GB1579724A - Alpha carboxylated benzyl esters and their use as insecticides - Google Patents

Description

(54) ALPHA CARBOXYLATED BENZYL ESTERS AND THEIR USE AS INSECTICIDES (71) We, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V., a company organised under the laws of the Netherlands, of 30 Carel van Bylandtlaan, The Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to alpha-carboxylated benzyl esters, to their preparation, and to compositions containing them for use as insecticides, acaricides and tickicides.

The present invention provides alpha-carboxylated-benzyl esters of the general formula:

0 0 C-YR Alo| Phenyl and their salts, wherein A is an optionally substituted aralkyl, alkyl or cycloalkyl group, Y is an oxygen or sulphur atom and R is alkyl, alkenyl, alkynyl, alkaryl, aralkyl, aryl, hydrogen, or a salt-forming cation.

Generally speaking, the alkyl, alkenyl, alkynyl groups represented by R preferably contain up to 7 carbon atoms and the aralkyl, alkaryl or aryl groups represented by R contain up to 10 carbon atoms. The salt-forming cation which R can also represent may be derived from an alkali metal, an alkaline earth metal, ammonia or a substituted ammonium compound.

It should be noted that optical isomers, cis-trans isomers and other kinds of geometric isomers of the compounds according to the general formula I are within the scope of the present invention as well as racemates and mixtures of isomers of one or more of the compounds according to the general formula I.

When A represents an optionally substituted cycloalkyl group in general formula I, the preferred compounds are those containing a cyclopropyl group of formula:

wherein Ra and Rb both represent a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms, especially methyl, or a halogen, especially chlorine, atom; or Ra and Rb together represent an alkylene group having from 2 to 6, especially 3, carbon atoms; or Ra represents a hydrogen atom and Rb represents an alkenyl group having from 2 to 6 carbon atoms, especially an isobutenyl group, or an haloalkenyl group having from 2 to 6 carbon atoms and from 1 to 3 chlorine or bromine atoms, especially a mono- or dichlorovinyl group; Rc and R( both represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, especially methyl, or Rc is hydrogen and Rd is an alkenyl group having from 2 to 6 carbon atoms, especially an isobutenyl group, or an haloalkenyl group having from 2 to 6 carbon atoms and from 1 to 3 chlorine or bromine atoms, especially a mono- or dichlorovinyl group; or Rc and Rd together represent an alkylene group having from 2 to 6, especially 3 carbon atoms.

When A represents an optionally substituted aralkyl group in general formula I, preferred compounds are those containing a substituted benzyl group of general formula:

wherein Z represents a halogen, preferably chlorine, atom, or an alkoxy group of 1 to 4 carbon atoms, e.g. methoxy, and Q represents an alkyl group of 1 to 6 carbon atoms, especially a branched chain group such as an isopropyl group.

When A represents an optionally substituted alkyl group in general formula I it preferably contains up to 6 carbon atoms; examples of suitable optional substituents are halogen, preferably chlorine, atoms, and alkoxy group of up to 6 carbon atoms. Examples of particular preferred compounds according to the present invention are: alpha-methoxycarbonyl-3-phenoxybenzyl 2,2,3,3-tetramethyl cyclopropane carboxylate; alpha-methylthiocarbonyl-3-phenoxybenzyl 2,2,3,3-tetramethyl cyclopropane carboxylate; alpha-methoxycarbonyl-3-phenoxybenzyl 2,2-dichlorovinyl-3 ,3-dimethylcyclopropane carboxylate; alpha-methylthiocarbonyl-3-phenoxybenzyl 2,2-dimethylvinyl-3,3-dimethylcyclopropane carboxylate; 2-(4-chlorophenyl)-2-isopropylacetic acid, alpha-methoxycarbonyl 3-phenoxybenzyl ester; alpha-2-butylthiocarbonyl-3-phenoxybenzyl 2,2,3,3-tetramethyl-cyclopropane carboxylate, The process for the preparation of the novel compounds of the invention may be carried out by known methods. Thus the novel compounds of formula I wherein Y is a sulphur atom may be prepared by a process which comprises reacting the corresponding alpha-cyanobenzyl ester of formula:

II I 0 Phenyl A--CC--O-CK c-o-/ wherein A has the meaning defined for formula I, with a thiol of formula R-SH in the presence of excess anhydrous hydrogen halide, preferably hydrogen chloride and subsequently treating the product formed with a hydrolysing agent. A suitable hydrolysing agent may be water or a dilute aqueous solution of an alkali such as potassium carbonate.

