Sulfite to sulfate

Rhenium oxides have been studied as catalyst materials in oxidation reactions of sulfur dioxide to sulfur trioxide, sulfite to sulfate, and nitrite to nitrate. There has been no commercial development in this area. These compounds have also been used as catalysts for reductions, but appear not to have exceptional properties. Rhenium sulfide catalysts have been used for hydrogenations of organic compounds, including benzene and styrene, and for dehydrogenation of alcohols to give aldehydes (qv) and ketones (qv). The significant property of these catalyst systems is that they are not poisoned by sulfur compounds. 

The deleterious effect of sulfur dioxide and sulfites in domestic water is increased corrosivity owing to the lowered pH. However, oxidation of sulfite to sulfate in aqueous solutions uses dissolved oxygen, and lliis may retard corrosion. While llte oxichition of sulfite and sulfiirous acid to sulfate and sulfuric acid in the atmosphere is an environmental concern, this reaction is too... 

Sulfite Oxidation Investigated in Micro Reactors Cas/liquid reaction 27 [CL 27] Oxidation of sulfite to sulfate... 

II. Sulfite oxidase family Sulfite oxidase Sulfite to sulfate... 

Colonna, S., Gaggero, N., Carrea, G. and Pasta, P., Oxidation of organic cyclic sulfites to sulfates a new reaction catalyzed by cyclohexanone monooxygenase. Chem. Commun., 1998, 415. 

Oxidation of cyclic sulfites to sulfates was accomplished with RuClj/aq. Na(IO )/CH3CN-CCiyO°C and a large-scale oxidation of D-mannitol-l,2 5,6-diacetonide-2,3-cyclic sulfite to the sulfate described (Fig. 5.17) [437]. The system RuO /aq. Na(10 )/CHCl3 converted cyclic sulfite diesters to the sulfates (Fig. 5.18) [438]. Oxidations of thiophene and aUcyl- and aryl-substituted thiophenes by RuCyaq. Na(ClO) were compared with similar reactions effected by stoich. [MnOJ- [439]. 

Sulfor oxidizing bacteria oxidize sulfide and sulfite to sulfate. The decrease of oxygen [94,95] as well as the alteration of pH [96] can be used as indicators of these reactions. With a Thiobacillus thioparus-containing sensor, a detected limit of 4 pmol/1 sulfite is reached [94]. The detection limit of a sensor with Thiobacillus thiooxydans for sulfide is 0.02 mmol/1 only [95]. 

Molybdoenzymes other than the nitrogenases are usually termed oxomolybdoenzymes. This prefix relates to the nature of the catalysis effected, i.e. the net effect of the conversion (xanthine to uric acid, sulfite to sulfate, nitrate to nitrite, or aldehyde to carboxylate) corresponds to the transfer of one oxygen atom to or from the substrate. Furthermore, molybdenum X-edge EXAFS studies have established that this metal is coordinated to one or more terminal oxo groups in each enzyme studied by this technique.204... 

The sulfur-oxidizing bacteria. Anaerobic conditions prevail in marine sediments, in poorly stirred swamps, and around hydrothermal vents at the bottom of the sea. Sulfate-reducing bacteria form high concentrations (up to mM) of H2S (in equilibrium with HS and s2-)318-320 This provides the substrate for bacteria of the genus Thiobacillus, which are able to oxidize sulfide, elemental sulfur, thiosulfate, and sulfite to sulfate and live where the aerobic and anaerobic regions meet.311 321-323 Most of these small gram-negative... 

Oxidation of sulfite to sulfate within cells occurs by a pathway through adenosine 5 -pHosphosulfate (APS, adenylyl sulfate). Oxidation via APS (Eq. 18-22) provides a means of substrate-level phosphorylation,... 

Sulfite oxidase catalyzes the oxidation of sulfite to sulfate, with cytochrome c as the ultimate physiological electron acceptor. Sulfite is oxidized at the molybdenum site, which is in turn reoxidized by the heme. 

The iodine produced reacts with S032- oxidizing sulfite to sulfate, and itself reduced to HI, as shown below ... 

In general, sulfide is oxidized via sulfite to sulfate, while thiosulfate can either be oxidized only to tetrathionate or may be split into sulfide and sulfite. Both compounds are then further oxidized to sulfate. During anaerobic sulfide or thiosulfate oxidation, elemental sulfur appears as sulfur globules inside or outside the cells. Sulfur metabolism in Anoxyphotobacteria has two main functions ... 

There are two possibilities to oxidize sulfite to sulfate in phototrophic bacteria ... 

In agreement with the statements of Trueper (1) one can say that principally different dissimilatory sulfur metabolic pathways exist in Anoxyphotobacteria for the oxidation of sulfite to sulfate (via APS or directly), the utilization of thiosulfate (splitting or formation of tetrathionate), and the oxidation of sulfide or elemental sulfur (by a "reverse" siroheme sulfite reductase or other mechanisms). 

