Formation of Chlorodibenzofurans upon Thermo-Chemical Reactions of Diphenyl Ether Herbicide (CNP).

Abstract

In order to obtain information on the thermochemical reactions of chloronitrofen (CNP) upon burning off dead grass and combustion of municipal solid wastes, pyrolysis of this compound, CNP, in a quartz glass reaction tube at 200-800°C under an air stream was performed and the obtained reaction products were analysed by GC-MS. GC-MS analyses of the evolved gaseous products and residues show that CNP began to decompose at 300°C and 90% of the original CNP disappeared at 500°C. Pyrolysis of CNP under an air stream was also shown to produce a variety of compounds, including nitrofen (NIP), polychlorinated diphenylethers (PCDPEs) and dibenzofurans (PCDFs). The formation of PCDPEs (mainly T3CDPE and T4CDPE) was observed on heating over 400°C and the maximum yield of these compounds was ca. 7.5 mol% of CNP at 600°C. The production of PCDFs (mainly DCDF and T3CDF) was also detected on heating over 400°C and the maximum yield of these compounds was ca. 0.5 mol% of CNP at 500°C. On the basis of these results, it can be presumed that the thermochemical reactions of CNP under an air stream start with denitrozation of CNP to form PCDPEs, and then followed by the decomposition and thermal ring closure of PCDPEs to form a small amount of PCDFs.