Isoindoline Pigments tautomeric forms

The history of isoindoline pigments is closely related to phthalocyanine chemistry. An important starting material for both pigment groups is diiminoisoindoline (10a) or its tautomeric form aminoiminoisoindoline (10b), which can be produced from phthalic anhydride and urea or by addition of ammonia to o-phthalodinitrile (9). 

---