Lead dithionate

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... 

Tile a-dithione 91, generated by photolysis of 92, is transformed into the dithiin 93 (417o) in the absenee of a trapping agent. The eonversion was proposed to proeeed by a [4 + 2] eyeloaddition of 91 with its dithiete tautomer 94 leading to the dithietane 95, whieh was followed by loss of S2 (85JOC1550). Sueh [4 + 2] dimerizations are often eneountered in the ehemistry of 1,2-dithietes as diseussed later. 

The various oxidation states of sulfur have been determined by polarography. The electrochemical oxidation of sulfide ions in aqueous solution may lead to the production of elementary sulfur, polysulfides, sulfate, dithionate, and thiosulfate, depending on the experimental conditions. Disulfides, sulfoxides, and sulfones are typical polarographically active organic compounds. It is also found that thiols (mer-captans), thioureas, and thiobarbiturates facilitate oxidation of Hg resulting thus in anodic waves. 

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. 

Naphtho[2,l-( ]pyrans 291 with carbon disulfide lead to dithiones 292 (08PS1145), perhaps via a Dimroth rearrangement of possible intermediates 293 (Scheme 122). 

Aqueous solutions of normal alkali sulphites are oxidised to dithionate by heating with lead dioxide,1 the latter being reduced to red lead. Manganese dioxide does not react in this way. 

Anodic oxidation of heterocyclic thiones leads generally to disulfides. Thus cyclic voltammetric data at a pyrolytic graphite anode of purine-2,6-dithione show three peaks. The first and second correspond to a disulfide formation from the 6- and 2-thione groups, respectively, whereas the third is due to an oxidation to purine-2,6-disulfonic acid.432 Similarly, the electrochemical oxidation of benzthiazole-2-thione and benzimidazole-2-thione in CH3CN-NaC104 at a platinum electrode afforded the corresponding disulfides in good yield.433... 

Desulfurization of l,6-dihydro-l,2,4-triazine-3,5-dithiones (288) leads either to tetrahydro-l,2,4-triazin-3-ones (289) or to tetrahydro-l,2,4-triazines (290), depending on the conditions (70BSF1606). 

The heating of 4-o-tolyl-l,3-dithia-2,5-diazolium hexafluoroarsenate 154 with a small excess of o-tolylcyanide 155 in liquid S02 leads to 1,2,4-dithiazolium hexafluoroarsenate 6 in low yield (Equation 24) <1996AXC2148>. The decomposition of the known pesticide, 3,5-dirncthyltctrahydro-2//-1,3,5-thiadiazine-2-thione 156 (DTTT), in water and in salt solutions was studied in detail. 4-Methyl-5-methylimino-l,2,4-dithiazolidine-3-thione 157 and 2,4-dimethyl-l,2,4-thiadiazolidine-3,5-dithione 158 were isolated by HPLC and identified among the noncyclic decomposition products (Equation 25) <1996MI503>. 

The reaction of the dimethylamine enamine of isobutyraldehyde with aryl isothiocyanates at or below 50°C leads to the iminotetrahydrothiazine-thiones 333 these compounds rearrange on heating to hexahydropyrimidine-2,6-dithiones 334 (equation 135)164... 

Treatment of N-substituted 2,5-dimethylpyrroles 818 with complex 813 in chloroform at 0°C gives 7//-[l,2,3>4,5]pentathiepino[6,7-r ]pyrroles 819 in moderate yields (36 0%) (Scheme 157) <2005OL5725>. Further reaction of pyrroles 819 with the same mixture at room temperature leads, in an extensive reaction cascade, to 4-alkyl-37/-di[l,2]dithiolo[4,3- 3,4-,7 pyrrole-3,5(47r)-dithiones 820 in high yield (74-85%). Compounds 818 can be converted into the tricycles 820 in a one-pot operation under unusually mild conditions (with excess of S2CI2 and DABCO). Pentathiepino[6,7-r ]pyrroles 819 were obtained directly with a nonequilibrated mixture of S2CI2 and DABCO, but in low yields (8-17%). 

Increasing the reaction time lead to the formation of the dithione in only very low yield (5 %). Also, the synthesis of 40 has been reported to have been accomplished using the same procedure starting from phthaloyl chloride and 2,5-dimethyl thiophene. Conversion of this to the mono- and di-thiones has been reported to be unsuccessful. 

When this reaction was carried out in the presence of DMAD in carbon disulfide, thiophene 253 was obtained in 51% yield (Equation 39). A tentative mechanism of formation of a-dithiones is shown in Scheme 72. First, episulfonium ions 254 are formed and then sulfur ylides 255 are obtained. From the ylides the a-dithiones 256 are formed, while the episulfonium ions 254, by reaction with DMAD to produce 257, finally lead to the formation of 253. 

A regiospecific synthesis of A -substituted (aminopyridinyl)imidazole 1286 started with ketone 1282 (cf. Section 4.02.9.2(i)). a-Oximination of ketone 1282 with isoamyl nitrite under basic condition provides oxime isomers 1283. Both as- and /ra t-oximes 1283 participate in the cyclization process when treated with l,3,5-trimethyl-l,3,5-triazinane, leading to imidazole iV-oxide 1284 that is then reduced with 2,2,4,4-treta-methyl-cyclobutane-l,3-dithione to give 1285 (Scheme 326) <2003JOC4527, 1999JME2180> (see also Section 4.02.9.3(i)). 

Flash photolysis of 1,2-dithiolium cations in ethanol also leads to the reduction of the cation at the expense of the solvent. Spectrometric evidence suggests the formation of a short-lived 1,2-dithiolyl radical accompanied by a more stable propane-1,3-dithionate anion. 

At 30 C, the solubility of calcium dithionate in water exceeds that of calcium sulfate by a factor of 105. According to the principle of Le Chatelier, under a high sulfur dioxide pressure the equilibrium of the given reaction lies on the right-hand side, while at a low pressure of sulfur dioxide essentially only calcium sulfate exists. This implies that when the digesters are depressurized, the high solubility of calcium sulfate is terminated, thus leading to calcium sulfate precipitation. 

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