US Patent No. 4, 695, 644 describes a process for preparing phenylchlorothionoformates in which trichloromethansulfenylchloride is reacted with sulphur dioxide in a biphasic aqueous organic solvent. The aqueous layer is separated and a phenol is added to the organic portion and subsequently a dehydrohalogenating agent.

The production of inter alia alkoxythiocarbonylhydrazines are described by K. A.

Jensen et al, Acta Chem. Scand. 23 (1969) 6,1916-1934. Various methods of preparing such compounds are described in this paper. Phenylhydrazine was said to react with an {[(alkylthio)-thiocarbonyl]thio}acetic acid by displacing the thioacetic acid group to produce the alkoxythiocarbonylphenylhydrazine product.

According to the present invention there is provided a method of preparing a compound of formula (I) where Rl, R2, R3, R4 and R5 are independently selected from hydrogen, halogen, trihalomethyl, pentahaloethyl, mono- or difluoromethyl, mono-, di- tri- or tetrafluoroethyl, fluoroalkylthio, fluoroalkoxy, methylthio, methylsulphonyl, or halomethylsulphonyl, Cl 2 alkyl or methoxy, X is -0-, -S-, -NR7-, -C=N-, -C=N-0-, -NR8-NR9-, where R7, R8 and R9 are independently selected from hydrogen or alkyl ; and R6 is an alkyl group ; which process comprises reacting a compound of formula (II) where R1, R2, R3, R4 and R5 are as defined above in relation to formula (I) ; with a compound of formula (III) where R6 is as defined in relation to formula (I) and Y is a leaving group other than a group SRX where Rx is CH2COOH or Cl 4alkyl.

As used herein the term"halogen"refers to fluorine, chlorine, bromine and iodine.

The term"alkyl"refers to straight or branched chains for example of from 1 to 18 carbon atoms in length, and suitably from 1 to 6 carbon atoms in length. The term"aryl"includes phenyl and naphthyl.

The reaction is suitably effected in the presence of an organic base, in particular a weak base such as pyridine, triethylamine or diisopropylethylamine, or an inorganic base such as Mn+(OH)n, Mn+(HCO3)n or (Mn+)2/n(CO3)2n/2 where M is a metal ion of valency n where n is especially 1 or 2, in particular an alkali or alkaline earth metal cation such as Na+ or K+ or Mg2+ or Ca2+.

Suitable leaving groups Y include halogens, -SR'°, -SM, SSM, -SC(S)OR'°, SSC(S)OR'°, OR'° or OM where Rlo is hydrogen or optionally substituted alkyl (provided that where Y is SRIO, R'° is other than a group CH2COOH or C,4alkyl) and M is as defined above, as well as other such groups including mesylate, tosylate, 1, 3-imidazole.

Suitable optional substitutents for alkyl groups RIO include nitro, =CRbRC, C(O)pRa, OR, S(O)mR, NR R, C(O)NR R, -NR C(O)pR, -NR CONR R, where R, R and R are

independently selected from hydrogen or hydrocarbyl, or Rb and Rc together form a substituted ring which optionally contains further heteroatoms such as S (O),,,, oxygen and nitrogen, p is an integer of 1 or 2, m is 0 or an integer of 1-3.

Particularly suitable groups Y are halogens, -SM, SSM, -SC(S)OR'°, SSC(S)OR'°, OR", or OM where R'° and M are as defined above.

Preferably however the leaving group Y is a halogen, and in particular chlorine.

The reaction is suitably effected in water or an organic solvent or mixtures thereof at temperatures of for example between -78°C to 110°C, preferably at about 5°C. Examples of preferred organic solvents are halogenated solvents such as dichloromethane, aromatic solvents such as toluene and xylene, ether solvents such as t-butylmethylether and tetrahydrofuran, ester solvents such as isopropylacetate, n-butylacetate and iso-butylacetate, alcohols such as methanol.

Particular groups Rl, R2, R3, R4 and R5 include hydrogen and halogen such as chlorine as well as trihalomethyl, in particular trifluoromethyl.

Suitably at least three of Rl, R2, R3, R4 and R5 are hydrogen. Suitably where one or more substituents other than hydrogen are present, one of these groups is at the meta position (R2 or R4). which in particular is trifluoromethyl.

Preferably R6 is an alkyl group in particular a methyl, ethyl or propyl group and especially methyl.

A particular group X is a group of formula -NR8-NR9-, in particular a hydrazine where R8 and R9 are hydrogen.

