Sulphenyl halides

Sulphenyl Halides.— Illustrative procedures for the synthesis of sulphenyl halides reported during the period under review employ well-established methods, Tetrachloropyridine-4-sulphenyl chloride is obtained from the corresponding disulphide by chlorinolysis, while the corresponding sulphonyl chloride is formed in AcOH or hydroxylic media. 2-Methyl-2-propanesulphenyl iodide is obtained from the thiol with la, or from the sulphenamide with HI addition reactions of selenium dichloride, or seleninyl chloride, to acetylene are specific examples of generally applicable reactions - (HC=CH + SeCU C1CH=CH-Se-Cl). The chlorination of CSa under activated charcoal catalysis has been developed as a continuous process, giving trichloromethanesulphenyl chloride. 

The characteristic reaction behaviour of sulphenyl halides is exemplified in a wide range of alkyl- or aryl-thiolation processes. 2,3-Dimethylindole gives (153) with 2,4-dinitrophenylsulphenyl chloride, and a-phenyl-thiolation of ketones (PhSCl + Ri CO CHR R R -CO-CR R SPh)  

Sulphenyl Halides.—This section describes first the preparations of sulphenyl halides of particular interest in the recent literature, then their properties and their addition and substitution reactions. More space is allocated this year for results from studies of organo-sulphur, -selenium, and -tellurium halides involving higher valency states. 

Chlorinolysis of disulphides is widely used as a direct synthesis of sulphenyl halides, and related cleavage by 7V-chIoroformimidoyl chloride has been studied 

Sulphenyl halides give cationoid species RS+ Y (Y = BF4 or SbF,) on reaction with the corresponding Ag salt an areneselenenyl hexafluoro-phosphate and a corresponding hexafluoroantimonate have been described. Further details of the equilibrium 2RSC1 RS(C1)SR + Cl- set up by an alkane-sulphenyl chloride in liquid SOj in the presence of a Lewis acid, or in H2SO4 or FSO3H, are available. Such cations have been suggested to be implicated in the reactions of disulphides and sulphenyl halides, and the reaction in these media 

Routine studies of the addition of sulphenyl halides to alkenes have been reported, most studies dealing with the kinetics of the reaction as a function of structure and stereochemistry. Among these reports is a notable 

Okuyama, and T. Fueno, Bull. Chem. Soc. Japan, 1974, 47, 1480. 

Sulphenyl Halides.—Sulphenyl chlorides are readily available by chlorinolysis of disulphides, and this remains the most commonly used method of synthesis. Chlorinolysis of penicillin esters gives the sulphenyl chloride, and a route to an azetidinone sulphenyl chloride has been devised in which the relatively unstable sulphenic acid produced by penicillin sulphoxide pyrolysis is treated with SOCh in CCl, to give [43 R =C1, R =CH(C02Me)CMe=CH2]. Sulphenyl iodides may be important intermediates in reactions at disulphide bridges in peptides and proteins, and a report of the preparation of a stable sulphenyl iodide is notable. The observation that methanesulphenyl chloride dimerizes (in SO2 in the presence of a Lewis acid) to give MeSSMeCl Cl MeS=SMeCl Cl may be useful in explaining the course of certain electrophilic reactions of sulphenyl chlorides, and should stimulate a search for new reactions of aliphatic compounds of this series. 

Chlorocarbonylsulphenyl chloride ClCOSCl and related compounds have uses in synthesis, of thiazol-2-ones, and of alkyl chlorides from the corresponding thiols. The latter procedure involves a disulphide RSSCOCl, treatment with PhB giving the alkyl chloride, though some elimination accompanies the substitution reaction, and is the major reaction for cyclohexanethiol. Whereas aminolysis of ClCOSCl occurs at carbonyl carbon, that of FCOSCl involves displacement of Cl from S.  

Helmbrecht, W. Klug, B. Koch, H. Reinke, and J. Sommerhof, J. Fluorine Chem., 1973, 3, 383. 

