Tefluthrin

Tefluthrin is the ISO common name for an organic compound that is used as a pesticide. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Pyrethroids such as tefluthrin are often preferred as active ingredients in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. It is effective against soil pests because it can move as a vapour without irreversibly binding to soil particles: in this respect it differs from most other pyrethroids.

Tefluthrin is the ISO common name for an organic compound that is used as a pesticide. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Pyrethroids such as tefluthrin are often preferred as active ingredients in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. It is effective against soil pests because it can move as a vapour without irreversibly binding to soil particles: in this respect it differs from most other pyrethroids. Tefluthrin (X=CH 3 ) is manufactured by the esterification of cyhalothrin acid chloride with 4-methyl-2,3,5,6-tetrafluorobenzyl alcohol. The latter was a novel compound when tefluthrin was invented and the choice of routes to it has been discussed.

History

By 1974, a team of Rothamsted Research scientists had discovered three pyrethroids suitable for use in agriculture, namely permethrin, cypermethrin and deltamethrin. These compounds were subsequently licensed by the NRDC, as NRDC 143, 149 and 161 respectively, to companies which could then develop them for sale in defined territories. Imperial Chemical Industries (ICI) obtained licenses to permethrin and cypermethrin but their agreement with the NRDC did not allow worldwide sales. Also, it was clear to ICI's own researchers at Jealott's Hill that future competition in the marketplace might be difficult owing to the greater potency of deltamethrin compared to the other compounds. For that reason, chemists there sought patentable analogues which might have advantages compared to the Rothamsted insecticides by having wider spectrum or greater cost-benefit. The first breakthrough was made when a trifluoromethyl group was used to replace one of the chlorines in cypermethrin, especially when the double bond was in its Z form. The second relied on a process chemists developed to practically manufacture the Z-cis acid by controlling the stereochemistry of the cyclopropane ring in addition to that of the double bond. This led to the commercialisation of cyhalothrin and made available a relatively large supply of the acid. Exploratory studies continued in which it was combined with a large number of commercially available benzyl alcohols. In the main, these had little or no biological activity but when penta-fluorobenzyl alcohol was used the ester with X=F not only had substantial intrinsic activity on Diabrotica balteata but continued to be effective when soil was present, in contrast to other known pyrethroids. Further research allowed the analogue with X=CH 3 (i.e. what became tefluthrin) to be identified after field trials as the optimum for development under the ICI code number PP993. It was first marketed in 1987 using the trademark Force. In 2000, the agrochemical business of ICI merged with that of Novartis to form Syngenta, which still manufactures and supplies tefluthrin. The US patent covering the parent compound expired in November 2002. Tefluthrin was registered for sale in the European Union until December 5, 2008, when it was added to a group of pesticides whose authorization was withdrawn and it could no longer be sold. However, on January 1, 2012, it was re-approved for use.

Metabolism

The mammalian LD 50 is 21.8 mg/kg (rats, oral). Phase I metabolism of tefluthrin proceeds via both oxidation and hydrolysis. Initial targets for oxidation are its methyl groups. Those on the cyclopropane ring and on the tetrafluorobenzene ring are oxidized to alcohol groups which can be further oxidized into carboxylic acids. Hydrolysis of tefluthrin occurs at the ester bond which results in cyhalothrin acid and 4-methyl-2,3,5,6-tetrafluorobenzyl alcohol, which can be further oxidized into the corresponding carboxylic acid. In phase II metabolism, the phase I metabolites are glucuronidated on any available alcohol groups to facilitate membrane transport and eventually excretion.

External links

PPDB pesticides properties database of tefluthrin MSDS of tefluthrin from Sigma-Aldrich Tefluthrin on Pubchem International Chemical safety information

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