NITRATION OF AROMATIC COMPOUNDS

Abstract: A method of nitrating electron-deficient carbocyclic or heterocyclic aromatic compounds such as pyridines, diazines and triazines and benzenoid aromatics having electron-withdrawing substituents involves first reacting the aromatic species with a sulphilimine species or with the corresponding N-alkali metal salt thereof to generate an N-(hetero)aryl-S,S-dialkyl, diaryl or alkylarylsulphilimine derivative. This intermediate may then be readily oxidised under relatively mild conditions using a peroxycarboxylic acid such as m-chloroperbenzoic acid, peracetic or peroxytrifluoroacetic acid. Good yields of nitrated products are obtained including some previously unprepared. The novel N-alkali(alkylaryl)sulphilimine reagents are prepared by reacting an alkali metal hydride, an alkali metal hydrogenous base or an alkyl lithium with the corresponding sulphilimine. Preferred salts are the N-lithio types and the preferred sulphilimine is diphenylsulphilimine. Where the salt is used reaction should be in an aprotic solvent but if the sulphilimine per se is the reagent a polar solvent is used.

Description: Nitration of Aromatic Compounds The present invention relates to a process for the nitration of aromatic compounds and in particular the nitration of both heterocyclic and carbocyclic electron deficient aromatics Typical heterocyclic electron deficient aromatics are such substances as pyridines, diazines (especially pyrimidines and pyrazines) and triazines whilst the carbocyclic electron deficient aromatics may be described as being benzenoid aromatics substituted with electron-withdrawing groups. In general, for the purposes of the present invention, an electron-deficient aromatic is defined as either a heterocyclic or carbocyclic aromatic bearing a leaving group which is commonly displaced by nitrogen nucleophiles. Such leaving groups include halogens, nitro groups, alkoxy groups and nitrile groups Conventional electrophilic nitration methods based on nitronium ion (NO ) chemistry are widely used in chemical synthesis and are highly successful in the case of nitration of carbocyclic aromatics such as toluene and with electron-rich heteroaromatics such as 1 ,2,4-triazolone. With electron-deficient aromatic systems such as benzenes containing electron-withdrawing groups and heterocyclic azines, diazines and triazines, however, methods based on nitronium ion chemistry are almost entirely ineffective. For example nitration of pyridine using potassium nitrate/oleum at 350°C yields less than 3% of 3-nitropyridine (R M Acheson, "An Introduction to the Chemistry of Heterocyclic Compounds, 3rd. Ed ", p237 (Interscience, 1976)). A number of strategies have been attempted to overcome these difficulties, including attempts at use of nucleophilic nitrating agents. For example, AgNO 2 or NaN0 2 have been used to generate nitrite ions which will displace halogen from the aromatic species. However, this reagent suffers from a number of serious defects Thus it is relatively expensive and at the same time environmentally undesirable as a chemical reagent It also exhibits a lack of specificity in its mode of attack, often yielding predominantly nitrite esters rather than nitro compounds It is known that nitroheterocycles may be prepared by oxidation of dialkylsulphilimine and related phosphinimine intermediates derived from aminoheterocycles (Taylor et al, J Org Chem 47 552 (1982) and Rakitin et al, Khim Geterot. Soed. 1536 (1990), and Coburn et al J Het. Chem 23 421 ( 1986) and J Het Chem. 26 1883 (1989)) However these processes are not initially attractive since the use of aminoheterocycles requires additional process steps to prepare these and suitable aminoheterocycles are of limited availability In the case of the phosphinimines (where furazan was used as the heteroaromatic nucleus) difficulties were experienced in the oxidation step and use of the rather exotic oxidant dimethyldioxirane (DMD) was necessary to obtain good yields of the nitro product Preparation of some phosphinimine derivatives of heteroaromatics by nucleophilic substitution has been reported and Tamura et al (J Org Chem 38, 4324 (1973)) reported the preparation of l -S,S-diphenylsulphilimino-2,4-dinitrobenzene from 2,4-dinitrofluorobenzene Vlasova et al (Org Prep Proced Int 26 33 1 ( 1994)) have reported some examples of nucleophilic substitution in heteroaromatics and also with 2,4-dinitrochlorobenzene using S,S-diphenylsulphilimine with the reactions being carried out in dichloromethane None of these sulphilimine or phosphinimine derivatives was subsequently oxidised to generate the corresponding nitro-compounds and indeed in some cases the starting materials for their generation were nitro- compounds (ie the departing group was a nitro-substituent) Vlasova et al commented that mildly activated nitroheterocycles such as 4- methyl- and 4-phenyl-3-nitrofurazan did not react with S,S-diphenylsulphilimine and also that S,S-diphenylsulfilimine hydrate (which they obtained as an intermediate in the preparation of the non-hydrated material) did not react with one of the selected heteroaromatics and was therefore a weaker nucleophile than the non-hydrate Their preferred reaction conditions thus avoided use of the hydrate and used as solvent non- polar species such as dichloromethane, carbon tetrachloride and benzene All of these solvents are less acceptable from an environmental point of view The present inventors on the other hand have now found that by vaπation of the reaction conditions and in particular by the selection of the solvent which is used, a much broader range of nucleophilic aromatic substitution reactions involving either dialkyl-, diaryl- or mixed alkylarylsulphilimines becomes possible and that under appropriate circumstances the hydrated form of such sulphilimmes can also be used with some advantage As well as substituted heteroaromatics, substituted benzenoid aromatics (carbocyclic aromatics) may be used as the starting materials Accordingly in a first aspect ofthe present invention there is provided a method of preparing N-aryi- and N-heteroarylsulphilimine derivatives of electron-deficient carbocyclic and heterocyclic aromatics which comprises the steps of a) reacting an electron-deficient heterocyclic or carbocyclic aromatic compound with a dialkyl-, diaryl- or mixed alkylaryisulphilimine in a polar solvent, and b) isolating the N-(hetero)aryl-S,S-dιalkyl-, diaryl- or