Pyrethrin

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Pyrethrin

The pyrethrins are a pair of natural organic compound

Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
s that have potent insecticidal activity. Pyrethrin I and pyrethrin II are structurally related esters with a cyclopropane

Cyclopropane

Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms....
core. They differ by the oxidation state

Oxidation state

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Encyclopedia

The pyrethrins are a pair of natural organic compound

Organic compound

Cyclopropane

Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical Electrical charge that an atom would have if all bonds to atoms of different elements were 100% Ionic bond....
of one carbon. They are viscous liquids that oxidize to become inactivated. They are non-persistent, being biodegradable, and break down on exposure to light or oxygen. The chemical structure of pyrethrins is the basis for a variety of synthetic insecticides called pyrethroid

Pyrethroid

A pyrethroid is a synthetic chemical compound similar to the natural chemical pyrethrins produced by the flowers of pyrethrums . Pyrethroids are common in commercial products such as household insecticides and insect repellents....
s such as bifenthrin

Bifenthrin

Bifenthrin is a pyrethroid insecticide that affects the insect nervous system of insects. Products containing bifenthrin include Talstar, Capture, Brigade, Bifenthrine, Ortho Home Defense Max, and Scotts LawnPro Step 3....
, permethrin

Permethrin

Permethrin is a common chemical synthesis chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron cell membranes by prolonging sodium channel activation....
and cypermethrin

Cypermethrin

Cypermethrin is a synthetic compound primarily used as an insecticide. It acts as a fast-acting neurotoxin in insects. It is easily degraded on soil and plants but can be effective for weeks when applied to indoor inert surfaces....
.

The pyrethrins are contained in the seed cases of the perennial plant

Perennial plant

A perennial plant or perennial is a plant that lives for more than two years. When used by gardeners or horticulturalists, this term applies specifically to perennial herbaceous plants....
pyrethrum

Pyrethrum

'Pyrethrum' refers to several Old World plants of the genus Chrysanthemum which are cultivated as ornamentals for their showy flower heads. It is also the name of a natural insecticide made from the dried flower heads of C....
(Chrysanthemum cinerariaefolium), which is grown commercially to supply the insecticide

Insecticide

An insecticide is a pesticide used against insects in all developmental forms. They include ovicides and larvicides used against the Egg and larvae of insects respectively....
. Although extracts of the plant were already used as insecticide, the structure was first published by Hermann Staudinger

Hermann Staudinger

Hermann Staudinger was a German chemist who demonstrated the existence of macromolecules which he characterized as polymers. For this work he received the 1953 Nobel Prize in Chemistry....
and Lavoslav Ružicka

Lavoslav Ružicka

Leopold Stjepan Ru?icka was a Croatian scientist, winner of the 1939 Nobel Prize in Chemistry. He received eight honoris causa doctorates in in science, medicine, and law; seven prizes and medals; and twenty-four honorary memberships in chemical, biochemical, and other scientific societies....
in 1924. Pyrethrins are neurotoxin

Neurotoxin

A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels.Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue....
s that attack the nervous systems of all insect

Insect

Insects are the biggest class of arthropods and the only ones with wings. They are the most diverse group of animals on the planet. They are most diverse at the equator and their diversity declines toward the poles....
s. When present in amounts not fatal to insects, they still appear to have an insect repellent

Insect repellent

An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects from landing or climbing on that surface....
effect. Pyrethrins are gradually replacing organophosphate

Organophosphate

An organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactor s that are essential for life....
s and organochloride

Organochloride

An organochloride, organochlorine, chlorocarbon, or chlorinated solvent is an organic compound containing at least one covalent bond chlorine atom....
s as the pesticide of first choice.

The majority of the world's supply of pyrethrin and Chrysanthemum cinerariaefolium come from Kenya. The flower was first introduced into Kenya and the highlands of Eastern Africa during the late 1920s. Now, Kenya produces as much as 70% of the world's supply of pyrethrum. A substantial amount of the flowers are cultivated by small scale farmers who depend on it as a source of income. It is a major source of export income for Kenya and source of over 3,500 additional jobs.

Total Synthesis of Pyrethrin I

The synthesis of pyrethrin I involves the esterification of (+)-trans-chrysanthemic acid with (S)-(Z)-pyrethrolone. One synthetic method for each of these is shown in the images below. Sobti and Dev of the Malti-Chem Research Centre in Nadesari, vadodara, India published this method for chrysanthemic acid in 1974. The starting material for the synthesis uses commercially available (+)-3a, 4a-epoxycarane (1). A lactone is eventually formed and the ring is opened by the use of a Grignard reagent to give (+)-trans-chrysanthemic acid. The preparation of (S)-Pyrethrolone is essentially a 2 step synthesis. The starting material (S)-4-hydroxy-3-methyl-2-(2-propynyl)-2-cyclopenten-1-one (7) is also commercially available as the alcohol moiety of ETOC^©. Etrakis(triphenylphosphine) palladium(0), copper(I) iodide, triethyl amine, and vinyl bromide are added to (7) to add two more carbons and form (8). The final step is the addition of an activated zinc compound to reduce the triple carbon bond to form the cis product, (S)-pyrethrolone (9). Although no journal articles specify the combining of the alcohol and acid moieties of Pyrethrin I, they could be combined through an esterification process to form the wanted product.

Pyrethrin

Total Synthesis of Pyrethrin I

Synthesis of the Acid Moiety of Pyrethrin I

Synthesis of the Alcohol Moiety of Pyrethrin I

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