Sulphoxides, purification

Dunn and Stich [78] and Dunn [79] have described a monitoring procedure for polyaromatic hydrocarbons, particularly benzo[a]pyrene in marine sediments. The procedures involve extraction and purification of hydrocarbon fractions from the sediments and determination of compounds by thin layer chromatography and fluorometry, or gas chromatography. In this procedure, the sediment was refluxed with ethanolic potassium hydroxide, then filtered and the filtrate extracted with isooctane. The isooctane extract was cleaned up on a florisil column, then the polyaromatic hydrocarbons were extracted from the isoactive extract with pure dimethyl sulphoxide. The latter phase was contacted with water, then extracted with isooctane to recover polyaromatic hydrocarbons. The overall recovery of polyaromatic hydrocarbons in this extract by fluorescence spectroscopy was 50-70%. 

The most commonly encountered of these are dimethyl sulphoxide (DMSO) and N,N-dimethylformamide (DMF). With these solvents it is often possible to remove most if not all by adding the quenched reaction mixture to a relatively large volume of water, and extracting this several times with ether. The combined organics are then washed with more water. Any remaining DMF or DMSO will need to be removed in further purification of the crude product. 

This solvent may be purified in an analogous manner to dimethylformamide. If a considerable amount of water is present, the dimethyl sulphoxide may be frozen out of the mixture prior to the purification procedure. 

Under these conditions, the formation of higher esters of sucrose is favoured so that, even in the presence of an excess of sucrose, the product will contain 10% or more of the diester. In practice this rarely is a disadvantage. Other solvents (dimethyl-sulphoxide, pyridine, N-acyl piperidine, etc.) cuid catalysts can be used, but the separation and purification of the sucrose ester still is costly. 

The reagents were purchased from Fluka and used without purification except dimethyl sulphoxide and acetonitrile, which were dried and distilled over calcium hydride. 

The intermediate sulphoxides may be isolated with care, but this purification is not necessary. Full details on the use of propargyl selenides in the synthesis of a,/S-unsaturated ketones have appeared. 

Manabe, T., Jasumi, A., Sugiyama, M. et al (1998) Alliina.se [S-alk(en)yl-L-cysteine sulphoxide lyase] from Allium tuberosum (Chinese chive) - purification, localization, cDNA cloning and heterologous functional expression. Eur. J. Biochem., 257,21—30. 

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