CA1224474A

CA1224474A - Alkylphosphonothioate insecticides and nematocides and intermediates therefor

Info

Publication number: CA1224474A
Application number: CA000390415A
Authority: CA
Inventors: Mohamed A.H. Fahmy
Original assignee: Rhone Poulenc Agrochimie SA
Current assignee: Bayer CropScience SA
Priority date: 1980-11-21
Filing date: 1981-11-19
Publication date: 1987-07-21
Also published as: IT8125205A0; GB2140808B; GB2087891B; NL8105228A; GB8332398D0; PH19084A; LU83780A1; DE3146056A1; RO85049B; ATA501181A; GB2140808A; AU7763181A; DD202167A5; IT1140285B; ES8400751A1; RO90683A; GB2087891A; DK515181A; IL64186A0; OA06955A

Abstract

ABSTRACT

"ALKYLPHOSPHONOTHIOATE INSECTICIDES AND NEMATOCIDES
AND INTERMEDIATES THEREFOR"

The invention relates to compounds having the formula in which R is alkyl of 1 to 8 carbon atoms, haloalkyl of 1 to 8 carbon atoms, alkenyl of 2 to 8 carbon atoms, haloalkenyl of 2 to 8 carbon atoms, alkynyl of 2 to 8 carbon atoms or haloalkynyl of 2 to 8 carbon atoms;
R1 is alkyl of 1 to 8 carbon atoms or aryl and, R2 is tertiary alkyl of 4 to 8 carbon atoms, which are useful as insecticides and nematocides, e.g., in controlling corn rootworm and Southern Armyworm, and to intermediates for their preparation.

Description

4~7~

DESCRIPTION
"ALKYLPHOSPHONOTHIOATE INSECTICIDES AND NEMATOCID~S
AND INTERMEDIATES THEREFOR"

This invention relates to 0-alkyl and 0-aryl S-(tertiary alkyl) alkylphosphonothioate compounds, their preparation/ insecticidal and nematocidal compositions containing them and intermediates for their preparation~
Certain alkylphosphonothioate insecticides are described in the prior art, for example, in U.S. Patent No. 3,209,020. However, none of the species described in that patent or in other known prior art possess a tertiary alkyl group attached to the sulphur atom.
It has now been found -that certain S-tertiary alkyl compounds possess particularly useful insecticidal or nemat~cidal activity.
The present invention accordingly provides compounds of -the general formula:-O ~ ORl R - P (I) wherein R represents alkyl of 1 to 8 carbon atoms, haloalkyl of 1 to 8 carbon atoms, alkenyl OI 2 to 8 carbon atoms, haloalkenyl of 2 to 8 carbon atoms, alkynyl of 2 to 8 carbon atoms, or haloalkynyl of 2 to 8 carbon atoms, 4~7~

Rl represents alkyl of 1 to 8 earbon atoms or aryl and R2 represents tertiary alkyl of 4 to 8 carbon atoms, which exhibit a wide range of inseetieidal and nematoeidal activity and are of particular interest in controlling eorn rootworm (Diabrotiea sp) beeause of their excellent activity against this pest and their long residual soil activity.
It is to be understood that, in this speeifieation and the accompanying claims, unless otherwise indicated, alkyl groups and moieties may be straight- or branched-chain.
In general formula I:
R preferably represents alkyl of 1 to 4 carbon atoms, especially methyl or ethyl;
Rl preferably represents alkyl of 1 to 4 carbon atoms (compounds in which Rl represents phenyl or phenyl substituted by one or more (preferably one) atoms or radicals selected from the group consisting of alkyl of 1 to 4 carbon atoms (preferably methyl), alkoxy of 1 to 4 carbon atoms (preferably methoxy)~ alkylthio of 1 to 4 carbon atoms, alkylsulphinyl of 1 to 4 carbon atoms, alkylsulphonyl of 1 to 4 carbon atoms, chlorine, bromine, fluorine, nitro, cyano and trifluoromethyl, are also preferred); and R2 preferably represents tert-butyl or tert-amyl.
Particularly preferred compounds of general formula I are those in which R represents methyl or ethyl, ~Z~4~7~