A catalytic enantioselective oxidation of cyclic sulfites to sulfates has been performed using cyclohexanone monooxygenase <1998CC415>. 

A sulfoxide group in a side chain can also be selectively oxidized (by OT-chloroperbenzoic acid (MCPBA)) without oxidation of cyclic sulfite to sulfate <2003HAC587>. On the other hand, the standard oxidation of cyclic sulfite to sulfate by NaI04 in the presence of R.UCI3 (Section 6.05.10.3) leads simultaneously to Ar-dihydroxylation of a double bond in a substituent <1999TL2235>. 

Applicable to natural and waste water. There may be interference from S2< Fe2+, and thiosulfate that leads to overestimation of sulfite, or from the presence of ions (Cu2+) that catalyze the conversion of sulfite to sulfate. 

Figure 2.11 Mechanism of the internal sulfite to sulfate oxidation showing the movement of the oxygen atoms (shown faded). The equatorial cluster belts and the central sulfur position of a W,l(SO,) fragment is illustrated (S atoms also faded).

Another inorganic reaction that can be catalyzed by supported porphyrins is the air oxidation of sulfite to sulfate. Sulfite is formed upon absorption of SO2 from flue gases. For this reaction, a 2-V-methylpyridiniumyl-substituted... 

Some of the effects of sulfur dioxide are attributable to its acidifying effects, either as sulfurous acid or, after oxidation, as sulfuric acid. In at least one case the ability to convert sulfite to sulfate has been correlated with resistance to toxicity. 

Sulfite Oxidase. This enzyme, isolated from bovine (26, 27) and chicken liver (28), catalyzes the oxidation of sulfite to sulfate. This is possibly a crucial function in animals as S032" (or S02, its gaseous precursor) is toxic while S042" is relatively innocuous. For example, one of the first signs of molybdenum deficiency in rats is a greatly increased susceptibility to S02 poisoning (28). In addition, a human child bom without sulfite oxidase activity did not survive for very long (29). 

An important technology for removal of S02 is Flue Gas Desulfurization (FGD), carried out in units known as scrubbers. Most scrubbers contact the flue gas with a slurry of lime or limestone to capture the sulfur oxides and produce a sludge containing calcium sulfite and calcium sulfate. However, disposal of sludge is another environmental problem, and some scrubbers include oxidation to convert all the calcium sulfite to sulfate (gypsum), which can be used for wallboard manufacture. Fluidized-bed combustion units add a sulfur... 

A number of oxidizing agents, among them Mn04, Cl2, I2, and Fe3+, will oxidize sulfite to sulfate. 

In humans, age-related differences have been observed in metabolism of sulfite to sulfate and in formation of sulfur trioxide (Constantin et al. 1996). Constantin et al. (1996) measured sulfur trioxide radicals and sulfite oxidase activity in polymorphonuclear leukocytes (PMNs) from four groups young adults (average age 25), older adults (average age 65), 3 centenarians (older than 100), and Down syndrome patients. They found significantly increased amounts of sulfur trioxide radicals in PMNs from healthy adults who had low sulfite oxidase activity. In centenarians and Down syndrome patients, generation of the sulfur trioxide radical was the primary mechanism for detoxification of sulfite. There was no correlation between the sulfur trioxide radical and sulfite oxidase activity. 

The typical S-oxidation with BVMOs allows the formation of chiral sulfoxides from organic sulfides. This oxidation has received much interest in organic chemistry due to its use in the synthesis of enantiomerically enriched materials as chiral auxiliaries or directly as biologically active ingredients. This reaction has been studied extensively with CHMO from Adnetohacter showing high enantioselectivi-ties in the sulfoxidation of alkyl aryl sulfides, disulfides, dialkyl sulfides, and cychc and acyclic 1,3-dithioacetals [90]. CHMO also catalyzes the enantioselective oxida-hon of organic cyclic sulfites to sulfates [91]. 

The hypohalites and their parent acids decompose to release oxygen (equation 114) and thus serve as very strong oxidizers in inorganic and organic chemistry. The hypohalites oxidize oxalates to carbon dioxide, nitrites to nitrates, sulfites to sulfates, divalent manganese to permanganate, halides to halates, and ketones to carboxylic acids, and so on. 

Sulfite oxidase contains an oxo-molybdenum center and a 6-type cytochrome. The proposed catalytic sequence (254-256) for the enzyme is shown in Fig. 16. Oxidation of sulfite to sulfate, a two-electron process, occurs at the molybdenum center with concomitant reduction of the molybdenum from VI to IV. Electrons are removed from the enzyme by interactions of the heme of the 6-type cytochrome with exogenous cytochrome c, a one-electron process. Thus, the proposed mechanism of Fig. 16 involves two separate intramolecular electron transfers be-... 

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