GB2064528A

GB2064528A - Cyclopropane Carboxylic Acid Ester Derivatives

Info

Publication number: GB2064528A
Application number: GB8037693A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1979-11-27
Filing date: 1980-11-25
Publication date: 1981-06-17
Also published as: IT1134448B; IE802442L; NZ195637A; OA06708A; RO80004A; DE3044391A1; DD154973A5; GB2064528B; SE453079B; BG42352A3; SE8008254L; IN155143B; AU6467780A; ES497098A0; DK501880A; YU41954B; BR8007688A; FR2470117A1; CS219296B2; ES8201940A1

Abstract

There is provided a compound of formula <IMAGE> wherein R<1> and R<2> are each independently selected from chlorine, bromine and methyl, in the form of a 1:1 mixture of the 1RcisS- and 1ScisR- isomers substantially free of 1ScisS- and 1RcisR-isomers, processes for preparing such compounds, and their use as pesticides. Compounds according to the invention contain up to four times as much of the most active isomer of the compound of formula I as a compound containing equal amounts of all eight possible isomers, and they are readily prepared by routes which do not involve any stereospecific synthesis or optical resolution steps.

Description

SPECIFICATION Cyclopropane Carboxylic Acid Ester Derivatives This invention relates to cyclopropane carboxylic acid ester derivatives, their preparation and their use as pesticides.

Cyclopropane carboxylic acid ester derivatives of general formula

wherein R1 and R2 are independently selected from chlorine, bromine and methyl, are known compounds having pesticidal activity, see for example UK Patent Specification No. 1,413,491 or US Patent No. 4,024,163. These derivatives are members of a class of pesticidal compounds commonly referred to in the art as "pyrethroid insecticides." Compounds of formula I contain two centres of asymmetry in the cyclopropane ring of the acid moiety and a third centre of asymmetry in the alcohol moiety, leading to the existence of eight possible isomers.In general, superior pesticidal activity resides among the compounds having cis-configuration about the cyclopropane ring, as disclosed by Itaya et al in "Synthetic Pyrethroids," ACS Symposium Series 42, Pages 45 to 54, and the isomer which has the greatest pesticidal activity is generally that isomer which is conveniently designated the 1 RcisSisomer, 1 Rcis- designating configuration in the acid moiety and S-designating configuration in the alcohol moiety, as described by Elliott eft at in Nature, Vol. 248, Pages 710 and 711(1974).

Attempts to produce 1 RcisS- single isomers rest either on synthesis routes which inherently produce intermediates containing the cyclopropane carboxylic acid moiety in exclusively 1 Rcisconfiguration or on a route which involves an optical resolution step to separate 1 Rcis- compounds from 1 Scis- compounds. Esterification of a 1 Rcis- intermediate to produce a derivative of formula I above leads to production of a mixture of 1 RcisR- and 1 RcisS- end products. Separation of these end products is possible by physical methods, at least in theory, since the 1 RcisR- and 1 RcisS- compounds are not enantiomers.However, although such separation of 1 RcisR and 1 RcisS- compounds has proved to be relatively readily attainable when R1 and R2 are both bromine atoms, it has proved to be more difficult and more costly in other cases, for example when R1 and R2 are both chlorine atoms.

There has now surprisingly been discovered a novel compound which contains weight for weight, up to four times as much of the most pesticidally active ( 1 RcisS-) isomer of a compound of formula I as a compound containing equal weights of all eight isomers of formula I. This novel compound has the advantage that it may be readily and relatively cheaply prepared, by a route which does not involve any asymmetric synthesis or optical resolution step.

This invention provides a compound of formula

wherein R1 and R2 are each independently selected from chlorine, bromine and methyl, in the form of a 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers substantially free of 1 ScisS- and 1 RcisR- isomers.

Compounds of the invention wherein R1 and R2 are both halogen atoms are preferred and R' and R2 are preferably both chlorine atoms.

According to a preferred embodiment of the invention there is provided a compound which comprises a 1:1 mixture of 1 RcisS- and 1 ScisF- isomers of a-cyano-3-phenoxybenzyl 3-(2,2dichlorovinyl)-2,2-dimethylcyclopropane carboxylate in the form of a crystalline solid having a melting point of at least 750C. Advantageously the melting point is at least 800C and is preferably in the range 84 to 870C.