alkylaryisulphilimine [or N-aryl-S,S-alkylarylsulphιlιmιne] deπvative which is formed As the sulphilimine reagent S,S-dιphenylsulphιlιmιne is particularly preferred since this is a commercially available mateπal Other possible sulphilimmes include S- methyl-S-phenyl- and S,S-dιmethylsulphιlιmιne Preferably the polar solvent is an alcohol or an ether, most preferably an alcohol of low molecular weight such as ethanol or other lower alcohols with chain length 4 carbon atoms or less The ether may be a cyclic ether such as tetrahydrofuran (THF) or 1 ,4-dιoxane Under the circumstances stipulated for this process, apart from the notably greater reactivity which has been observed by the present inventors (for example the less reactive pyridine, pyrimidine and pyrazine heterocycles may be successfully reacted under these conditions), a substantially more economical use of the sulphilimine reagent is achieved Thus whereas the method of Vlasova et al involves use of three equivalents of S,S-diphenylsulphilimine to one equivalent of aromatic reagent, in the present process only two equivalents are used of which one is recovered in the form of a salt (eg. the halide salt) and may be reconverted to the diphenylsuiphilimine reagent by treatment with butyllithium. An additional advantage is the use of environmentally acceptable solvents as noted earlier. With the exception of the above noted l -S,S-diphenylsulphilimino-2,4- dinitrobenzene, all of the N-(hetero)aryl-S,S-diphenylsulphilimine compounds generated using the process of the present invention are novel materials. This includes the following compounds: 6-chloro-2-pyrazinyl-S,S-diphenylsulphilimine, 3-nitro-2- pyridinyl-S,S-diphenylsulphiIimine, 4-nitro-3-chlorophenyl-S,S-diphenylsulphilimine, 2-chloro-3-nitro-4-pyridinyl-S,S-diphenylsulphilimine, 2-pyrazinyl-S,S- diphenylsulphilimine, 2-(n-propoxy)-4-chloro-6-( l ,3,5-triazinyl)-S,S- diphenylsulphilimine, 2,3,5,6-tetrachloro-4-pyridinyl-S,S-diphenylsulphilimine, 3,4,5,6- tetrachloro-2- pyridinyl-S,S-diphenylsulphilimine, 2-(n-propoxy)-4,6-( 1 ,3,5-triazinyl)- bis-S,S-diphenylsulphilimine, 2,4-bιs-(n-propoxy)-6-( 1 ,3,5-triazinyl)- diphenylsulphiϋmine, 6-chloro-4-pyrirnidiny!-S,S-diphenylsulphilimine, 5-nitro-2- pyridiny]-S,S~diphenylsulphilimine, 4-chioro-2-pyrimidinyl-S,S-diphenylsulphilimine, 2,4-dichioropyrimidinyl-S,S-diphenylsulphilimine, 4,6-dichloropyrimidinyl-S,S- diphenylsulphilimine, 2,5,6-trichloropyrimidinyl-S,S-diphenylsulphilimine, 4,5,6- trichloropyrimidinyl-S,S-diphenylsulphilimine and 2,3,5,6-tetrafluoro-4-pyridinyl-S,S- diphenylsulphilimine, 3,5-dinitro-2-pyridinyl-S,S-diphenylsulphilimine and 3,5,6- trifluoro-2-pyridinyl-S,S-diphenylsulphilimine. The formulae for these compounds appear respectively as 1 to XX in Figures 1 and 2. All of these materials are stable crystalline solids or oils. The present inventors have further provided an entirely novel class of related reagents which, in addition to substitution of electron-withdrawing groups, enable vicarious substitution of the hydrogen on carbocycles and heteroaromatics by diarylsulphilimino groups to proceed under easy conditions. According to a second aspect of the present invention therefore there is provided a class of novel reagents comprising N-alka!i metal salts of S,S-dialkyl-, diaryl- or alkylarylsulphilimmes having the general formula (XL): where R l and R are independently alkyl and/or aryl groups and M is lithium, sodium or potassium. A particularly preferred class of reagents of this type are the N-lithio salts and especially N-lithio-S,S-diphenylsulphilimine. These novel reagents may be readily prepared by reacting the corresponding sulphilimine with alkyl lithiums with chain length 1 to 4 atoms, preferably n- butyllithium, alkali metal hydrides such as lithium, sodium or potassium hydrides, alkali metal hydrogenous bases such as lithium, sodium or potassium N,N- di(isopropyl)amides or the respective N,N-bis(trimethylsilyl)amides or other suitable base. When these reagents are applied to the process which comprises the first aspect of this invention, a yet broader range of reaction products may be obtained. However for these reagents it has been found that the reaction should be carried out in an aprotic solvent. Accordingly in a further aspect ofthe present invention there is provided a process for the preparation of N-(hetero)arylsulphilimine derivatives of electron-deficient carbocyclic aromatics and heteroaromatics comprising the steps of: a) reacting an electron-deficient carbocyclic or heterocyclic aromatic compound with an N-alkali metal salt of an S,S-dialkyl-, diaryl- or alkylaryisulphilimine in an aprotic solvent, and b) isolating the N-(hetero)aryl-S,S-dialkyl-, diaryl- or alkylaryisulphilimine derivative which is formed. Preferably the N-alkali metal salt used is an N-lithio sulphilimine salt and particularly preferred is N-lithio-S,S-diphenylsulphilimine which is readily derived from the commercially available compound S,S-diphenylsu!philimine. Although the corresponding salts derived from sodium and potassium would react in a similar manner these are likely to be more difficult to prepare than the lithium salts and therefore comprise less desirable reagents from a practical point of view As the aprotic solvent 1 ,4-dioxane, dimethoxyethane, diethyleneglycol dimethylether (diglyme) or most especially tetrahydrofuran are preferred. In a yet further aspect the present invention provides a process for the nitration of electron-deficient carbocyclic and heterocyclic aromatic compounds which comprises the steps of- a) reacting an electron-deficient carbocyclic or heterocyclic aromatic (as hereinbefore defined) with a dialkyl-, diaryl- or alkylaryisulphilimine in a polar solvent or with the corresponding N- lithium salt thereof in an aprotic solvent to generate the corresponding N-(hetero)aryl-S,S-dialkyl-, diaryl or alkylaryisulphilimine derivative thereof; b) treating the product of step (a) with an oxidising agent to convert the sulphilimino group to a nitro-group; and c) isolating the nitrated aromatic compound obtained in step (b). The reaction of step (a) is as previously described In the second, oxidation, step the inventors have found, in contradistinction to earlier work with phosphinimines, that the sulphilimine derivatives may be readily oxidised with commercially available oxidants such as m-chloroperbenzoic acid A more economical and potentially industrially-applicable process thus results