Iron sulfates, decompositions

C. Further warming to 65°C forms white iron sulfate monohydrate [17375-41 -6], FeSO H2O, which is stable to 300°C. Strong beating results in decomposition with loss of sulfur dioxide. Solutions of iron(II) sulfate reduce nitrate and nitrite to nitric oxide, whereupon the highly colored [Fe(H20) (N0)] ion is formed. This reaction is the basis of the brown ring text for the quaUtative deterrnination of nitrate or nitrite. 

Synthetic Iron Oxides. Iron oxide pigments have been prepared synthetically since the end of the seventeenth century. The first synthetic red iron oxide was obtained as a by-product of the production of sulfuric acid from iron sulfate containing slate. Later, iron oxide pigments were produced direcdy by the thermal decomposition of iron sulfates. In the 1990s, about 70% of all iron oxide pigments consumed are prepared synthetically. 

Admixtures are 1-2% nitrogen and NO, which can be removed by passing bivalent iron sulfate through the solution. Moreover, N20 is also produced by nitrates and nitrites reduction under definite conditions or by hyponitrite decomposition. 

Red iron oxide pigments are mainly obtained by roasting and calcining processes. a-Fe203 is obtained by oxidative calcination of all decomposable iron compounds. Decomposition of iron sulfate and a-FeOOH and the oxidation of Fe Oq are industrially important. 

Sulfates (e.g., iron sulfate) are decomposed in special furnaces with appropriate refractory finings. Operating temperatures often exceed 700 °C. Elemental sulfur coke, pyrites, fuel oil, etc., are also added to maintain the high temperature required for decomposition of sulfates. 

Matthias tested another general approach to generate alkoxyl radicals from peroxide by cleavage of the 0-0 bond with iron sulfate and copper salts. The preparation of such peroxide was anticipated from mesylate 32 by substitution with H2O2 and a base (Scheme 27). While the preparation of mesylate was successful, attempts to substitute 32 with the anion of H2O2 led to an extensive decomposition of the starting material and we were therefore unable to assess the fragmentation of peroxide 33. 

According to Buxbaum (1998), high quality pigments called copperas red were obtained by the thermal decomposition of iron sulfate hydrate (FeS04.7H20). Fuller (1973) indicates that it was... 

Traditionally, sodium dichromate dihydrate is mixed with 66° Bh (specific gravity = 1.84) sulfuric acid in a heavy-walled cast-iron or steel reactor. The mixture is heated externally, and the reactor is provided with a sweep agitator. Water is driven off and the hydrous bisulfate melts at about 160°C. As the temperature is slowly increased, the molten bisulfate provides an excellent heat-transfer medium for melting the chromic acid at 197°C without appreciable decomposition. As soon as the chromic acid melts, the agitator is stopped and the mixture separates into a heavy layer of molten chromic acid and a light layer of molten bisulfate. The chromic acid is tapped and flaked on water cooled roUs to produce the customary commercial form. The bisulfate contains dissolved CrO and soluble and insoluble chromic sulfates. Environmental considerations dictate purification and return of the bisulfate to the treating operation. 

Dasler, W. et al., Ind. Eng. Chem. (Anal. Ed.), 1946,18, 52 Like other monofunctional ethers but more so because of the four susceptible hydrogen atoms, dioxane exposed to air is susceptible to autoxidation with formation of peroxides which may be hazardous if distillation (causing concentration) is attempted. Because it is water-miscible, treatment by shaking with aqueous reducants (iron(II) sulfate, sodium sulfide, etc.) is impracticable. Peroxides may be removed, however, under anhydrous conditions by passing dioxane (or any other ether) down a column of activated alumina. The peroxides (and any water) are removed by adsorption onto the alumina, which must then be washed with methanol or water to remove them before the column material is discarded [1], The heat of decomposition of dioxane has been determined (130-200°C) as 0.165 kJ/g. 

Cyclic voltammetry of iron(III) porphyrin-sulfate complexes has been described. Thiosulfate can add to iron(III) porphyrins to give an adduct which is high-spin at normal temperatures but low-spin at low temperatures. The tetraphenylporphyrin adduct undergoes decomposition slowly in DMF to give [Fe (tpp)] plus tetrathionate. In DMSO tetraphenylporphyrinatoiron(III) oxidizes thiosulfate by an autocatalytic process. Tetrathiotungstate complexes of iron(III)-tetra-phenylporphyrin undergo spontaneous reduction to iron(II) products with a half-life of about 30 minutes at ambient temperature. " ... 

It also is obtained by thermal decomposition of iron (II) sulfate or the brown... 

Thermal decomposition of iron(in) sulfate yields iron(in) oxide with evolution of sulfur trioxide ... 

Crude material prepared in glass on 3 g mol scale was distilled uneventfully at 40°C/ 0.067 mbar from a bath at 70—80°C. A 30 mol batch prepared in a glass-lined vessel with a stainless steel thermo-probe (and later found to contain 15 ppm of iron) decomposed very violently during distillation at 75°C/13 mbar from a bath at 130°C. Thermal analysis showed that the stability of the methyl (and ethyl) ester was very sensitive to traces of heavy metals (iron, copper, chromium, etc.) and was greatly reduced. Addition of traces of hydrated iron(II) sulfate led to explosive decomposition at 25°C. 

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