Rl represents alkyl of 1 to 4 carbon atoms and R2 represents t-butyl or t-amyl. Other particularly preferred compounds are those in which R represents methyl or ethyl, Rl represents phenyl or phenyl substituted by a chlorine or fluorine atom, or by a methyl, methoxy or trifluoromethyl group and R2 represents t-butyl or t-amyl.
The compounds of general formula I can be prepared by the application of known methods. By the expression "known methods" as used in this specification is meant methods heretofore used or described in the literature.
According to a feature of the invention the compounds of general formula I are prepared by the process which comprises reacting an S-alkyl alkylphosphonothioic halide of the general formula:-O X
R - P / (II) wherein R and R2 are as hereinbefore defined and X
represents a halogen atom, preferably chlorine, with an alcohol or phenol of the general formula RlOH, wherein R
is as hereinbefore defined,in the presence of a base.
The process proceeds in accordance with the reaction scheme~
o / x 1l / ORl R - P + RlOH base R - P + base . HX

~II) SR2 2 wherein R, Rl, R2 and X are as hereinbefore defined.

rme reaction is advantageously carried out at a temperature of about 0C to 100C in an organic solvent in the presence oi a tertiary amine, or an alkali metal salt of the alcohol or the phenol ~lOH, prepared from the alcohol or phenol and an alkali metal such as sodium.
Suitable organic solvents are, for example, benzene, toluene, cyclohexane and 2-butanone, or an alcohol RlOH.
Suitable tertiary amines include trirnethylamine, triethylamine, dimethylaniline, diethylaniline and pyridine.
rme S-alkyl phosphonothioic halides of general formula II wherein R1, R2 and X are as hereinbefore defined also constitute a feature of the present invention.
r~he synthesis of S~alkyl alkylphosphonothioic halides is usually accomplished by methods o-ther than the direct addition of thiols to alkylphosphonic dihalides because direct reaction is normally accompanied by an undesirable side reaction in which both halogen atoms in the phosphonic dihalide are substituted by an alkyl thiol.
r~he side reaction is a particular problem when normal alkyl thiols are used. Thus, when the synthesis of normal S-alkyl alkylphosphonothioic chlorides is desired, alternative routes are selected.

It has been discovered that tertiary alkylthiols reac-t smoothly with alkylphosphonic dihalides to give mono addition of one thiol in good yield, according to the following equation:

/ solvent ll / X
5 RP + HSR2 + base ~ RP + base.HX
\X \ S~2 III
wherein R, R2 and X are as hereinbefore defined . According to a feature of the present invention, the compounds of general formula II are prepared by reacting a compound of the general formula III wherein R and X are as hereinbefore defined with a compound of the general formula R2$H, ~Iherein R2 is as hereinbeiore defined, in a solvent, in -che presence of a base, at a temperature of about 20C to 100C. In the compounds of general formula II, preferably R represents alkyl of 1 to 4 carbon atoms, particularly methyl or ethyl;
preferably R2 represents tert-butyl or tert-amyl, and preferably X represents chlorine.
Suitably the reaction is carried out in an organic solvent, in the presence of a tertiary amine such as trimethylamine, triethylamine, pyridine, dimethylaniline or diethylaniline.

7~

Suitable organic solvents, which are preferred, include benzene, toluene, cyclohexane, acetone and

2-butanone.
Generally, the reaction is conducted at a temperature of about 20C to lOO~C, but the temperature is not critical except insofar as it is sufficient to make the reaction proceed at a reasonable rate and is not excessive. It has been found advantageous to add the tertiary amine to the other reactants at a temperature of about 20C to 30C and then to heat the entire reaction mixture to a temperature of about 70C to 80C to complete the reaction.
The reaction is normally carried out with an approximately equal molar ratio of the alkyl phosphonic dihalide, thiol and the base. An excess of about 10 to 20% of the alkylphosphonic dihalide can be used relative to the other reactantsO ~Iowever, the use of a sli~ht excess of the thiol and the base relative to the alkylphosphonic dihalide (5-10/~ excess) did not appreciably affect the yield~
Particularly preferred compounds of general formula II are S-tert~butyl ethylphosphonothioic chloride, S-tert-amyl ethylphosphonothioic chloride, S-tert-butyl methylphosphono'chioic chloride, and S-tert-amyl methyl-phosphonothioic chloride which are used as intermediatesin the following Examples 1 to 16.