Compounds of the invention may be prepared by a process which comprises treating a mixture of the 1 RcisS-, 1 S-cisS-, 1 RcisR- and 1 ScisR- isomers of a compound of formula I with a solvent, and separating off a 1:1 mixture of the 1 RcisS- and 1 ScisR-isomers substantially free of 1 RcisR- and 1 ScisS- isomers as a crystalline solid from a solution of the compound of formula I which contains 1 ScisS- and 1 RcisR- isomers.

The process may conveniently be effected by cooling a solution of the mixture of 1 RcisS-, 1 ScisS-, 1 RcisR- and 1 ScisR- isomers.

Alternatively, the process may in at least some cases be effected by contacting the mixture of 1 Rc1sS-, 1 ScisS-, 1 RcisR- and 1 ScisR- isomers with the solvent at or below ambient temperature and separating the residual solid crystalline 1:1 mixture of 1 RcisS- and 1 ScisR- isomers from the resulting solution which contains 1 ScisS- and 1 RcisR- isomers.

The solvent used should be one in which the 1 RcisS-ll ScisR- enantiomer pair is substantially less soluble than the 1 ScisS-/1 RcisR- enantiomer pair.

Suitable solvents include the lower liquid alkanes of up to 8 carbon atoms, for example pentane or the petroleum ethers from 30/50 petroleum ether to 100/120 petroleum ether, preferably 40/60 or 60/80 petroleum ether; and the liquid C14 alkanols such as isopropanol.

Crystallisation of the 1 RcisS-/1 ScisR- enantiomer pair may be effected at a temperature in the range -500C to 200C, preferably OOC to 1 OOC, depending on the concentrations of the various present isomers.

Separation and recovery of the crystalline compound of the invention from the supernatant solution, which contains 1 ScisS- and 1 RcisR- isomers, may be effected by methods such as filtration, centrifugation or decantation.

The solution of the compound of formula I which contains 1 ScisS- and 1 RcisR- isomers is a useful raw material for the preparation of additional amounts of compound according to the invention. It has been further discovered that, on treatment with a suitable base, under appropriate conditions racemisation may take place at the carbon atom of the alcohol moiety in the compound of formula I, so that a proportion of the 1 ScisS- and 1 RcisR- isomers in the solution may be converted into 1 ScisRand 1 RcisS- isomers respectively, and additional amounts of compound according to the invention may be isolated as described above.

Accordingly, the preferred process of the invention further comprises treating the solution of the compound of formula i which contains 1 ScisS- and 1 RcisR- isomers with a base, and separating off from the solution a 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers, during or after the treatment with the base.

If in the preferred process of the invention the mixture of the 1 RcisS-, 1 ScisS-, 1 RcisR- and 1 ScisR- isomers is completely dissolved in the solvent, and the resulting solution contains equal quantities of all four cis-isomers, at least some of the 1 RcisS- and 1 ScisR- isomers are separated from the solution in the form of a 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers substantially free of 1 RcisR- and 1 ScisS- isomers as a crystalline solid before or during the treatment with the base.

Suitable bases for use in the process of the invention include ammonia, primary, secondary and tertiary amines, alkali metal hydroxides, alkali metal carbonates, alkali metal alkoxides, and basic ion exchange resins. Preferred amine bases contain one or more C14 alkyl and/or benzyl groups, or are alkylene diamines of up to 4 carbon atoms, for example ethylenediamine, or are heterocyclic amine bases having 5 or 6-ring atoms and containing the nitrogen atom and optionally an oxygen, a sulphur or an additional nitrogen atom attached to carbon atoms in the ring, for example pyrrolidine, morpholine or piperidine.

If desired, the preferred process of the invention may be effected in two separate steps, optionally in two different locations. For example the treatment with the base may be effected at an elevated temperature, for example a temperature in the range of from 200C to 1 000C, preferably 200C to 600 C, for fast racemisation,followed by cooling to effect crystallisation of the 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers as described above. If the base is present in solution, both steps of the process may be effected in a single reaction zone, or the elevated temperature step may be effected in one reaction zone and the crystallization step may be effected in another reaction zone.

However, the base may be in the solid phase, e.g. a basic ion exchange resin, for example those sold under the trade names Dowex and Amberlite such as Dowex AGIX 8, Amberlite IRA 400 or Amberlite 1 R 45, or solid potassium carbonate, and the process may be effected under anhydrous conditions, optionally in the presence of a C14 alkanol such as methanol, with the base in one reaction zone, for example a packed column, for the elevated temperature step, the solution of isomers of the compound of formula I being removed to another reaction zone for the crystallisation step.

