GB2243830A - An insecticidal cyclopropane carboxylic acid ester - Google Patents

Abstract

The invention provides (S)- alpha -cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1yl)-2,2- dimethylcyclopropanecarboxylate, substantially free from other isomers of the same compound, a process for its preparation, compositions comprising it, and methods for the user of the compositions for the control of insect pests.

Description

INSECTICIDAL COMPOUND This invention relates to an insecticidal compound, a process for its preparation, compositions comprising it, and methods for the use of the compositions for the control of insect pests.

UK Patent Application No 2161804-A discloses the enantiomeric pair of isomers represented by (S)- -cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)2,2 -dimethylcyclopropanecarboxylate and (R)-a-cyano-4-fluoro-3-phenoxybenzyl (lS,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclo- propane-carboxylate. The insecticidal activity of this racemate is also described in UK Patent Application No 2161804-A.

Further research by the Applicants has established that substantially all of the insecticidal activity of the previously described racemate is associated with one of these two enantiomers. This enantiomer has not previously been described in substantially pure form. Use of the single enantiomer as an insecticidal active ingredient offers the advantage of employing a lower amount of material for a given level of insecticidal effect than would be necessary for a corresponding mixture of active and less active enantiomers, thereby improving cost-effectiveness.

Accordingly, the invention provides (S)-a-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2- -dimethylcyclopropanecarboxylate, substantially free from other isomers of the same compound, and hereinafter referred to as "The Active Isomer". The term "substantially free" as used herein signifies the presence of less than 10% by weight of other isomers of the same compound.

The Active Isomer may be prepared by chromatographic separation of a diastereomeric mixture of (S)-a-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethyl- -cyclopropanecarboxylate and (R)-a-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclo propanecarboxylate, for example by high pressure liquid chromatography.

This diastereomeric mixture may be prepared by the reaction of 4-fluoro-3-phenoxybenzaldehyde and a (1R,cis)-1-halocarbonyl-2,2-dimethyl 3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)cyclopropane (for example (1R,cis)-1-chlorocarbonyl-2,2-dimethyl-3-(Z-2-chloro-3,3,3-trifluoroprop 1-en-1-yl)cyclopropane) in the presence of an alkali metal cyanide (for example, sodium cyanide), preferably in a two-phase system in the presence of a phase transfer catalyst, for example a quaternary ammonium salt such as tetrabutylammonium bromide. The acid halide may be prepared by standard techniques from the (lR,cis) acid, the preparation of which is described in UK Patent Application Nos 2035307 and 203538.

The Active Isomer may be used to combat and control infestations of insect pests. The insect pests which may be combated and controlled by the use of the Active Isomer include those pests associated with agriculture (which term includes the growing of crops for food and fibre products, horticulture and animal husbandry), forestry, the storage of products of vegetable origin, such as fruit grain and timber, and also those pests associated with the transmission of diseases of man and animals.

In order to apply the Active Isomer to the locus of the pests it is usually formulated into compositions which include in addition to the insecticidally active ingredient suitable inert diluent or carrier materials, and/or surface active agents.

The Active Isomer may be the sole active ingredient of the composition or it may be admixed with one or more additional active ingredients such as insecticides, insecticide synergists, herbicides, fungicides or plant growth regulators where appropriate.

Suitable additonal active ingredients for inclusion in admixture with the Active Isomer may be compounds which will broaden the spectrum of activity of the compounds of the invention or increase their persistence in the location of the pest. They may synergise the activity of the Active Isomer or complement the activity, for example by increasing the speed of effect, improving kill or knockdown of target insect pests, or overcoming repellency. Additionally, multi-component mixtures of this type may help to overcome or prevent the development of resistance to individual components.

