Ozonation degradation of nitrochlorobenzene isomers in aqueous solution: II. Products and mechanism

To study the mechanisms of degradation of chloronitrobenzenes in water by ozonation, the processes of ozonational degradation of p-nitrochlorobenzene(pCNB), m-nitrochlorobenzene(mCNB) and o-nitrochlorobenzene (oCNB) were investigated by means of GC-MS and LC-MS. The products of these three CNBs mainly contained phenolic matters such as chlorophenol, nitrophenol and nitrochlorophenol, as well as carboxylic matters such as oxalic acid and malonic acid, maleic acid, muconic acid. In the process of ozonation degradation of pCNB, -Cl and-NO₂ could be replaced by ·OH, meanwhile, chlorophenol and nitrophenol were formed. But in the processes of ozonation degradation of oCNB and mCNB, neither nitrophenol nor chlorophenol was detected. The hydrogen on the phenyl of all these three CNBs could be replaced by ·OH, thus nitrochlorophenol was produced, and ten different nitrochlorophenols were detected by GC/LC-MS. The difference in the substitutional place of -Cl and -NO₂ on the phenyl of CNB could lead to the difference of the electron cloud density of carbon and the natural bond orbital (NBO) population. The probability of the reaction between ·OH and the hydrogen on the phenyl had a certain relationship with the electron cloud density of carbon and NOB, but had little relationship with the bond energy. The reaction between ·OH and CNBs could be similar to the electrophilic substitution reactions of aryl.