When the base is present in solution in the preferred process of the invention and both steps of the process are effected in a single reaction zone, the treatment with the base and crystallisation of the 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers may be effected simultaneously at a temperature in the range -500C to 200 C, preferably OOC to 200C. In such a simultaneous base treatment and crystallisation process, the 1 RcisS- and 1 ScisR-isomers are continuously removed from solution by crystallisation so that the supernatant solution is always rich in 1 ScisS- and 1 RcisR- isomers and racemisation is always able to occur. Accordingly, in such a process the starting material may be a racemic mixture of all four cis-isomers of the compound of formula I which is introduced directly into the reaction zone. The 1 ScisS- and 1 RcisR- isomers will dissolve more readily to give a solution which is rich in those isomers. Racemisation then occurs and the 1:1 mixture of 1 RcisS- and 1 ScisR- isomers crystallises out of solution continuously until substantially all of the 1 ScisS- and 1 RcisR- isomers have dissolved and a final equilibrium has been reached. Additional quantities of the racemic mixture of all four cis-isomers may be added continuously or in discreet portions throughout the time span of such a process.

When the preferred process of the invention is not being effected with a base in the solid phase, it is preferred for the base to comprise ammonia, a primary, secondary or tertiary amine, or an alkali metal carbonate, preferably sodium or potassium carbonate, in aqueous solution.

It has been found that the rate of racemisation may be enhanced when the solution of the 1 ScisS- and 1 RcisR- isomers of the compound of formula I is treated with the base in the presence of a C14 alkanol, for example methanol. The rate of racemisation may also be enhanced when the solution is treated with the base in the presence of a phase-transfer catalyst. The phase-transfer catalyst is preferably a quaternary ammonium halide. The substituents in the quaternary ammonium halide are for example C14 alkyl groups and/or benzyl groups. Preferred quaternary ammonium halides are tetrabutyl ammonium and benzyl triethyl ammonium chlorides and bromides.

The compounds of the invention contain a high proportion of the most pesticidally-active isomer of the relevant compound of formula I. The invention therefore also provides a pesticidal composition which comprises a compound of formula I in accordance with the invention as defined above in association with a suitable carrier therefor, the composition being substantially free of 1 ScisS- and 1 RcisR- isomers of the compound of formula I. The invention further provides a method of combating pests, e.g. insect or acarid pests, at a locus which comprises applying to the locus a compound of formula I in accordance with the invention or a composition in accordance with the invention.

A carrier in a composition of the invention may be a solid or a liquid, including a material which is normally gaseous but which has been compressed to form a liquid, inorganic or organic, and of synthetic or natural origin. The active ingredient is suitably formulated with at least one carrier to facilitate its application to the locus, for example plants, seeds or soil, to be treated, or to facilitate storage, transport or handling.

Preferably a composition of the invention contains at least two carriers, at least one of which is a surface-active agent. The surface-active agent may be an emulsifier, a dispersing agent or a wetting agent. It may be non-ionic or ionic. Pesticidal compositions are generally formulated and transported in a concentrated form which is subsequently diluted by the farmer or other user before application. A surface-active agent facilitates this process of dilution.

Any of the carriers commonly used in the formulation of pesticides may be used in the compositions of the invention, and suitable examples of these are to be found, for example, in British Patent Specification No. 1,232,930.

The composition of the invention may for example be formulated as a wettable powder, microcapsules, a dust, granules, a solution, an emulsifiable concentrate, an emulsion, a suspension concentrate or an aerosol. The composition may have controlled release properties, or may be suitable for use as a bait.

Wettable powders usually contain 25, 50 or 75% w of active ingredient and may contain, in addition to inert solid material, 310% w of a dispersing agent and, where necessary, 0-10% w of a stabiliser, a penetrant and/or a sticker. A dust is usually formulated as a dust concentrate having a composition similar to that of a wettable powder but without a dispersant, and is diluted in the field witl further solid carrier to give a composition usually containing 1 0% w of active ingredient.