The following Exarnples illustrate the preparation of compounds of general formulae I and II and the pesticidal properties of the former.

S-tert-Butyl ethylp_osphonothioic chloride 0 Cl CH3CH2 P \ IH3 s f CH

To a solution o~ ethylphosphonic dichloride (32.0 g, 0022 mol) in 300 ml toluene, was added 2-methyl-2-propanethiol (18 g, 0.2 mol). ~hile stirring,triethyl-amine (22 g, 0.22 mol) was added dropwise; the temperature of the reaction mixture was maintained at 30-35C during the addition of the amine. After addition of the amine the mixture was stirred overnight at room temperature.
The amine hydrochloride which precipitated was filtered off and the toluene solution was concentrated under vacuum.
Hexane (200 ml)- was added and the solution obtained was filtered.
The solvents were stripped off under vacuum and the residual liquid was distilled. The product (25 g, 72.5% yield) di.stilled at 72-73C/007 mmHg. Proton magnetic resonance spectroscopy in deuterochloroform (CDC13) with Si(Me)4 as reference confirmed the structure ~LZ~ 7~

of the title compound.

Preparation of 0-ethyl-S-tert-butyl ethylphosPhonothioate To a solution of S-tert-butyl ethylphosphonothioic chloride (obtained as described in Example 1) (8.0 g, 0.048 mol) in toluene (50 ml) was added a solution of sodium ethoxide (0.04 mol) in ethanol (40 ml). The addition was carried out dropwise, with stirring under a nitrogen atmosphere. Stirring was continued overnight at room temperature, and then approximately 80% of the solvents were removed under vacuum. Toluene (100 ml) was added and the sodium chloride formed from the reaction was filtered off.
Toluene was stripped off under vacuum and the residual liquid was distilled. The product (5.8 g, 69.6% yield) distilled at 69-72C/0,2 mmHg.
Analysis of the proton magnetic resonance spectrum of this product confirmed the structure of the title compound.
EXAMPLE 3 to 6 In a manner analogous to that of Example 2, the following compounds were prepared.

1l /OR
R - P \

~2~ '7~

Example R Rl R2 B.p.C/mmH~.

C2H5 CH3 t-butyl 64-67/0.7 l~ C2H5 C3H7 t-butyl 61-63/0,05 2 5 (CH3)2CH t-butyl 42-43/0.05 6 C2H5 C2H5 t-amyl 56-58/0.07 Preparation of 0-phenyl-S-ter_-butyl ethylphosphonothioate O /=\
11/~
2 5 \ 1 3 To a solution of S-text-butyl ethylphosphonothioic chloride (5 g, 0.025 mol), and phenol (2.35 g, 00025 mol) in acetone (20 ml), was added, in one portion, triethylamine (2.5 g, 0.025 mol); the mixture was stirred overnight under nitrogen at room temperature. The reaction mixture was then diluted with toluene (100 ml) and washed once with 5% w/v sodium hydroxide solution, and twice with water. The solution was dried over anhydrous sodium sulphate and the solvent was stripped off under vacuum. The residual liquid 4~L'7~

was subjected to high vacuum (0.2 mmHg) at 60C for 15 minutes to yield the desired product as confirmed by its proton magnetic resonance spectrum in deutero-chloroform (CDC13) with Si(Me)4 as reference.
EXAMPLES 8 to 15 ... . . .
In a manner analogous to that of Example 7, the following compounds were prepared.

