PESTICIDAL COMPOSITIONS

Abstract: Compositions for treating timber, especially timber to be exposed to the ground or to water, comprising creosote and a compound of formula I: wherein Z and Z¹ are the same or different and are each halo, halophenyl or haloalkyl, X is hydrogen or cy ano, and Y is hydrogen or a fluorine atom. The compositions are unusually stable and have a prolonged protective action against termites, beetles, mol­ uscs, woodworm and the like.

Description: It is known to use pesticides of the pyrethroid class to protect timber from attack by insects and other pests (see Japanese Patent Application No. 52-66603; 1975; Sumitomo "Chemical Abstracts", vol. 93, No. 1, July 1980, page 223, No: 22 16u; Record of the 1980 Annual Convention of the British Wood Preserving Association, page 54-64). However, pyrethroids are relatively expensive pesticides and this can be disadvantageous when a high volume, low cost material such as wood is being treated. Furthermore, pyrethroids are known to be short-lived when exposed to damp soil (see for example the Record of the 1980 Annual Convention of the British Wood Preserving Association, page 61), possibly by the degradation of the pyrethroids by soil microorganisms. The most commonly used timber-protecting pesticides, in many cases, are thus still relatively toxic but cheap compounds such as lindane (gamma-hexachlorocyclohexane). It has also been known for many years to use creosote to protect timber. Creosote has the advantage of being cheap, but wood treatment with creosote is unpleasant to handle, being oily and smelly. In addition, the creosote has to be applied to the timber in such quantities that it may later bleed out of the timber again and cause a fire hazard. One solution which has been adopted is to pretreat the timber with CCA (a mixture of copper, chromium and arsenic compounds) before treatment with creosote. However, CCA is fairly toxic, and a two-stage treatment process adds to the cost of the treated timber. It is not possible to mix CCA with creosote to give a single step process, as the mixture is not stable. Indeed, the problem of instability is encountered with many such mixtures. It has now suprisingly been found that mixtures of certain halogenated pyrethroid insecticides and creosote are relatively stable and have a relatively prolonged protective action even when the timber is exposed to damp soil or water. It was now found that pyrethroids are surprisingly stable in contact with the ground when applied to the timber in a composition comprising creosote and a compound of formula (I): Wherein: Z and Z' are the same or different and each is halo, halo-phenyl or haloalkyl; X is hydrogen or a cyano group; and Y is hydrogen or a fluorine atom. Structural formula (I) is intended to encompass all the geometric and optical isomers. More particularly the acid moiety of the ester may be selected from ,the (+)-cis-isomer, the (+)-trans-isomer, the (±)-cis-isomer, the (±)-trans-isomer and the (±)-cis, trans-isomer, the stereochemistry referring to that of the cyclopropane ring. Moreover, when X is cyano the alcohol moiety of the ester may be selected from the (+)-isomer, the (-)-isomer or the (±)-isomer. Particularly useful esters are those wherein Z and Z¹ are both selected from chloro and bromo. The preferred pyrethroids of this invention are: 3-phenoxybenzyl-(±)-cis,trans-2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropane-1-carboxylate (permethrin),(-)-α-cyano-3-phenoxybenzyl-(+)-cis-2,2-dimethyl-3-(2,2-dibromovinyl) cycloproprane-1-carboxylate (deltamethrin), and (S)-α-cyano-3-phenoxybenzyl-(1R, 3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylate (alphamethrin, 'FASTAC'), and α-cyano-3-phenoxybenzyl-2,2-dimethyl-3-(2-chloro-2-trifluoromethylvinyl)cyclopropane-1-carboxylate (cyhalothrin). Permethrin is particularly preferred. Conveniently, the ratio of permethrin to creosote is within the range 0.001: 99.999 to 99.99: 0.01. Preferably the said ratio is between 0.01: 99.99 and 5.0: 95.0, most preferably between 0.1: 99.90 and 0.5: 99.50. Corresponding ratios of other compounds of Formula I may be derived by comparing their insecticidal potencies with that of permethrin. Other insecticides, fungicides, preservatives, dyes, solvents and diluents may be added as desired, in which case the overall content of the pyrethroid is preferably about 0.01% to 1%, conveniently 0.1% to 0.5%. A composition to be used in accordance with the invention may be applied to timber to be protected by simply painting the composition onto the timber, or the timber may be sprayed or dipped into a bath of the composition. It is particularly preferred for the composition to be applied to the timber under high pressure. Instances where it is desirable to protect timber from attack by pests will be well known to the man skilled in the art, but particularly important applications include stakes or poles which are to be sunk partially or wholly into the ground (eg fence posts and telegraph posts), marine structures such as pilings or piers, and railway sleepers. Compositions to be used in accordance with the invention have been found to offer three main advantages. Firstly, the presence of the compound of formula (I) enables the quantity