GB2057426A

GB2057426A - Formamidine sulphide and disulphides and thiocarbamoyl guanidines having herbicidal activity, their preparation and use

Info

Publication number: GB2057426A
Application number: GB8019484A
Authority: GB
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1979-06-15
Filing date: 1980-06-13
Publication date: 1981-04-01
Also published as: SU1042611A3; FR2464946B1; DE3022057A1; CA1147729A; CH652889A5; SU1005648A3; FR2459230A1; BR8003690A; IL60315A; FR2464946A1; IL60315A0; FR2459230B1; GB2057426B

Abstract

A method of combatting weeds comprising applying to the soil pre- emergence and/or post-emergence of said weeds at a dosage rate of from 1 to 6 kg/ha one or more herbicide compounds having the general formula <IMAGE> in which: each R represents a phenyl group which may be substituted by one or more substituents selected from halogen atoms, an alkyl group having one to three carbon atoms and a haloalkyl group having 1 to 3 carbon atoms, R<1> and R<2> independently represent an alkyl group having 1 to 3 carbon atoms, and alkoxyl group having 1 to 3 carbon atoms or R<1> and R<2> together form an alkylidenic chain of 4 or 5 carbon atoms which may be interrupted by a heteroatom, and n is 1 or 2. Many of the compounds of formulae (I) and (II) are new. The compounds may be prepared by the following reactions: <IMAGE>

Description

SPECIFICATION Formamidine sulphide and disulphides and thiocarbamoyl guanidines having herbicidal activity, their preparation and use This invention relates to compounds having herbicidal activity and in particular, to formamidine sulphides and disulphides and to thiocarbamoyl guanidines, to their use and to their preparation. A restricted number of formamidine disulphides are disclosed in literature, although their herbicide properties were not recognised.

P. K. Srivastrava et al have prepared the following formamidine disulphides in the form of bromo hydrates:

disclosed in P. K. Srivastrava et al., Tetrahedron Letters 23, 2725, 1 968

disclosed in P. K. Srivastrava et al., J. Ind. Chem. Soc. 40, 803, 1963 and

disclosed in P. K. Srivastrava et al., Indian J. Chem. 1, 354,432, 1963.

However no analytical data for the characterisation of the above three compounds is reported, probably because, due to their instability, they cannot be isolated as free bases. The literature also discloses a limited number of derivatives belonging to the class of thiocarbamyl-guanidines although their herbicidal properties were not recognised.

Held, Gross and Schubert in Zeitschrift der Chemie 13,341(1973) disclose that oxidation of the N,N-dimethyl-N'-phenyl-thiourea with thionyl chloride, yields N1,N'-dimethyl-N2,N3 diphenyl-N3-[N,Ndimethyl-thiocarbamoyl]-guanadine of the formula:

Srivastrava et al. in J. Ind. Chem. Soc. 40, 803 (1 963) disclose derivatives of thiocarbamoyl guanidine non-substituted on the nitrogen atom inposition 1 and on the nitrogen atom of the thiocarbamoylic group in the form of bromohydrates. We have now found that certain formamidine sulphides and disulphides possess high herbicidal activity.Therefore according to the present invention there is provided a method of combatting weeds comprising applying to the soil pre-emergence and/or post-emergence of said weeds at a dosage rate of from 1 to 6 kg/ha one or more herbicide compounds having the general formula

in which: each R represents a phenyl group which may be substituted by one or more substituents selected from halogen atoms, alkyl group having one to three carbon atoms and haloalkyl groups having 1 to 3 carbon atoms, R1 and R2 independently represent an alkyl group having 1 to 3 carbon atoms, an alkoxyl group having 1 to 3 carbon atoms or R' and R2 together form an alkylidenic chain of 4 or 5 carbon atoms which may be interrupted by a heteroatom, and n is 1 or 2.

Many of the compounds of formulae (I) and (II) are new and according to one embodiment of the invention there is provided compounds of general formula (I) and (II) described above with the proviso that in formula (II) when R1 = R2 = CH3, R is a substituted phenyl group.

Compounds of formulae (I) and (II) are endowed with herbicide activity against both monocotyledons and dicotyledons and can be usefully utilized, as such or in form of suitable composition, in combatting infesting weeds both in the pre-emergence and post-emergence of said weeds.

