Dithionate, reduction

Dithionites. Although the free-dithionous acid, H2S2O4, has never been isolated, the salts of the acid, in particular zinc [7779-86-4] and sodium dithionite [7775-14-6] have been prepared and are widely used as industrial reducing agents. The dithionite salts can be prepared by the reaction of sodium formate with sodium hydroxide and sulfur dioxide or by the reduction of sulfites, bisulfites, and sulfur dioxide with metallic substances such as zinc, iron, or zinc or sodium amalgams, or by electrolytic reduction (147). 

Sodium hydrosulfite or sodium dithionate, Na2S204, under alkaline conditions are powerful reducing agents the oxidation potential is +1.12 V. The reduction of -phenylazobenzenesulfonic acid with sodium hydrosulfite in alkaline solutions is first order with respect to -phenylazobenzenesulfonate ion concentration and one-half order with respect to dithionate ion concentration (135). The SO 2 radical ion is a reaction intermediate for the reduction mechanisms. The reaction equation for this reduction is... 

Thiazolidine-2,4-dione, 2-dialkylamino-bisimide synthesis, 5, 129 Thiazolidine-2,4-diones IR spectroscopy, 6, 242 tautomerism, 6, 270 Thiazolidine-2,5-diones synthesis, 5, 138 Thiazolidine-4,5-diones synthesis, 5, 129 6, 316-317 Thiazolidine-2,4-dithiones tautomerism, 6, 270 Thiazolidines "C NMR, 6, 243 conformation, 6, 242, 247 dihydrothiazines from, 2, 93 hydrolysis, 6, 273 IR spectra, 6, 242 ring fission, 5, 80 synthesis, 5, 118 6, 316-321 Thiazolidines, imino-tautomerism, 6, 273 Thiazolidines, methyl-conformation, 6, 242 Thiazolidine-2-thione, 3-acyl-reduction, 1, 469 Thiazolidine-2-thione, 4-alkyl-synthesis, 6, 318... 

Further examples of reductions with sodium dithionate are given in References 220-222. The stereoselective syntheses of 1,3- and 1,4-dienes and pheromones are described in Reference 223. 

The silver(II) oxidation of dithionate " is of interest because this reductant is rather inert and oxidation is often preceded by rate-determining disproportiona-... 

COVALENT COMPOUNDS, METAL IONS OXIDATION-REDUCTION tion (see Cr(Vr)-dithionate, p. 287). The stoichiometry is... 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

Cycloaddition reactions involving dithione intermediates derived by the reductive extrusion of sulfur atoms from [1,2,3,4,51pen tathi enopino[6,7-i>]pyrroles provided access to 1,4-dithin-fused pyrroles (i.e., 89) <06OL4529>. 

The removal of inorganic salts from reaction mixtures afforded by polymeric materials may be simply and effectively accomplished by dialysis,166 178 after decomposition of remaining periodate with ethylene glycol130 131 or butylene glycol. 161 170 Alternatively, the iodate and periodate ions may be removed as such, or after reduction to free iodine. The iodate and periodate ions have been effectively precipitated by means of sodium carbonate plus manganous sulfate,6 or by lead dithionate,191 barium chloride,24 192 193 strontium hydroxide194 202 or barium hydroxide,203 204 lead... 

Reduction of A-arylmaleimides with sodium dithionate gives monomeric and dimeric products a mechanism has been proposed. ... 

There is one report of reductive cleavage of the imidazole ring. Treatment of 122 with sodium dithionate in aqueous ammonia yielded amidine 123, which on hydrolysis with acid gave 124. Compound 124 was obtained directly on reduction with sodium dithionate in aqueous ethanolic sodium bicarbonate (83JHC1003). 

Scheme 6.35 Benzoins obtained from the reduction of benzils in the presence of thiourea derivative rac-36 and sodium dithionate.

In the case of the reduction of ferric salts by sulphur dioxide it has been suggested 9 that the reduction most probably proceeds in stages, a red ferric ferrisulphite, Fe[Fe(S03)3], being first formed, which on warming yields the ferrous salt and the dithionate, thus ... 

The direct sulphur to sulphur linking in the first formula is in harmony with the formation of the salt by reduction of the sulphite and with the stability of the salt in the presence of alkalis,1 but it is discounted by the absence of dithionate from the oxidation products, and by the easy fission of the substance into sulphite and sulphoxylate on treatment with an aldehyde. 

Figure 11.8 Self-assembled cyclic-D,L-a-peptide nanotubes containing NDI as the core, (a) Reversible reduction of the NDIs with sodium dithionate. (b) Self-assembly of the peptide NDI nanotube after reduction reaction via chemical or electrochemical methods.

Reduction of Ferric Chelates by HSO3 and Formation of Dithionate. FeJ+(EDTA) is reduced by HSO3, producing dithionate and a small amount of S0/2 (24). The rate of reduction of Fe +(EDTA) is first order in [HSO3] and [Fe +(EDTA)], and inversely first order in [Fe2+(EDTA)]. 

The improvement over the existing Japanese processes can be made by developing a more efficient ferrous chelate such that it can provide better absorption efficiency for NO, faster reaction rates between NO and S02> and better stability for the ferrous chelate toward oxidation, compared to Fe +(EDTA) or Fe +(NTA) employed in Japanese processes. The development of an efficient and cost-effective method for the reduction of ferric chelate to ferrous chelate without producing dithionate ions could make the process attractive. In addition to these areas, the study of several alternative approaches and novel ideas could develop into a much more efficient and cost-effective scrubber system employing metal chelate additives. 

In order to introduce a second hydroxyl group al C-l 1 of the ester (99) its sodium salt was treated with p-nitrobenzene diazonium chloride in methanol. The resulting product on methylation and then reduction with potassium dithionate afforded the amino ester (100). Diazotization and methanolysis produced ethyl ( )-camosate dimethyl ether (101), which on saponification produced camosic acid dimethyl ether (102). Wenkert [22] accomplished demethylation of dextrorotatory camosic dimethyl ether with boron tribromide. Thus the work of Meyer lacks only the... 

Reduction of 5,7-diaminopyrido[3,4-6]pyrazine with NaBH4 gives the 1,2-dihydro derivative whose enantiomers can be separated by reaction with (K)-1 -(1 -naphthyl)ethylisocyanate <89JMC2089, 89JMC2363). Reduction of the iV-oxides with sodium dithionate gives the deoxygenated product <92S1206>. 

Dithionous acid, H2S2O4, is not obtainable as a pure compound, but several salts of the acid are known. The acid formally contains sulfur(III), and this suggests reduction of sulfites as a method of preparation. Such a process is illustrated in the following equation ... 

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