1 ~ ~1 R - P

Æxample R R R
_ 1 2 2H5 o-methyl-phenyl tert-butyl C2H5 p-chloro-phenyl L ert-butyl C2H5 phenyl tert--amyl 11 C2~5 m-trifluoromethyl- tert-amyl phenyl 12 C2H5 p-fluoro-phenyl tert-amyl 13 C2H5 p-chloro-phenyl tert-amyl 14 C2H5 o-chloro-phenyl tert-amyl CH3 phenyl tert-amyl Meta-cresol (4.6 g) was dissolved in acetone (100 ml) and potassium carbonate was added. The mixture was stirred at room temperature for 30 minutes, and ~2~ 7'~

_ 11 --S-tert-but~l methylphosphonotllio;c chloride (7~5 g) was l:hen aclded.
Stirring was continued overnight, and the ~olution was then filtered and the solvent evaporated.
Water (100 ml) was added and the mixture extracted with diethyl ether (100 ml)O The ethereal extract ~as was~ed once with 5% w/v potassium hydroxide solution, then ~ with water and was finall~ dried and evaporated to give 4.0 g of 0-3-tolyl-S-tert-butyl methylphosphonothioate.
The product was identified by its proton magnetic resonanc~ spectrum. Its purity is higher than 90%~
EX~MPLE 17 Testing for corn rootworm intrinsic activity, and activity against Southern Armyworm.
A. Corn ~ootworm Intrinsic Activi ~ ~CRW?
. _ _ Ihe test compound is prepared as a one percent w/v stock solu-tion with acetone or ethanol. Ihe stock solution is then diluted with an aqueous solution o~
Tween-20 (500 ppm) and water to the appropriate concentration (i.e. 500, 100, 1, 0.1 or 0.05 ppm o~ test compound). Two ml of the test solution is pipetted into a 9 cm petri dish containing two layers o~ ~ilter paper.
Second instar larvae are introduced and the dish closed~
Observations ~or mortality and moribund larvae are made after two days (48 hours~ exposure. Insecticidal activity is primarily ~y contact and vapour action with minimal ingestion.
*trade mark ~2~ 7~

B. Southern Arm~torm Intrinsic ~ctivity (SAW~
Stock solution (1% w/v) of test compound in acc~one was pxepared and dilu-ted to the desired concentration using a 500 ppm ~ween-20 aqueous solution~
Lima bean leaves are dipped into the solution and transerred to petri dishes (100 x 15 mm) each containing two filter papers moistened with 2 ml water, Each petri dish contained one leaf and was left open to dry out the solution on the leaf. Five third instar larvae of Southern Arm~torm ~Spod~ptera eridania) were added to the lea* and the dish was finally covered.
The dishes were kept at 78F for 72 hours and percentage kill was recorded.
Ihe results of Tests ~ and B are tabulated in Table 1 which shows the percentage kill obtained using compounds prepared in the indicated Exa~ples.

*trade mark ~2~

_ 13 -% Kill C R W S A W
~te in ppm . _ . _ .
\ 1 0.1 0. ~5 5001.00 Example N~ . . _

3 100 100 100 10090 L~ 100 70 _ 10015 L~5 _ 80 ~5 16 100 100 100 _

4~'7 These results show the excellent insecticidal activity of the compounds according to the invention which can be used for combatting numerous insects such as coleoptera (e.g~ Diabrotica sp) or corn rootworm and lepLdoptera.
For use in practice, the compounds of general formula I are generally employed in the form of compositions, which also constitute a feature of -the invention, and which generally comprise, in addition to the active compound of general formula I, at least one agriculturally acceptable carrier and/or surface-ac~ive agent. The proportion of active ingredient in these compositions is generally from 0.001% to about 95% by weight: the proportion of surface active agent is generally from O to 20% by weight.
In the present specification, the term "carrier"
denotes an organic or inorganic, natural or synthetic material with which the active ingredient is associated in order to facilitate its application to the plants or to the soil. The carrier can be solid (e.g. clays, natural or synthetic silicates, silica, resins, waxes and solid fertilisers) or liquid (e.g. water, alcohols, petroleum fractions, aromatic or paraffinic hydrocarbons, chloro-hydrocarbons and liquefied gases).

