Purification, general sulfur compounds

Purification. The LPG generally requires treatment for removal of hydrogen sulfide [7783-06-4] H2S, organic sulfur compounds, and water in... 

General Synthesis Scheme. A schematic diagram of a plant producing synthetic liquid fuels and chemicals from coal via the Fischer-Tropsch synthesis is shown in Fig. 11-3. Gasification of coal with steam and oxygen is followed by a purification step to eliminate solids, sulfur compounds, and most of the carbon dioxide. Two stages of synthesis are employed to attain a high conversion of the synthesis gas. Recovery and treatment of primary... 

The increased solubility of substituted phthalocyanines (vide infra) enables more common purifications as used for other organic compounds. Usually the purification is done by chromatography either on alumina or silica gel, but recrystallization and extraction procedures can also be used. In some cases, the methods used for unsubstituted phthalocyanines can also be practiced, although the increased molecular weight accompanied by a reduced thermal stability makes sublimation more difficult.97 98 However, for substituted phthalocyanines, the stability towards acid may be reduced97 and, therefore, purification by treatment with sulfuric acid cannot generally be recommended. 

The preparation and properties of the dithiocarboxylic acids and their metal complexes have been reviewed several times.38"11 The formation of C—C bonds in the direct reaction of CS2 requires sufficiently nucleophilic carbon bases, directly or potentially accessible in the form of ambifunction-al phenoxides, organometalfic compounds, CH acidic compounds, enamines or ketimines. Carba-nions react with CS2 to give dithiocarboxylates. The preparation and purification of the adds is performed via their salts. Metal complexes are in general readily available. The bonding in these complexes is mostly of the type (27) but a bonding mode (28) is also found. Action of elemental sulfur upon heavy metal complexes of (29) aromatic dithiocarboxylic acids yields the perthio complexes (29) of these compounds. 

Reaction-extraction This technique involves chemical modification of solutes in solution in order to more easily extract them in a subsequent extraction operation. Applications generally involve modification of impurity compounds to facilitate purification of a desired product. An example is the oxygenation of sulfur-containing aromatic impurities present in fuel oil by using H2O2 and acetic acid, followed by hquid-liquid extraction into an aqueous acetonitrile solution [Shiraishi and Hirai, Energy and Fuels, 18(1), pp. 37-40 (2004) and Shiraishi et al., Ind. Eng. Chem. Res., 41, pp. 4362-4375 (2002)]. Another example involves esterification of aromatic alcohol impurities to facihtate their separation from apolar hydrocarbons by using an aqueous extractant solution [Kuzmanovid et al., Ind. Eng. Chem. Res., 43(23), pp. 7572-7580 (2004)]. 

Synthetic methods for preparation of 1,2,4,5-tetroxanes have been reviewed recently <2001COR601, 2002RMC113>. The most general method involves acid-catalyzed addition of hydrogen peroxide to carbonyl compounds and subsequent cyclization of the hydroperoxide intermediates. The direct synthesis is carried out normally in the presence of either sulfuric, perchloric, or methanesulfonic acids and affords symmetrically substituted tetroxanes (Equation 26). In many cases, for example, where the carbonyl compound is unsubstituted in the a-position, tetroxanes are contaminated with hexaoxonanes and open-chain hydroperoxides. Selective removal of the more reactive hydroperoxides can be achieved with dimethyl sulfide or potassium iodide. Recrystallization usually removes residual hexaoxonanes but, failing that, heating the mixture with perchloric acid in acetic acid can convert hexaoxonanes to tetroxanes or convert the thermodynamically less stable hexaoxonanes to more water-soluble lactones, which may facilitate the purification process <2002RMC113>. 

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