Formation of 2,6-dichloro-1,4-benzoquinone from aromatic compounds after chlorination

Abstract Halobenzoquinones are a group of disinfection byproducts formed by chlorination of certain substances in water. However, to date, the identities of halobenzoquinone precursors remain unknown. In this study, the formation of 2,6-dichloro-1,4-benzoquinone (DCBQ), a typical halobenzoquinone, from 31 aromatic compounds was investigated after 60 min of chlorination. DCBQ was formed from 21 compounds at molar formation yields ranging from 0.0008% to 4.9%. Phenol and chlorinated phenols served as DCBQ precursors, as reported previously. Notably, DCBQ was also formed from para -substituted phenolic compounds. Compounds with alkyl and carboxyl groups as para -substituents led to relatively higher molar formation yields of DCBQ. Moreover, p -quinone-4-chloroimide, 2,6-dichloroquinone-4-chloroimide (2,6-DCQC), and para -substituted aromatic amines (e.g., aniline and N -methyl aniline) served as DCBQ precursors upon chlorination. It was deduced that DCBQ was formed from the para -substituted aromatic amines via 3,5-dichloroquinone-4-chloroimide, a structural isomer of 2,6-DCQC. These results suggested that DCBQ was formed by chlorination of natural organic matter containing para -substituted phenolic species and para -substituted aromatic amines, despite the absence of phenol in water.