In general any peroxycarboxvlic acid may be employed such as vaπous perbenzoic acids, particularly m-chloroperbenzoic acid, peracetic acid or peroxytπfluoroacetic acid Yields in the first, nucleophilic substitution, step are typically in the range of 60% to quantitative and in the second, oxidation, step in the range of 10 to 63% In general, even in the case of compounds which have previously been obtainable via conventional electrophilic nitrations, the yields are greater with the present two-step process than have been achieved before It will be readily appreciated that in addition to the generation of mono-nitro- substituted aromatics, the ability of the aforementioned novel N- hthιo(alkyl/aryl)sulphιlιmιne reagents to bring about vicarious hydride substitution in which a ring hydrogen atom either ortho- or para- (but especially the former) to a nitro-group already present in the πng is substituted, enables polynitro heterocyclic and carbocyclic aromatics to be produced quite readily Such materials have previously often been either very difficult or indeed impossible to prepare Compounds such as 3,4-dιmtrochlorobenzene, 2-chloro-6-nιtropyrazιne, 4- nιtro-2,3,5,6-tetrachloropyπdιne, 2-nιtro-3,4,5,6-tetrachloropyπdme and 4-nιtro- 2,3,5,6-tetrafluoropyπdιne have been prepared and additionally the novel compound 2- chloro-3,4-dιnιtropyπdιne has now been obtained Such polynitro-substituted aromatics are regarded as important precursors for the production of new types of thermally- and impact-insensitive high explosives matenals The invention will now more particularly be described with reference to the following examples Formulae referenced below which correspond to either starting materials or to nitro compound products (formulae XXXI to XXXVIIΪ and XXI to XXX) appear respectively on Figures 3 and 4 Example 1 : Prepnrntioii or 2-clιloro-6-ιιitropyrnzine (XXI) from 2.6- dichloropyrnzine (XXXI). 1st step. S,S-Diphenylsulphilimιne monohydrate (0 540g, 2 46 mmol, 2 equiv ) was weighed out into a 100ml triple-necked round-bottomed flask THF (tetrahydrofuran, 15 ml) was added, causing the sulphilimine to dissolve The THF had been purified by distillation 2,6-Dichloropyrazine (XXXI, 0 183g, 1 23 mmol, 1 equiv ) was added to the solution in the flask The central neck of the flask was fitted with a Liebig condenser, a magnetic stirrer bar was placed in the flask and stoppers were placed in the remaining two necks of the flask The contents of the flask were stirred and refluxed for 18 hr This was accomplished using a paraffin oil bath heated on a hotplate-stirrer device During the first hour of reflux a white precipitate appeared At the end of the 18 hr the flask was lifted out of the oil bath and allowed to cool to room temperature The white precipitate was separated from the solution by gravity filtration The white solid was shown by Η nmr spectroscopy and elemental analysis to be the salt diphenyl(aminosulphonium) chloride, the side product of N-aryl S,S- diphenylsulphilimine formation The THF was removed from the filtrate using a rotary evaporator A yellow brown oil remained, which was shown by nmr to be a slightly impure form ofthe desired product 2-chloro-6-S,S-diphenylsulphiliminopyrazine (I, 0.366g, 95%) The impurity, 5% of the starting material 2,6-dichloropyrazine, was removed when the crude product was purified by flash column chromatography The column was packed with lOg of Merck Kieselgel 60 flash silica (particle size 0 040 - 0.063mm) and eluted under pressure using small bellows with a 1 .2 vol /vol mixture of dichloromethane and petrol (b pt 40-60°C) followed by pure dichloromethane The crude product was dissolved in approx 1 ml of the eluting solvent and put onto the column using a long pipette HPLC grade dichloromethane was used and the petrol had been distilled prior to use The desired product had a retention factor of 0 16 on a thin layer chromatography plate pre-coated with Merck Kieselge! 60 F-254 and eluted in dichloromethane, i e Rf = 0 16 (CH2CI2) The impurity had a retention factor of 0 50 (CH 2 C1 2 ) Data for the product of the first step, 2-chloro-6-S,S-diphenylsulphiliminopyrazine (I) ! H nmr (CDC1 3 , 300MHz) 7 60 (IH, s, ArH) 7 42-7 78 (6H, m, ArH) 7 71-7 79 (4H, m, ArH) 8 10 (IH, s, ArH) where s = singlet, m = multiplet, ArH = proton attached to aryl group, CDCK = deuterated chloroform and a Bruker AC 300 spectrometer was used E I mass spectrometry, 313, 315 (M\ 4%, 1%) 278 (M-Cl, 1 ) 204, 206 (M- SPh, 3, 1) 186 (SPh 2 , 100) 109 (SPh, 17) 92 (M-Cl-SPh 2 , 1 1 ) 83 (18), accurate mass for molecule containing Cl correct to 0 1 ppm The figures outside the brackets denote the molecular masses of the fragments seen and the contents of the bracket give the identity of the fragment and the intensity of its peak as a percentage M denotes the molecular fragment The mass spectra were obtained using a Kratos Analytical Profile MS and a Shimadzu GC- 14A 2nd step. The oxidising agent 3-chloroperoxybenzoιc acid (0 1 8g, 1 15 mmol, 6 equiv ) was weighed out into a 100ml triple-necked round-bottomed flask of the type used in the first step The three necks ofthe flask were fitted with a stopper, a water condenser and a thermometer respectively, and a magnetic stirrer bar was placed in the flask 10ml of HPLC grade 1 ,2-dιchloroethane was added to the flask, and the flask and its contents were cooled to -5°C using ice-salt mixture 2-Chloro-6-S,S- diphenylsulphilimino-pyrazine (I, 60mg, 0 19 mmol, 1 equiv ) was added to the flask The contents ofthe flask were stirred, the ice bath was removed, the flask was allowed to warm up to room temperature and was then placed in the paraffin oil bath used in the first step The reaction mixture was refluxed for 2 hr and then allowed to cool The mixture was washed with two 10ml portions of 0 5 M aqueous sodium hydroxide followed by two 10ml portions of distilled water The reaction mixture was then dried over 5g of anhydrous magnesium sulphate The dry reaction mixture was separated from the solid magnesium sulphate by gravity filtration and then 1 ,2-dichloroethane was removed on a rotary evaporator leaving a brown oil The oil was purified by flash column chromatography using the type of silica and eluting solvent described in the first step 2-Chloro-6-nitropyrazιne (XXI) was obtained as a yellow oil (0 018g) in 20% yield; Rf=0 59 (CH 2 C1 ), Η nmr (CDCh, 300 MHz) 8 90 (I H, s), 9 30 ( l H,s) The side-product of oxidation, diphenyl sulphone, was also obtained (0 029g) Example 2: Preparation of 2,3-dinitropyridme (XXII) from 2-chloro-3- nitropyridine (XXXII). 