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  • Thermal decomposition and isomerization of cis-permethrin and beta-cypermethrin in the solid phase.

Thermal decomposition and isomerization of cis-permethrin and beta-cypermethrin in the solid phase.

Pest management science (2002-02-21)
Paola González Audino, Susana A Licastro, Eduardo Zerba
ABSTRACT

The stability to heart of cis-permethrin and beta-cypermethrin in the solid phase was studied and the decomposition products identified. Samples heated at 210 degrees C in an oven in the dark showed that, in the absence of potassium chlorate (the salt present in smoke-generating formulations of these pyrethroids), cis-permethrin was not isomerized, although in the presence of that salt, decomposition was greater and thermal isomerization occurred. Other salts of the type KXO3 or NaXO3, with X being halogen or nitrogen, also led to a considerable thermal isomerization. Heating the insecticides in solution in the presence of potassium chlorate did not produce isomerization in any of the solvents assayed. Salt-catalysed thermal cis-trans isomerization was also found for other pyrethroids derived from permethrinic or deltamethrinic acid but not for those derived from chrysanthemic acid. The main thermal degradation processes of cis-permethrin and beta-cypermethrin decomposition when potassium chlorate was present were cyclopropane isomerization, ester cleavage and subsequent oxidation of the resulting products. Permethrinic acid, 3-phenoxybenzyle chloride, alcohol, aldehyde and acid were identified in both cases, as well as 3-phenoxybenzyl cyanide from beta-cypermethrin. A similar decomposition pattern occurred after combustion of pyrethroid fumigant formulations.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Potassium chlorate, anhydrous, free-flowing, Redi-Dri, ACS reagent, ≥99%
Sigma-Aldrich
Potassium chlorate, ACS reagent, ≥99.0%
Sigma-Aldrich
Potassium chlorate, puriss. p.a., ACS reagent, reag. Ph. Eur., ≥99%
Sigma-Aldrich
Potassium chlorate, puriss., 99-101%
Millipore
Potassium chlorate Supplement, suitable for microbiology