The compounds of general formula (I) may be prepared by oxidation of trisubstituted thioureas (formula Ill) in the presence of an organic base, to yield the disulphides of formula (I) in which n = 2 (reaction 1). Desulphurization of the disulphides in the presence of triphenylphosphine yields the corresponding sulphides of formula (I) in which n = 1 (reaction 2). The sulphides of formula (I) in which n = 1 can also be obtained by reacting a trisubstituted thiourea (formula Ill) with the imidoyl-chloride (formula IV) in the presence of a halogenhydric acid accepting base (reaction 3). These reactions are represented schematically below:

Reaction (1) is conducted by oxidizing thiourea (II) in the presence of an organic base and in an inert solvent. Suitable oxidizing agents include halogen e.g. bromine and iodine. Tertiary amines e.g.

triethyl- or tributyl-amine can be used as the organic base.

Excellent yields have been obtained employing methylene chloride (CH2Cl2) or chloroform (CHCl3) as a solvent.

Under the conditions described above the reaction occurs at room temperature and in very short times. At the conclusion of the reaction the mixture is washed with water, dried, and the solvent is evaporated. The resulting product can be utilized as such, or can be crystallized from non-polar solvents.

Reaction (2) may be advantageously conducted by reacting equimolar amounts of the disulphide and triphenyl-phosphine, in diethylether at about 0 C. The resulting triphenyl-phosphine sulphide precipitates and is removed by filtration at the end of the reaction. The reaction mixture is treated according to conventional laboratory techniques and the formamidine sulphide thus obtained may be purified by crystallization from hydrocarbons.

Reaction (3) leads directly to the formamidine sulphides without preparation of the corresponding disulphides. The reaction is conducted in an aprotic solvent and in the presence of a halogenhydric acidaccepting base.

A preferred technique for conducting reaction (3) comprises adding a solution of the thiourea derivative (II) and of a slight excess of base (tertiary amine) in methylene chloride, to a solution of imidoyl chloride (III) in methylene chloride. The mixture is stirred at room temperature and the reaction occurs in a short time. The product is then isolated according to -conventional laboratory techniques.

The compounds of general formula (II) may be prepared by reacting a formamidine sulphide or disulphide of formula (I) with a catalytic amount of a strong anhydrous acid (reaction 4)

Reaction (4) is preferably conducted by adding a catalytic amount of an acid having a sufficient force to salify the basic groups of the sulphide or disulphide of formula (I), to a solution of the latter in an aprotic polar solvent e.g. chloroform (CHCl3).

Suitable strong acids include anhydrous halogenhydric acid or a trihaloacetic acid. The reaction rate depends upon the particular compound of formula (I) and on the amount of acid used. For amounts of acid equal to 0.1. equivalents per mol of compound of formula (1), the reaction is completed at room temperature within a few minutes.

Once the reaction has taken place, the chloroformic solution is washed with a saturated aqueous solution of sodium bicarbonate (NaHC03) and is then dried. The solvent is then evaporated under vacuum to yield a residue of the corresponding compound of formula (II) which may be purified by crystallization.

The process for the preparation of the compounds of general formulae (I) and (II) can be summarized as reported in the following scheme:

The compounds of formulae (I) and (II) reported in the following Table 1, have been prepared according to the processes described above. Compounds of formulae TABLE 1

Compound Elemental analysis (%) (1) (2) (3) rough formula No. Formula n R R R calculated found NMR (#, ppm) m.p. ( C) IR (cm-1) M.W.

1 1 1 4-CH3-C6H4 i C3H7 i C3H7 C 72.05 72.45 7,3-6,5 (m) 1610; 1590 C26H42N4S H 9.07 8.78 4-3,4 (q) 1360-1370 N 12,00 10.35 2,3 (s) 466.74 1,07-0,97 (d) 2 1 2 4-Cl-C6H4 CH3 CH3 C 50.58 50.28 H 4.72 4.56 N 13.11 13.01 3 1 2 4-Cl-C6H4 -CH2-CH2-O-CH2-CH2 C 51.66 51.66 C22H24N4S2O2Cl2 H 4.73 4.71 150-152 N 10.95 11.06 511.50 cont. of TABLE 1

4 1 2 4-Cl-C6H4 -CH2-(CH2)3-CH2- C 56.79 55.52 C24H26N4SCl2 H 5.56 5.50 105-107 N 11.04 11.14 507.56 5 1 2 3,4-Cl2-C6H3 -CH2-(CH2)3-CH2- C 50.00 49.07 136.138 C26H28N4S2Cl4 H 4.55 4.41 576.44 N 9.72 9.42 6 1 2 3,4-Cl2-C6H3 i C3H7 i C3H7 C 51.66 50.32 C26H26N4S2Cl4 H 5.63 5.46 130-132 N 9.21 8.21 608.53 7 1 1 3,4-Cl2-C6H3 -CH2-(CH2)3-CH2- 1590-1560 C24H26N4S2Cl4 C 52.95 5478 1370-1110 H 4.81 4.86 133-136 544.38 N 10.29 9.46 cont. of TABLE 1