Granules usually have a size in the rangeoffrom 10to 100 BS mesh (1.676-0.152 mm) and may be manufactured by agglomeration or impregnation techniques. Generally, granules will contain T25% w active ingredient and 0-1 0% w of additives, for example a stabiliser, slow release modifier and/or a binding agent.

Emulsifiable concentrates usually contain, in addition to a solvent, and, when necessary, cosolvent, 1 0-50% w/v active ingredient, 220% w/v emulsifier and 0-20% w/v of other additives, for example a stabiliser, a penetrant and/or a corrosion inhibitor.A suspension concentrate is a stable, nonsedimenting, flowable product and usually contains 1075% w active ingredient, 0.5-1 5% w of dispersing agent, 0.110% w of suspending agent, for example protective colloid and for a thixotropic agent, and 0-1 0% w of other additives including, for example, a defoamer, a corrosion inhibitor, a stabiliser, a penetrant and/or a sticker, and as dispersant, water or an organic liquid in which the active ingredient is substantially insoluble; certain organic additives and/or inorganic salts may be dissolved in the dispersant to assist in preventing sedimentation or as anti-freeze for water.

The aqueous dispersions and emulsions formed by diluting a wettable powder or an emulsifiable concentrate of the invention with water, also lie within the scope of the present invention. Such dispersions and emulsions may be of the water-in-oil or of the oil-in-water type, and may have a thick "mayonnaise"-like consistency.

A composition of the invention may also contain other ingredients, for example, one or more other compounds possessing pesticidal, herbicidal or fungicidal properties, or attractants, for example pheromones or food ingredients, for use in baits and trap formulations.

The invention will be better understood from the following Examples.

Example 1 1:1 mixture of 1 RcisS- and 1 ScisR- Isomers of a-cyano-3-phenoxy-benzyl 3-(2,2-dichlorovinyl)2,2-dimethylcyclopropane Carboxylate by Crystallisation Process using Isopropanol 5.0 g of a racemic mixture of cis-isomers of cg-cyano-3-phenoxybenzyl 3-(2,2-dichlorovinyl)-2,2dimethylcyclopropane carboxylate was dissolved in 30 ml isopropanol with gentle warming. The resulting solution was cooled to 1000 and allowed to stand at that temperature for 20 hours.A precipitate settled out and was separated off by filtration to give 1.4 g of solid product in the form of colourless crystals, m.p. 77-81 00. High-performance liquid chromatography analysis showed the product to be a 90% pure 1:1 mixture of 1 RcisS- and 1 ScIsR- isomers of the starting material.

3.2 g of solid product obtained as above was recrystallised from pentane, yielding 2.0 g of a colourless crystalline solid, mp 84--880C. This product was shown by high-performance liquid chromatography analysis to be about 99% pure 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers of the starting material.

Example 2 1:1 Mixture of 1 RcisS- and 1ScisR- Isomers of a-cyano-3-phenoxy-benzyl 3-(2,2-dichlorovinyl)2,2-dimethylcyclopropane Carboxylate by Crystallisation Process using 40/60 Petroleum Ether 10 g of a racemic mixture of cis-isomers of a-cyano-3-phenoxybenzyl 3-(2,2-dichlorovinyl)-2,2dimethylcyclopropane carboxylate was dissolved in 1 50 ml 40/60 petroleum ether with gentle warming. The resulting solution was cooled to 200C and ailowed to stand at that temperature for 3 days. A colourless crystalline precipitate settled out and was isolated by filtration. The yield obtained was 3.3 g, had mp 79-81 C and was shown by high performance liquid chromatography to be a greater than 90% pure 1:1 mixture of 1 RcisS- and 1 ScisR- isomers of the starting material.

Portions of the product obtained in the above process were recrystallised once, twice and three times from 40/60 petroleum ether. The resulting products, which were all colourless crystalline solids had mp 83--860C, 84--860C and 86-870C, respectively and were shown by high performance liquid chromatography to be 99% pure, greater than 99.9% pure and 100% pure samples of the desired pair of isomers.

Example 3 1:1 Mixture of 1 RcisS- and 1 ScisR- Isomers of -cyano-3-phenoxy-benzyl 3-(2,2-dichlorovinyl)2,2-dimethylcyclopropane Carboxylate by Treatment of Solid Racemate with 40/60 Petroleum Ether 10 g of a racemic mixture of cis-isomers of -cyano-3-phenoxybenzyl 3-(2,2-dichlorovinyl)-2,2dimethylcyclopropane carboxylate was stirred with 75 ml 40/60 petroleum ether for 5 days at ambient temperature (2000). Filtration gave 4.1 g of colourless crystals, mp 81.5--830C, which were shown by high performance liquid chromatography to be about 97% pure 1:1 mixture of 1 RcAsS- and 1 ScisRisomers of the starting material.

