Sulphenes formation

The phenyl analogue likewise gave a high yield of benzoylethylene. Along the same line, King and Harding have reported a sulpho-Cope rearrangement which appears to involve sulphene formation. Vinyl allyl sulphone, when heated to 170 °C in the liquid phase or to 800 °C in the gas phase, probably was converted into the sulphene (87). In the gas phase, pent-4-enal was isolated, whereas in the liquid phase addition of phenol led to a phenyl sulphonate. 

King and Lee have provided evidence that the normal elimination route for sulphene formation involves an 2 mechanism with direct and initial attack on the a-proton by the base, not initial substitution for the chloride. Using the axial and equatorial isomers of trans-l-chXoTO-sulphonyldecalin with triethylamine as the base, it was found that the axial isomer formed sulphene 71 times as fast as did the equatorial isomer. By comparison, it was found that the equatorial isomer hydrolysed 14 times as fast as did the axial isomer, and this reaction presumably involved attack at sulphur. 

Ylides of Sulphur, Selenium, Tellurium, and Related Structures 359 was proposed that sulphene formation was involved in each reaction, with the triphenylphosphine adding to the sulphene and displacing SO2 to afford the phosphonium ylide, which was protonated by the conjugate acid of the amine. Sulphenes have been reported to react with tropone to afford an adduct which rearranged on heating to an o-hydroxystyrene (lOQ. ... 

Sulphonyl phosphates, reactions of 638 Sulphonyl radicals 215 cyclization of 1099 ESR spectra of 1090-1093 formation of 1094-1098 structure of 1090-1094 thermodynamic data for 1094 Sulphonyl sulphenes 196 Sulphonyl sulphoxides alkylation of 311 synthesis of 262... 

The latter anomalous" behaviour has been ascribed to the direct formation of pentacoordinated products from P(III) and the substrate as distinct from nucleophilic displacement by phosphorus so that the stability of the T.S. leading to the pentacoordinated molecule dictates the rate. >11 >LI There is no doubt that several reactions which display the anomalous rate sequence (eg with peroxides, sulphenate esters and dithietenes) do give pentacoordinated products and the proposal is given further support by the reaction of diethyl peroxide with a series of cyclic phosphines in which the rate sequence parallels the stability of the P(V) products.II Furthermore, under the appropriate conditions pentacoordinated products are also formed from alkenes (eqn. 2) and alkynesl . (eqn. 3) and although rate data is only available for... 

Radicals can affect thiol groups in proteins and peptides in a number of different ways. The response might be formation or loss of disulphide bridges. More dramatic free radical exposure can lead to the formation of sulphenic, sulphinic and sulphonic acids. The loss of free thiol groups can be assessed utilizing the methods described here. 

The cystine link also has a profound effect upon the mechanical properties of the fibre. The disulphide bond is covalent and not very sensitive to pH, but there are a number of reagents which can break it down. Water can bring about hydrolysis, especially when in the form of steam with the formation of sulphenic acid groups ... 

If a wool fibre be immersed under tension in water at 100 C for one hour it will become distorted permanently in other words, will have acquired a permanent set. Binding forces of a more powerful nature than hydrogen bonds must have been created. The explanation proposed by Speakman Nature, 1933, 132, 930) was that the water severs the cystine linkage with the formation of sulphenic acid and sulphide radicals ... 

The thieten 1,1-dioxide (48) has been prepared by cycloaddition of an enamine and sulphene at 0°C. Mild thermolysis causes a ready retrocyclo-addition to occur. Additional stable 3-sultines have been isolated, by the reaction of the anion of a sulphoxide with a ketone and cyclization of the resulting j3-hydroxy-sulphoxide with sulphuryl chloride. Treatment of 2-methylthietan (49) with alumina at 150-350 °C results in the formation of tetrahydrothiophen and but-3-enethiol. ... 

Cycloaddition of diphenylisobenzofurans to (101), to sulphenes, to 2-phenyl-3-spirocyclopropylazirines, and to o-benzoquinonedi-imines have been reported. The preparation and trapping of 1-methoxy- and 1-benzyl-isobenzofuran have been described and a high degree of regio-and stereo-specificity is observed in the reactions of a range of 1-substituted isobenzofurans with quinone acetals, for example in the formation of... 

