| abstract |
A process is disclosed for producing pure 6,13- dihydroquinacridone, which is a suitable intermediate for the production of a quinacridone pigment, the process comprisingn (i) heating a cylindrical reactor, which has an atmosphere free of molecular oxygen, so that at least one surface of an inner wall of the cylindrical reactor reaches a temperature of from 250 to 400°C; (ii) introducing 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester, either in powder from or in the form of a mixture of powder with a liquid, through a feed port in an upper portion of the cylindrical reactor; (iii) maintaining the said powder or mixture in substantial contact with the inner wall of the cylindrical reactor such that an intramolecular alcohol-elimination reaction of the 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester takes place; and (iv) removing the 6,13-dihydroquinacridone thus produced through an outlet in a lower portion of the cylindrical reactor. n An apparatus suitable for performance of the process is also described. |