The particular insecticide, herbicide or fungicide included in the mixture will depend upon its intended utility and the type of complementary action required. Examples of suitable insecticides include the following: (a) natural pyrethrins or pyrethroids such as permethrin, fenvalerate, deltamethrin, biphenthrin, fenpropathrin, cyfluthrin, tefluthrin, empenthrin, ethofenprox, tetramethrin, bioallethrin, fenfluthrin, prallethrin, 5-benzyl-3-furylmethyl (E)-(1R,3S)-2,2-dimethyl-3-(2 oxothiolan-3-ylidene- methyl)cyclopropane carboxylate and pentafluorobenzyl (cis)-3-[2-fluoro-2-(methoxycarbonyl)ethenyl]2,2 -dimethylcyclopropane carboxylate;; (b) organophosphates such as profenofos, sulprofos, dichlorvos, methyl parathion, azinphos-methyl, demeton-s-methyl, heptenophos, thiometon, fenamiphos, monocrotophos, triazophos, methamidophos, dimethoate, phosphamidon, malathion, chlorpyrifos, phosalone, fensulphothion, fonofos, phorate, phoxim, pyrimiphos-methyl, fenitrothion and diazinon; (c) carbamates (including aryl carbamates) such as pirimicarb, cloethocarb, carbofuran, ethiofencarb, aldicarb, thiofurox, carbosulfan, bendiocarb, fenobucarb, propoxur and oxamyl; (d) benzoyl ureas such as triflumuron and chlorofluazuron; (e) organic tin compounds such as cyhexatin, fenbutatin oxide and azocyclotin; (f) macrolides such as avermectins or milbemycins, for example abamectin, avermectin and milbemycin; (g) hormones and synthetic mimics thereof such as juvenile hormone, juvabione, ecdysones, methoprene and hydroprene;; (h) pheromones; (i) organochlorine compounds such as benzene hexachloride, DDT, chlordane, dieldrin and endosulfan.

In addition to the major chemical classes of insecticide listed above, other insecticides having particular targets may be employed in the mixture if appropriate for the intended utility of the mixture. For instance selective insecticides for particular crops, for example stem borer specific insecticides for use in rice such as cartap or buprofezin, can be employed. Alternatively, insecticides or acaricides specific for the control of specific insect growth stages, for example ovolarvicides such as clofentezine, amitraz, chlordimeform, flubenzimine, hexythiazox and tetradifon; motilicides such as dicofol or propargite; adulticides such as bromopropylate, chlorobenzilate; or insect growth regulators such as hydramethylnon, cyromazine, methoprene, chlorfluazuron and diflubenzuron may also be included in the compositions.

Examples of suitable insecticide synergists for use in the compositions include piperonyl butoxide, sesamex and dodecyl imidazole.

Suitable herbicides, fungicides and plant growth regulators for inclusion in the compositions will depend upon the intended target and the effect required. An example of a rice-selective herbicide which can be included is propanil; an example of a plant growth regulator for use in cotton is "Pix"; and examples of fungicides for use in rice include blasticides such as blasticidin-S. The choice of other ingredients to be used in admixture with the active ingredient will often be within the normal skill of the formulator, and will be made from known alternatives depending upon the total effect to be achieved.

The ratio of the Active Isomer to any other active ingredient in the composition will depend upon a number of factors including the type of insect pest to be controlled, and the effects required of the mixture.

However, in general, the additional active ingredient of the composition will be applied at about the rate at which it would be applied on its own, or at a lower rate if synergy occurs.

The compositions may be in the form of dusting powders wherein the active ingredient is mixed with a solid diluent or carrier, for example kaolin, bentonite, kieselguhr or talc, or they may be in the form of granules wherein the active ingredient is absorbed in a porous granular material, for example pumice.

Alternatively, the compositions may be in the form of liquid preparations to be used as dips, sprays or aerosols. Dips and sprays are generally aqueous dispersions or emulsions of the active ingredient in the presence of one or more known wetting agents (surface active agents).

Aerosol compositions may contain the active ingredient or ingredients, a propellant and an inert diluent, for example odouless kerosene or alkylated benzenes. In a preferred form, aerosol compositions may contain from 0.005% to 4% of active ingredient or ingredients, the remainder of the composition comprising a solvent, selected from odouless kerosene and alkylated benzenes, and a propellant. Aerosol compositions may optionally incorporate other additives, for example perfumes or corrosion inhibitors.