The reaction is suitably carried out in an inert solvent, for example an ether such a diethyl ether or dioxan and may be effected at temperatures below about 5"C, preferably 0 C.

Those compounds of the invention wherein R is other than hydrogen or a salt- arming cation and oxygen atom may also be prepared from the corresponding alpha-cyan,benzyl ester of formula IV by a process which comprises reacting the said ester with an alcohol of formula R-OH in the presence of excess anhydrous hydrogen halide, preferably the chloride and subsequently treating the product formed with a hydrolying agent.

Alternatively the compounds of the invention wherein Y is an oxygen atom may be prepaied by a process which comprises reacting a corresponding alpha-thioamidobcnzyl ester of formula

wherein A has the meaning defined in formula I, with a halide of formula R -halide, preferably an iodide, in the presence of acetonitrile. The reaction may be effected at room temperature over a period of 4 to 6 days. The reaction mixture may be worked up in any conventional way.

The alpha-carboxylated-benzyl esters of the invention are of interest as pesticides, in particular as insecticides, tickicides and acaricides for agricultural and domestic outlets. The invention therefore includes within its scope pesticidal compositions comprising a carrier and/or a surface-active agent together with, as active ingredient, an alpha-carboxylatedbenzyl ester of formula I. The invention also includes a method of combating insect, tick and/or acarid pests at a locus which comprises applying to the locus a pesticidally effective amount of an alpha-carboxylated-benzyl ester of the invention or composition containing such a compound.

The term 'carrier' as used herein means a material, which may be inorganic or organic and of synthetic or natural origin, with which the active compound is mixed or formulated to facilitate its application to the plant, seed, soil or other object to be treated, or its storage, transport or handling. The carrier may be a solid dr a liquid. Any of the materials usually applied in formulating pesticides, herbicides, or fungicides may be used as the carrier.

Suitable solid carriers are natural and synthetic clays and silicates, for example natural silicas such as diatomaeious earths; magnesium silicates, for example, talcs; magnesium aluminium silicates, for example, attapulgites and vermiculites; aluminium silicates, for example, kaolinites, montmorillinites and micas; calcium carbonates; calcium sulphate; synthetic hydrated silicon oxides and synthetic calcium or aluminium silicates; elements for example, carbon and sulphur; natural and synthetic resins such as, for example coumarone resins, polyvinyl chloride and styrene polymers and copolymers; solid polychlorophenols; bitumen; waxes such as for example, beeswax, paraffin wax, and chlorinated mineral waxes; and solid fertilisers, for example superphosphates.

Suitable liquid carriers are water, alcohols, for example, isopropanol and glycols; ketones for example, acetone, methyl ethyl ketone, and cyclohexanone; ethers; aromatic hydrocarbons, for example, benzene, toluene and xylene petroleum fractions, for example, kerosine and light mineral oils; chlorinated hydrocarbons, for example, carbon tetrachloride, perchloroethylene, trichloroethane; and liquefied normally vaporous, gaseous compounds. Mixtures of different liquids are often suitable.

The surface-active agent may be an emulsifying agent or a dispersing agent or a wetting agent; it may be nonionic, or ionic. Any of the surface-active agents usually applied in formulating pesticides herbicides or fungicides, may be used. Examples of suitable surface-active agents are the sodium or calcium salts of polyacrylic acids and lignin sulphonic acids; the condensation products of fatty acids or aliphatic amines or amides containing at least 12 carbon atoms in the molecule with ethylene oxide and/or propylene oxide; tatty acid esters of glycerol, sorbitan, sucrose or pentaerythritol; condensates of these with ethylene oxide and/or propylene oxide; condensation products of fatty alcohols or alkyl phenols for example p-octylphenol or p-octylcresol, with ethylene oxide and/or propylene oxide; sulphates or sulphonates of these condensation products; alkali or alkaline earth metal salts, preferably sodium salts, or sulphuric or sulphonic acid esters containing at least 10 carbon atoms in the molecule, for example, sodium lauryl sulphate, sodium secondary alkyl sulphates, sodium salts of sulphonated castor oil, and sodium alkylaryl sulphonates such as sodium dodecylbenzene sulphate; and polymers of ethylene oxide and copolymers of ethylene oxide and propylene oxide.