1st step. Apparatus and method as in Example 1 S,S-Diphenylsulphilimine monohydrate (0.519g, 2 37 mmol, 2 equiv ) and 20ml ethanol were added to a 100ml triple-necked round-bottomed flask set up for reflux 2-Chloro-3-nitropyridine (0 188g, 1 18 mmol, 1 equiv ) was added and the reaction mixture was refluxed for 7 hr and then allowed to cool Since the side-product diphenyl(amιnosulphonιum) chloride was soluble in ethanol it was not removed by filtration at this stage Instead, ethanol was removed from the reaction mixture on a rotary evaporator leaving an impure yellow solid This was purified by flash column chromatography (eluting solvent 3 2 vol /vol CH 2 CI 2 -petrol (b pt 40-60°C), gradient to 100% CH 2 C1 2 ) The desired product, 2-S,S-diphenylsulphilimino-3-nitropyridιne (II) was obtained as a crystalline yellow solid in 76% yield (0 290g), Rf=0 20 (CH 2 CI 2 ), m pt 132- 134°C, elemental analysis, found C, 63 42, H, 4 04, N, 12 97, requires C, 63 14, H, 4 05, N, 12.99; Η nmr (CDCh, 300 MHz) 6 46-6 50 (IH, dd, ArH) 7 45-7 48 (6H, m, ArH) 7.88-7 91 (4H, , ArH) 8 06-8 08 (I H, dd, ArH) 8 15-8 19 ( I H, dd, ArH), dd=doublet of doublets, mass spectrometry (El) 323 (M\ 7%) 293 (M-NO, 1 ) 258 (3) 214 (M-SPh, 1) 186 (SPh 2 , 100) 168 (12) 152 (6) 139 ( 1 1 ) 109 (SPh, 9) 77 (Ph, 14), accurate mass 3 7ppm 2nd step. A flask containing 3-chloroperoxybenzoιc acid (0 224g, 1 30mmol, 6 equiv ) and 1,2-dichloroethane (10ml) was cooled to -5°C in an ice-salt bath as described in Example 1. 2-S,S-diphenylsulphilimino-3-nιtropyridine (II, 0 07g, 0 22mmol) was added. The mixture was allowed to warm up to room temperature, refluxed for 2 hr and then cooled to -10°C A white precipitate of the oxidation side-product 3- chlorobenzoic acid appeared, and this was removed from the mixture by gravity filtration 1 ,2-Dιchioroethane was then removed from the reaction mixture on a rotary' evaporator The desired product, 2,3-dιnitropyridine (XXII), was obtained as a yellow oil in 9% yield after purification by flash column chromatography (eluting solvent 3 4 vol./vol. CH 2 CI 2 -petrol (b pt 40-60°C), gradient to 100% CH 2 C1 2 ) The side-product diphenyl sulphone was also obtained Data for 2,3-dinitropyridine. Rf=0 58 (CH 2 CI 2 ), Η nmr (CDC1 3 , 300 MHz) 7 80-7 85 ( I H, m, ArH) 8.51 -8 54 (IH, m, ArH) 8 77-8 79 (IH, m, ArH); mass spectrometry (El) 169 (M\ 100) 147 (4) 105 ( 10) 99 (33) 77 (M- 2NO 2 , 13) accurate mass, 3 9ppm Example 3. Preparation of 1 -chloro-3,4-dinitrobenzene (XXIII) from l -chloro-4- nitrohenzene (XXXIII). 1st step. A 100ml triple-necked round-bottomed flask containing a magnetic stirrer bar, a 20ml syringe with Luer needle and a 5ml syringe with Luer needle were dried in an oven for 24 hr at 150°C The techniques described in this section are appropriate for the handling of pyrophoric materials i e oxygen and water are excluded The flask was removed from the oven, the central neck was fitted with a nitrogen bubbler and the remaining two necks were fitted with rubber septa The flask was flushed with nitrogen. S,S-diphenylsu!philimine monohydrate ( 1 097g, 5mmol, 1 equiv ) was added to the flask The 20ml syringe was removed from the oven and used to add 15ml of anhydrous THF to the flask The THF had been freshly distilled over calcium hydride The solution in the flask was degassed by attaching a long needle to a nitrogen supply and putting the needle through one of the septa so that the end of the needle was in the solution Bubbles of nitrogen were allowed to pass through the solution in this way for 10 min The long needle was then removed The 5ml syringe was removed from the oven and flushed with nitrogen for 5 min It was then used to add n-butyllithium (4ml of a 2 5 M solution in hexanes, 10 mmol, 2 equiv., DANGER pyrophoric compound !) dropwise to the stirred solution which immediately turned yellow, indicating the presence of N-lithio-S,S-diphenylsulphiiimine The empty 5ml syringe was placed in a large beaker of butan- 1 -ol immediately after use 1 -Chloro-4- nitrobenzene (XXXIII, 0 788g, 5 mmol, 1 equiv ) was added to the yellow solution by briefly removing one of the septa, and the mixture was stirred under nitrogen at room temperature for 24 hr The mixture was then exposed to the air and the THF removed on a rotary evaporator The crude product was purified by flash column chromatography (eluting solvent 1 2 vol /vol CH 2 Cl 2 -petrol (b.pt. 40-60°C)) 1 - Chloro-3-S,S -diphenylsu!philimιno-4-nitrobenzene (III, 0 34g) was obtained as a crystalline yellow solid in 19% yield, Rf=0 43 (CH C1 2 ), elemental analysis, found, C, 60.06, H, 3.57, N, 7 90, required, C, 60 58, H, 3 67, N, 7 85; Η nmr (CDCU, 300MHz) 6 56-6 60 ( IH, dd, ArH) 6 94-6 95 (I H, d, ArH) 7 49-7 52 (6H, , ArH) 7.69-7 73 (IH, d, ArH) 7 83-7 88 (4H, m, ArH), mass spectroscopy (El) 356, 358 (M\ 1%), 0 3%) 1 86 (SPlι 2 , 100) , accurate mass, 35 C1, 2 5 ppm 2nd step. 3-Chloropero\ybenzoιc acid (0 320g, 1 S6mmol, 6 equiv ) and 1 ,2- dichloroethane (20ml) were cooled to -5°C in a 100ml triple-necked flask using an ice- salt bath l-Chloro-3-S,S-dιphenylsLilphilimmo-4-nιtrobenzene (III, 0 1 l Og, 0 3 1 mmol, 1 equiv ) was added, the flask was allowed to warm up to room temperature and was then refluxed for 2 hr After cooling, the reaction mixture was washed with two 10 ml portions of 0 5M aqueous sodium hydroxide followed by two 10ml portions of distilled water and then it was dried over anhydrous magnesium sulphate (see Example 1 ) After removal of the magnesium sulphate by gravity filtration, 1 ,2- dichloroethare was removed from the reaction mixture on a rotary evaporator The crude product was purified by flash column chromatography (eluting solvent 1 3 vol./vol CH 2 Cl 2 -petrol (b pt 40-60°C), gradient to 100% CH 2 CI 2 ) and the desired product l-chloro-3,4-dinιtrobenzene (XXIII) was obtained as a pale yellow solid in 32% yield (0.020g), Rf=0 79 (CH 2 C1 2 ), Η nmr (CDCh, 300MHz) 7 69-8 18 (3H, m, ArH), mass spectrometry (El) 202,204 (M\ 1 5%, 5%) 172, 174 (M-NO, 4, 1 ) 1 56, 158 (M-NO 2 , 38, 13) 139, 141 (42, 14) 128, 130 (8,3), accurate mass, 35 C1, 5 4ppm Example 4: Preparation of 2-ehloro-3.4-diιιitronyridine (XXIV) from 2-chloro-3- nitropyridine (XXXII). 