Dithionite ions, reactions

The dihydrate Na2S204.2H20 can be precipitated by salting out with NaCl. Air and oxygen must be excluded at all stages in the process to avoid reoxidation. The dithionite ion can also be produced in situ on an industrial scale by reaction... 

We have been investigating the oxidation-reduction reactions of the binuclear iron site in the protein matrix (27-32). The methemerythrin form contains both irons in the +3 oxidation state and can be reduced in two steps (by dithionite ion (27, 31), reduced methylviologen, and photochemically using a riboflavin/EDTA mixture (28)) to the deoxy form in which both irons are in the +2 oxidation state. The intermediate (semi-met), in which one iron is +3 and the other iron +2, has been... 

The direct disproportionation of the bisbenzenechro-mium(I) ion to bisbenzenechromium(O) and higher oxidation levels of the uncomplexed metal ion is not complete in alkaline medium, and is also undesirable because some of the metal is lost for further complexing. The quantitative reduction of the cation with dithionite ion according to the reaction ... 

However, the reaction goes to completion because SO2 is complexed by SO2 and also dimerizes to dithionite ion. Thus, 02 - is a stronger and more effective reducing agent than dithionite ion in aprotic solvents. In aqueous media, the equilibrium constant for the reduction of... 

Pyridinium salts can be reduced with the mildly nucleophilic dithionite ion to produce mixtures of di-hydropyridines. Much work has been carried out since the early observation that NADPH could be obtained from NADP with this reagent. Reduction produces mainly the 1,4-dihydro isomer with minor amounts of the 1,2- or 1,6-dihydro adducts. The reduction is believed to proceed via a stable and sometimes isolable sulfinate intermediate (91). In acid solution this decomposes with loss of sulfur dioxide to form the dihydropyridine (92 Scheme 19). Various substituted pyridinium species undergo this reaction and the Isomer ratio obtained is dependent upon the nature of the solvent, temperature and pH. With l-methyl-4-carbamoylpyridinium bromide (93) and dithionite in aqueous sodium carbonate at 0-5 C for 10 min the only isolated product was the 1,2,5,6-tetrahydropyridine (94) obtained in 16% yield, but the 3-carbamoyl salt gave the 1,4-dihydronicotinamlde (95) in 90% yield, free of the 1,6-isomer. The 3-chloropyridlnium ion (96) gave a moderate yield of the 1,4-dlhydropyridlne (97). 

Zeaxanthin (C ) has been incorporated in DMPC and egg lecithin vesicles. This a,(D-bipolar carotenoid reinforces the DMPC vesicle with respect to mechanical stability and water permeability but has no effect on fluid egg lecithin membranes (Lazrak et al.,1987). Electron-poor derivatives with electron-withdrawing carboxyl or pyridinium end groups should reversibly take up electrons in a type of reversible Michael reaction and then act as organic wires. There are, however, no reports on stable anion radicals of such chro-mophores in the literature. Claims of electron transport through vesicle membranes are very probably erroneous. It has been shown by reduction of an entrapped indigo dye that bixin derivatives in DPPC vesicle membranes favor the transport of borohydride and dithionite ions through the membrane rather... 

The interfacial area can be measured in specific systems using chemical reactions in which the absorption rate kinetics are a known function of the gas-liquid interfacial area. For example, Vasquez et al. (2000) compared three different chemical methods (i) Danckwerts method using the absorption of CO2 in sodium or potassium carbonate buffer solutions, (ii) the sodium sulfite method involving the oxidation of sulfite ions, and (iii) the sodium dithionite method involving the oxidation of dithionite ions. All three methods were shown to produce similar interfacial area measurements. 

Aqueous solutions of dithionite ion can also be determined by iodometric titration to a blue starch endpoint (reaction [XXVIII]) ... 

The reduction of toluidine blue by 8204 in HCI-H2O has a 1.39 order in dithionite ion. The reaction rate increases with increase in H+. The rate is affected by the ionic strength and dielectric constant of the medium and addition of 804 and N03 retard the rate. ... 

Write the half-equations for this reaction and identify the reducing agent and the oxidizing agent. Hint-ffit product contains the dithionite ion, S204. )... 

Sulfite and hydrogen sulfite ions reduce iodine into iodides (see iodometry). They also reduce permanganate ions. They are simultaneously converted into sulfate ions (Bunsen s method) or into dithionite ions 8205 depending on the experimental conditions. The reaction must be carried out in a very acidic medium in order for the + II oxidation state of manganese to be reached and also to avoid the precipitation of manganese dioxide. Reduction reactions of permanganate are... 

The same study [47] also inferred from the analysis of voltammetric curves that the electrochemical reduction of bisulfite leads to the formation of the dithionite ion according to the redox reaction ... 

Reaction of free-base porphyrin compounds with iton(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iton(III) porphyrin complexes (hemins), which usually have the anion of the iton(II) salt for the fifth or axial ligand, ate isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iton(II) complexes are obtained from iton(III) porphyrin complexes by reduction with dithionite, thiolate, borohydtide, chromous ion, or other reducing agents. 

Reduction by sodium dithionite. A small amount of sodium dithionite, solid or in solution, is added to a luciferase solution made with 50 mM phosphate, pH 7.0, containing 50 pM FMN. The amount of dithionite used should be minimal but sufficient to remove oxygen in the solution and to fully reduce the flavin. The solution made is injected into an air-equilibrated buffer solution containing a long-chain aldehyde and luciferase to initiate the luminescence reaction. With this method, the reaction mixture will be contaminated by bisulfite and bisulfate ions derived from dithionite. 

The main kinetic consideration is the time-scale of the redox reaction if the relevant electron-transfer reaction is slow, then we run the risk that measurements are taken before a true equilibrium has been attained after the addition of each aliquot. In practice, however, most analytes are oxidized or reduced within a very short time-scale - probably within microseconds if mixing is efficient, and provided that the oxidant (e.g. H2O2, Mn04, Ce or Cr20j ) or reductant (e.g. chromous ion, Cr, dithionite, 8204, or thiosulfate, S203 ) is sufficiently powerful. Note that while oxidation of Cr to form is fast, the... 

As previously reported, the radical addition of CF2Br2 on glycals (initiated by sodium dithionite) affords difluorobromomethylated compounds. These latter molecules are easily dehydrohalogenated in the presence of TBAF. Under such conditions, these difluorovinyl compounds can add a fluoride ion (from TBAF). The subsequent elimination of the acetate moiety yields trifluoromethyl unsaturated compounds. The double bond can then be reduced (Figure 6.37). The same kind of reaction occurs in the presence of DAST with gcm-difluor-omethylene compounds, which are obtained by addition of an ylide onto an ulose (Figure 6.37). 

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