Organic sulfoxides

ASR Sulfoxide [Alberta Sulfur Research] A process for removing residual sulfur dioxide and hydrogen sulfide from the tail gases from the Claus process by wet scrubbing with a solution containing an organic sulfoxide. Elemental sulfur is produced. It had not been piloted in 1983. 

Sulfoxide Reduction Sulfoxide reduction is a two-electron-transfer reversible reaction resulting in thioethers. Organic sulfoxides are used mainly as agrochemicals, and their reduction (abiotic and microbially mediated) has been found in anaerobic soils, sediments, and groundwater (Larson and Weber 1994). 

Lower members of the series of salts formed between organic sulfoxides and perchloric acid are unstable and explosive when dry. That from dibenzyl sulfoxide explodes at 125°C [1], Dimethyl sulfoxide explodes on contact with 70% perchloric acid solution [2] one drop of acid added to 10 ml of sulfoxide at 20° C caused a violent explosion [3], and dibutyl sulfoxide behaves similarly [4]. A fatal explosion resulted from mistakenly connecting a DMSO reservoir to an autopipette previously used with perchloric acid [5], (The editor has met a procedure for methylthiolation of aromatics where DMSO was added to excess 70% perchloric acid he did not feel justified in trying to scale it up.) Explosions reported seem usually to result from addition to excess sulfoxide. Aryl sulfoxides condense uneventfully with phenols in 70% perchloric acid, but application of these conditions to the alkyl sulfoxide (without addition of the essential phosphoryl chloride) led to a violent explosion [4]. Subsequent investigation showed that mixtures of phenol and perchloric acid are thermally unstable (ester formation ) and may decompose violently, the temperature range depending on composition. DSC measurements showed that sulfoxides alone... 

Prinzler, H.W., Tauchmann, H., and Tzcharnke, C., Thin-layer chromatographic separation of organic sulfoxides and dinitrothioethers some observations on reproducibility and structural influence. II. Separation of sulfoxide mixtures by one- and two-dimensional thin layer chromatography, J. Chromatogr., 29, 151, 1967 Chem Abs., 67, 96615m, 1967. 

Sulfoxides. Lower members of the series of salts formed with organic sulfoxides are explosive when dry.16 27 28... 

Oertel, R. P. Protein conformational changes induced in human stratum comeum by organic sulfoxides An infrared spectroscopic investigation. Biopolymers 76 2329-2345, 1977. 

Organic sulfoxides are useful intermediates for the construction of many chemically and biologically significant molecules. Most of the current methods for the oxidation of sulfides to sulfoxides " suffer from over-oxidation to sulfones. Even when controlling the reaction temperature, it is difficult to avoid over-oxidation in most of the reported procedures. 

Both dimethyl sulfoxide (CH3S(0)CH3) and dimethyl sulfone (CH3S(02)CH3) are known to rapidly react with OH (which leads to effective further oxidation), and in the presence of liquid water to be very likely removed by absorption in the liquid phase. The effective absorption of dimethyl sulfoxide and dimethyl sulfone in water is due to their high solubility the Henri constant is > 5 10" for both organic sulfoxides. Therefore, effective DMS removal from air can be provided not only by its complete oxidation to CO2, H2O, and SO2, but also by means of formation of highly soluble compounds following scrubbing. Such a no-by-product approach to VOC removal in the wet pulse corona will be considered later in Section 11.8. 

The environmental significance of organic sulfoxides results primarily from their importance as agrochemicals specifically, the organophosphorus and carbamate insecticides containing sulfoxide moieties. Studies suggest that reduction of these chemicals can be the primary pathway for their transformation in anoxic sediments. For example, reduction of phorate sulfoxide to phorate in anoxic pond sediments occurred with half-lives ranging from 2 to 41 days (Equation 3.38) (Tratnyek and Wolfe, 1988). 

Suitable polymerization catalysts are organic metal carboxylates. Lithium salts are highly soluble in the reaction system and large in the catal5 ic effect, but expensive. Potassium, rubidium, cesium, and alkatine earth metal salts are considered poorly soluble in the reaction system. Sodium salts can preferably be used since they are cheap and moderately soluble in the polymerization system. Thus, sodium acetate is a preferred catalyst. Another class of catalysts are cyclic amine compounds, A-heteroaromatic compounds, and organic sulfoxide compounds. 

Several approaches have been described for the preparation of optically active sulfoxides [5-7]. The three main routes to obtain these compounds are as follows (i) the asymmetric sulfoxidation of prochiral sulfides, (ii) nucleophilic substitution using a chiral sulfur precursor, and (iii) the kinetic resolution of racemic sulfoxides. The first of tiiese methods involves the use of various oxidants and catalysts and has been the most extensively employed. There are many examples in the scientific literature and reviews are available on this approach. In recent years, much attention has been focused on the synthesis of organic sulfoxides by emplo5dng conditions compatible with the green chemistry procedures [8-10]. For this reason, mild oxidants such as molecular oxygen or hydrogen peroxide are considered in combination with novel catalysts in order to develop a mild and environmentally friendly process. 

ScoRRANO, G. Equilibria and Reactions of Organic Sulfoxides in Moderately Concentrated Acids. Accounts Chem. Res. 6, 132—138 (1973). 

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