Thermal Decomposition of Chlorpyrifos - an Experimental Investigation

Organophosphate compounds are a group of chemicals that are commonly used in pest control. One widely used organophosphate is chlorpyrifos (CPF), which has been associated with acetylcholinesterase inhibition (AChE), an acute neurotoxin. Further, under thermal decomposition conditions, such as those that occur in bushfires, CPF has been shown to produce a dioxin-like compound 2,3,7,8-tetrachloro-[1,4]-dioxinodipyridine (TCDDpy). To assist in understanding the reaction of CPF, an experimental methodology was developed which enabled the study of its thermal decomposition. CPF was pyrolysed in a three-zone furnace, leading to the formation of its major degradation product, 3,5,6-trichloro-2-pyridinol (TCP). The study revealed that ethylene gas and a solid sulfur/phosphorous compound were also generated with the TCP product. TCP undergoes further thermal decomposition to form several chlorinated products. Experiments undertaken under oxidative conditions revealed that TCP (at temperatures above 900 K and at a residence time of 9 s) also produced HCl and cis and trans forms of TCDDpy. The results of this study compare favourably with our previous theoretical work.