The compositions of the invention may be formulated as wettable powders, dusts, granules, solutions, emulsifiable concentrates, emulsions, suspension concentrates and aerosols. Wettable powders are usually compounded to contain 25, 50 and 75% of toxicant and usually contain, in addition, to solid carrier, 31-0% w of a dispersing agent and, where necessary, 0.10% w of stabiliser(s) and/or other additives such as penetrants or stickers.

Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant, and are diluted in the field with further solid carrier to give a composition usually containing 2-10% w of toxicant. Granules are usually prepared to have a size between 10 and 100 BS mesh (1,676-0.152 mm), and may be manufactured by agglomeration or impregnation Techniques. Generally, granules will contain 2-25% w toxicant and 0-10% w of additives such as stabilisers, slow release modifiers and binding agents. Emulsifiable concentrates usually contain, in addition to the solvent and, when necessary, co-solvent. 10-50 w toxicant, 2-20% w/v emulsifiers and 0-20% w/v of appropriate additives such a. stabilisers, penetrants and corrosion inhibitors.

Suspension concentrates are compounded so as to obtain a stable, non-sedimenting flowable product and usually contain 10-75% w toxicant, 0.5-15% w of dispersing agents, 0.1-10% w of suspending agents such as protective colloids and thixotropic agents, 0-10% w of appropriate additives such as defoamers, corrosion inhibitors, stabilisers, penetrants and stickers, and as carrier, water or an organic liquid in which the toxicant is substantially insoluble; certain organic solids or inorganic salts may be dissolved in the carrier to assist in preventing sedimentation or as antifreeze agents for water.

Aqueous dispersions and emulsions, for example, compositions obtained by diluting a wettable powder or a concentrate according to the invention with water, also lie within the scope of the present invention. The said emulsions may be of the water-in-oil or the oil-in-water type, and may have a thick 'mayonnaise' -like consistency.

The compositions of the invention may also contain other ingredients, for example, other compounds possessing pesticidal, herbicidal or fungicidal properties.

The invention is further illustrated in the following examples.

EXAMPLE I alpha-isopropylthiocarbonyl-3-phenoxybenzyl 2,2,3, 3-tetratnethyl cyclopropanecarboxylate.

Dry hydrogen chloride gas was bubbled through a solution of isopropylthiol (10 ml) and 3-phenoxy-alpha-cyanobenzyl 2,2,3 ,3-tetramethylcyclopropanecarboxylate (3g) in ether (100 ml) at 0 C for 4 hours. The cold solution was then added with care to a stirred 40% potassium carbonate solution (100 ml) and the mixture stirred vigorously for 4 hours at 30"C. The ethereal layer was separated, dried over magnesium sulphate and the solvent removed under reduced pressure. The residue was purified by column chromatography on silica gel using a 1:7 mixture of ether in hexarre as eluent. The required product was obtained as an oil nrl95 1.5490.

Analysis : Calculated for 5H3004S : C 70.4; H7.1% Found : C 70.8 ; H 7.2% EXAMPLE 2 alpha-Methylthiocarbonyl-3-phenoxybenzyl 2,2-dichlorovinyl-3, 3-dimethylcyclopropane- carb oxylate Alpha-thioamido-3-phenoxybenzyl 2,2-dichlorovinyl-3, 3-dimethylcyclopropanecarboxylate (4g) and methyl iodide (8g) was dissolved in acetonitrile (30 ml) and the solution left to stand under atmospheric conditions for 5 days. The solution was decanted from th ammonium iodide crystals which precipitated and the solvent removed under reduced pressure. The residue was purified by chromatography on silica gel using a 1:1 mixture of dichloromethane in hexane as eluent. The required product was obtained as an oil n?0 1.5777.

Anaylsis: Calculated for C23H2204S Cl2 : C 59.4 ; H 4.8 ; Cl 15.2% Found : C 59.7 ; H 4.8 ; Cl 14.8% EXAMPLE 3 Alpha-methylthiocarbonyl-3-phenoxybenzyl alpha'-isopropyl-4-methoxy benzylcarboxy- late A solution of alpha-cyano-3-phenoxybenzyl alpha'-isopropyl-4-methoxybenzylcarboxylate (2.0g) and methylthiol (20 ml) in ether (150 ml) was cooled to -5 C and dry hydrogen chloride bubbled through the solution for 4 hours. Water (100 ml) was added carefully to the reaction mixture and the ethereal layer was separated and dried over magnesium sulphate. The solvent was removed to give a pale yellow oil which was purified by chromatography on silica gel using a 4:1 mixture of hexane: ether. The required product was obtained as an oil, nD19.5 1.5708.