~2~

The surface-active agent can be an emulsifying, dispersing, deflocculating or wetting agent of the iOIliC
or non-ionic type. Examples which may be mentioned are salts of polyacryl.ic acids, salts of lignosulphonic acids, salts of phenolsulphonic or naphthalenesulphonic acids, condensates of ethylene oxide with fatty alcohols, fatty acids or fatty amines, substituted phenols tin particular alkylphenols or arylphenols), salts of sulphosuccinic acid est~rs, taurine derivatives (in particular alkyltaurates), and phosphoric acid esters of condensates of ethylene oxide with alcohols or with phenols.
The compositions can also contain other ingredients, e.g. thickeners, thixotropic agents, protective colloids, adhesives, penetrating agents and stabilisers, and also other known active ingredients having pesticidal properties (in particular herbicidal, fungicidal and insecticidal properties), properties which assist plant growth (in particular fertilisers) or properties which regulate plant growth. More generally, the compounds according to the invention can be combined with any of the solid or liquid additives used in the customary techniques for the preparation of pesticidal compositions.
The compositions according to the invention can be prepared in the form of wettable powders, dusting powders, granules, solutions, emulsifiable concentrates, emulsions, suspension concentrates and aerosols.

The wettable powders, or spraying powders, usually contain Erom 20 to 95% by weight o:E active ingredient and g~ne~all~ contain, in addition to a solid carrier, from 0 to 5% by weight of wetting agent, and from 0 to 10% by weight of one or more stabilisers and/or other additives, such as penetrating agents, adhesives or anti-caking agents and dyestuffs.
They are prepared by mixing the constituents in mixers and by grinding them in mills or other suitable grinders, e.g. air grinders, so as to obtain the desired particle size.
The composition of an 80% w/w wettable powder according to the invention is given below by way of example (in the following Examples percentages are by weight):

active ingredient 80%
sodium alkylnaphthalenesulphonate 2%
sodium lignosulphonate 2%
anti-caking silica 3%
20 kaolinite 13%
Another example of a wettable powder according to the invention is given below:

active ingredient 50%
sodium alkylnaphthalenesulphonate 2%
low-viscosity methylcellulose 2%
diatomaceous earth 46%

lZZ4~

Another example of a wettable powder according to the invention is given below:

active ingredient 90%

5 sodium dioctylsulphosuccinate 0.2%
synthetic silica 9~%
Granules, which are intended to be placed on the soil, are usually prepared so that they have dimensions of between 0.1 and 2 mm, and they can be manufactured by agglomeration or impregnation. In general, the granules will conkain from 0.5 to 25% of active ingredient and from 0 to 10% by weight of additives, such as stabilisers, slow-release modifiers, binders and solvents.
Emulsifiable concentrates, which can be applied, after dilution, by spraying, usually contain from 10 to 50% by weight/volume of active ingredient. In addition to the active ingredient and the solvent, they can also contain, if necessary, from 2 to 20% by weight/volume of an emulsifying agent and from 2 to 20% by weight/volume of suitable additives, such as surface-active agents, stabilisers, penetrating agents, corrosion inhibitors, dyestuffs and adhesives.
Suspension concentrates, which can also be applied by spraying, are prepared so as to give a stable fluid product which does not settle out, and they usually contain from 10 to 75% by weight of active ingredient, 1~2~4t7~

