To sulfite

Sulfur Compounds. Aqueous sulfide and H2S, an odiferous compound in some waters, are oxidized rapidly (initially to sulfite and sulfurous acid) the rate constants ate 3x10 and 3 X 10 , respectively. Thiocyanate is oxidized by ozone to cyanide and sulfate via the intermediate formation of sulfite (47). 

Ma.nufa.cture. In a typical process, a solution of sodium carbonate is allowed to percolate downward through a series of absorption towers through which sulfur dioxide is passed countercurrently. The solution leaving the towers is chiefly sodium bisulfite of typically 27 wt % combined sulfur dioxide content. The solution is then mn into a stirred vessel where aqueous sodium carbonate or sodium hydroxide is added to the point where the bisulfite is fully converted to sulfite. The solution may be filtered if necessary to attain the required product grade. A pure grade of anhydrous sodium sulfite can then be crystallized above 40°C because the solubiUty decreases with increasing temperature. 

Ana.lytica.1 Methods. Various analytical methods involve titration with oxidants, eg, hexacyanoferrate (ferricyanide), which oxidize dithionites to sulfite. lodimetric titration to sulfate in the presence of formaldehyde enables dithionite to be distinguished from sulfite because aldehyde adducts of sulfite are not oxidized by iodine. Reductive bleaching of dyes can be used to determine dithionite, the extent of reduction being deterrnined photometrically. Methods for determining mixtures of dithionite, sulfite, and thiosulfates have been reviewed (365). Analysis of dithionite particularly for thiosulfate, a frequent and undesirable impurity, can be done easily by Hquid chromatography (366). 

The anhydrous monoclinic crystalline form has a density of 1.679 g/cm (59) no hydrates are known. SolubiUty in water is given in Table 4. Ammonium thiosulfate solutions decompose slowly below 50°C and more rapidly at higher temperatures. The anhydrous salt decomposes above 100°C to sulfite and sulfur (60) ... 

Salads. A combination of citric acid and ascorbic acid is used as an alternative to sulfites in prevention of enzymatic browning in fresh prepared vegetables (56). 

Multiblended inhibitors based on tannins, for use in either closed loop HW systems or steam raising boiler plants. Tannin-based multiblends are often offered as an alternative to sulfite-based multiblends. 

Where no data exist, one wishes to be able to estimate thermochemical quantities. A simple and convenient method to do that is through the use of the method of group additivity developed by Benson and coworkers15,21 22. The earlier group values are revised here, and new group values calculated to allow extension of the method to sulfites and sulfates. In addition, a method based on the constancy of S—O bond dissociation energies is applied. 

At the second stoichiometric point, all of the sulfiirous acid has been converted to sulfite, and the pH is determined using 2 For th calculation, we need the concentration of SO3, for which we need to know the volume of NaOH solution required to reach the second stoichiometric point. Start by finding the number of moles of sulfurous acid ... 

The ingestion of sulfites can also worsen asthma. These agents are often found in processed potatoes, shrimp, dried foods, beer, and wines. Patients sensitive to sulfites should be warned not to ingest these products, as they have been known to cause severe exacerbations, particularly in severe asthmatics. 

Sodium hydrosulfite is produced through the Formate process where sodium formate solution, sodium hydroxide, and liquid sulfur dioxide reacted in the presence of a recycled stream of methanol solvent. Other products are sodium sulfite, sodium bicarbonate, and carbon monoxide. In the reactor, sodium hydrosulfite is precipitated to form a slurry of sodium hydrosulfite in the solution of methanol, methyl formate, and other coproducts. The mixture is sent to a pressurized filter system to recover sodium hydrosulfite crystals that are dried in a steam-heated rotary drier before being packaged. Heat supply in this process is highly monitored in order not to decompose sodium hydrosulfite to sulfite. Purging is periodically carried out on the recycle stream, particularly those involving methanol, to avoid excessive buildup of impurities. Also, vaporized methanol from the drying process and liquors from the filtration process are recycled to the solvent recovery system to improve the efficiency of the plant. 

Takemoto BK, Noble RD, Harrington HM. 1986. Differential sensitivity of duckweeds (Lemnaceae) to sulfite II. Thiol production and hydrogen sulphide emission as factors influencing sulphite phytotoxicity under low and high irradiance. New Phytologist 103 541-548. 