8 1 1 3,4-Cl2-C6H3 i C3H7 i C3H7 7.3-6.57 (m) 1610-1570- C24H34N4SCl4 C 54.17 65.63 4.0-3.3 (q) 1360 H 5.94 5.73 0.95-107 (d) 160-165 576.48 N 9.72 8.45 9 1 2 3,4-CF3-C6H3 -CH2-CH2-O-CH2-CH2- C24H24F6N4O3S2 S 11.08 11.15 9.68 9.32 114-115 578.59 10 1 2 4-Cl-C6H4 i C3H7 i C3H7 C 58.09 57.70 156-158 C26H24N4S2Cl2 H 6.37 6.77 537.62 N 10.42 10.48 11 1 2 4-Cl2-C6H4 CH3 CH3 C 54.68 54.64 107-108 1610-1590 C18H20N4SCl2 H 5.1 4.9 1575 595.36 N 14.17 14.42 1080 cont. of TABLE 1

12 1 1 4-Cl-C6H4 i C3H7 i C3H7 C 62.62 62.87 146-151 1695-1590 C24H25N4SCl2 H 5.93 5.84 1575-1370 N 11.78 9.67 475.49 13 1 1 4-Cl-C6H4 i C3H7 i C3H7 C 61.77 63.49 1600-1590 C26H36N4SCl2 H 6.78 6.90 1570-1360 N 11.08 9.33 159-165 505.56 14 1 2 3,4-Cl2-C6H3 -CH2-CH3-O-CH2-CH2- C22H22N4S2Cl4 C 45.52 44.63 H 3.82 3.68 123-125 580.38 N 9.65 9.48 15 1 2 3,4-Cl2-C6H3 CH3 CH3 C 43.54 43.68 C16H18N4SCl4 H 3.62 3.55 67-71 495.8 N 11.26 11.15 16 1 1 3,4-Cl2-C6H3 CH3 CH3 C 46.57 48.86 7.35-645 C18H18N4SCl4 (6 H, m) H 3.8 4.00 2.73 (12 H, s) 95-97 N 12.07 10.95 464.25 cont. of TABLE 1

17 1 1 C6H5 CH3 CH3 C 66.22 66.2 7.4-6.6 1620, 1585 C18H22N4S (10H,m) H 6.79 6.8 2.68 (12H,s) 100-102 1300, 750 N 17.16 17.25 690 326.47 18 1 2 C6H5 CH3 CH3 C 60.3 60.45 1610, 1585 C18H22N4S2 H 6.2 6.2 2.9 (12 H, s) 1260, 1100, N 15.65 15.65 56-60 920, 830 357.47 765, 698 19 1 2 4-CH3-C6H3 i C3H7 i C3H7 C 67.42 67.53 C28H42N4S2 H 8.49 8.72 114-119 498.80 N 11.23 11.32 20 1 2 3-CF3-C6H3 CH3 CH3 S 12.96 12.46 oil C20H20F6N4S2 N 11.33 11.39 494.51 21 1 2 3-CF3-C6H4 -CH2-(CH2)3-CH2- S 11.16 10.23 oil C26H25F6N4S2 N 9.75 9.73 574.68 22 1 2 3-CF3-C6H4 i C3H7 i C3H7 S 10.57 10.67 111-112 C28H36F6N4S2 606.72 cont. of TABLE 1

23 1 1 3-CF3-C6H4 CH3 CH3 7.45-6.8 (m) 1600, 1590 C20H18N4F6S 2.65 (s) 96-100 1575, 1370 1320, 1210 462.45 24 1 1 3-CF3-C6H4 -CH2-(CH2)3-CH2- F 21.01 20,10 C26H26F6N2S N 10,38 11,22 oil 542.58 25 1 1 3-CF3-C6H4 i C3H7 i C3H7 1605, 1565, 130-133 1370, 1360, 1320, 1255, 1220 cont. of TABLE 1

Compound Elemental analysis (%) (1) (2) Rough Formula P.F. ( C) (3) No. Formula R R R calculated found NMR (#, ppm) m.p. IR (cm-1) P.M.

