Preliminary Exploration On The Formation Of Polyhalogenated 9H-Carbazole Via Chloroperoxidase-mediated Oxidation Of Carbazole In The Presence Of Halides

Polyhalogenated carbazoles?polyhalogenated 9H-carbazoles,PHCs?,with a complex chemical structure similar to polychlorinated dibenzofurans,are a class of emerging environmental organic contaminants.Preliminary studies on toxicological experiments have shown that PHCs exhibited dioxin-like toxicity and were persistent and bioaccumulative.There are 135 congeners for PHCs with a pure halogenation.Although PHCs in the environment was firstly discovered in the 1980 s,these emerging halogenated compounds were not seriously considered until recent years.Recently,more than 20 PHCs have been detected in sediment and soil samples.To date,research on the environmental behaviors and ecotoxicology of PHCs is relatively limited and warrants further investigations.The most environmental sources of PHCs are unknown,except several PHCs have been discovered exist anthropogenic sources.On the basis of summarizing the environmental distribution,source,toxicity and analytical methods of PHCs comprehensively,This paper explored the possible environmental sources of PHCs preliminarily.A natural source of PHCs with bromine and chlorine was put forward,that is the PHCs with bromine and chlorine can be formed via CPO-mediated oxidation of carbazole in the presence of bromide,chloride and hydrogen peroxide.The reaction was simulated in the Lab.In the presence of bromide,chloride and hydrogen peroxide,the halogenation of carbazole occurs via halogen active substances formed by CPO-catalyzed halogenation of bromide and chloride.More than 20 PHCs have been detected in environmental media,however,40 PHCs have been detected in simulative experiment,including-Cl,-Cl₂,-Cl₃,-Cl₄,-Br,-Br₂,-Br3,-Br₄,-ClBr,-ClBr₂,-ClBr3,-Cl₂ Br,-Cl₃ Br,-Cl₂Br₂ substituted PHCs.We chosed Comprehensive two-dimensional Gas Chromatograph-Time of flight mass spectrometer-computer?GC×GC-TOF MS?as the analytical instrument because of good separation results compared with Gas Chromatograph-Mass Spectrometer-computer?GC-MS?,40 mass spectra were acquired by analyzing on GC×GC-TOF MS,it contributes to detect more undiscovered PHCs in environmental media.Besides,the species and amounts of PHCs were examined though changing the concertrations of bromide,chloride and CPO,.When the concertrations of carbazole,bromide,chloride,CPO and hydrogen peroxide were 1?mol·L^-1,1?mol·L^-1,10000?mol·L^-1,0.001U·m L^-1 and 0.1mmol·L^-1 respectively,producing-Br?-Br₂?-Cl?-Cl₂?-ClBr substituted PHCs.When the concertrations of CPO was 0.1U·mL^-1 and other conditions remain,the reaction rate increased,pruducing-Cl₂?-Cl₃?-Cl₄?-ClBr?-Cl₂Br?-Cl₃ Br substituted PHCs.When the concertrations of carbazole,bromide,chloride,CPO and hydrogen peroxide were 1?mol·L^-1,5?mol·L^-1,100000?mol·L^-1,0.1U·m L^-1 and 0.1mmol·L^-1 respectively,pruducing-Br₂?-Br3?-Br₄?-Cl₂?-Cl₃?-Cl₄?-ClBr?-ClBr₂?-ClBr3?-Cl₂Br₂?-Cl₂Br?-Cl₃ Br substituted PHCs.The transformation path of carbazole to PHCs is prior to form low halogenated PHCs,and been halogenated to high halogenated PHCs furtherly.When bromide and chloride coexist,bromide was halogenated firstly.The 3-,3,6-,1,3,6-and 1,3,6,8-are the most stable structures of the mono-,di-,tri-and tetra-isomers of pure halogenated PHCs.The concertration of bromide relative to carbazole and the concertration ratio of bromide and chloride will affect the species of PHCs largely.The research will provide a scientific reference to the source analysis of different species PHCs found in sediment and soil samples,and lay a foundation for exploring new natural sources and qualitative and quantitative analysis of PHCs.