Franke [47] undertook a comprehensive electroanalytical study of K2S207 mixtures with K2S04, which is formed by Eqs. (47) and (48) and V2Os, a widely-used oxidation catalyst for S02. Pure pyrosulfate under N2 or air (Fig. 38a,b) shows only the reduction to S02 and sulfate, Eq. (48) (all potentials are vs. Ag/Ag+). When S02 is added, a new reduction and oxidation peak appear (Fig. 38c,d). When the electrolyte was pre-saturated with K2S04 (ca. 4 wt.%) (Fig. 39) the gas composition had no direct effect on the voltammetry. Although the equilibrium for Eq. (49) lies well to the right at this temperature, 400 °C, the kinetics are quite slow in the absence of a catalyst. The equilibrium between pyrosulfate and sulfate, Eq. (47), lies well to the left (K = 2 x 10-6), but will proceed to the right in the absence of S03. Thus, the new peaks are sulfate oxidation, Eq. (43), and S03 reduction to sulfite ... 

Adverse reactions to sulfites appear to occur mainly among a small percentage of asthmatics, but it is possible for individuals without asthma to be sulfite sensitive. It is typically more of a problem in individuals with severe asthma who are also taking corticosteroid drugs to control their disease. Among these individuals, the prevalence of sulfite sensitivity is about 8%, while it is about 1% in asthmatics who are not dependent on steroids (Taylor and Bush, 1986). 

The mechanism of sulfite-induced asthma is not well-understood. Reactions to sulfited foods probably depend on the sulfite residue level in the food, the sensitivity threshold of the individual, the type of food consumed, and whether sulfite exists in the free (more toxic) form or combined (less toxic) form. The toxicology of sulfites has been reviewed by Madhavi and Salunkhe (1995). Sulfite sensitivity is not a true allergic reaction (Taylor et al., 1988). The FDA initially estimated that more than 1 million Americans are sensitive to sulfites, but more recent estimates lowered the number of asthmatics who may be sulfite sensitive to 80,000-100,000 (Bush et al., 1986). 

Table 7.2 ARMS data. Products responsible for adverse reaction complaints attributed to sulfiting agents, 1980-June 2000. (Data include adverse reactions reported to FDA before ARMS was officially established in 1985)...

TAYLOR S L, BUSH R K, SELNER J C, NORDLEE J A, WIENER M B, HOLDEN K, KOEPKE J w and busse w w (1988), Sensitivity to sulfited foods among sulfite-sensitive subjects with asthma , J Allergy Clin Immunol, 81(6), 1159-67. 

Write a balanced half-reaction that shows the oxidation of thiosulfate ions, 8203 , to sulfite ions, SOs ", in a basic solution. 

The possible roles in sulfur (and sulfide or sulfane-) oxidation of a sulfur dioxygenase or of electron-transport-linked hydration/dehydrogenation are outlined above, but the fate of the sulfite product may be more complex than previously considered. Vishniac and Santer (1957) showed that S-labeled sulfide was rapidly oxidized first to thiosulfate (and polythionates) and then to sulfate by T. thioparus. This observation was incorporated into the original Peck scheme (Eqs. 15.13-15.17) by Peck and Fisher (1962), who realized that the complete oxidation of thiosulfate (after reductive scission to sulfite and sulfide Eq. 15.3) could be explained if there was recycling of sulfide to produce thiosulfate ... 

Gunnison, A. F., and E. D. Palmes. Persistence of plasma 5-sulfonates following exposure of rabbits to sulfite and sulfur dioxide. Toxicol. Appl. Pharmacol. 24 266-278. 1973. 

This enzyme [EC 4.1.1.12], also known as desulfinase, catalyzes the conversion of aspartate to alanine and carbon dioxide. Pyridoxal phosphate is a required cofactor. The enzyme will also catalyze the decarboxylation of aminomalonate as well as the desulfination of 3-sulfino-alanine to sulfite and alanine. 

Hypersensitivity to LMWHs, heparin, or pork products hypersensitivity to sulfites or benzyl alcohol (multidose vials) history of heparin-induced thrombocytopenia (tinzaparin) active major bleeding thrombocytopenia associated with positive in... 

A, while the distance from the siroheme iron to the nearest cluster iron atom is 4.4 A. One of the cluster sulfur atoms is in van der Waals contact with the siroheme ring. The X-ray structure and spectroscopic experiments (Madden et al., 1989) suggest that a cysteine thiol sulfur serves as the bridging ligand between the cluster and the siroheme. The sixth coordination site of the siroheme appears to be vacant and solvent exposed. This site presumably represents the location of substrate binding to sulfite reductase. 

The flavylium ions of direct flavanol-anthocyanin adducts (i.e., A" -F and F-A" ") and anthocyanin dimers (A+-AOH) have the same UV-visible spectra as anthocyanins. Species in which the anthocyanin is substituted in the 4-position (A" -F, A" -AOH) are expected to be resistant to sulfite bleaching and hydration whereas F-A is as susceptible to water addition as their anthocyanin precursor. ... 

---