from 0.5 to 15% by weight of surface-active agent, from 0~1 to l~o by weight of thixotropic agents, from 0 to 10%
of suitable additives, such as anti-foam agents, corrosion inhibitors, stabilisers, penetrating agents and adhesives, and, as the carrier, water or an organic liquid in which the active ingredient is substantially insoluble; certain organic solids, or inorganic salts, can be dissolved in the carrier in order to assist in preventing sedimentation or to act as anti-freeze agents for water.
Aqueous dispersions and aqueous emulsions, which are obtained by diluting the abovementioned compositions with water, in particular the wettable powders and emulsiEiable concentrates according to the invention, are also included in the general scope of the present invention~
The emulsions thus obtained can be of the water-in-oil type or of the oil-in-water type and they can have a thick consistency such as that of a mayonnaise.
All these aqueous dispersions and emulsions, or spraying mixtures, can be applied by any suitable means to the crops in which weeds are to be destroyed, mainly by spraying, at doses which are generally of the order of 500 to 1,000 litres of spraying mixture per hectare.
As indicated above, the invention also relates to a method for the control of insects in crops, which comprises applying an effective amount or at least one of the compounds of ~eneral iCormula I to the aerial part of - ~2~t7~

the crops and/or to the soil or incorporating the compound into the soil~
For the control of insects, the compounds of general Eormula I are used at concentrations of from 0~01%
to about 1% by weight of the total formulation~ As nematocides, the active component is effective within the range of about 0.5 to 5 kg/hectare~ Under ideal conditions, depending on the pest to be controlled, the lower rate may offer adequate protection. On the other hand, adverse weather conditions, resistance of the pest and other factors may re~uire that the active ingredient be used in higher proportions.
When the pest is soil-borne, the formu~ation containing the active ingredient is distributed evenly over the area to be treated in any convenient manner. The active component can be washed into the soil by spraying with water over the area or can be left to the natural action of rainfall. After application, the formulation can be distributed in the soil by ploughing or disking.
Application can be prior to planting or after planting but before sprouting has taken place or after sproutiny.

SUPPLEMENTARY DISCLOSURE
, Dry triethylamine (dried over a 4A molecular sieve 1.52g; 2.1ml; 0.015mol) was added at laboratory temperature to a solution of 2-fluorophenol (1.68g;
0.015mol) in acetone (Pronalysis grade, 30ml). The solution was then stirred magnetically at laboratory temperature while S-tert-butyl ethylphosphonothioic chloride (2.0g; 0~01mol) was added dropwise over 4 minutes, during which time the temperature rose to 33C and a solid began to separate. Stirring was continued at ambient temperature for 17 hours. The reaction mixture was then poured into water (50ml) and extracted with diethyl ether (2 x 25ml). The combined ethereal extracts were washed with 2N aqueous sodium hydroxide solution (2 x 25ml) and water (2 x 25ml), dried over anhydrous sodium sulphate, filtered and evaporated to give 0-(2-fluorophenyl)-S-tert-butyl ethylphosphonothioate in the form of a brown oil (2.2g, 71.4% yield). The product was 98% pure and was identified by its phosphorus and proton magnetic resonance spectrum.
By proceeding in a similar manner but replacing the 2-fluorophenol by 3-fluorophenol and 4-fluorophenol, there were prepared, respectively, the ~Z~ 7~

followin~ products which were identified by their phosphorus and proton magnetic resonance spectra:-0-(3-fluorophenyl)-S-t_ -butyl ethyl-phosphonothioate (purity 98%);
0-(4-fluorophenyl)-S-tert-butyl ethy~hosphono-thioate tpurity 99/O)~

~ ,

Claims

The embodiments of the invention, in which an exclusive privilege or property is claimed, are defined as follows:

1. A compound of the general formula:

(I) wherein R represents alkyl of 1 to 8 carbon atoms, haloalkyl of 1 to 8 carbon atoms, alkenyl of 2 to 8 carbon atoms, haloalkenyl of 2 to 8 carbon atoms, alkynyl of 2 to 8 carbon atoms, or haloalkynyl of 2 to 8 carbon atoms, R1 represents alkyl of 1 to 8 carbon atoms or aryl, and R2 represents tertiary alkyl of 4 to 8 carbon atoms.

