Sulphines formation

Sulphinic acids. Aromatic sulphinic acids are found in Solubility Group II. They may be detected by dissolving in cold concentrated sulphuric acid and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to the formation of a para-substituted aromatic sulphoxide. Thus the reaction with benzenesulphinic acid is ... 

Phenylsulphine prepared in situ from phenylmethanesulphinyl chloride and triethyl-amine reacted with 1 -morpholinocyclohexene to form the addition product 169 having the enamine structure218. A similar experiment with phenylsulphine and 2-pyrrolidinocyclo-hexene gave only 2-phenylmethanesulphinyl cyclohexanone 170. The latter is most probably formed by hydrolysis of the corresponding enamine sulphoxide upon isolation. The reaction of sulphines with enamines is apparently a stepwise process involving the transient formation of the dipolar intermediate 171 which is stabilized by proton transfer, giving the enamine sulphoxide. 

The interaction of sulphones with other electrophiles—formation of sulphoxides and sulphinates... 

As has been mentioned in an earlier section, aqueous chlorination of sulphoxides leads to sulphones. If excess reagents are used, sulphonyl chlorides may be formed directly from sulphoxides in good yields (equation 75)89,90,193. In order for this reaction to be synthetically useful, the sulphoxide used should be symmetrical. The product is presumably formed in a stepwise manner via the sulphinyl chloride [RS(0)C1] and the sulphinic acid [RS(0)0H]. In the case of chloromethyl dichloromethyl sulphoxide, the only sulphonyl chloride formed is chloromethanesulphonyl chloride (equation 76) and this may be readily separated from the other products by distillation90,193. Similarly, oxidation of dichloromethyl methyl sulphoxide and methyl trichloromethyl sulphoxide with chlorine in aqueous acetic acid leads to the formation of methanesulphonyl chloride in 75% and 86% yields respectively. Other species are also produced but these are much more volatile and thus easily removed (equations 77 and 78). In the absence of acetic acid the yields are somewhat reduced. 

Several studies confirm an ortho effect leading to a dominating aryl sulphur bond cleavage. For example, the introduction of a bulky ortho substituent17 will provide the formation of the aliphatic sulphinic acid. A series of cyclic sulphones was studied18,19 at the mercury cathode and the results (see Table 2) appear to be fully in agreement with those expected when considering the preliminary works presented above. 

Coulometric measurements demonstrated the formation of the thioether with an electricity consumption of one Faraday per mole. However, the thioether yield was only of the order of 50% and, in addition, the presence of sulphinate ion in the electrolysis solutions was shown by methylation with CH3I, when methyl phenyl sulphone was formed and determined. 

Sulphines may react as dienophiles with 1,3-dienes with the formation of cyclic sulphoxides. Unstable 2,2-dichloro-5,6-dihydro-2ff-thiin-l-oxide 191 was formed in an exothermic reaction between 173aandcyclopentadieneat — 40 (equation 101). The simplest, parent sulphine, CH2 = S = O, prepared in situ by treatment of a-trimethylsilylmethanesulphinyl chloride with cesium fluoride, reacts with cyclopentadiene to give bicyclic, unsaturated sulphoxide 192 as a mixture of two diastereoisomers in a 9 1 ratio (equation 102). On the other hand, a,j8-unsaturated sulphine 193 (generated by thermolysis of 2-benzylidene-l-thiotetralone dimer S-oxide) in boiling toluene behaves as a 1,3-diene and was trapped by norborene forming sulphoxide 194 in 78% yield ° (equation 103). 

Despite the aversion of the sulphonyl group to function as a nucleophile, there are a limited number of literature reports that deseribe sueh a process . The first of these does not lead to a reduetion at sulphur and is thus not direetly relevant, but the report by Braverman and Duar deseribes reaetions in whieh an acetylenie sulphinate ester ean undergo a [2,3] sigmatropie rearrangement to an allenie t-butyl sulphone. Reaetion of this sulphone with the appropriate eleetrophile, for example bromine, gave a y-sultine, formation of whieh requires the partieipation of the sulphonyl group in an intramoleeular cyclization process. The reactions are outlined in equation (40). 

Greater commercial significance is attached to certain derivatives of sodium dithionite, including sodium formaldehyde-sulphoxylate (12.53 hydroxymethanesulphinate) (Scheme 12.23) and the less important sodium acetaldehyde-sulphoxylate (12.54 hydroxye thane -sulphinate). These reducing agents have been of particular interest in printing, especially in the flash-ageing process [228-231]. The formation of sodium formaldehyde-sulphoxylate by reaction of sodium dithionite with formaldehyde is shown in Scheme 12.23 the bisulphite formed can be further reduced with zinc to produce another molecule of the sulphoxylate. 

The formation of thioamides from amines (methylamine, dimethylamine and morpholine) and dithioester sulphines, prepared from dithio esters and peracids, is thought to proceed via the intermediates shown in equation 102325. 

S-Nitrososulphinates can be made by treating sulphinic acids with N2O4 at about —20 °C in ether (equation 32)76. Use of nitrous acid on alkyl nitrites leads to the formation of the corresponding hydroxylamines (equation 33) in a reaction where it is believed that the first formed nitrososulphinate nitrosates another molecule of the reactant sulphinic acid77. 

The reaction has been rationalized as involving an attack of lithium teUurolate on a lithi-ated sulphone, promoting the elimination of lithium phenyl sulphinate and the formation of a labile epitelluride that readily collapses into stilbene and elemental tellurium. 

A. Hantzsch and A. Holl recommended purifying the compound by crystallization from hot ethyl alcohol. A. Mente found it among the products of the action of ammonium carbonate on sulphuryl chloride and F. Ephraim failed to obtain it during the action of urethane on sulphuryl chloride. E. Divers and M. Ogawa observed the formation of this compound in the spontaneous decomposition of ammonium sulphinate. 

These compounds are suggested if sulphur is present. If nitrogen is also present the compound may be an aminosulphonic acid. The infrared spectrum will show absorption at 3400-3200 cm -1 (OH str.) and 1150 and 1050 cm-1 (S=0 str. in a sulphonic add) or at 1090cm-1 (S=0 str. in a sulphinic acid). For derivative preparations for sulphonic acids see Section 9.6.26, p. 1284. The presence of an aromatic sulphinic add may be further confirmed by dissolving in cold concentrated sulphuric add and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to formation of a para-substituted aromatic sulphoxide. The reaction is ... 

Clearly, the major primary decomposition processes are loss of SO and loss of CO, both of which require prior formation of a C—0 bond. This virtually demands isomerization to an internal sulphinate ester (7),... 

By [H and 13C 2D NMR, it has been demonstrated that the addition of bisulphite takes place on the C-4, but it has not been possible to assess whether the adduct is a sulphinate or a sulphonate. Only 33S NMR spectroscopy has allowed the unambiguous determination of the structure of the product. Indeed, the 33S spectrum of the adduct shows a single signal that can be attributed only to sulphonate 13 on the basis of chemical shift (—3.3 ppm) and line width (40 Hz). The line width value is particularly indicative of the formation of an —SO3 moiety because it suggests that the sulphur electronic environment should be highly symmetric. In the case of a sulphur atom with an unsymmetrical electronic environment, such as in sulphinates, a broader signal should be expected. 

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