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compounds having two acyl groups linked to an NH group. Open chain and cyclic imides are known. The latter are the most important ; they are derivatives of dibasic acids, for example, phthalimide (I; melting point, 233.5°-238°C), succini-mide (II; melting point, 125°-127°C), and the imide of o-sul-fobenzoic acid (III; saccharin, melting point, 226°-230°C):
Cyclic imides are obtained by the action of ammonia on the anhydrides of dibasic acids or by the heating of various derivatives of these acids, for example, ammonium salts or amides. Unlike amides, imides are quite devoid of basic properties and are weak acids. The hydrogen atom in the imino group is easily replaced by an atom of a metal or halogen. The metal salts and N-bromo derivatives of cyclic imides (for example, potassium phthalimide, N-bromosuccinimide) are widely used in organic synthesis. [10–417-1 ]