Wetting agents, dispersing agents and emulsifying agents may be of the cationic, anionic or non-ionic type. Suitable agents of the cationic type include, for example, quaternary ammonium compounds, for example cetyltrimethylammonium bromide. Suitable agents of the anionic type include, for example, soaps, salts of aliphatic monoesters of sulphuric acid, for example sodium lauryl sulphate, salts of sulphonated aromatic compounds, for example sodium dodecylbenzenesulphonate, sodium lignosulphonate, calcium lignosulphonate, ammonium lignosulphonate, butylnaphthalenesulphonate and a mixture of the sodium salts of diisopropyl- and triisopropyl naphthalenesulphonates.Suitable agents of the non-ionic tyoe include, for example, the condensation products of ethylene oxide with fatty alcohols such as oleyl alcohol or cetyl alcohol, or with alkyl phenols such as octyl phenol, nonyl phenol and octyl cresol.

Other non-ionic agents are the partial esters derived from long chain fatty acids and hexitol anhydrides, the condensation products of the said partial esters with ethylene oxide, and the lecithins.

The compositions may be prepared by dissolving the active ingredient in a sutiable solvent, for example a ketonic solvent such as diacetone alcohol, or an aromatic solvent such as trimethylbenzene, and optionally adding the mixture so obtained to water which may contain one or more known wetting, dispersing or emulsifying agents.

Other suitable organic solvents are dimethylformamide, ethylene dichloride, isopropyl alcohol, propylene glycol and other glycols, diacetone alcohol, toluene, kerosene, white oil, methylnaphthalene, xylenes, trichloroethylene, N-methyl-2-pyrollidone and tetrahydrofurfuryl alcohol (THFA).

The compositions which are to be used in the form of aqueous dispersions or emulsions are generally supplied in the form of a concentrate containing a high proportion of the active ingredient or ingredients, the said concentrate to be diluted with water before use.

These concentrates are often required to withstand storage for prolonged periods and, after such storage, to be capable of dilution with water to form aqueous preparations which remain homogeneous for a sufficient time to enable them to be applied by conventional spray equipment. The concentrates may contain 1-99% by weight of the active ingredient or ingredients. When diluted to form aqueous preparations, such preparations may contain varying amounts of the active ingredient depending upon the purpose for which they are to be used. For agricultural or horticultural purposes, an aqueous preparation containing between 0.0001% and 0.1t by weight of the active ingredient or ingredients is particularly useful.In use, the compositions are applied to the pests, to the locus of the pests, to the habitat of the pests, or to growing plants liable to infestation by the pests, by any of the known means of applying pesticidal compositions, for example by dusting or spraying or in a granular formulation.

The Active Isomer and compositions comprising it are very toxic to a variety of insect, and other invertebrate pests, including, for example, the following: Myzus persicae (aphid) Aphis gossypii (aphid) Aphis fabae (aphid) Megoura viceae (aphid) Aedes aegypti (mosquito) Anopheles spp. (mosquitos) Culex spp. (mosquitos) Dysdercus fasciatus (capsid) Musca domestica (housefly) Pieris brassicae (white butterfly) Plutella maculipennis (diamond back moth) Phaedon cochleariae (mustard beetle) Aonidiella spp. (scale insects) Trialeuroides spp. (white flies) Bemisia tabaci (white fly) Blattella germanica (cockroach) Periplaneta americana (cockroach) Blatta orientalis (cockroach) Spodoptera littoralis (cotton leafworm) Heliothis virescens (tobacco budworm) Chortiocetes terminifera (locust) Diabrotica spp. (rootworms) Agrotis spp. (cutworms) Chilo partellus (maize stem borer) Nilaparvata lugens (planthopper) Nephotettix cincticeps (leafhopper) Panonychus ulmi (European red mite) Panonychus citri (citrus red mite) Tetranychus urticae (two-spotted spider mite) Tetranychus cinnabarinus (carmine spider mite) Phyllcoptruta oleivora (citrus rust mite) Polyphagotarsonemus latus (broad mite) Brevipalpus spp. (mites) The Active Isomer and compositions comprising it are particularly useful for the control of lepidopteran pests of cotton, for example Spodoptera spp. and Heliothis spp.. and for the control of pests which inhabit the soil, for Example Diabrotica spp.They may be used, optionally in conjunction with other insecticidally active ingredients or knockdown agents, for the control of public health pest such as flies and cockroaches, and for the control of insect and acarine pests which infest animals, such as Lucilia sericata, ixodid ticks such as Boophilus spp., Ixodes spp., Amblyomma spp., Rhipicephalus spp., and.Dermocentor spp. They are effective in combating both susceptible and resistant strains of these pests in their adult, larval and intermediate stages of growth, and may be applied to the host animal by topical, oral or parenteral administration.

