Chlorpyrifos chlorination

Degradation of the insecticide chlorpyrifos has been examined in solutions of aqueous chlorine in which the primary oxidant is hypochlorous acid/hypochlorite. The final product was 2,3,5-trichloropyrid-2-one produced either directly, or via initial oxidative conversion of the thioate ester by replacement of the sulfur with oxygen (Duirk and Collette 2006). An analogous oxidation was found with diazinon (Zhang and Pehkonen 1999). 

Chemicals degraded by WRF include pesticides such as organochlorines DDT and its very toxic metabolite DDE [8, 9] and organophosphate pesticides such as chlorpyrifos, fonofos and terbufos [10] polychlorinated biphenyls (PCBs) of different degrees of chlorine substitution [11-13], some even to mineralization [14, 15] diverse polycyclic aromatic hydrocarbons (PAHs) in liquid media and from contaminated soils or in complex mixtures such as creosote [16-18] components of munition wastes including TNT and its metabolites DNT [19-23], nitroglycerin [24] and RDX [25]. 

The inclusion of a third-order term did not yield a significantly better fit (p > 0.6). There are no indications that PAHs and nonpolar chlorinated hydrocarbons have a different Ks - Ko dependence. By contrast, the moderately polar pesticides such as hexachlorocyclohexanes (HCHs), dieldrin, chlorpyrifos, heptachlor, and trifluralin (open and closed diamonds in Figure 3.3) have Ks values that are 0.6 log units lower than PAHs and PCBs with similar Ko values (p < 0.001). 

Qilorpyrifos reacted with fi ee chlorine to form chlorpyrifos oxon, which is more toxic than the parent compound. Both compounds further hydrolyze to a more stable product, 3,5,6-trichloro-2-pyridinol [110]. 

Duirk SE, Collette TW (2006) Degradation of chlorpyrifos in aqueous chlorine solutions pathways, kinetics and modeling. Environ Sci Technol 40 546-551... 

Chlorpyrifos (73) is the only phosphate of importance containing a pyridine ring. Partial hydrolysis of 2,6-dichloropyridine, followed by peroxide mediated chlorination, gives the required 3,5,6-trichloropyridin-2-ol intermediate (66MI10700, 67USP3355456). The phosphate is a broad spectrum insecticide with some vapour activity. 

The first six organophosphorus and chlorinated organophosphorus pesticides dominate wheat-based products. Exhibit 7 shows that virtually all wheat-based products are, at a minimum, contaminated with malathion and chlorpyrifos-methyl. These data also suggest that although corn-based products can contain malathion and chlorpyrifos-methyl, they are much less likely to be contaminated by the first six organophosphorus and chlorinated organophosphorus pesticides. 

Biocides most often found in the indoor environment are chlorinated hydrocarbons like chlordane, DDT, dieldrin, lindane, heptachlor and methoxychlor, pyrethroids like cyfluthrin, cypermethrin, and permethrin, organophosphates like chlorpyrifos, diazinon, dichlorvos, isofenfos, and malathion, carbamates like ben-diocarb, carbaryl and propoxur and chlorophenols like pentachlorophenol (PCP), chlorocresol (4-chloro-3-methylphenol) and o-phenylphenol. Residues formed in house dust may vary in different countries (Butte, 2003), but biocides like chlorpyrifos, DDT, methoxychlor, permethrin, pentchlorophenol and propoxur seem to be the active compounds in biocide formulations even in different continents, as they are found equally in house dust samples form Germany and the USA (Becker et al., 2002 Butte, 2003 Camann, Colt and Zuniga, 2002). Concentrations of biocides in house dust are mostly in the milligram per kilogram range, they seldom exceed a microgram per cubic meter in indoor air. 

The best laundry procedure for 100% cotton and 65/35 polyester/cotton fabric is to presoak the fabric for 3 hours in the washing machine filled with warm water (70 liters at 50°C) to which 280 mL of chlorine bleach has been added. After the 3 hours, empty the machine, and give the fabric a single warm wash (at 50°C). Less than 0.1% chlorpyrifos residue remains on both cotton and polyester/cotton when the bleach soak pre-treatment is used however, when a single wash, without the bleach pre-soak is used, approximately 40% of the chlorpyrifos residue remains on the cotton fabric and 28% on the polyester/cotton blend. 

In relation to this article, those chlorinated pesticides which are rapidly degraded in the environment, and considered as non-persistent, will not be discussed. Compounds such as atrazine, chlorpyrifos and the phenoxy acid herbicides (2,4-D), mecoprop, MCPA, etc.) all contain organic chlorine and may... 

Beginning in the mid to late 1960 s the biodegradable organophosphorus and carbamate insecticides began to replace the chlorinated hydrocarbons as the rootworm control chemicals of choice. Dlazinon, oxydisulfoton, and phorate were the first, and were quickly followed by bufencarb, trimethacarb, fonofos, and fensulfothion. In the mid to late 1970 s the introduction of new chemicals continued as ethoprop, carbofuran, chlorpyrifos and terbufos came into use. 

Studies on the env ironmental exposure of anticholinesterase pesticidc.s on humans are very limited. One study involved individuals exposed to chlorpyrifos (a chlorinated OP) with respect to their lymphocyte subpopulations in blood (Thrasher et at., 2002). Chlorpyrifos-exposed individuals, whether showing clinical symptoms of anticholinesterase toxicity or not, had a decrease in the relative percentage of CD5 (found on B la, a. subpopulaticn of B cells involved in the production of autoreactivc antibodies) and decreased mitogenesis of... 

In relevant studies, the comparative in vivo and in vitro effects of OPs such as chlorpyrifos and fenthion were assessed in cultured neuroactive PC-12 cells and in treated animals (Bagchi, ei al, 1995, 1997), Although dissimilar polyhalogenated cyclic hydrocarbons, such as endrin and chlordanc, and chlorinated acetamide herbicides, such as alachlor, were also compared to the OP insecticides, the in viva and in vitro effects of OPs, chlorpyrifos, and fenthion were evaluated (Bagchi et al, 1995, 1997). 

Figures 1 and 2 show the Fukui functions for electrophilic attack of both compounds. The most prominent maxima / can be easily correlated to the observed metabolic reactions. The phenyl ring of chlorpyrifos shows three side maxima of the Fukui function. The three chlorine substituents occupy exactly these positions, thereby blocking possibly hydroxylation.

The insecticide chlorpyrifos, developed by Dow, is mainly produced not from pyridine, but by reaction of glutarimide and PCI5 followed by nucleophilic chlorine exchange, via 3,5,6-trichloropyrid-2-one. 

Hexaflumuron has very low toxicity to mammals so its manufacturing facility would offer little interest to terrorists seeking explosive or hazardous targets. It is a replacement for the neurotoxic pesticide chlorpyrifos a broad-spectrum chlorinated organophosphate... 

---