Method for preparing 3,6-diaminopyrazine-2,5-dicarboxylic acid and synthetic intermediate thereof

A method for preparing a compound of Formula (I) or a salt thereof, the method comprising:

• simultaneously contacting an aqueous solution of a compound of Formula (II) or a salt thereof:
• and an aqueous solution comprising a metal oxidant, each added at a constant flow rate through constant flow control equipment, into a vessel that contains an aqueous solution comprising a proton acceptor to form a reactant solution, and mixing the reactant solution to form the compound of Formula (I) or a salt thereof;
• or
• simultaneously adding the aqueous solution of the compound of formula (II) or the salt thereof containing the proton acceptor and the aqueous solution of a metal oxidant at a constant rate respectively to the vessel to form the reactant solution, and mixing the reactant solution to form the compound of Formula (I) or a salt thereof;
• wherein X1+and X2+are each independently selected from the group consisting of H+, Li+, Na+, K+, Rb+, Cs+, NH4+, Be2+, Mg2+, Ca2+, Sr2+, and Ba2+;
• wherein the constant rate of the aqueous solution of the compound of formula (II) or a salt thereof and the constant rate of the aqueous solution of the metal oxidant may be same or different;
• wherein the compound of Formula (I) or a salt thereof is formed within seconds of the simultaneous contacting of the aqueous solutions;
• and wherein yield of the compound of Formula (I) or a salt thereof is at least 80%.