Substitution reactions of simple sulphenyl chlorides with features of additional interest include 1,3-dithiolan formation by reaction of 1,2-disulphenyl chlorides at a methylene group o to —CHO formation of cK-chloro- -keto-sulphides from sulphenyl chlorides and adducts of phosphines with 1,2-dicarbonyl compounds free-radical substitution of saturated alkanes by C6CI5SCI and synthesis of aa-dinitroalkyl sulphides by treatment of gem-dinitroalkanes with sulphenyl chlorides in the presence of base.  

Chartier, Bull. Soc. chim. France, 1972,2887 V. Zabelaite, L. Rasteikiene, M. G. Linkova, 

---

Radical addition, 312-323 carbon tetrachloride, 320 halogens, 313 hydrogen bromide, 316 sulphenyl halides, 320 vinyl polymerisation, 320 Radical anions, 218 Radical rearrangements, 335 Radicals, 20, 30,299-339 acyl, 306, 330, 335 addition to 0==C, 313-323 alkoxyl, 303... 

The photostimulated reactions of thiolate anions with 2-halo-2 -nitropropane derivatives yield both oc-nitrosulphides via an S l pathway and disulphides (equation 71a)282 284. In contrast with the case of the oxidative dimerisation products of the mono-enolates, the disulphides are formed via an ionic mechanism nucleophilic attack by the thiolate anion on the a-halogen and subsequent reaction of a second thiolate with the sulphenyl halide. As expected for such a process, disulphide formation is favoured (and thus a-nitrosulphide formation is disfavoured) the more nucleophilic the thiolate (i.e. derived from a less acidic thiol) and the easier the abstraction of the halo-substituent (i.e. I > Br > Cl). Use of the protic solvent methanol instead of the usual dipolar aprotic solvents for the reaction of equation 71a is detrimental to the yield of the S l substitution products exclusively disulphides are formed285 (equation 71b). Methanol solvation probably retards the dissociation of the radical anion intermediate in the SRN reaction, into radical and anion, and hence retards the chain reaction relative to the ionic reaction. The non-nucleophilic methylsulphinate ion gives only an S l reaction product with 2-bromo-2-nitropropane286. 

Addition reactions of sulphenyl halides (in particular chlorides) to acetylene derivatives have been extensively explored and recently reviewed (Modena and Scorrano, 1968). Although free radical processes may be involved under specific conditions, the addition of both arene-and alkanesulphenyl halides normally occurs by an ionic mechanism, the sulphenyl halide sulphur being the electrophilic centre. 

The addition of sulphenyl halides is in each case trans stereospecific... 

Electrophilic addition of sulphenyl halides to alkenes occurs, by all the evidence, via cyclic thiiranium ions (Mueller, 1969) and a comparison of the rates of addition to the double and triple bond would be quite interesting. Unfortunately, direct kinetic data for strictly comparable and typical cases are not available. Phenylacetylene has been reported (Kharasch and Yannios, 1964) to react 102 times slower than styrene (in acetic acid at 25°) with 2,4-dinitrobenzenesulphenyl chloride. On the other hand, Thaler (1969), by means of competitive experiments carried out in dilute paraffin solutions at — 70°, estimated that methane-sulphenyl chloride adds to mono- (and di-)alkylacetylenes 50-100 times more slowly than to the corresponding alkenes (cis) (but only ca. twice slower than to trans dialkylethylenes). The paucity of information does not allow generalizations and further work in this area seems desirable also with respect to the much larger rate differences observed in those bromine additions to triple and double bonds which also occur via bridged species. 

Steps (a) and (b) of Scheme 6 constitute the Arens mechanism. Therefore, equation (244) was simply a case of attack on Cl in which the ion-molecule (PhC=C CISC,-H,-p) was the key intermediate. Attack of acetylide on the sulphur of the sulphenyl chloride leads to the product given in equation (244). Support for this step is the well-known reaction of sulphenyl chloride with carbanions to yield sulphides . The disulphides which sometimes turn up in the haloalkyne-thiolale processes (see Table 6) are easily explained by the sulphenyl halide reacting with the thiolates. 

The A -unsaturated-5a-thiol (350) reacted with bromine or chlorine to give the 3j8-halogeno-2a,5a-epithio-derivative (353). ° It is suggested that a 5a-sulphenyl halide e.g. (351)] is first formed, and then attacks the olefinic bond to give the sulphonium ion (352), which suffers nucleophilic attack upon C(3) by halide ion. Lead tetra-acetate similarly afforded the 3j8-acetoxy-2a,5a-epithio-compound. 