The following Examples illustrate various aspects of this invention.

In the preparation Examples the products were usually identified and characterised by means of nuclear magnetic resonance (NMR) spectroscopy and infra red (IR) spectroscopy. In each case where a product is specifically named its spectral characteristics are consistent with the assigned structure. Except where stated otherwise, exemplified compounds having one or more asymmetrically substituted carbon atoms were prepared in racemic form.

In the Examples, gas liquid chromatography (GLC) retention times were determined on a Hewlett Packard 5890 Gas Chromatograph, using a Chrompak C.P. Sil 5 C.B. column of 12.5m length and 0.2mm internal diameter. Unless otherwise stated, the injection temperature was1000C, and a temperature gradient of 150C per minute employed, up to a maximum temperature of 2800C, maintained for 4 minutes. The carrier gas was helium at a column head pressure maintained at 11 psi. Alternative injection and maximum temperatures are indicated in the Examples where appropriate. 1H NMR spectrometry was performed at a frequency of 270 MHz on a Jeol FX 270 NMR spectrometry unless otherwise indicated. 90Mhz, 60 Mhz and 400 MHz 1H NMR spectrometry were performed using Jeol FX 90Q, Jeol PMX 60 SI and Jeol GX 400 spectrometers. 19F NMR spectrometry was performed using a Jeol FS 90Q spectrometer at a frequency of 84.26 MHz. All NMR shift values (S) are quoted in ppm relative to a standard (TMS or CFCl3). In the NMR data, the following abbreviations are used: s=singlet, d=doublet, t=triplet, q=quartet, dd=double doublet, m=multiplet, b=broad. Molecular ion (M+) peaks were determined on one of three mass spectrometers: Jeol DX 303, Kratos MS 80 or Hewlett Packard HP 5992.

EXAMPLE 1 This Example illustrates the preparation of (lR,cis)-1-chlorocarbonyl 2,2-dimethyl-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)cyclopropane Stage 1 (1RS,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2- dimethylcyclopropanecarboxylic acid * (lOOg) was added to a stirred mixture of (-)-ephedrine (34g), water (13cm3), and hexane (1000cm3). A thick white precipitate was formed. The stirred mixture was heated to the reflux temperature and chloroform added until all of the precipitate had dissolved. The mixture was then allowed to cool slowly whereupon a crystalline precipitate was formed. The crystalline material was collected, dried and recrystallised three times from trichloroethylene.

Analysis of a small sample of the crystalline ephedrine salt was conducted by coupling an acidified sample with (R)-octanol in the presence of dicyclohexylcarbodiimide. The (R)-octyl ester obtained was shown by GLC analysis and optical rotation to be derived from the (-)-ephedrine salt of (1R,cis)-acid of 96.7% purity. The bulk of the (-)-ephedrine salt was acidified with 2M aqueous hydrochloric acid solution (200cm ) and the recovered acid extracted with dichloromethane. The organic extract was dried over anhydrous magnesium sulphate, and the solvent evaporated under reduced pressure to leave (1R,cis)-3-(Z-2-chloro-3,3,3-trifluoropropl- en-1-yl)-2,2-dimethylcyclopropanecarboxylic acid (15.6g) of 96.7% optical purity.

Optical Rotation: la] = +450 (0.0555g in 5cm3 chloroform containing 0.05% ethanol.

The separation of the substantially pure (1RS,cis)-isomer mixture from a mixture of cis and trans isomers is described in UK Patent Application No 2035307-A.

Stage 2 The resolved acid from stage 1 (5g) was added to thionyl chloride (7.5cm3) and the mixture heated at the reflux temperature fpr 3 hours.

Excess thionyl chloride was removed by evaporation under reduced pressure to leave (lR,cis)-1-chlorocarbonyl-2,2-dimethyl-3-(Z-2-chloro- -3,3,3-trifluoroprop-1-en-1-yl)cyclopropane as a yellow oil which was used without further purification.

Infra red: C=0 at 1775 cm 1 1H NMR 6 (CDC13): 6.6 (d); 2.5 (m); 1.3,1.4 (2xs) EXAMPLE 2 This Example illustrates the preparation of (RS)- -cyano-4-fluoro-3- phenoxybenzyl (lR,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2- dimethyl-cyclopropanecarboxylate, and the separation of the diastereomeric mixture.