By comparison with the products of Examples 1 to 3 above, it should be noted that 1 RcisS-cg- cyano-3-phenoxybenzyl 3-(2,2-dichlorovinyl)- 2,2-cyclopropane carboxylate and the 1 ScisRenantiomer both have mp 53--540C.

Example 4 1:1 Mixture of 1 RcisS- and 1 ScisR- Isomers of cr-cyano-3-phenoxybenzyl 3-(2,2-dibromovinyl)2,2-dimethylcyclopropane Carboxylate by Crystallisation Process using 60/80 Petroleum Ether 10.0 g of a racemic mixture of cis-isomers of a-cyano-3-phenoxybenzyl 3-(2,2-dibromovinyl)2,2-dimethylcyclopropane carboxylate was treated by a process similar to those of Examples 1 and 2 using 60/80 petroleum ether as solvent. Recrystallisation of the initial product yielded 3.8 g of colourless crystals, m.p. 93--97 OC, which were shown by high performance liquid chromatography to be an about 80% pure sample of the desired pair of isomers.A further two recrystallisations of this product yielded respectively 3.1 5 g and 2.7 g of colourless crystals, of m.p. 99-101 C and 100101 OC, which were shown by high performance liquid chromatography to contain greater than 95% and 99% respectively of the desired pair of isomers.

Example 5 1:1 Mixture of 1 RcisS- and 1 ScisR- Isomers of ct-cyano-3-phenoxybenzyl 3-(2-methylpropenyl)2,2-dimethylcyclopropane Carboxylate by Crystallisation Process using 40/60 Petroleum Ether 15.3 g of a racemic mixture of cis-isomers of cz-cyano-3-phenoxybenzyl 3-(2-methylpropenyl)2,2-dimethylcyclopropane carboxylate in the form of a colourless oil was treated by a process similar to those of Examples 1 and 2, using 40/60 petroleum ether as solvent. 5.75 g of initial colourless crystalline product had mp 60--660C and was shown by NMR analysis at 360 MHz to be a 90% pure 1:1 mixture of 1 RcisS- and 1 ScisR- isomers of the starting material. This initial product was recrystallised three times from 40/60 petroleum ether, yielding respectively 4.7 g, 4.3 g and 4.0 g of product having mp 65--700C, 69--720C and 70--720C. These products were shown by NMR analysis at 360 MHz to be 95% pure, 98% pure and greater than 99.5% pure 1:1 mixtures of the desired pair of isomers.

Example 6 1:1 Mixture of 1 RcisS- and 1 ScisR- Isomers of a-cyano-3-phenoxybenzyl 3-(2;2-dichlorovinyl)- 2,2-dimethylcyclopropane Carboxylate by Process using Isopropanol as Solvent 12.9 g of a racemic mixture of cis-isomers of a-cyano-3-phenoxybenzyl 3-(2,2-dichlorovinyl1- 2,2-dimethylcyclopropane carboxylate was dissolved in 52 ml isopropanol at 200 C, and 2.0 ml of eao solution of ammonia in water was added with stirring. After stirring at 200C for 21 hours, the reaction mixture was cooled and stirred at OOC to 50C for a further 4 hours.The precipitate which settled Out was filtered off, washed with 5 ml of isopropanol at 5 C and with 1 5 ml of 60/80 petroleum ether to give 5.1 g of solid product in the form of colourless crystals, mp 77--81 OC. High-performance liquid chromatography showed the product to be a 90% pure 1:1 mixture of 1 RcisS- and 1 ScisR- isomers of the starting material. Similar analysis of the filtrate showed the ratio of the concentrations of the 1 ScisS- and 1 RcisR- isomers to those of the 1 RcisS- and 1 ScisR- isomers to be about 3:2.

