Thermal decomposition and isomerization of cis-permethrin and beta-cypermethrin in the solid phase.
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.
González Audino
Paola
P
Centro de Investigaciones de Plagas e Insecticidas (CIPEIN-CITEFA/CONICET), Zufriategui 4380, Villa Martelli (1603) Buenos Aires, Argentina.
Licastro
Susana A
SA
Zerba
Eduardo
E
D002704:Chlorates / Q000494:pharmacology; D006358:Hot Temperature; D007536:Isomerism; D008968:Molecular Conformation; D015394:Molecular Structure; D026023:Permethrin / Q000737:chemistry / Q000378:metabolism*; D011722:Pyrethrins / Q000737:chemistry / Q000378:metabolism*; D012492:Salts / Q000494:pharmacology
D002704:Chlorates; D011722:Pyrethrins; D012492:Salts; C017160:cypermethrin; D026023:Permethrin; C022842:chloric acid