On-line monitoring by membrane introduction mass spectrometry of chlorination of organics in water. Mechanistic and kinetic aspects of chloroform formation

Chloroform formation during the chlorination of simple organic molecules mo deling humic substances, such as phenol and di- and trihydroxybenzenes, was studied by on-line membrane introduction mass spectrometry (MIMS), Under t he reaction conditions employed, chloroform was rapidly formed from 1,3-dih ydroxybenzene, 1,4-dihydroxybenzene, phenol and 1,2,3-trihydroxybenzene wit h yields of 17, 13, 7 and 5%, respectively. With the exception of aniline, which afforded a 17% chloroform yield, non-phenolic compounds, such as nitr obenzene, chlorobenzene, toluene, benzene and cyclohexanol, furnished low y ields. Mechanistic studies showed that phenol is chlorinated consecutively and produces initially chlorophenol, It is suggested that chloroform might be formed mainly from chlorinated 3,5-cyclohexadienone-type intermediates. MIMS was also used to determine the reaction rates and to study the kinetic s of the chlorination. A good Hammett linear correlation for an electrophil ic substitution mechanism was found for the compounds C6H5X (X = NH2, OH, C H3, H, Cl and NO2). Copyright (C) 2000 John Wiley & Sons, Ltd.