Ionic additions which transform cyclopropenes into cyclopropanes are well known. The electrophilic addition of sulphenyl halides proceeds by a two-step mechanism to give trans-disubstituted products but with little regioselectivity. Cyclic sulphonium ion intermediates are probably involved as illustrated for 1-methylcyclopropene. Electrophilic... 

Sulphonyl halides are readily prepared by the nitric acid oxidation of sulphenyl halides, which are in turn easily formed by reaction of disulphides with sources of halogens. Thus, alkanesulphenyl chlorides are oxidized to the corresponding sulphonyl chlorides, in high yields301,550-552, as depicted in equation 142. 

The reactions of acetylenes with sulphenyl halides and related compounds have been reviewed. A-(Benzenesulphenyl)-/ -nitroaniline (326) reacts with 1 -pentyne in acetonitrile in the presence of boron trifluoride etherate to yield solely the 2-azabutadiene derivative 327235. 

Many investigations have been performed on the addition of sulphenyl halides, particularly chlorides, to alkenes and alkynes. Thiiranium and thiirenium ions, respectively, would be intermediates. The generality of these ions as intermediates in the addition to alkenes has been questioned in a critical review article. Modena and coworkers listed relative reactivities in the addition of 4-chlorobenzenesulphenyl chloride to alkenes and alkynes. Alkynes appear to be less reactive than alkenes, but the ratio very much depends upon structure. The highest ratio was observed for the parent pair ethene ethyne, namely 2.82 X 10 ... 

By far the most evidence for electrophilic sulphur is found in the sulphenyl halides (RSCl, RSBr) Although these compounds may in theory react either as sources of RS or X (X = halogen), none of the observed reactions of the sulphenyl halides indicate the latter mode of heterolysis. Kharasch et have presented good evidence for the existence of the 2,4-dinitrobenzene-sulphenium ion (Ar ) in strongly acidic media evidence has also been presented of a strong solvent effect upon the rate of reaction of 2,4-dinitroben-zenesulphenyl chloride and cyclohexene - and of a definite substituent effect in the reaction of this sulphenyl chloride with some substituted styrenes in acetic acid . Such observations are entirely consistent with an electrophilic heterolytic ad tion mechanism involving attack by the sulphenyl chloride in the sense iC -Cl. 

Such a structure is analogous to those suggested for halogen addition, acid-catalysed hydration, and sulphenyl halide addition, but has. suffered severe criticism. To follow the analogy, such an intermediate would be expected to... 

The order of susceptibility towards substituent effects is much less in the acetylene series than in the olefins, but its direction is similar. A similar statement may be made about the direction, rates, and kinetics of addition of sulphenyl halides. While the simple acetylenes, such as sym-diphenylacetylene and 3-hexyne, required catalytic quantities of aluminium chloride before undergoing addition by 2,4-dinitrobenzene sulphenyl chloride , the rates of reaction of acetylene itself with some p-substituted benzene sulphenyl chlorides alone have been measured. The effect of the p-substituents... 

Mo-dinitrogen complexes with thiols and sulphenyl halides 28... 

Various derivatives of sulphur may be prepared by the reaction of sulphur monochloride, sulphur dichloride or sulphenyl halides with thiolates the products depend on the reactant stoichiometry. 

Sulphenyl halides are very prone to nucleophilic attack > > (equation 21) and in particular excess mercaptan reacts with them to give the corresponding disulphide (equation 16). 

The hydrolysis of sulphenyl halides is believed to form sulphenic acids (equation 22). These compounds, however, have never been isolated in this reaction rather thiolsulphinate esters are formed by fast reaction of sulphenic acids with sulphenyl halides (equation 23). 

Disproportionation of sulphenic adds has also been suggested as a possible route for the formation of these compounds (equation 24). The hydrolysis of sulphenyl halides under not carefully controlled conditions and particularly in concentrated solutions lead to disulphides and thiolsulphonates because of the easy disproportionation of thiol-sulphinates (equation 25). 

---