26 11 3,4-Cl2-C6H3 CH3 CH3 C 46.57 46.08 C18H16N4SCl4 H 3.88 3.76 125-127 N 12.08 11.81 463.8 27 11 C6H5 CH3 CH3 C 66.2 66.55 7.53-6.6 1625, 1580, C16H22N4S (10H, m) 1300 H 6.8 6.85 2.9 (8H, s) 119-120 1080, 765, 695 N 17.15 17.2 2.53 (6H, s) 326.47 28 11 4-CH3-C6H4 -CH2-CH2-O-CH2-CH2- C 65.72 65.2 C24H30N4SO2 H 6.89 6.95 142-145 N 12.74 13.01 438.59 29 11 4-CH3-C6H4 -CH2-(CH2)3-CH2- C 71.85 68.98 193-197 C26H34N4S H 7.88 7.68 N 12.89 12.82 434.65 cont. of TABLE 1

30 11 4-CH2-C6H4 CH3 CH3 C 67.75 66.99 170,5- C20H26N4S H 7.39 7.33 172,5 N 15.8 16.1 354.52 31 11 4-Cl-C6H4 CH3 CH3 C 54.68 54.46 C18H20N4SCl2 H 5.1 4.97 161-163 N 14.17 14.22 396.36 32 11 4-Cl-C6H4 -CH2-(CH2)3-CH2- C 60.62 60.62 C24H28N4SCl2 H 5.93 5.99 186-189 N 11.78 11.83 475.49 33 11 4-Cl-C6H4 -CH2-CH2-O-CH2-CH2- C 55.12 53.29 C22H24N4SO2Cl2 H 5.04 4.86 189-194 N 11.69 11.22 479.41 34 11 3-CF3-C6H4 -CH2-CH2-O-CH2-CH2- N 10.25 9.86 F 20.86 20.66 174-175 546.52 35 11 3-CF3-C6H4 CH3 CH3 S 6.93 6.72 oil 462.45 cont. of TABLE 1

36 11 3-CF3-C6H4 -CH2-(CH2)3-CH2- S 5.91 5.59 142-146 542.58 37 11 3,4-Cl2-C6H3 -CH2-CH2-O-CH2-CH2- C 48.19 47.29 C22H22N4O2Cl4 H 4.04 3.98 153-165 548.32 N 10.21 9.99 38 11 3,4-Cl2-C6H3 -CH2-(CH2)3-CH2- N 52.95 52.08 C24H26N4SCl M 4.81 4.75 156-160 N 10.29 10.08 544.38 The compounds of general formulae (I) and (II) are endowed with a high herbicide activity-exerted against both monocotyledons and dicotyledons as will be illustrated hereinafter.

Depending on the particular compound, the optimum herbicide activity may be achieved by application in pre-emergence or in post-emergence, that is before the infesting weeds have emerged from the soil or after infesting weeds have emerged from the soil or after emergence. The herbicide compounds of the invention prove also to be selective with respect to useful cultivations such as wheat, maize, soya and cotton.

For agricultural applications the active compounds are distributed on the soil as such or, more preferably, in form of suitable compositions consisting of one or more of the compounds as active principle and one or more suitable carriers. Suitable compositions include wettable powders, liquid pastes, granular formulates and other conventional herbidide formulations. Suitable carriers include, depending on the type of composition, silica, caolin, diatomaceous earths, bentonite, pomix, organic solvents and water.

The compositions may also include additives e.g. surfactants, emulsifiers and thickeners.

A list of carriers and additives is reported on "McCutcheons -- Detergent and Emulsifiers North American and International Editions, 1977 Annual. McCutcheons Publication Co., Glen Rock, New Jersey (U.S.A.)".

The preparation of the compositions. is carried out according to conventional procedures. If desired in the compositions may be included also other active ingredients such as fertilizers, insecticides or fungicides. The amount of active principle (compounds of formulae I and II) to be distributed on the soil depends on various factors such as the environmental conditions, the kind of agricultural cultivation to be protected from infesting weeds, the type of composition and the particular active principle. Generally, the compounds of formulae (I) and (II) are applied at a dosage rate of from 1 to 6 kg/ha which is suitable for obtaining good results in combatting infesting weeds, the preferred dosage rate being from 2 to 3 kg/ha.

The invention will now be illustrated by the following Examples.

EXAMPLE 1 Preparation of N',N1-dimethyl-N2-phenyl-formamidine sulphide (Compound 18 Reaction 1) A chloroform solution of iodine (5.2 g in 100 ml) was added dropwise and under stirring to a solution of N,N-dimethyl-N'-phenyl-thiourea (5 g, 0.0277 moles)-and triethylamine (7.5 ml) in chloroform (50 ml). The addition was continued until the iodine colour remained persistent in the reaction mixture.

