Diethyl succinylsuccinate

The DuPont company used the succinic acid ester process, in which diethyl succinate is first cyclised to diethyl succinylsuccinate (2.39) in a sodium/alcohol mixture. One mole of the product is next condensed with two moles of aniline under oxidising conditions, forming diethyl 2,5-dianilino-3,6-dihydroterephthalate (2.40). Ring closure at 250 °C gives dihydroquinacridone, from which quinacridone is obtained by oxidising away the two extra hydrogen atoms. 

Several methods of synthesis of the quinacridones are reported. Each of these involves several stages, accounting at least in part for the somewhat higher cost of these pigments. The two most important methods to the parent compound are outlined in Scheme 4.11. In both routes, the starting material, diethyl succinylsuccinate, 4.42,... 

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