Sulfinic acids removal

These acids are less stable, less soluble and less acidic than the corresponding sulfonic acids. The common impurities are the respective sulfonyl chlorides from which they have been prepared, and the thiolsulfonates (neutral) and sulfonic acids into which they decompose. The first two of these can be removed by solvent extraction from an alkaline solution of the acid. On acidification of an alkaline solution, the sulfinic acid crystallises out leaving the sulfonic acid behind. The lower molecular weight members are isolated as their metal (e.g. ferric) salts, but the higher members can be crystallised from water (made slightly acidic), or alcohol. 

N, O-Diacylated or O-alkylated N-hydroxysulfonamides release nitroxyl (HNO) upon hydrolysis or metabolic dealkylation, as determined by gas chromatographic identification of nitrous oxide in the reaction headspace [27-29, 38]. Scheme 7.5 depicts the decomposition of a representative compound (7) to a C-acyl nitroso species that hydrolyzes to yield HNO. Either hydrolysis or metabolism removes the O-acyl or O-alkyl group to give an N-hydroxy species that rapidly decomposes to give a sulfinic acid and an acyl nitroso species. This C-acyl nitroso species (8) hydrolyzes to the carboxylic acid and HNO (Scheme 7.5). These compounds demonstrate the ability to relax smooth muscle preparations in vitro and also inhibit aldehyde dehydrogenase, similar to other HNO donors [27, 29]. 

Bicarbonate washing ensures removal of the sulfonic and sulfinic acids. 

Another route of metabolism for cysteine sulfinic acid is transamination to 3-sulfinylpyruvate, a compound that undergoes ready loss of S02 in a reaction analogous to the decarboxylation of oxaloacetate (reaction o, Fig. 24-25). This probably represents one of the major routes by which sulfur is removed from organic compounds in the animal body. However, before being excreted the sulfite must be oxidized to sulfate by the Mo-containing sulfite oxidase. The essentiality of sulfite oxidase is evidenced by the severe neurological defect observed in its absence (Chapter 16). 

A solution of 170 mg (1 mmol) of 4-methylbenzenesulfinic acid in 15 mL of F.t,0 is added at 20 °C to a solution of 117 mg (1 mmol) of amyl nitrite acid and 132 mg (2 mmol) of cyclopentadiene. Upon addition of the sulfinic acid, the solution turns green, which subsequently disappears. After 1 h the solvent is removed under vacuum. The residue is taken up in dioxane and, on addition of water, 75 mg of a white precipitate are obtained yield 30% mp 108-110°C. 

Removal of the mercapto (or thione) function is most commonly achieved using Raney nickel, although concentrated HCl at high temperatures or nickel boride have been employed. Thiohydantoins are transformed into imidazolidin-4-ones by sodium in amyl alcohol (70JHC439). Oxidative desulfurization procedures too are often used the reactions probably proceed through the unstable sulfinic acid species which very readily eliminates sulfur dioxide. The high resistance of sulfonic acids to acid hydrolysis renders unlikely the possibility that they are reaction intermediates. 

Applications. In 1994 ca. 305 10 " t of liquid sulfur dioxide was consumed just in the USA, of which 40% was utilized in the manufacture of sulfur-containing chemicals such as sulfites, hydrogen sulfites, thiosulfites, dithionites and salts of hydroxyalkane sulfinic acid and alkane sulfonates. It is also utilized in cellulose manufacture, in the chemical dressing of manganese ores, in the removal of sulfur-containing impurities from mineral oils, for disinfection and preservation in the food industry and for the treatment of water. 

Also known as thiourea dioxide (TUDO) or amino(imino)methanesulfinic acid (FAS), formamidine sulfinic acid is a reducing agent mainly used in the bleaching of deinked pulps to remove colored dyes [23-28]. 

General directions for preparation of sulfinic acids 498 500 Sulfur dioxide is led into a well cooled ethereal solution of the alkylmagnesium halide until no more precipitation occurs. After removal of the ether, the white crystalline residue of the magnesium sulfinate can be recrystallized directly from water, and the magnesium salts of ethane-, propane-, butane-, isopentane-, cyclohexane-, and benzene-sulfinite were prepared in this way magnesium 1-dodecanesulfinite501 was prepared at —35° to —40°. 

For preparation of the free sulfinic acids498 the magnesium sulfinite is suspended in a little water and treated under good cooling with concentrated hydrochloric or sulfuric acid. The oil that separates is taken up in ether, the sulfinic acid is removed from the ether by sodium carbonate solution, liberated again by acid, and taken up again in ether. Finally the ether is removed in a current of air at a low temperature. 

Thiophenesulfinic acid 541,542 2-Thiophenesulfonyl chloride is dissolved in several parts of water and cooled whilst being treated gradually with zinc dust. When the odor of the sulfonyl chloride has disappeared the pasty mixture is filtered and the solid is washed free from zinc chloride by water. The residue consisting of zinc thiophenesulfinite and the excess of zinc dust is treated with sodium carbonate solution which converts the zinc salt into the sodium salt which is readily soluble in water. The solution is filtered, greatly concentrated on a water-bath, and acidified. The sulfinic acid is taken up in ether. On removal of the ether it is obtained as an oil that solidifies to needles, m.p. 67°, when kept in a vacuum over sulfuric acid. 

The figure clarified that the de-SOx performance was improved as the heat treatment temperature rose, and in 900 C, it reached the performance over 80%. The de-SOx performance was stable after the reaction initiation over SO hours, and as the product material, sulfuric acid was continuously recovered. The material balance between removed SO2 and recovered sulfinic acid agreed in the propotimi over 98%. 

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