Patent ID: 8691979

Claim:
A method for the preparation of a diaminophenothiazinium compound, the method comprising the steps of (i) Thiosulfonic Acid Formation (TSAF); and (ii) Oxidative Coupling (OC); wherein the diaminophenothiazinium compound has the following formula: and: each of —R 1 and —R 9 is independently —H or —R A ; and each —R A is independently selected from C 1-4 alkyl; C 2-4 alkenyl; halogenated C 1-4 alkyl; C 5-10 aryl; halogenated C 5-10 aryl; C 1-4 alkylene-C 5-10 aryl and halogenated C 1-4 alkylene-C 5-10 aryl; each of —R 3NA and —R 3NB is independently selected from: C 1-4 alkyl; C 2-4 alkenyl; halogenated C 1-4 alkyl; C 5-10 aryl; halogenated C 5-10 aryl; C 1-4 alkylene-C 5-10 aryl and halogenated C 1-4 alkylene-C 5-10 aryl; each of —R 7NA and —R 7NB is independently selected from: C 1-4 alkyl; C 2-4 alkenyl; halogenated C 1-4 alkyl; C 5-10 aryl; halogenated C 5-10 aryl; C 1-4 alkylene-C 5-10 aryl and halogenated C 1-4 alkylene-C 5-10 aryl; and X − is an anionic counter ion; wherein step (i) Thiosulfonic Acid Formation (TSAF) comprises a step in which a compound of formula I is oxidized in the presence of a thiosulfate and an oxidizing agent selected from sodium persulfate, potassium persulfate, and ammonium persulfate to give a compound of formula II: wherein —R 9 , R 7NA and —R 7NB are as previously defined; and each of —R 10NA and —R 10NB is independently selected from: —H; C 1-4 alkyl; C 2-4 alkenyl; halogenated C 1-4 alkyl; C 5-10 aryl; halogenated C 5-10 aryl; C 1-4 alkylene-C 5-10 aryl and halogenated C 1-4 alkylene-C 5-10 aryl; and wherein step (ii) Oxidative Coupling (OC) comprises a step in which a compound of formula IIa is oxidatively coupled to a compound of formula III, using an oxidising agent selected from sodium persulfate, potassium persulfate, or ammonium persulfate, to give a compound of formula IV: wherein: each of —R 1 and —R 9 is independently —H or —R A ; —R A , —R 3NA , —R 3NB , —R 7NA and —R 7NB are as previously defined.