1st step. A solution of N-lιthio-S,S-diphenylsulphilimine (1 23 mmol, 1 equiv ) in 15ml anhydrous THF was prepared using S,S-diphenylsulphilimine monohydrate (0 270g, 1.23 mmol, 1 equiv ) and n-butyllithium (0 98ml of a 2 5 M solution in hexanes, 2 46 mmol, 2 equiv ) using the method, apparatus and precautions described in Example 3 2-chloro-3-nitropyπdine (XXXII, 0 195g, 1 23mmol) was added to the solution and it was stirred under nitrogen at room temperature for 24 hr At the end of this time, the mixture was exposed to the air and the THF was removed on a rotary evaporator The crude product was purified by flash column chromatography (eluting solvent 1 3 vol /vol CH 2 CI 2 -ρetrol (b pt 40-60°C), gradient to 100% CH 2 CI 2 ) and the desired product 2-chloro-3-nitro-4-S,S-diphenylsulphiliminopyridine (IV) was obtained as a yellow solid in 49% yield, Rf=0 15 (CH 2 C1 2 ), Η nmr (CDCI 3 , 300MHz) 6 75-6 81 (IH, d, ArH) 7 40-7 55 (6H, m, ArH) 7 63-7 73 (4H,m, ArH) 7 85-7.90 (I H, d, ArH), mass spectrometry (El) 357,359 (M\ 5%,2%) 291 (1 ) 232 (3) 186 (SPh 2 , 100) 125 (12) 105 (52) 77 (Ph, 24), accurate mass, 35 C1, 4 2 ppm 2nd step 3-Chloroperoxybenzoic acid (0 290g, 1 68mmol, 6 equiv ) and 1 ,2- dichloroethane ( 10ml) were weighed out into a triple-necked round-bottomed flask and cooled to -5°C using an ice-salt bath 2-Chloro-3-nιtro-4-S,S- diphenylsulphiliminopyridine (IV, 0 l OOg, 0 28mmol) was added, the contents of the flask were allowed to warm up to room temperature, refluxed for 2 hr and then cooled to -10°C, allowing the side-product of oxidation, 3-chlorobenzoic acid, to precipitate out of solution The precipitate was removed by gravity filtration and 1,2- dichloroethane was removed from the resulting filtrate using a rotary evaporator The crude product was purified by flash column chromatography (eluting solvent 1 :2 vol./vol (b.pt 40-60°C)) The desired product, 2-chloro-3,4-dinitropyridine (XXIV), was obtained as a yellow oil in 9% yield; Rf=0 54 (CH 2 C1 2 ), Η nmr (CDC1 3 , 300MHz) 8.02-8 08 (IH, d, ArH) 8 83-8 90 ( I H, d, ArH), mass spectrometry (El) 203,205 (M * , 39%, 12%) 173 (3) 155 (3) 129 (7) 84 (100), accurate mass, 35 C1, 1.7ppm Example 5: Preparation of 4-nitro-2,3.5.6-tetrachloronyridine (XXV) from pentachloropyridine (XXXV). 1st step S,S-diphenylsulphilimine ( 1 08g, 4 92 mmol, 2 equiv ) was weighed into a 100ml triple-necked round-bottomed flask THF ( 15 ml) was added, causing the solid sulphilimine to dissolve Pentachloropyridine (XXXV, 0 618g, 2 46 mmol, 1 equiv ) was added to the solution m the flask The central neck of the flask was fitted with a water condenser, and the remaining two necks fitted with glass stoppers A magnetic stirrer was used to stir the solution The contents of the flask was stirred and refluxed for 4 hr, using a paraffin oil bath heated on a hotplate stirrer device At the end of the 4 hr the reaction mixture was cooled to room temperature and the white precipitate of diphenylaminosulphonium chloride which had appeared during the reaction was removed by filtration This salt was saved for recycling THF was removed from the filtrate using a rotary evaporator The white solid which remained after rotary evaporation was purified using flash column chromatography The column was eluted with a 1 4 volume/volume mixture of dichloromethane and petrol (b pt 40-60°C) Two products were obtained 4-S,S-diphenylsulphilimιno-2,3,5,6-tetrachloropyridine (VII, 0 473g, 46%), m pt 143- 144°C, Rf=0 65 (CH 2 CI 2 ), elemental analysis, found, C, 48.95, H, 2 18, N, 6 85, C Π H K SCL, requires, C,49 06, H, 2 42, N, 6 73, δ„ (CDCh, 300 MHz) 7 45-7 51 (6H, m, ArH) 7 84-7 91 (4H, m, ArH), δ c (CDCK, 100 6 MHz) 121.6 (C3 of pyridine) 126 2, 129 9, 131 9 (ortho, e/a and para phenyl Cs) 140 4 (phenyl C attached to sulphur) 145 65, 156 8 (C2, C4 of pyridine), m/z (El) 416, 414 (M\ 4%, 3%) 381 (M-Cl, 1 ) 307 (M-SPh, 1 ) 270 (2) 232, 230 (6, 5) 186 (SPh 2 , 78) 84 (100) 77 (Ph, 14), accurate mass, 4 x 3S Cl, 2 7ppm, ' 7 C1 + 3 x 35 C1, 3 1 ppm 2-S,S-diphenylsulphilimino-3,4,5,6-tetrachloropyridine (VIII, 0 181g, 18%), m p 175°C, Rf=0 80 (CH 2 C1 2 ); elemental analysis, found, C, 48.99, H, 2 16, N, 6 71 , Cι 7 HιoN 2 SCl 4 requires C, 49 06, H, 2 42, N, 6 73, δ„ (CDCK, 300 MHz) 7 49-7 52 (6H, m, ArH) 7.81 -7 88 (4H, m, ArH); m/z (El) 414, 416 (M + , 14%, 1 8%) 379 (M-Cl, 1) 339 (M-Ph, 1 ) 305, 307 (M-SPh, 18, 23) 186 (SPh 2 , 100) 109 (SPh, 12) 77 (Ph, 16), accurate mass, 4 x ' °C1, 1 6 ppm, j7 C! + 3 x " °C1, 1 2 ppm 2nd step. The oxidising agent 3-chloroperoxybenzoic acid (0 497g, 2 87 mmol, 6 equiv ) was weighed out into a 100ml triple-necked round-bottomed flask The three necks of the flask were fitted with a stopper, a water condenser and a thermometer, and a magnetic stirrer bar was placed in the flask HPLC grade 1 ,2-dichloroethane (20 ml) was added to the flask and the contents of the flask were cooled to -5°C by suspending the flask in a plastic bowl filled with a mixture of ice and salt (i e. sodium chloride) 4-S,S-dιphenylsulphilimino-2,3,5,6-tetrachloropyridine (VII, 0 200g, 0.481 mmol, 1 equiv ) was added to the reaction mixture, and the mixture allowed to warm up to room temperature At this point the reaction mixture was lime green. It was then refluxed for 2 hr, during which time the colour changed from green to yellow The reaction mixture was then cooled to -5°C and the precipitate of 3-chlorobenzoic acid which appeared at this temperature was removed by filtration 1 ,2-dichloroethane was removed from the filtrate using a rotary evaporator and the crude product was purified using flash column chromatography (eluting solvent 1 4 vol. /vol CH 2 C1 2 - petrol (b pt 40-60°C), gradient to 1 1 vol /vol CH 2 Cl 2 -petrol (b.pt 40-60°C) 4- Nitro-2,3,5,6-tetrachloropyridine (XXV, 0 046g) was obtained as a yellow oil in 37% yield, Rf=0 82 (CH 2 C1 2 ), v 1M (CHCh)/cm " ', 1 337 (s, N0 2 ) 1 563 (s, NO 2 ), δ c (CDC1 3 , 100 6 MHz) 121 4 (C3 and CS) 147 8 1 (C2 and C6) 1 55 1 (C4), m/z (El) 260, 262 (ML * , 9%, 12%) 230, 232 (M-NO, 20, 24) 214, 216 (M-N0 2 , 20, 24) 179, 181 (M-CI- N0 2 , 5, 7) 139 ( 100), accurate mass, 4 x 5 CI, 1 9 ppm 4-S,S-Diphenylsulphoximino-2,3,5,6-tetrachloropyridine (XXVII) was obtained as a side product; m pt 158-1 59°C, Rf=0 63 (CH 2 CI 2 ), δ π (CDCb, 300MHz) 7 45-7.60 (6H, m, ArH) 8 00-8 1 1 (4H, m, ArH), m z (El) 430, 432 (M ~ \ 12%, 16%) 397 (M-Cl, 2) 305, 307 (M-SOPh, 2, 2) 270, 272 (7, 7) 218 (Ph 2 SON, 13) 202 (12) 186 (SPh 2 , 13) 154 (20) 125 (SOPh, 100) 109 (SPh, 34) 77 (Ph, 58), accurate mass, 4 x 35 C1, 1 4 ppm Example 6: Preparation of 2-nitro-3.4.5.6-tetrachloropyridine (XXVI) from pentaehloropyridine (XXXVl. 