After 1 5 minutes the stirring was stopped and the reaction mixture repeatedly washed with water (750 ml) and dried with anhydrous Na2SO4. After removal of the solvent a yellow oil was obtained which, crystallized from n.hexane, provided 4 g of the desired product.

EXAMPLE 2 Preparation ofN1,N1-dimethyl-N2-phenyl-formamide sulphide (Compound 17, Reaction 2) A solution of N',N1-dimethyl-N2-phenyl-formamidine disulphide prepared as described in Example 1 (350 mg) in diethylether (2 ml) was additioned, under stirring, with 256 mg of triphenyl-phosphine, with external cooling by means of a water and ice bath.

At the conclusion of the reaction (about 3 hours), the white precipitate of triphenyl-phosphine sulphide was removed by filtration at 0aC. The solvent was then removed under vacuum and the residue, crystallized from n.hexane, to yield 112 mg of the desired product free from impurities.

EXAMPLE 3 Preparation of N',N-dimethyl-N2-phenyl-formamide sulphide (Compound 17, Reaction 3) A solution of N,N-dimethyl-N'-phenyl-thiourea (0.9 g) and phosgen (COCI2) (2 g), in methylene chloride, was stirred for 8 hours at room temperature. After removal of the solvent under vacuum, the residue (imidoyl chloride) was dissolved in a solution of triethyl-amine (0.7 ml) and anhydrous methylene chloride (20 ml). A solution of N,N-dimethyl-N'-phenyl-thiourea (0.9 g) and triethyl-amine (0.7 ml) in methylene chloride (20 ml) was added dropwise to said solution under stirring and at room temperature. After a period of eight hours under stirring the reaction mixture was washed with the water, dried with anhydrous sodium sulphate, and the solvent was removed under vacuum. The residue was crystallized from petroleum ether, to yield 1.4 g of the desired product (yield = 86%).

EXAMPLE 4 Preparation of N',N'-dimethyl-N2,N3-diphenyl-N3-[(N,N-dimethyl) thiocarbamoyll guanidine (Compound 27, Reaction 4) 43,u1 of trifluoroacetic acid were added to a solution of N',N1-dimethyl-N2-phenyl-formamidine- disulphide (2 g, 5.58 10-3 mols) obtained as described in Example 1 in chloroform (200 ml). The reaction mixture was allowed to rest for 1 5 minutes at room temperature, after which it was washed with a saturated solution of NaHCO3, and dried with anhydrous Na2SO4. After removal of the solvent by evaporation under vacuum, the residue was crystallized from n.hexane/benzene (70:30) to yield 1.3 g of the desired product (yield 71%).

EXAMPLE 5 Determination of the herbicide activity Pots were prepared (upper diameter = 10 cm, height = 10 cm) which contained sandy soil, and each pot was sowed with one of the infesting weeds under examination. Water was supplied to each pot in the amount necessary for germination of the seeds.

The pots were divided into three sets.

The first set was not treated with any herbicide and was used as a control.

The second set was treated, one day after sowing, with a water-acetone dispersion (20% by vol./vol.) of the compounds of the invention, in order to determine the herbicide activity in the preemergence stage.

The third set was treated, 1 5 days after sowing (namely when the plants had already reached a height of 5 to 10 cm, depending on the species) with a water-acetone dispersion (20% by vol./vol.) of the compounds of the invention in order to determine the herbicide activity in the post-emergence stage.

All the pots were kept under observation in a conditioned chamber at temperatures ranging from 15 to 240 C, relative humidity = 70%, photoperiod = 12 hours, light intensity = lux.

Every second day all the pots were uniformly watered in order to secure a humidity degree sufficient for a good growth of the plants.

28 days after treatment, examination was carried out to ascertain the vegetative stage of the plants, the results thereof being expressed according to the scale of values from 0 (growth equal to the control) to 4 (no growth or complete killing of the plants).

The herbicide activity was tested on the following weeds: Monocotyledons A = Echinochloa crusgalli Avenafatua Loliumitalicum D = Sorghum spp.

