Hypochlorite treatment of a simulated food-processing mixture produces 3,4-dichloromaleimide and 3,3-dichloro-4-(dichloromethylene)-2,5-pyrrolidinedione (C5HCl4NO2). The tetrachloro compound and two analogs, which can be synthesized from citraconic anhydride and itaconic anhydride, are direct-acting Ames mutagens in Salmonella typhimurium TA100 tester strain. These novel five-carbon cyclic imides are structurally similar to 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), the principal mutagenic compound present in paper pulp bleaching liquors. Molecular structure analysis of the mutagens was based on X-ray crystallography, 13C NMR, and mass spectrometry of synthetic chlorinated imides with identical mass spectra and gas chromatographic retention indices. The tetrachloroimide accounts for much of the mutagenicity of the dichloromethane-extractable pH 2 fraction from chlorination of a simulated food-processing system consisting of chicken frankfurters. In the Ames TA100 tester strain it has a mol...