1st step. See first step of example 5, where 2-S,S-diphenylsulphilimino-3, 4,5,6- pyridine (VIII) was prepared 2nd step. The oxidising agent 3-chloroperoxybenzoic acid (0.075g, 0 434 mmol) was weighed out into a 100ml triple-necked round-bottomed flask The three necks of the flask were fitted with a glass stopper, a water condenser and a thermometer A magnetic stirrer bar was placed in the flask HPLC grade 1,2-dichloroethane (5 ml) was added to the flask, and the mixture cooled down to -5°C using an ice-salt bath 2- S,S-diphenylsulphilimino-3,4,5,6-tetrachloropyridine (VIII, 0 030g, 0 073 mmol) was added and the flask allowed to warm up to room temperature At this point the reaction mixture was blue-green The mixture was refluxed for 2 hr, changing colour from blue to yellow At the end of the reaction, the mixture was cooled to -5°C, and the precipitate of 3-chlorobenzoic acid was removed by filtration. 1 ,2-Dichloroethane was removed from the filtrate on a rotary evaporater, and the crude product was purified by flash column chromatography (eluting solvent, 1 6 vol. /vol CH 2 Cl2- petrol (b.pt. 40-60°C), gradient to 1.1 vol /vol CH 2 C1 2 - petrol (b.pt. 40-60°C) 2-Nitro- 3,4,5,6-tetrachloropyridine (XXVI, 0.012g) was obtained as a yellow oil with a caramel odour in 63% yield, Rf= 0 79 (CH 2 C1 2 ), m/z (El) 262,260 (M~, 13%, 12%) 230, 232 (M-NO, 61 , 49) 214, 216 (M-N0 2 , 94,75) 181 , 179 (M-C1-N0 2 , 47) , accurate mass, 4 x 35 C1, 1 7 ppm A white solid, 2-S,S-diphenylsulphoximino-3,4,5,6-tetrachloropyridine (XXVIII) was obtained as a side-product, Rf^O 68 (CH 2 C1 2 ), δ„ (CDC1 3 , 300 MHz) 7 48-7 59 (6H, m, ArH) 8 05-8 1 1 (4H, m, ArH), m z (El) 430, 432 (M\ 1%) 353, 355 (M-Ph, 4, 5) 305, 307 (M-SOPh, 2, 1 ) 202 (Ph 2 SO, 2) 125 (PhSO, 12) 109 (SPh, 16) 77 (Ph, 20), accurate mass, 4 x °C1, 1 4 ppm Example 7: Preparation of 4-nitro-2.3.5.6-tetrafluoropyridine (XXIX) from pentafliioropyridine (XXXVI). 1st step S,S-diphenylsulphilimιne ( 1 08g, 4 92 mmol) was weighed into a 100ml triple-necked round-bottomed flask THF (20 ml) was added, causing the solid sulphilimine to dissolve. Pentafluoropyridine (XXXVI, 0 416 g, 2 46 mmol) was added to the solution in the flask The reaction mixture was then treated in a similar manner to that already described for pentachloropyridine (see example 5, 1 st step, above), except that the reaction period was 6 hr During flash chromatography, the column was eluted with a 1 2 vol /vol CH 2 Cl2-petrol (b pt 40-60°C) mixture The product, 4-S,S-diphenylsulphilimino-2,3,5,6-tetrafluoropyridine (XVIII) was obtained as a white solid in 84% yield, m pt 87-88°C, Rf=0 58 (CH 2 CI ), δ„ (CDCh, 300 MHz) 7.50-7 59 (6H, m, ArH) 7 81 -7 88 (4H, m, ArH), δ (CDCh, 100 6 MHz) 126 7, 130.0, 132 2 {orlho, ela and para phenyl Cs), 135 0, 137 6 (C3 and C5, 2m), 138 7 (SC of Ph) 143 3, 145 7 (C2 & C6, 2m), 144 8 (C4, ), δ F (CDCh, 376 4 Mhz) 4.25 (C3 F & C5 F), 67 15 (C2 F & Cό F) 2nd step 4-S,S-DiphenyIsulphilimino-2,3,5,6-tetrafluoropyridine (XVIII, 0 168 g, 0.481 mmol, 1 equiv.) was treated with 3-chloroperoxybenzoic acid (0 497 g, 2.87 mmol) in a manner similar to that already described above (example 5, 2nd step) After warming to room temperature, the mixture was blue-green It was then refluxed for 18 hr, during which time the colour changed from blue to yellow The product mixture was then treated further as described in example 5, 2nd step, except that in the flash chromatography an isocratic system was used ( 1 4 vol /vol mixture of CFI 2 Cl 2 and petrol (b pt 40-60°C)) 4-Nitro-2,3,5,6-tetrafluoropyridine (XXIX) was obtained as a yellow oil in 21% yield, Rf=0 88 (CH 2 C1 2 ), v m „ (CHCl 3 )/cm " \ 1581 (NO ) 1370 (NO 2 ), δ F (CDCh, 376 4 MHz) 17 9 (F3, F5), 81 3 (F2, F6); m/z (El) 177 (M-F, 3%) 158 (M-2F, 31 ) 166 (M-NO, 2) 150 (M-N0 2 , 6) Some 4-(S,S- diphenylsulphoximino)-2,3,5,6-tetrafluoropyridine was detected as a side-product (16% yield) Example 8: Preparation of 3,5-dinitro-2-pyridinyl-S.S-diphenylsιιlphilimine- (XIX) from 2-chloro-3.5-dinitropyridine (XXXIV). To a solution of S,S-diphenysulphihmine monohydrate (0 947g,4 32mmol) in THF (20ml) was added 2-chloro-3,5-dinιtropyridιne (XXXIV, 0 439g, 2 l όmmol) The mixture immediately turned yellow and was refluxed for 30 min THF was removed in vacuo, the crude product purified by flash column chromatography ( 1 2 v/v CH 2 C1 2 - 40-60°C petrol) and the desired product, 3,5-dinitro-2-pyridinyl-S,S- diphenylsuiphilimine (XIX), obtained as a crystalline yellow solid in quantitative yield, Rf=0.52 (CH 2 C 1 2 ), δn (CDC , 300 MHz) 7 45-7 52 (6H, m, ArH) 7 86-7 93 (4H, m, ArH) 8 90-8 94 (2H, 2d, ArH), m/z (El) 368 (M\ 12%) 303 (2) 243 (M-SOPh, 10) 213 (M-SOPh-NO, 8) 202 ( 1 5) 1 86 (SPh,, 100) 1 54 (Ph 2 , 12) 14 1 (6) 109 (SPh, 20) 77 (Ph, 22), accurate mass, 2 2 ppm This product would be expected to form a useful precursor for the preparation of 2,3,5-trinitropyridine Example 9: Preparation of 1.2.4-trinitrobenzene (XXIIIB) from 2.4- dinitrophenyl- S,S-diphenylsnlphilimine 2,4-dinitrophenyl- S,S-diphenylsulphilimine was prepared by the method of Tamura et al (J Org Chem 38, 4324 ( 1973)) The 2,4-dinitrophenyl- S,S-diphenylsulphi!imιne (0 043g, 0 1 1 8mmol) was added to a solution of 3-chloroperoxybenzoic acid (0 122g, 0 705mmol) in 1 ,2-dichloroethane (5ml) which had been cooled to -5"C and the mixture allowed to warm up to room temperature and then refluxed for 18hrs After 4 hrs the mixture turned from green to yellow. At the end of the reflux a sample was removed and the 1 ,2-dichloroethane left to evaporate in the air T i c and Η nmr of the crude product suggested that 1 ,2,4- trinitrobenzene (XXIIIB) had formed in approximately 20% yield (relative to sulphoximine side product), Rf=0 61 (CH 2 C l 2 ), δ„ (CDC h, 300mHZ) 8 64-8 65 (I H, d, ArH) 8 82-8 83 ( I H, d, ArH), third peak obscured Example 10: Preparation of 1.2.4-trinitrohenzene (XXIIIB) from l-flnoro-3.4- dinitrobenzene (XXXVIII). 