Dithionite ion

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... 

The dithionite ion has a remarkable eclipsed stmcture of approximate C2v symmetry (Fig. 15.32b). The extraordinarily long S-S distance (239 pm) and the almost parallel SO2 planes (dihedral angle 30°) are other unusual features. Electron-spin-resonance studies have shown the presence of the S02 radical ion in solution ( 300ppm), suggesting the establishment of a monomer-dimer equilibrium 8204 ... 

Another interesting structure is that of the dithionite ion, S2042, which is shown as... 

Reduction of Fe-protein by electron carriers such as ferredoxin or flavodoxin or by inorganic dithionite ion. 

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... 

Dissociation of the dithionite ion can proceed both in aqueous and in nonaqueous media. There is a special equation to determine the average values of equilibrium constants of the forma-... 

Disulfide bridges (crosslinkages) 65, 80 cleavage of 115-116 cleavage with performic acid 115 locating 119 in proteins 80 reduction of 115, 785 Dithioerythritol 115 Dithionite ion 779 Dithiothreitol 98,115, 822 Dityrosine linkages 81 DMSO reductase 890 DNA... 

Dissociation of the dithionite ion can proceed both in aqueous and in nonaqueous media. There is a special equation to determine the average values of the equilibrium constants (Keq) of the formation of S02 from S204 (Lough McDonald 1987), namely, Keq = [SO2 ]2/ [S2On0 - 0.5 [S02 ]. ... 

The results of this calculation for the above-mentioned decomposition experiment are given in Fig. 6.14 by the continuous lines. The crosses illustrate the variation of the concentration of dithionite and sulphite in solution obtained by titration of samples taken at fixed times. It can be seen that the concentrations obtained by calculation from the experimental currents (continuous line) are in good agreement with the ones obtained by titration (crosses). Note also that the increase of the concentration of sulphite is twice as high as the drop of the sodium dithionite concentration. Indeed, for each dithionite ion that is decomposed, two sulphite ions are... 

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 ... 

Disulfur dinitride, 6 126 Disulfur pentoxydiehloride, 3 124 analysis of, 3 126 Dithiocarbamates, of selenium(II) and tellurium(II), 4 91 Dithionic acid, salts of, 2 167 Dithionite ion, formation of, from sulfur dioxide by sodium hydride, 5 13... 

Complete electrolysis yields SOj which dimerizes to dithionite ion (colorless) — "02SS02 Kd, 2.4 X 101 M-1... 

Air will oxidize the dithionite ion (which allows it to be used as an oxygen trap), and many metals are reduced to the zero oxidation state by the ion. 

The reduction of sulfites in aqueous solutions containing an excess of S02, usually by zinc dust, or of S03 by formate in aqueous methanol, gives the dithionite ion Solutions of this ion are not very stable and decompose according to the stoichiometry ... 

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). 

Figure 11. Schematic diagram of viologen-mediated transmembrane reduction of MV + by dithionite ion. Rapid bimolecular reduction of external MV + is followed by slow first-order reduction of internal accom-...

The dithionite ion (S2 O4 ) provides an example of a group of this kind with the eclipsed configuration. 

The rhodium dithionite complex 1 is composed of the rhodium dinuclear moiety (RhCp )2((i-CH2)2 and the dithionite ion S2042-. The dithionite ion is very attractive as the external stimuli-responsive ligand because the ion has a weak covalent S—S bond (2.389 10 A), which is easily cleaved to form radical species by stimuli [9]. 

Jiittner et al. [155] developed an electrochemical method for the simutaneous removal of SO2 and NO c- The process is shown schematically in Fig. 30. Flue gas is passed to an absorption column containing dithionite ions (8204 ). Dithionites are powerful reducing agents. The dithionite is oxidized to sulphite and NO is reduced to compounds such as NHJ, NH2HSO3, and NH2OH, while SO2, is not absorbed. Also, small amounts of N2O are formed. The solution is fed to the cathodic compartment of the electrochemical cell. 

Figure 1532 Structure of (a) the disulfite ion 8265 in (NH4)2S20s, and (b) the dithionite ion 8264 Na2S204.2H20.

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