E = Setaria glauca F = Digitaria sanguinalis G = Alopecurus myosuroides H = Panicum dichotomiflorum = Festuca pratense J = Bromus sterilis Poa annua Dicotyledons L = Stellaria media M = Ipomea purpurea N = Vigna sinensis O = Rumex acetosella P = Galinsoga parviflora o = Convolvolus sepium R = Convolvolus ariensis S = Geranium dissect T = Sida spinosa U= Brassica V = Gypsophila muralis W= Galium aparine The following Table 2 reports the herbicide activity of compounds of the invention according to the tests described above.

TABLE 2

Compound No. Dose Monocotyladons Dicotyledons (see Table 1) Treatment (kg/ha) A B C D E F G H I J K L M N O P Q R S T U V W 2 Pre-emergence 6 4 4 4 4 4 4 4 4 4 4 4 Post-emergence 2 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 11 Post-emergence 2 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 15 Pre-emergence 6 3 4 3 3 4 4 4 4 Post-emergence 6 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 16 Post-emergence 6 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 17 Post-emergence 6 2 2 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 20 Post-emergence 2 4 3 3 4 3 2 4 4 2 26 Pre-emergence 6 2 4 4 4 4 4 4 4 4 Post-emergence 6 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 35 Pre-emergence 6 4 3 3 Post-emergence 2 4 4 3 4 4 4 4 4 4 4 4

Claims

1. A method for combatting weeds comprising applying to the soil pre-emergence and/or post-emergence of said weeds at a dosage rate of from 1 to 6 kg/ha one or more herbicide compounds having the general formula

in which: each R represents a phenyl group which may be substituted by one or more substituents selected from halogen atoms, alkyl group having one to three carbon atoms and haloalkyl groups having 1 to 3 carbon atoms, R' and R2 independently represent an alkyl group having 1 to 3 carbon atoms, an alkoxyl group having 1 to 3 carbon atoms or R' and R2 together form an alkylidenic chain of 4 or 5 carbon atoms which may be interrupted by a heteroatom, and n is 1 or 2.

2. A method of combatting weeds as claimed in Claim 1 substantially as herein described with reference to any one of the Examples.

3. A herbicide composition comprising one or more compounds having the general formula

in which R, R', R2 and n are as defined in Claim 1, together with a carrier.

4. A herbicide composition as claimed in Claim 3 substantially as herein described with reference to any one of the Examples.

5. A process for preparing a compound of the general formula

in which R, R1, R2 and n are as defined in Claim 1, which comprises the following step or steps: (1) treating a trisubstituted thiourea of the formula

in which R, R' and R2 are as defined in Claim 1, with an oxidant in the presence of a base in an inert solvent to yield a compound of formula (I) in which n = 2, optionally (2) treating the product of step (1) with triphenyl-phosphine in diethylether at about OOC to yield a compound of formula (I) in which n = 1, optionally (3) treating the product of step (1) or step (2) with a strong anhydrous acid in an aprotic solvent at room temperature to yield a compound of formula (II).

6. A process as claimed in Claim 5, in which step (1) is conducted utilizing bromine or iodine as the oxidant.

7. A process as claimed in Claim 5 or Claim 6 in which step (3) is conducted utilizing a halogenhydric or trihaloacetic acid as the strong anhydrous acid.

8. A process as claimed in any one of claims 5 to 7 in which steps (1) and (3), utilize methylene chloride (CH2CI2) or chloroform (CHCI2) as a solvent.

9. A process for the preparation of a compound of the general formula

in which R, R1 and R2 are as defined in Claim 1, which comprises reacting a trisubstituted thiourea of formula:

in which R, R1 and R2 are as defined in Claim 1, with an imidoyl chloride of formula:

in which R, R1 and R2 are as defined in Claim 1 in the presence of a slight excess of an organic base and in an inert solvent.

10. A method of preparing a compound of general formula (I) or (II) substantially as herein described with reference to any one of Examples 1 to 4.

11. A herbicide compound of the general formula

in which R, R1, R2 and n are as defined in Claim 1 with the proviso that in formula (II) when R = R2 = CH3, Ris a substituted phenyl group.

12. A compound as claimed in Claim 11 of formula (I) in which n = 1.

13. A compound as claimed in Claim 11 of formula (I) in which n = 2.

14. A compound as claimed in Claim 11 of formula (II).

15. A compound as claimed in any one of claims 11 to 14 in which R1 and R2 independently represent an alkyl group having 1 to 3 carbon atoms.

16. A compound as claimed in any one of claims 11 to 14 in which R' and R2 together represent I -CH2-(CH2)3--CH2- or -CH2-CH2 -0-CH2-CH2.

17. A compound as claimed in Claim 11 substantially as herein described with reference to any one of the Examples.