1st step To a solution of l -fluoro-3,4-dinitrobenzene (XXXVIII, 0 014g, 0 075 mmol) in THF (3ml) was added two equivalents of diphenylsuiphilimine monohydrate (0.033g, 0 1 50mmol) and the mixture refluxed for 5 hrs THF was removed /// vacua and the crude product purified by flash column chromatography ( 1 1 v/v CH 2 Cl -40- 60°C petrol) The desired product resulting from substitution at the fluorine position was obtained as a yellow solid (21 mg, 76%), Rf= 0 29 (CH 2 C 1 2 ), δ π (CDC h,, 300MHz) 6 89-6 94 ( l H,dd, ArH) 7 02 ( I H, d ArH) 7 50-7 60 (6H, m, ArH) 7 71 - 7.78 (4H, m, ArH) 7 92-7.95 ( I H, d, ArH), m/z (El) 367 (M\ 6%) 337 (M-NO, 9) 321 (M-N0 2 , 3) 186 (SPh 2 , 100) 109 (SPh, 16) 77 (Ph, 22), accurate mass, 0 6 ppm A side-product resulting from substitution of the 3-nitro group, l -fluoro-3-(S,S- diphenylsulphilimιno)-4-nitrobenzene, was obtained as a yellow solid (6mg, 22%), Rf=0.36 (CH 2 C 1 2 ); δ H (CDC h, 300 MHz) 6 27-6.35 (I H, ddd, ArH) 6 60-6 67 (I H, dd, ArH) 7 45-7 52 (6H, m, ArH) 7 80-7 1 (5H, m, dd, ArH) 2nd step To a solution of 3-chloroperoxybenzoic acid (0 059g, 343mmol) in 1 ,2- dichloroethane (5ml) cooled to -5°C was added 3,4-dinitrobenzyl- l -S,S- diphenylsulphilimine (0 021g, 0 057mmol) and the mixture refluxed for 2 hrs The solvent was left to evaporate in the air Although there was insufficient material to detect the products by Η nmr, a spot at Rf=0 61 (CH 2 C1 2 ) suggested that 1,2,4- trinitrobenzene (XXIIIB) was present (by analogy with the preparation of 1 ,2,4- trinitrobenzene described in Example 9). Example 11 : Preparation of l-πιιoi -3.4-diιιitrobenzene (XXIIIA) from 1-flnoro- 4-nitrobenzene (XXXIIIA) 1st step To a solution of diphenylsuiphilimine monohydrate ( 1 092g, 5mmol) in anhydrous degassed THF (20ml) being stirred under nitrogen was added BuLi (4ml of a 2.5M solution in hexane, l Ommol), the mixture turned deep yellow and was stirred for 30 min. 1 -fluoro-4-nttrobenzene (XXXIIIA, 0 530ml, 0 706g, 5mmol) was added and the mixture was stirred under nitrogen at room temperature for 18hrs THF was removed in vacuo, and the crude product was purified by flash column chromatography (1 7 v/v CH 2 C l 2 -40-60 n C petrol gradient to 1 3 v/v CH 2 C l 2 -40-60°C petrol) The desired product, 4-nitrobenzyl- l -fluoro-3-S,S-diphenylsulphi!irnine, was obtained as a brilliant yellow oil (0 213g, 1 3%), Rf = 0 1 8-0 3 1 (CH 2 C 1 2 ), δ„ (CDC h, 300MHz) 6 27-6 35 ( I H, dd, ArH) 6 60-6 67 (I H, dd, ArH] 7 45-7 52 (6H, m, ArH) 7 80-7.91 (5H, m, dd, ArH), δ, (CDC 1 , 376 5 MHz) 58 1 (m), m/z (El) 340 (M + , 11%) 323 ( 1 ) 232 (M-SPh, 1 ) 1 86 (SPh 2 , 100) 171 (3) 154 (Ph 2 ,7) 125 (SOPh, 3) 109 (SPh, 6) 77 (Ph, 10), accurate mass, 3 Oppm 2nd step To a solution of 3-chloroperoxybenzoic acid (0 16 lg, 0 935mmol) in 1 ,2- dichloroethane (5ml) cooled to -5°C was added a solution of 4-nitrobenzyl- l -fluoro-3- S,S-diphenylsu!philimme (0 053g, 0 1 56mmoi) in 1 ,2-dιchloroethane (5ml) The mixture was allowed to warm up to room temperature, refluxed for 2 hrs and then the 1,2-dichloroethane removed in vacuo. The crude product was purified by flash column chromatography (1 5 v/v CH 2 C l 2 -40-60°C petrol gradient to 100% CH 2 C1 2 ) The desired product, l -fluoro-3,4-dιnιtrobenzene (XXIIIA), was obtained as a yellow oil (0.014g, 48%); Rf = 0 68 (CH 2 C 1 2 ), δ„ (CDC h,, 300 MHz) 7 42- 7 50 (IH, ddd, ArH) 7.60-7 64 (IH, dd, ArH) 8 02-8 09 (I H, dd, ArH), m/z (El) 186 (M + , 100%) 156 (M-NO, 1 ) 140 (M-N0 2 , 4) 122 ( 1 ) 1 12 (6) 94 (M-2N0 2> 32) 82 (43), accurate mass, 7.8ppm A side-product, l -fluoro-3-(S,S-diphenylsulphoximino)-4- nitrobenzene, was obtained as a yellow solid (0 016g, 29%), Rf=0 48 (CH 2 C1 2 ), δn (CDCh, 300 MHz) 6 57-6.63 ( I H, ddd, ArH) 7 05-7 12 (IH, dd, ArH) 7 45-7.53 (6H, m, ArH) 7 80-7 86 (I H, dd, ArH) 8 08-8 17 (4H,m, ArH), m/z (El) 356 (M + , 100) 337 (M-F, 1 ) 310 (M-NO 2 , 2) 259 (2) 218 (Ph 2 S0 2 , 5) 202 (SOPh 2 , 17) 154 (Ph 2 , 30) 141 ( 10) 125 (PhSO, 41 ) 109 (SPh, 45) 77 (Ph, 48), accurate mass, 1 3ppm Example 12: Preparation of 2-nitro-3.5.6-triflιιoropyridine (XXX) from 2.3.5.6- tetraflnoropyridine (XXXVII). 1st step S,S-Diphenylsulphιlιmιne ( 1 08g, 4 92 mmol) was weighed into a 100ml triple-necked round-bottomed flask THF (20ml) was added and then 2,3,5,6- tetrafluoropyridme (XXXVII, 0 372g, 0 248ml, 2 46 mmol) was added using a syringe The mixture was refluxed for 4 hours The white precipitate was removed by filtration and THF was removed from the filtrate using a rotary evaporator The crude product was purified by flash column chromatography (column eluted with a 1 2 volume/volume mixture of dichloromethane and 40-60°C petrol) The product, 3 ,5,6- trifluoro-2-pyridinyl-S,S-diphenylsulphiIimιne (XX), was obtained as a pale yellow solid (0 777g, 95%), m p 1 19- 121 , RfM) 48 (CH 2 C 1 2 ), elemental analysis, found, C, 61 .40, H, 3 12, N, 8 32, C| 7 H n N 2 SF; requires C, 61 43, H, 3 34, N, 8 43, δ„ (CDC h, 300 MHz) 7 10-7 19 ( 1 H, dd, ArH) 7 45-7 53 (6H, m, ArH) 7 77-7 81 (4H, m, ArH), δ c (CDCh, 100 6 MHz) 1 14 1 (C4) 127 5- 131 7 (ortho, meta, para C of Ph) 132 9- 135 8 (C5) 137 6 (SC of Ph) 143 2- 145 7 (C6) 145 2- 147 8 (C3) 148 6 (C2), δ κ (CDC h, 376 5 MHz) 6 6, 27 2 (F3, F5) 67 4 (F6), m/z (El) 332 (M+, 25%) 255 (M- Ph, 4) 223 (M-SPh, 33) 186 (SPh 2 , 100) 171 (4) 152 ( 10) 109 (SPh, 18) 77 (Ph, 37), accurate mass 0.8ppm 2nd step. The oxidizing agent 3-chloroperoxybenzoic acid (0 497g, 2 87 mmol) was weighed out into a 100ml triple-necked round-bottomed flask and 1 ,2-dichloroethane (20ml) was added. The flask was cooled to -5°C using an ice-salt bath and 3,5,6- trifluoro-2-pyridinyl-S,S-diphenylsulphilimine (XX, 0 160g, 0 481 mmol) was added The mixture was allowed to warm up to room temperature (turning blue-green) and was then refluxed for 3 hours (turning yellow) The reaction mixture was cooled to -5°C and the precipitate of 3-chlorobenzoιc acid was removed by filtration 1,2- Dichloroethane was removed from the filtrate using a rotary evaporator and the crude product was purified by flash column chromatography (eluting solvent 14 volume/volume dιchloromethane-40-60"C petrol) 2-Nιtro-3,5,6-trifluoropyridιne (XXX) was obtained as a yellow oil (0063g, 74%), Rf=065 (CH 2 C1 2 ), δ„ (CDCh, 300 MHz) 765-776 (IH, dd, ArH), δ, (CDCh, 3765 MHz) 421, 457, (F3, F5) 795 (F6);mz(EI) 178 (M\ 5) 159(M-F, 3) 148 (M-NO, 2) 139(M-2F, 100) 132 (M- NO 2 , 7), accurate mass 29 ppm