The filtrate and the washings from the above process sequence were concentrated, the resulting material was dissolved in 30 ml isopropanol and 2.0 ml of .880 solution of ammonia in water was added with stirring and the above process steps were repeated to yield a further 2.1 g of colourless crystals, mp 74--790C, which were shown by high-performance liquid chromatography to be a 85% pure 1:1 mixture of 1 RcisS- and 1 ScisR- isomers of the starting material. Similar analysis of the filtrate showed the ratio of the concentrations of the 1 ScisS- and 1 RcAsR- isomers to those of the 1 RcisS- and 1 ScisF- isomers to be about 4:1.

Example 7 1:1 Mixture of 1 RcisS- and 1ScisR- Isomers of a-cyano-3-phenoxybenzyl 3-(2,2-dichlorovinyl)2,2-dimethylcyclopropane Carboxylate by Process using 40/60 Petroleum Ether as Solvent 10 g of a racemic mixture of cis-isomers of a-cyano-3-phenoxybenzyl 3-(2,2-dichlorovinyl)-2,2dimethylcyclopropane carboxylate was stirred with 75 ml 40/60 petroleum ether and 1 ml of a 0.5 molar solution of sodium carbonate in a 1:1 v/v mixture of water and methanol containing 10% w/v tetrabutylammonium bromide. The reaction mixture was stirred for 5 days at ambient temperature (2000). Filtration gave 5.6 g of colourless crystals, mp 80--820C, which were shown by highperformance liquid chromatography to be a 96% pure 1:1 mixture of 1 RcAsS- and 1 ScAsR- isomers of the starting material. Similar analysis of the filtrate showed the ratio of the concentrations of the 1 ScisS- and 1 RcisR- isomers to those of the 1 RcisS- and 1 ScisR- isomers to be 3.4:1.

Claims

1. A compound of formula

2. A compound of Claim 1 wherein R1 and R2 are both chlorine atoms.

3. A compound which comprises a 1:1 mixture of 1 RcisS- and 1 ScisR- isomers of a-cyano-3- phenoxybenzyl 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate in the form of a crystalline solid having a melting point of at least 750C.

4. A compound according to Claim 1 substantially as hereinbefore described with particular reference to any one of the Examples.

5. A process for preparing a compound according to any one of Claims 1 to 3 which comprises treating a mixture of the 1RcisS-, 1S-cisS-, 1 RcisR- and 1 ScisR- isomers of a compound of formula I with a solvent, and separating off a 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers substantially free of 1 RcisR- and 1 ScisS- isomers as a crystalline solid from a solution of the compound of formula i which contains 1 ScisS- and 1 RcisR- isomers.

6. A process according to Claim 5 which comprises cooling a solution of the mixture of 1 RcisS-, 1 S-cisS-, 1 RcisR- and 1 ScisR-isomers.

7. A process according to Claim 5 which comprises contacting the mixture of 1 FcisS-, 1 ScisS-, 1 RcAsR- and 1 ScisR- isomers with the solvent at or below ambient temperature and separating the residual solid crystalline 1:1 mixture of the 1 RcisS- and 1 ScisF- isomers from the resulting solution which is rich in the 1 ScisS- and 1 RcisR- isomers.

8. A process according to Claim 5, 6 or 7 which further comprises treating the solution of the compourid of formula-I which contains 1 ScisS- and 1 RcisR- isomers with a base, and separating off from the solution a 1:1 mixture of the 1 RcisS- and 1 ScisR- isomers substantially free of 1 RcisR- and 1 ScisS- isomers, during or after the treatment with the base.

9 : A proceess-according to Claim 8 wherein the solution of the isomers of the compound of formula hontains a lower liquid alkane of up to 8 carbon atoms or a liquid C14 alkanol as solvent.

10.A process according to Claim 9 wherein the base comprises ammonia, a primary, secondary or tertiary~amine, or an alkali metal carbonate, in aqueous solution.

1 t. A process according to Claim 10 wherein the solution is treated with the base in the presence of a C1~4 alkanol.

12. A process according to Claim 10 or 11 wherein the solution is treated with the base in the presence of a phase-transfer catalyst.

13. A process according to Claim 5 substantially as hereinbefore described with particular reference to any one of the Examples.

14. A pesticidal composition which comprises a compound according to any one of Claims 1 to 4 in association with a suitable carrier therefor, the composition being substantially free of 1 ScisS- and 1 RcisR- isomers of the compound of formula I.

15. A method of combating pests at a locus which comprises applying to the locus a compound according to any one of Claims 1 to 4 or a composition according to Claim 14.