Preparation of trans-thiazineindigo pigments

A process for preparing symmetrical or asymmetrical trans-thiazineindigo pigments of the formula (1)

• where
• R1 and R2 are identical or different and each is a radical required to complete a ring system selected from the group consisting of aromatic carbocyclic ring systems, aromatic heterocyclic ring systems, aliphatic carbocyclic ring systems and aliphatic heterocyclic ring systems, said ring systems optionally being substituted, and
• R3 is hydrogen, C1-C12-alkyl or phenyl,
• which comprises
• a) condensing, in an aqueous medium, a compound of the formula (2) with a compound of the formula (3a) or (3b);
• or a compound of the formula (4) with a compound of the formula (3a), or (3b), or (3a) and (3b)
• where
• R4 is hydrogen or a metal ion selected from the group consisting of Na+, K+and Zn2+/2,
• R5 is a leaving group, and
• Hal is Cl or Br;
• by maintaining the reaction mixture at a temperature between 30 and 65° C. for at least 1 hour and then
• b) maintaining the reaction mixture at a temperature between 100 and 180° C. and a pressure between 1.5 and 50 bar for at least 1 hour in the presence of an amide.