Stage 1 A mixture of (lR,cis)-l-chlorocarbonyl-2,2-dimethyl-3-(Z-2-chloro-3,3,3- trifluoroprop-l-en-1-yl)-cyclopropane (2.61g), 4-fluoro-3-phenoxybenzaldehyde (2.16g), sodium cyanide (0.5g), hexane (25cm3), water (10.5cm3) and tetra-n-butylammonium bromide (catalytic quantity) was stirred at the ambient temperature for 20 hours, at which time analysis of a withdrawn sample by GLC showed approximately 67% conversion to a product. Ethyl acetate was added to the mixture and the organic layer separated and washed with sodium bicarbonate solution and brine.The organic layer was dried and the solvents evaporated under reduced pressure to leave a yellow oil which was purified by column cromatography on a silica support, eluted with petroleum ether (boiling range 60-800C) containing 5% by volume ethyl acetate to give an oil (2.6g solidified on standing) shown by GLC to contain 95% of the diastereomeric title compound.

GLC Retention Time: 9.40 and 9.53 minutes Stage 2 The product of stage 1 was separated by high pressure liquid chromatography using hexane containing 4% by volume ethyl acetate as eluent. 3 fractions were obtained, and were characterised as follows by analysis of their spectral data: Fraction 1 (R)-a-cyano-4-fluoro-3-phenoxybenzyl (lR,cis)-3-(Z-2-chloro-3,3, 3- trifluoroprop-1-en-1-yl)-2, 2-dimethyl-cyclopropanecarboxylate Melting point (after recrystallisation from isopropanol): 95.2-95.8 C Optical rotation [α]D (0.2142g in 25cm CHCl3): +11.963 (25 C) GLC Retention time: 3.49 minutes Fraction 2 (S)-a-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3 trifluoroprop-1-en-1-yl)2, 2-dimethyl-cyclopropanecarboxylate (Active Isomer).

This isomer was obtained as an oil with a trace of aldehyde impurity. The crude oil was purified by column chromatography on silica gel using dichloromethane as eluent, and the resultant oil was seeded with a trace of the enantiomeric pair of isomers represented by (S)-a-cyano-4-fluoro-3- phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2dimethyl- cyclopropanecarboxylate and (R)-a-cyano-4-fluoro-3-phenoxybenzyl (1S,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2dimethylcyclopropane-carboxylate, obtained by the method described in UK Patent Application No 2161804-A, to give a crystalline solid material after cooling to OOC: Melting point: 37-390C Optical rotation lalD (0.2831g in 25cm3 CHCl3): +26.537 (250C) GLC Retention time: 3.77 minutes Fraction 3: This fraction was shown by GLC to contain a mixture of the two diastereomers isolated in Fractions 1 and 2 in a ratio of 11:9, contaminated with unreacted starting material.

EXAMPLE 3 This Example illustrates the insecticidal properties of the Active Isomer.

The activity of the Active Isomer (as isolated as Fraction 2 of Example 2 above, was determined using a variety of insect pests. The Active Isomer was used in the form of a liquid preparations containing 100 parts per million (ppm) by weight of the product. The preparation was made by dissolving the product in acetone and diluting the solutions to give the required concentration of product using as a diluent water containing 0.01% by weight of a nonylphenol ethoxylate wetting agent sold under the trade name SYNPERONIC NX (registered trade mark).

The test procedure adopted with regard to each pest was essentially the same and comprised supporting a number of the pests on a medium which was usually a host plant or a foodstuff on which the pests feed, and treating either or both of the pests and the medium with the preparation.

The mortality of the insects was then assessed at periods varying from 1 to 6 days after the treatment.

The results of the tests are given in Table II at the rate of application indicated (in ppm) in the second column of the Table, as a grading of observed mortality designated as A, B or C, wherein A indicates 80-100% mortality, B indicates 50-79% mortality, and C indicates less than 50U mortality.

In Table II, the test type is designated by a letter code, and the species, support medium, type and duration of the test are given for each code in Table I.