2. A compound according to claim 1 wherein R
represents alkyl of 1 to 4 carbon atoms.

3. A compound according to claim 1 wherein R1 represents alkyl of 1 to 4 carbon atoms.

4. A compound according to claim 1 wherein R1 represents phenyl or phenyl substituted by one or more atoms or radicals selected from the group consisting of alkyl of 1 to 4 carbon atoms, alkoxy of 1 to 4 carbon atoms, alkylthio of 1 to 4 carbon atoms, alkylsulphinyl of 1 to 4 carbon atoms, alkylsulphonyl of 1 to 4 carbon atoms, chlorine, bromine, fluorine, nitro, cyano, and trifluoromethyl.

5. A compound according to claim 1, 2 or 3 wherein R2 represents t-butyl or t-amyl,

6. A compound according to claim 4 wherein R2 represents t-butyl or t-amyl.

7. A compound according to claim 1 wherein R
represents methyl or ethyl, R1 represents alkyl of 1 to 4 carbon atoms and R2 represents t-butyl or t-amyl.

8. A compound according to claim 1 wherein R
represents methyl or ethyl, R1 represents phenyl or phenyl substituted by a chlorine or fluorine atom, or by a methyl, methoxy or trifluoromethyl group and R2 represents t-butyl or t-amyl.

9. O-Ethyl-S-tert-butyl ethylphosphonothioate.

10. A compound according to claim 1 wherein R
represents C2H5, R1 represents CH3 and R2 represents t-butyl.

11. A compound according to claim 1 wherein R
represents C2H5, R1 represents C3H7 and R2 represents t-butyl.

12. A compound according to claim 1 wherein R
represents C2H5, R1 represents (CH3)2CH and R2 represents t-butyl.

13. A compound according to claim 1 wherein R
represents C2H5, R1 represents C2H5 and R2 represents t-amyl.

14. O-Phenyl-S-tert-butyl ethylphosphonothioate.

15. A compound according to claim 1 wherein R
represents C2H5, R1 represents o-methyl-phenyl and R2 represents tert-butyl.

16. A compound according to claim 1 wherein R represents C2H5, R1 represents p-chloro-phenyl and R2 represents tert-butyl.

17. A compound according to claim 1 wherein R
represents C2H5, R1 represents phenyl and R2 represents tert-amyl.

18. A compound according to claim 1 wherein R
represents C2H5, R1 represents m-trifluoromethylphenyl and R2 represents tert-amyl.

19. A compound according to claim 1 wherein R
represents C2H5, R1 represents p-fluoro-phenyl and R2 represents tert-amyl.

20. A compound according to claim 1 wherein R
represents C2H5, R1 represents p-chloro-phenyl and R2 represents tert-amyl.

21. A compound according to claim 1 wherein R
represents C2H5, R1 represents o-chlorophenyl and R2 represents tert-amyl.

22. A compound according to claim 1 wherein R
represents CH3, R1 represents phenyl and R2 represents tert-amyl.

23. O-3-Tolyl-S-tert-butyl methylphosphonothioate.

24. A process for the preparation of a compound of general formula I depicted in claim 1 wherein R, R1 and R2 are as defined in claim 1 which comprises reacting an S-alkyl alkylphosphonothioic halide of the general formula:

(II) wherein R and R2 are as defined in claim 1 and X
represents a halogen atom, with an alcohol or phenol of the general formula R1OH wherein R1 is as defined in claim 1 in the presence of a base.

25. Process according to claim 24 in which the reaction is carried out at a temperature of about 0°C
to 100°C in an organic solvent in the presence of a tertiary amine or an alkali metal salt of the alcohol or phenol of general formula R1OH.

26. Insecticidal or nematocidal compositions which comprise a compound according to claim 1 in association with at least one agriculturally acceptable carrier and/or surface active agent.

27. A method for the control of insects in crops which comprises applying to the crops or to the soil in which they are growing a composition according to claim 26.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

28. O-(2-Fluorophenyl)-S-tert-butyl ethylphosphonothioate.

29. O-(3-Fluorophenyl)-S-tert-butyl ethylphosphonothioate.

30. O-(4-Fluorophenyl)-S-tert-butyl ethylphosphonothioate.