Analysis : Calculated for C27H28OsS : C 69.8 ; H 6.1% Found : C 69.0 ; H 6.4% EXAMPLES 4-11 Following procedures similar to those described in the foregoing Examples, further compounds were prepared and are described in Table I.

TABLE I Example Compound R.I. or Number m.p. Analysis 4 alpha-methoxycarbonyl-3-phenoxybenzyl 48-49 C Calculated for C23H26O5 C 72.3 ; H 6.9% 2,2,3,3-tetramethylcyclopropane Found C 72.6 ; H 6.9% carboxylate.

5 alpha-methylthiocarbonyl-3-phenoxybenzyl nD19 1.5505 Calculated for C23H26SO4 C 69.3 ; H 6.6% 2,2,3,3-tetramethylcyclopropane carboxylate Found C 69.5 ; H 6.6% 6 alpha-methoxycarbonyl-3-phenoxybenzyl nD19 1.5639 Calculated for C26H25ClO5 C 68.9 ; H 5.6% alpha'-isopropyl-4-chlorobenzylcarboxylate Found C 68.9 ; H 5.6% 7 alpha-methoxycarbonyl-3-phebnoxybenzyl 2- nD19 1.5610 Calculated for C23H22Cl2O5 C 61.5 ; H 4.9% (2,2-dichlorovinyl)-3,3-dimethylcyclopropane Found C 61.7 ; H 5.0% carboxylate 8 alpha-methylthiocarbonyl-3-phenoxybenzyl nD20.5 1.5829 Calculated for C26H25ClSO4 :C 66.6 ; H 5.4 ; C17.6% alpha'-isopropyl-4-chlorobenzylcarbonylate Found : C 66.6 ; H 5.3 ; C17.2% 9 alpha-methylthiocarbonyl-3-phenoxybenzyl nD18.5 1.5622 Calculated for C25H28SO4 C 70.7 ; H 6.7% 2,2-dimethyl-3-isobutenylcyclopropane Found C 71.5 ; H 6.9% carboxylate Example Comopound R.I. or Analysis Number m.p.

10 alpha-but-2-ylthiocarbonyl-3-phenoxybenzyl nD18.5 1.5484 Calculated for C26H32SO4 C 70.9 ; H 7.3% 2,2,3,3-tetramethylcyclopropanecarboxylate Found C 712 ; H 7.4% 11 alpha-methylthiocarbonyl-3-phenoxybenzyl nD20 1.5295 Calculated for C24H30SO4 C 69.5 ; H 7.3% 2-methylheptan-3-ylcarboxylate Found : C 69.7 ; H 7.3% 12 alpha-methoxycarbonyl-3-phenoxybenzyl oil Calculated for C20H22O5 C 70.2 ; H 6.4% propionate Found C 69.7 ; H 6.4% 13 alpha-methoxycarbonyl-3-phenoxybenzyl oil Calculated for C17H13Cl3O5 C 50.8 ; H 2.7% trichloroacetate Found C 50.1 ; H 3.2% 14 alpha-methoxycarbonyl-3-phenoxybenzyl 51-52 C Calculated for C17H16O5 C 68.0 ; H 5.4% acetate Found C 68.4 ; H 5.8% 15 alpha-methoxycarbonyl-3-phenoxybenzyl oil Calculated for C19H20O5 C 69.5 ; H 6.1% 2-methylpropionate Found C 69.4 ; H 5.9% Example Compound R.I. or Analysis Number m.p.