TABLE I

Code Letters Test Species Support Type of Duration medium/food test (days) TU Tetranychus urticae French bean Contact 3 (spider mite - adult) leaf MP Myzus persicae French bean Contact 3 (aphids) leaf NL Nilaparvata lugens Rice plant Contact 3 (Brown planthopper nymph) MD Musca domestica Plastic pot Contact 1 (Housefly - adult) MD/K Musca domestica Plastic pot Knockdown 4 hrs (Housefly - adult) TABLE I (Contd.)

P14 ital Code Letters Test Species Support Type of Duration medium/food test (days) BG Blatella germanica Plastic pot Residual 3 (cockroach - nymph) HV Heliotis virescens Cotton leaf Residual 3 (tobacco budworm - larvae) CP Chilo Partellus Oilseed rape Residual 3 (stemborer - larvae) DB Diabrotica balteata Filter paper/ Residual 3 (rootworm - larvae) maize seed "Contact" indicates a test in which both the medium and the pests vere treated.

"Residual" indicates a test in which the medium vas treated prior to infestation with the pests.

TABLE II

Product Rate TU MP NL MD MD/K BG HV CP DB (ppm) Active Isomer 100 A A A A A A A A A EXAMPLE 4 This Example illustrates the comparative activity of the Active Isomer and the enantiomeric pair of isomers represented by (S)-er-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3 trifluoroprop-1-en-1-yl)-2 , 2-dimethylcyclopropanecarboxylate and (R)-a-cyano-4-fluoro-3-phenoxybenzyl (1S,cis)-3-(Z-2-chloro-3,3,3 trifluoroprop-1-en-1-yl)-2, 2-dimethylcyclopropane-carboxylate.

The comparative activities of the enantiomeric pair of isomers represented by (S)-a-cyano-4-fluoro-3-phenoxybenzyl (lR,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2- dimethylcyclopropane- carboxylate and (R)-a-cyano-4-fluoro-3-phenoxybenzyl (lS,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2- dimethylcyclopropane- carboxylate ("The Racemate", as disclosed in UK Patent Application No. 2161804-A) and (S)-a-cyano-4-fluoro-3-phenoxybenzyl (lR,cis)-3-(Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2- -dimethylcyclopropanecarboxylate ("The Active Isomer") were assessed against a number of insect species using a general method in which the test compound and a standard chemical were applied to the pest on a suitable medium at a number of application rates, and mortalities assessed after a specific time interval appropriate to the pest under investigation; each application was replicated five times.These data were analysed statistically to generate LC50 values (the application rate at which 50% mortality was achieved) for the test chemical and the standard, and the activity of the test chemical expressed as an LC50 Ratio, calculated according to the formula: LC Ratio = LC50 value of Test Chemical LC50 value of Standard The results are given in Table III below. In Table III, the test details are indicated by two letter codes which have the following meanings: TU: Tetranychus urticae (adults). Contact test assessed at 3 days after treatment. Standard chemical: cyhexatin.

HV: Heliothis virescens (lust instar larvae). Residual test assessed at 2 days after treatment. Standard chemical: lambda-cyhalothrin.

MD: Musca domestica (adults). Contact test assessed at 2 days after treatment. Standard chemical: cyhalothrin Comparison of the LC Ratio values observed for the Active Isomer with those observed for the Racemate demonstrates that the Active Isomer is up to 3.5 times more active than the Racemate: TABLE III Test Compound LC Ratio against Species: TU HV MD Racemate 0.44 1.93 2.23 Active Isomer 1.39 6.77 2.92 mean value from two tests

Claims (4)

1. CLAIMS 1. (S)-a-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z-2-chloro-3,3,3 trifluoroprop-1-en-1-yl)-2 , 2-dimethylcyclopropanecarboxylate, substantially free from other isomers of the same compound.
2. 2. A process for the preparation of the compound as claimed in claim 1 which comprises chromatographic separation of the diastereomeric mixture comprising (S)-a-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-
3. 3 (Z-2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclopropane- carboxylate and (R)-a-cyano-4-fluoro-3-phenoxybenzyl (1R,cis)-3-(Z- -2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclopropane carboxylate 3. An insecticidal composition comprising an insecticidally effective amount of the compound according to claim 1 in association with an insecticidally inert diluent or carrier.
4. 4. A method of combating insect pests at a locus which comprises applying to the locus an insecticidally effective amount of a composition according to claim 3.