Compounds of formula (III) may be prepared by the known methods. For example, the reduction of trichloromethansulphenylchloride, followed by the isolation of thiophosgene and subsequent reaction with an alkoxide will yield a compound of formula (III) where Y is chlorine and R6 is methyl. The problem with this and similar processes is that it is necessary to isolate and deal with thiophosgene which is unstable.

The applicants have found an improved method for the production of compounds of formula (III) which does not require the isolation of thiophosgene.

In a further aspect, the invention provides a method of preparing a compound of formula (III) by reacting a compound of formula (IV)

where Y1, Y2, Y3 and Y4 are each leaving groups such as halogen and particularly chlorine, provided that at least one of Y1, YZ or Y3 is a group Y of formula (III), with a compound of formula (V) where R6 and MI is hydrogen or a group M as defined above ; in the presence of a reducing agent.

Suitable reducing agents include hydrogen or a hydrogen transfer reagent such as isopropanol or formic acid or salts, a sulfur containing compound such as hydrogen sulphide or salts, a dihydrogen sulfite or dithionite or salts, in particular alkali metal salts such as sodium hydrogen sulfite, sodium sulfite or sodium dithionite, sulfur dioxide, or a transition metal or salt such as ferrous chloride, stannous chloride, acidic zinc, acidic copper or potassiumhexacyanoferrate.

A particularly preferred reducing agent is hydrogen sulfite salts such as alkali metal hydrogen sulfites like sodium hydrogen sulfite.

Suitable leaving groups YI, Y2, Y3 and Y4 are those described above in relation to Y in formula (III). Preferably however, yl, y2, Y3 and Y4 are the same and are all halogens such as chlorine.

The reaction is preferably effected in the presence of a catalyst. Examples of catalysts which may be used in this reaction include iodide salts, such as potassium iodide.

The reaction may be carried out in a solvent which may comprise water or mixtures of water and miscible solvents such as alcohols preferably methanol, or optionally with a second immiscible phase. Preferably the immiscible phase is an organic solvent. Examples of preferred organic solvents are halogenated solvents such as dichloromethane, aromatic solvents such as toluene and xylene, ether solvents such as t-butylmethylether and tetrahydrofuran, ester solvents such as isopropylacetate, n-butylacetate and iso-butylacetate.

The reaction is suitably carried out at temperatures for example of from -20 to 1 50°C, conveniently at about 0°C.

In a preferred embodiment, the compounds of formula (III) are produced using the improved method described above and reacted with a compound of formula (II) in-situ. Thus in a particularly preferred embodiment, compounds of formula (I) are produced by mixing together a compound of formula (II) as defined above, a compound of formula (IV) as defined above, a compound of formula (V) as defined above and a reducing agent. For example, it has been found that methyl-2- (3-trifluoromethylphenyl) thionocarbazate can be produced when 3-trifluoromethylphenylhydrazine is added to a mixture of trichloromethansulfenylchloride, sodium hydrogen sulfite and sodium methoxide.

The present invention provides a high yielding process for the formation of intermediates such as methyl-2- (3-trifluoromethylphenyl) thionocarbazate by reaction of mixtures of3-trifluoromethylphenylhydrazine and methylchlorothionoformate. The by- products of this reaction are generally easy to handle and dispose of. For example in this particular example, the by-product is hydrogen chloride or an alkali metal chloride salt.

The invention will now be particularly described by way of example.

Example 1 Step 1 Preparation of methvlchlorothionoformate Trichloromethansulfenylchloride (lg), dichloromethane (5ml), water (2ml), potassium iodide (13mg) and sodium hydrogen sulfite (1. 3g) were stirred vigorously in a round-bottomed flask at 0°C.

Concentrated sulfuric acid (0. 3g) was added dropwise and the resulting mixture was stirred at room temperature for ten hours. The phases were separated and the organic layer was dried over sodium sulfate before 1. 06 ml of 25% (w/w) sodium methoxide in methanol was added.

Step 2 Preparation of methvl-N,N'-3-trifluoromethylphenylthiocarbazate A 3 neck round-bottom flask fitted with a thermometer and nitrogen inlet, was charged with 3-trifluoromethylphenylhydrazine (1. 6g), pyridine (0. 56ml) and dichloromethane (Sml). The flask was cooled to 5°C before the methylchlorothionoformate

prepared in step 1 above was added dropwise whilst stirring. The reaction mixture was allowed to warm to room temperature. The reaction mixture was quenched into water (10mol), and the phases separated. The organic layer was washed with saturated sodium bicarbonate solution and then dried over sodium sulfate, before the solvent was removed under reduced pressure to afford a brown oil (1. 9g).