New Intermediates and Dyes for Synthetic-polymer Fibres. Benzimidazothioxanthenoisoquinolinone Dioxides and Sulphones of 7H-Benzimidazo(2,1-a)benz(d,e)isoquinolin-7-one

Condensation of benzo(k,l)thioxanthene-3,4-dicarboxylic acid-7,7-dioxide with o-phenylenediamine give a mixture of the new heterocycles benzimidazo(1,2-b)thioxantheno(2,1,9-d,e,f)isoquinolin-7-one-16,16-dioxide and benzimidazo(2,1-a)thioxantheno(2,1,9-d,e,f)isoquinolin-8-one-5,5-dioxide. Separation of these isomers is reported, together with their characterisation by unambiguous synthesis. Similar reaction with substituted o-phenylenediamines affords other isomer mixes of the above. These new dyes colour polyester fibres in orange hues of excellent fastness to light and sublimation