Claims: Claims 1 A process for the nitration of electron-deficient carbocyclic and heterocyclic aromatic compounds which comprises the steps of - a) reacting an electron-deficient carbocyclic or heterocyclic aromatic (as hereinbefore defined) with a dialkyl-, diaryl- or alkylaryisulphilimine in a polar solvent or with the corresponding N- lithium sodium or potassium salt thereof in an aprotic solvent to generate the corresponding N-(hetero)arvl-S,S-dιalkyl, diaryl- or alkylaryisulphilimine derivative thereof, b) treating the product of step (a) with an oxidising agent to convert the sulphi mmo group to a nitro-group, and c) isolating the nitrated aromatic compound obtained in step (b) 2 A process according to claim 1 wherein the sulphilimine is a diphenylsuiphilimine 3 A process according to claim 1 or claim 2 wherein the sulphilimine is a lithium salt thereof 4 A process according to any of claims 1 to 3 wherein the heterocyclic aromatic compound is a pyridine, diazine or tπazine 5 A process according to claim 4 wherein the diazine is a pyrimidine or a pyrazine 6 A process according to any of claims 1 to 5 wherein the oxidising agent used in step (b) is a peroxycarboxylic acid 7 A process according to claim 6 wherein the peroxycarboxylic acid is a perbenzoic acid, particularly m-chloroperbenzoic acid 8 A process according to claim 6 wherein the peroxycarboxylic acid is peracetic acid or peroxytπfluoroacetic acid 9 A process according to any of claims 1 , 2 and 4 to 8 when dependent thereon, wherein the polar solvent used in step (a) is an alcohol with chain length 4 carbon atoms or less or a cyclic ether 10 A process according to claim 9 wherein the polar solvent is ethanol, 1 ,4- dioxane or tetrahydrofuran 1 1 A process according to claim 3 wherein the aprotic solvent used in step (a) is 1,4-dιoxane, dimethoxyethane, diethyleneglycol dimethyl ether or tetrahydrofuran 12 A nitrated carbocyclic or heterocyclic aromatic compound when obtained by a process as claimed in any of claims 1 to 1 1 13 2-chloro-3,4-dinιtropyridιne 14 A process for preparing N-aryl- and N-heteroarylsulphilimine derivatives of electron-deficient carbocyclic and heterocyclic aromatics which comprises the steps of a) reacting an electron-deficient heterocyclic or carbocyclic aromatic compound with a dialkyl-, diaryl- or mixed alkylaryisulphilimine in a polar solvent, and b) isolating the N (hetero)aryl-S.S-dιalkyl-, diaryl- or alkylaryisulphilimine deπvative which is formed 15 A process according to claim 14 wherein the sulphilimine is S,S- diphenyisulphihmme 16 A process according to claim 14 or claim 15 wherein the polar solvent used in step (a) is an alcohol with chain length 4 carbon atoms or less or a cyclic ether 17 A process according to claim 16 wherein the polar solvent is ethanol, 1 ,4- dioxane or tetrahydrofuran 18 A process according to any of claims 14 to 17 wherein the heterocyclic aromatic compound is a pyridine diazine or tπazine 19 A process according to claim 18 wherein the diazine is a pyrimidine or a pyrazine 20 A N-(hetero)ary!-S,S-dιalkyl-, diaryl- or alkylaryisulphilimine compound when produced by the process as claimed in any of claims 14 to 19 21 A process for the preparation of N-(hetero)arylsulphιhmιne derivatives of electron-deficient carbocyclic aromatics and heteroaromatics comprising the steps of a) reacting an electron-deficient carbocyclic or heterocyclic aromatic compound with an N-alkali metal salt of an S,S-dιalkyl-, diaryl- or alkylaryisulphilimine in an aprotic solvent, and b) isolating the N-(hetero)aryl-S,S-dιalkyl-, diaryl- or alkylaryisulphilimine derivative which is formed 22 A process according to claim 21 wherein the alkali metal is lithium 23 A process according to claim 21 or claim 22 wherein the sulphilimine is S,S- diphenylsulphilimine 24 A process according to any of claims 21 , 22 or 23 wherein the aprotic solvent is 1,4-dιoxane, dimethoxyethane, diethyleneglycol dimethyl ether or tetrahydrofuran 25 A process according to any of claims 21 to 24 wherein the heterocyclic aromatic compound is a pyridine diazine or tπazine 26 A process according to claim 25 wherein the diazine is a pyrimidine or a pyrazine 27 A N-(hetero)aryl-S,S-dιalkyl-, diaryl- or alkylaryisulphilimine compound when produced by the process as claimed in any of claims 21 to 26 28 Any one of the compounds 6-chloro-2-pyrazιnyl-S,S-dιphenylsulphιhmιne, 3- nιtro-2-pyπdιnyl-S,S-dιphenylsuiphιltmιne, 2-nιtro-5-chlorophenyl-S,S- diphenyisulphilimine, 2-chloro-3-nιtro-4-pyπdmyl-S,S-dιphenylsulphιlιmιne, 2- pyrazιnyl-S,S-dιphenylsulphιlιmιne, 2-(n-propoxy)-4-chloro-6-( l ,3,5-tπazιnyl)-S,S- diphenylsulphi mine, 2,3,5,6-tetrachloro-4-pyπdιnyl-S,S-dιphenylsulphιlιmιne, 3,4,5,6- tetrachloro-2-pyπdιnyl-S,S-dιphen Isulphilimine, 2-(n-propoxy)-4,6-( 1 ,3,5-tπazmyl)- bis-S,S-dιphenylsuiphιhmιne, 2,4-bιs-(n-propoxy)-6-(1 ,3,5-tπazιnyl)- diphenylsulphihmine, 6-chloro-4-pyπmιdιnyl-S,S-dιphenylsulphιlιmιne, 5-nιtro-2- pyπdιnyl-S,S-dιphenylsulphιlιmme, 4-chloro-2-pyπmιdιnyl-S,S-dιphenylsulphιhmιne, 2,6-dιchloro-4-pyπmιdιnyl-S,S-dιphenylsulphιhmιne, 4,6-dιchloro-2-pyπmιdιnyl-S,S- diphenylsulphilimine, 2,5,6-tπchloro-4-pyπmιdιnyl-S,S-dιphenylsulphιlιmιne, 4,5,6- tπchloro-2-pyπmιdιnyl-S,S-dιphenylsulphιlιmιne, 2,3,5,6-tetrafluoro-4-pyπdιnyl-S,S- diphenylsulphihmine, 3,5-dιnιtro-2-pyπdιnyl-S,S-dιphenylsulphilιmine and 3,5,6- tπfluoro-2-pyπdιnyl-S,S-dιphenylsulphιlιmιne 29 An N-alkah metal salt of an S,S-dιalkyl-, diaryl- or alkylaryisulphilimine 30 A salt according to claim 29 where the alkali metal is lithium 31 A salt according to claim 29 or claim 30 wherein the sulphilimine is dimethylsulphi mine 32 A salt according to claim 29 or claim 30 wherein the sulphilimine is diphenylsuiphilimine 33 A method for preparing the N-alkali metal salt of claim 29 which comprises reacting the corresponding sulphilimine with a reagent selected from the group comprising alkylhthiums with chain length 1 to 4 carbon atoms alkali metal hydrides and alkali metal nitrogenous bases in an aprotic solvent 34 A method according to claim 33 wherein the reagent is n-butylhthium 35 A method according to claim 33 wherein the reagent is the N,N- dι(isopropyl)amιde or the N,N-bιs(tπmethylsιlyl)amιde of lithium, sodium or potassium 36 A method according to any one of claims 33 to 35 wherein the aprotic solvent is 1 ,4-dιoxane, dimethoxyethane, diethyleneglycol dimethyl ether or tetrahydrofuran

Inventors: CLARIDGE ROBERT PETER, MILLAR ROSS WOOD, SANDALL JOHN PAUL BENET, THOMPSON CLAIRE, CLARIDGE, ROBERT, PETER, MILLAR, ROSS, WOOD, SANDALL, JOHN, PAUL, BENET, THOMPSON, CLAIRE
Applicants: CLARIDGE ROBERT PETER, MILLAR ROSS WOOD, SANDALL JOHN PAUL BENET, SECR DEFENCE, THOMPSON CLAIRE, CLARIDGE, ROBERT, PETER, MILLAR, ROSS, WOOD, SANDALL, JOHN, PAUL, BENET, THE SECRETARY OF STATE FOR DEFENCE, THOMPSON, CLAIRE
Application year: 1996
Main classification: C07D213
IPC codes: C07C201, C07C205, C07C381, C07D213, C07D239, C07D241, C07D251