PROCESS FOR PREPARING CYCLIC IMIDES OF DICARBOXYLIC ACIDS

Inventia trateaza prepararea imidelor ciclice ale acizilor dicarboxilici, prin reactia dintre anhidride ciclice ale acizilor dicarboxilici si uree, fara utilizarea unui solvent si fara a folosi un exces de uree. In topitura anhidridei de acid dicarboxilic ureea este adaugata treptat, mentinându-se mediul de reactie acid, sfârsitul reactiei fiind indicat de valoarea pH-ului. In acelasi timp, gazele si vaporii formati în cursul reactiei sunt captati în reactie. Avantajele inventiei sunt, printre altele, asigurarea lui la un randament marit si protejarea mediului ambiant de poluare. In a new process for the prodn. of cyclic dicarboxylic acid imides by reaction of cyclic dicarboxylic acid anhydrides and urea without solvent and without excess urea, the urea is introduced stepwise into the molten dicarboxylic acid and the reaction mixture is kept constantly acidic. Gases and vapours which sublime from the mixture during the reaction are collected and, after regeneration, returned to the reaction mixtures. Pref. in the prodn. of phthalamide, urea is pref. introduced into phthalic anhydride in 4 portions at 180-200, 200-220 and 230-240 deg. C, the addition being ended at 4-5.5. In the prodn. of tetrahydrophthalimide, urea is pref. added at 110-150 deg. C in 4 portions, at 110-130, 130-150, 150-170 and 170-180 deg. C, the addition being terminated at pH 3-4.