16 alpha-methylthiocarbonyl-3-phenoxybenzyl oil Calculated for C20H22O4S : C 67.0 ; H 6.2% valerate Found C 68.1 ; H 6.7% 17 alpha-methylthiocarbonyl-3-phenoxybenzyl oil Claculated for C20H22O4S C 67.0 ; H 6.2% isovalerate Found C 67.4 ; H 6.1% 18 alpha-methylthiocarbonyl-3-phenoxybenzyl oil Calculated for C19H18O4S C 66.7 ; H5.3% cyclopropylcarboxylate Found C 66.7 ; H 5.2% 19 alpha-methylthiocarbonhl-3-phenoxybenzyl 45-7 C Claculated for C23H28O4S : C 69.0 ; H 7.1% 2-isopropyl-3-methylbutanoate Found C 69.5 ; H 7.6% 20 alpha-methylthiocarbonyl-3-phenoxybenzyl oil Calculated for C21H22O4S C 68.1 ; H 6.0% 2,2-dimethylcyclopropyl-1-carboxylate Found C 67.7 ; H 6.0% EXAMPLE 21 The insecticidal and tickicidal activity of the compounds according to the present invention was assessed employing the following pests: insects : Musca domestica (M.d.) Phaedon cochleariae (P.c.) Megoura viciae (M.v.) Spodoptera littoralis (S.l.) Heliothis zea (H.z.) Ticks : Boophilus microphus (B.m.) The test methods employed for each species appear below: (i) Musca domestica (M.d.). A 0.4% by weight solution in acetone of the compound to be tested was prepared and taken up in a micrometer syringe. Two to three day old adult female houseflies (Musca domestic) were anaesthetized with carbon dioxide, and 1 Ill of the test solution was applied to the ventral side of the abdomen of each fly, 20 flies being tested. The treated flies were held in glass jars covered with paper tissue held by an elastic band. Cotton-wool pads soaked in dilute sugar solution were placed on top of the tissue as food. After 24 hours the percentage of dead and moribund flies were recorded.

(ii) Phaedon cochleariae (P.c.) and Megoura viciae (M.v.). The compounds were formulated as solutions or suspensions in water containing 20% by weight of acetone and 0.05% by weight of Triton X-100 ("TRITON" is a registered Trade Mark) as wetting agent.

The formulations contained 0.4% by weight of the compound to be tested. Turnip and broad bean plants, trimmed to one leaf each, were sprayed on the undersurface of the leaf with the above formulation. Spraying was effected with a spraying machine, delivering 340 litrcs per hectarc, the plants passing under the spray on a moving belt. After spraying, the plants were left for --1 hour drying period and then each plant was enclosed within a 450 ml bottle from which the bottom had been removed. Ten adult 2-3 week old mustard beetles (Phaedon cochteariae) were placed on the sprayed leaf of each turnip plant and ten apterous (6 day old) vetch aphids (Megoura viciae) were placed on the sprayed leaf of each broad bean plant. The opcn ends of the bottle were then closed with squares of paper tissue held with elastic bands. Mortality counts were made after 24 hours.

(iii) Spodoptera littoralis (S.l.). Pairs of leaves were removed from broad bean plants and placed on filter paper inside plastic petri dishes. The leaves were sprayed as in (ii), using the same concentrations. After spraying the leaves were left for 2-1 hour drying period and then each leaf pair was infested with ten larvae of the Egyptian cotton leafworm (Spodoptera littoralis). After 24 hours the percentage of dead and moribund larvae were recorded.

(iv) Boophilus microplus (B.m.). The compounds to be tested were formulated as solutions or fine suspensions in acetone containing 10% by weight of polyethylene glycol having an average molecular weight of 400. The formulations contained 0.1% by weight of the compound to be tested. 1 ml of the above-mentioned solution was applied evenly to a filter paper situated inside a petri dish. After the paper was sufficiently dry it was folded in half and partly crimped along the outer edge to form a packet. About 80-100 larval ticks (Boophilus microplus) were transferred into the packet which was then sealed completely.

The packets were placed inside an incubator, maintained at 27"C and 80% relative humidity, before assessing mortality 24 hours later.

(v) Heliothis Zea (H.z.) A 0.2% by weight solution of the compound to be tested was prepared by adding 2 ml of a 1% to acetone solution to 8 ml of 0.05% AHOX 1045A solution.

The cut broad bean plant was sprayed with 4 ml of test solution using a hand sprayer.

Immcdiately after spraying 5 larvae of the corn earworm (Heliothis zea) were transfered to each plant which was inserted into water through the centre hole of a test board and covered with a wire scrcen. 44-46 hours after spraying the percentage of dead and moribund larvae were recorded.

The results of those tests are shown in Table Il in which the test species ae identified by the initials noted above and A denotes complete kill, B some kill and C no kill of the tests species.

