Pyrethroid

  A pyrethroid is a synthetic chemical compound similar to the natural chemical pyrethrins produced by the flowers of pyrethrums (Chrysanthemum cinerariaefolium and C. coccineum). Pyrethroids are common in commercial products such as household insecticides and insect repellents. They are usually broken apart by sunlight and the atmosphere in one or two days, and do not significantly affect groundwater quality.

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Pyrethroids are axonic poisons that work by keeping open the sodium channels in the neuronal membranes of insects. The sodium channel is a small hole through which sodium ions are permitted to enter the axon and cause excitation. When left open, nerves cells will produce repetitive discharges and eventually cause paralysis ^[1].

Pyrethroids are usually combined with piperonyl butoxide, a known inhibitor of key liver enzymes. This prevents the liver enzymes from clearing the pyrethroid from the body of the insect, and assures the pyrethroid will be lethal and not merely a paralyzing agent. Combined, pyrethroids are toxic to most beneficial insects like bees or dragonflies.

The pyrethroid chrysanthemic acid is produced industrially in a cyclopropanation reaction of a diene as a mixture of cis- and trans isomers followed by hydrolysis of the ester ^[2]:

The compound is the starting material for many derivatives by re-esterfication.

Commercial Pyrethroid Insecticides/Repellants

• Allethrin, the first pyrethroid synthesized (active ingredient of Raid)
• Bifenthrin, active ingredient of Talstar, Capture, Ortho Home Defense Max, and Bifenthrine
• Cypermethrin
• Deltamethrin
• Permethrin, used to treat clothing and mosquito nets, as well as the tick control product Damminix ^[3] and the mite control product MiteArrest ^[4]; widely used, especially in the US military
• Resmethrin, active ingredient of Scourge
• Sumithrin, active ingredient of Anvil
• Tetramethrin
• Tralomethrin
• Transfluthrin, active ingredient of Baygon

References