of creosote applied to the timber to be reduced. The treated timber is therefore less oily and smelly, more pleasant to handle and less likely to bleed creosote in a way which may represent a fire hazard. Secondly, it has been found that the creosote stabilises the compound of the formula (I), when the treated timber is buried partially or wholly in the ground, thereby prolonging the period of effective protection afforded by the compound of formula (I). Thirdly, whereas known methods have necessitated two successive treatments, for example CCA and then creosote, which is time-consuming and expensive, the present invention enables a single treatment step to be employed to provide effective protection against termites (in the ground) or wood-boring crustaceans or molluscs (in the sea). It has been found that effective protection can be given to timber in accordance with the invention against the following arthropod and fungal pests: wood-boring beetles such as pinhole borers (e.g. Platypus spp., Diapus quinquespinatus, Xyleborus spp., and I ps sexdentatus ), shothole borers (e.g. Xylothrips religiosae and Heterobostrychus aequalis ), powder post beetles (e.g. Minthea spp and Lyctus brunneus ), wood worm (e.g. Anobium punctatum ) and longhorn beetles (e.g. Arhopalus ferus , A. rusticus and Hylotrupes bajulus ); termites (e.g. Cryptotermes cyanocephalus ); marine crustaceans such as the gribble; marine molluscs such as the ship worm; staining fungi; moulds; and white, brown and soft rot fungi. The invention will now be illustrated by way of example. Example 1 Blocks of Scots pine wood ( Pinus silvestris ) were treated, one side only, with a 0.5% w/w solution of permethrin in white spirit or with a 0.5% w/w solution of permethrin in creosote (British Standard BS144) to give a surface loading to about 200 g of solution per square metre of wood. The blocks were then buried in the ground and shavings were taken at 1, 3, 6 and 9 months after the initial burial, the permethrin in the shavings being extracted into methanol and analysed by g.l.c. The averaged results, in micrograms, are given in Table 1. Initial 1 month 3 months 6 months 9 months Permethrin + creosote 428 419 419 460 449 permethrin alone 382 289 179 170 152 It can be seen that a considerable amount of permethrin is lost when it is used alone, but not when creosote is present, the apparent increase in the latter being caused by variations in the initial loading across the surface of the block. Examples 2 Example 1 was repeated, using cypermethrin or deltamethrin instead of permethrin and analysing the blocks after 3 months. The results are given in table 2: Average µg pyrethroid per sample Initial after 3 months Cypermethrin plus creosote (0.25%) 194 201 Cypermethrin (0.25%) 199 140 Deltamethrin (0.05%) plus creosote 40 48 Deltamethrin (0.05%) 40 33 Example 3 The method of Example 1 and 2 was repeated, except that the wood was exposed to sea-water instead of to the soil. The results are given in Table 3: average µg pyrethroid per sample Initial 1 month 3 months Permethrin (0.5%) 421 391 415 Permethrin (0.5%) and creosote 557 580 661 Cypermethrin (0.25%) 198 183 167 Cypermethrin (0.25%) and creosote 194 215 202 Deltamethrin (0.05%) 40 41 35 Deltamethrin (0.05%) and creosote 40 41 49 Example 4 : Stability data To demonstrate that, as stated above, many combinations of pyrethroids and biocidal agents such as fungicides are unstable when mixed, mixtures of permethrin, deltamethrin, tributyl tin oxide (TBTO), tributyl tin phosphate (TBTP), tributyl tin benzoate (TBTB) and copper naphthenate (CuNap) (all known fungicides) were made up in oil solution stored at room temperature, 35 o C or 50 o C and analysed for chemical content after a period of time. The following results were obtained: Insecticide (%w/w) Fungicide (%w/w) Storage Period Result Permethrin 0.1% TBTO 1% 3 months unstable at the higher temperatures Permethrin 0.1% TBTP 1.5% 12 months stable Deltamethrin 0.02% TBTO 1.5% 2 weeks unstable Deltamethrin 0.02% TBTB 1.0% 12 months 15% loss of pyrethroid at higher temperatures Deltamethrin 0.01% CuNap 3.0% 6 months unstable For comparison, the use of a composition in accordance with the invention yielded the following stability data (Table 4B): Initial 1 Month 3 Months 6 months Permethrin (0.129%) in creosote (ambient temperature) 0.129 0.129 0.122 0.126 Permethrin (0.129%) in creosote (50 o C) 0.129 0.129 0.125 0.123

Claims: Use of creosote for stabilising compounds of formula I in a composition for the treatment of timber which is to be sunk wholly or partially into the ground, or railway sleepers, the composition comprising creosote and a compound of formula I : wherein Z and Z¹ are the same or different and each is halo, halophenyl or haloalkyl, X is hydrogen or a cyano group, and Y is hydrogen or a fluorine atom. Use of creosote according to claim 1, wherein the compound of formula I is permethrin. Use of creosote according to claim 1, comprising 0.1 to 1 % of the compound of formula I and 99.0 to 99.9 % of creosote.

Inventors: CARTER, STUART WILLIAM, COX, TIMOTHY RICHARD GRAHAM, RICHARDSON, BARRY ARTHUR
Applicants: THE WELLCOME FOUNDATION LIMITED
Application year: 1984
Main classification: B27K3
IPC codes: A01N53, B27K3, A01N61