EXAMPLE 13 The acaricidal activity of the compounds according to the invention was assessed employing the following pest: Tetranychus urticae (T.u.) The test method employed was a follows. Leaf discs cut from french bean plants were innoculated with 10 red spider mites in the manner described in Example 12 for the insects Phaedon cochleariae and Megoura viciae 1 hour after drying. Mortality counts were made 24 hours after innoculation. The results of these tests are shown in Table III employing the same notation as used in the previous example.

TABLE II Compound Example No. M.d. P.d. S.1. M.v. B.m. H.z.

1 A 2 A B A A A A 4 B A B B A A 5 A B A A A A 6 B A A A A A 7 A A A A A A 8 A C A A A A 9 A B B A A A 10 C C B A A A 11 A TABLE III Acaricidal Activity Compound of T.u.

Example No.

Claims (14)

5 B 8 B WHAT WE CLAIM IS:

1. Alpha-carboxylated-benzyl esters of the general formula:

o O C-YR I C-yR-Ye I - eny A----O-CH and their salts, wherein A is an optionally substituted aralkyl, alkyl or cycloalkyl group, Y is an oxygen or sulphur atom and R is alkyl, alkenyl, alkynyl, alkaryl, aralkyl, aryl, hydrogen, or a salt-forming cation.

2. Esters according to claim 1 wherein R represents alkyl, alkenyl, alkynyl groups containing up to 7 carbon atoms or an aralkyl, alkaryl or aryl group containing up to 10 carbon atoms or a salt-forming cation derived from an alkali metal, an alkaline earth metal, ammonia or a substituted ammonium compound.

3. Esters according to claim 1 or 2 wherein A represents an optionally substituted cyclopropyl group of formula

wherein Ra and Rb both represent a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms or a halogen atom; or Ra and Rb together represent an alkylene group having from 2 to 6 carbon atoms; or Ra represents a hydrogen atom and Rb represents an alkenyl group having from 2 to 6 carbon atoms or an haloalkenyl group having from 2 to 6 carbon atoms and from 1 to 3 chlorine or bromine atoms; Kc and Kd both represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or Re is hydrogen and Rd is an alkenyl group having from 2 to 6 carbon atoms or an haloalkenyl group having from 2 to 6 carbon atoms and from 1 to 3 chlorine or bromine atoms; or Re and Rd together represent an alkylene group having from 2 to 6 carbon atoms.

4. Esters according to claim 1 or 2 wherein A represents a substituted aralkyl group of formula:

wherein Z represents a halogen atom, or an alkoxy group of 1 to 4 carbon atoms and Q represents an alkyl group of 1 to 6 carbon atoms.

5. Esters according to claim 1 or 2 wherein A represents an alkyl group of up to 6 carbon atoms optionally substituted by halogen or alkoxy.

6. Esters according to any one of the preceding claims specifically mentioned herein.

7. A process for the preparation of the compounds of formula I wherein Y is a sulphur atom which comprises reacting the corresponding alpha-cyanobenzyl ester of formula:

o CN Phenyl ^-c-o-uX wherein A has the meaning defined for formula I, with a thiol of formula R-SH in the presence of excess anhydrous hydrogen halide and subsequently treating the product formed with a hydrolysing agent.

8. A process for the preparation of compounds of formula I wherein R is other than hydrogen or a salt-forming cation and Y represents an oxygen atom which comprises reacting the corresponding alpha-cyanobenzyl ester of formula IV with an alcohol of formula R-OH in the presence of excess anhydrous hydrogen halide and subsequently treating the product formed with a hydrolysing agent.

9. A process for the preparation of compounds of formula I wherein Y is a sulphur atom which comprises reacting a corresponding alpha-thioamidobenzyl ester of formula:

C CSNW2 0 Phenyl II I A-c-O-C wherein A has the meaning defined in formula I, with a halide of formula R-halide in the presence of acetonitrile.

10. A process for the preparation of esters of formula I substantially as herein before described and with reference to the Examples.

11. Esters prepared according to any one of the processes claimed in claims 7 to 10.

12. Pesticidal composition comprising a carrier and/or a surface active agent and, as active ingredient, an alpha-carboxylated benzyl ester as claimed in any one of claims 1 to 6 or 11.

13. Pesticidal composition according to claim 12 substantially as hereinbefore described and with reference to the Examples.

14. A method of combating insect, tick and/or acarid pests at a locus which comprises applying to the locus a pesticidally-effective amount of an alpha-carboxylated-benzyl ester claimed in any one of claims 1 to 6 or 11 or composition containing such a compound claimed in claim 12 or 13.