The reader will have noted that some unanswered questions were left in some of our earlier sections. For example, recall Reference 34 cited in Section V. A we did not evaluate on which side the equilibrium for reaction 54 lies. Because we subsequently considered the thermochemistry of sulphonyl sulphenates, we can now provide a partial, but admittedly long-winded, answer for the Ar = Ph species (46). The reader is reminded that A Hf(g, 46) — 52 kcal mol 1 and of the finding of Turecek and coworkers34 that the heat of formation of gaseous benzenesulphenic acid (84) is —8 kcal mol-1. Likewise, the reader may recall from Section VII.D our estimation for solid benzenesulphonic acid that AH (s, 20) = — 117 kcal mol- L These data cannot be immediately combined because of the discrepancy in the state for which the three species other than H20 are known. Do we wish to consider condensed phase species, in which case we need the sublimation energy of the sulphonyl sulphenate 46 and the sulphenic acid 84, or to consider gas phase species, in which case we need the sublimation energy of the sulphonic acid 20 ... 

The sole thermochemical values known to the author for any sulphenic acid, RSOH, are the ionization and ion fragmentation reaction energetics derived values of R = Me, — 45 CH2= CH—, <4 HC=C—, 24 and Ph—, —8kcalmol-1, R. Turecek, L. Brabec, T. Vondrak, V. Hanus, J. Hajicek and Z. Havlas, Collect. Czech. Chem. Commun., 53,2140 (1988). In that we know the heat of formation of no sulphonic acid in the gas phase, we cannot provide an answer to Is it better to view the above ArS02—O—SAr species as an anhydride or an ester That is, our... 

Earlier, it was shown that sulphenes, formed by reaction of sulphonyl halides with a base, reacted with alcohols to give sulphonate esters. These same reactive intermediates have also been used for the formation of sultones, by reaction with carbonyl-containing compounds424-428, as shown in equation 98. If the carbonyl compound contains an a-... 

In some instances extrusion of S02 does not occur, as with the ketosulphone (74) which fragments to yield ketene and the sulphene (75). Both the singlet and the triplet excited states are reactive. There is some doubt as to the concertedness of the process and a 1,4-biradical is proposed as an intermediate formed by C—S bond fission82. Irradiation of the sulphone (76) in acetonitrile or dichloromethane also results in the formation of a sulphene (77) which loses SO to afford the ketone (78). An alternative reaction path, that of S02 extrusion, affords a biradical from which 1,3,4,6-tetraphenylcyclohexa-l,4-diene is formed83. 

Addition of in situ-generated sulphenes (see Section I.A.2) to a,/ -unsaturated carbonyl compounds to give y-unsaturated <5-sultones is described in an early paper by Gandini and coworkers (equation 45)64. Their study compares the behaviour of sulphenes towards a,/ -unsaturated carbonyl compounds to that of ketenes and, by analogy, two possible mechanisms for the formation of <5-sultones via / -sultones are outlined in equation 46. 

From a study of the hydrolysis of sultone 4 in D20-0D solution, Kaiser and his coworkers showed that carbanion formation occurs rapidly and reversibly from the sultone in basic solution136. They were able to eliminate the concerted mechanism (equation 99) as a major reaction pathway and concluded that a carbanion-sulphene mechanism (equation 100) does not provide an important pathway for the hydrolysis of five-membered sultones. 

Kinetic studies in the benzothiazole series include examination of the base-catalysed reaction between 2-fluoro-6-nitrobenzothiazole and aliphatic amines, " investigation of the mechanism of formation of sulphenic acid amides... 

Rate-determining reactions between [NaSgOe]" and [OH], and [SgOe] and [H+] are suggested. There is a report of the kinetics of formation and decomposition of the higher polythionic acids. The acid-catalysed hydrolysis of methyl toluene-p-sulphenate, ArS(OMe), has been studied in moist organic solvents ... 

Classically, imines have been obtained via derivatisation of carbonyl compounds although problems exist in the use of unreactive carbonyl compounds and/or volatile imines. This transformation has nevertheless been achieved in excellent yields in the absence of solvent merely by treating carbonyl compounds dispersed on alumina with amines that have been similarly dispersed on alumina, Trimethylsily1 trifluoromethanesulphonate has been found to catalyse formation of imines from carbonyl compounds and 1,N-bis-(trimethysilyl )amines, these reactions also proceeding in excellent yield.The same research group also discovered that sulphen-imines could be isolated from reactions between tJ-bis (trimethyl-... 

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). 

Further studies of the formation of sulphoxides from sulphenates have been reported, by a [2,3]sigmatropic rearrangement (93) to (94), and unexpectedly from the reaction of cyclohexen-l-ol with phenylsulphenyl... 

Sulphonyl Halides and Sulphenes.—It is becoming clear that reactions of alkanesulphonyl chlorides in the presence of a tertiary amine are likely to give poor yields of simple sulphonation products, due to the formation of sulphenes (RCHaSOgCl RCH=SOa) and artefacts resulting from them. Electron-withdrawing groups in the substituent facilitate sulphene... 

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