	3	3-4	4	3-4