Sulphinate ions

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. 

The kinetics of the nitrosation of benzenesulphinic acid have been determined79. The reaction is very rapid and requires stopped-flow techniques. This makes benzenesulphinic acid an excellent trap for free nitrous acid, on par with the more well-known hydrazoic acid and hydrazinium ion80. In mildly acid solution reaction occurs via the sulphinic acid molecule and also the sulphinate ion. As expected, the latter is the more reactive and reaction takes place at the diffusion limit. All evidence points to the fact that the first nitrosation by NO+ is the rate-limiting step. 

Under well-defined experimental conditions the cathodic cleavage can therefore be considered as a source of sulphinate ions at low potential even when R is aliphatic. For example45,46, the reductions of MeS02Cl, CH2=CHS02C1 or PhCH=CHSQ2Cl lead... 

On the other hand, sulphinate ion was shown to be formed in acetonitrile since adding in situ an electrophile (e.g. gaseous CH3C1) leads to the corresponding sulphone. However, thioethers and thiols are formed in this case too (Scheme 8). 

A comparison of the relative rran,s-effects of iS-bonded sulphite and sulphinate ions pC) in [Co(NH3)5X] + ions was described in Chapter 5 (ref. 29). Anation by NCS ion was studied and a D-mechanism established. Data for the anation of rra/w-[Co(en)2(S03)(OH2)]+ ion are collected in Table 2. These results are inter-... 

Becker and Gosselck have reported the addition of sulphonyl carbanions to dimethylvinylsulphonium ion to give cyclopropanes. Interestingly, the sulphinate ion was not displaced in these reactions. Instead, the initial adduct (83) underwent a proton transfer, converting a sulphonium ylide into a sulphonyl ylide, and the latter apparently... 

Using a soliddiquid two-phase system of the sodium arenesulphinite in 1,2-dimethoxyethane, or in the complete absence of a solvent, permits the use of less reactive haloalkanes [3,4], This is a particularly good method for the preparation of sulphones where the sulphinic acid salts are readily available and, in addition to the synthesis of the tolyl sulphones listed in Table 4.28, it has been used to prepare phenyl sulphones [3]. Phenyl sulphones have also been prepared in good yield using a polymer supported catalyst [5] (Table 4.29). As the system is not poisoned by iodide ions, reactive iodoalkanes can be used and there is the additional advantages in the ease of isolation of the product and the re-use of the catalyst. 

Although the fragmentation reactions of the molecular ions of sul-phones and sulphoxides varied, the first step in rationalizing their behaviour was initial isomerization to sulphinate (64) and sulphenate esters (65). A variety of reactions of this type has been collated by Fields and Meyerson (1968), who pointed out that isomerization of sulphoxides to sulphenate esters was a known thermal reaction (see also, Kutz and Weininger, 1968, Kinstle et al., 1968b). In experiments designed to compare the mass-spectral and thermal behaviour of a series of sulphoxides, it was observed that the thermal isomerization appeared to proceed, but no comparable behaviour was observed in the mass spectra (Entwistle et al., 1967). 

Recently, the e.s.r. spectra of some arylsulphonyl radicals, ArS02, have been reported (McMillan and Waters, 1966) these unstable radicals were generated in a flow system by oxidation of the sulphinic acids with ceric ion. Similar radicals have been generated in the solid state by y-irradiation of sulphones (Ayscough et al., 1966). 

Oxidative amidation of sulphinic acids occurs under rather forcing conditions (18% oleum) to give a sulphonamide as product (equation 109)446. The severity of the reaction conditions means that this approach is not one that is generally applicable for the conversion. A far preferable method involves the rather mild oxidation of the ammonium salts of arenesulphinic acids with either hypochlorite ions or chlorine, in aqueous solution (equation 110)447. 

The previous examples all undergo cleavage to afford biradicals. Other workers have demonstrated that in some systems fission results in the formation of ionic species. Thus the irradiation of the sulphones 52 effects C—S heterolysis, the expulsion of the sulphinate and the formation of the ion 53. In water, this is trapped and undergoes fission to yield the ketones and aldehydes (54)61. The study has been extended to more complicated systems... 

The oxidation of thiols is accelerated remarkably by traces of catalyst and this reaction forms the basis of petroleum sweetening processes. Although transition metal ions are the most effective catalysts, any additive capable of catalysing electron transfer accelerates the reaction. Nitrobenzene in dimethylformamide/potassium hydroxide [118], 2-nitro-thiophene, tetracyanoethylene, and 4-nitropyridine-N-oxide [118] are all good catalysts for the oxidation of 1-butane thiol. The alkaline hydrolysis of disulphides containing aryl, carbonyl, and alpha unsaturated groups also results in catalysis, apparently due to the setting up of a sulphinate—sulphenate redox cycle [119—121]. 

Nitronate salts have been shown to be oxidized to gem-dinitro-compounds by nitrite ion and persulphate in the presence of catalytic amounts of ferricyanide. gem-Cyanonitro- and a-nitro-sulphones were similarly obtained from reactions involving use of cyanide and sulphinate salts respectively. A 1,M-dinitro-compound... 

The above outlined scheme leads to the conclusion that completely ionized thiols would give exclusively sulphinic and sulphonic acids nevertheless, the experimental results indicate formation of ca. 5% of disulphide in the oxidation of potassium benzenethiolate even with base in large excess. Since formation of disulphide would require the presence of undissociated thiol, other mechanisms must be operative. Again it is possible that the intervention of trace metal catalysis in the oxidation reaction has to be taken into account. Cullis, Hopton and Trimm reported that copper ions in concentrations as low as 10 M are still active as catalysts and indeed it is very hard to detect metal ions at such low concentrations and to exclude adventitious impurities of this order of magnitude. 

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