Nickel thiosulfate

Electrocatalysis in oxidation has apparently first been shown for ascorbic acid oxidation by Prussian blue [60] and later by nickel hexacyanoferrate [61]. More valuable for analytical applications was the discovery in the early 1990s of the oxidation of sulfite [62] and thiosulfate [18, 63] at nickel [62, 63] and also ferric, indium, and cobalt [18] hexacyanoferrates. More recently electrocatalytic activity in thiosulfate oxidation was shown also for zinc [23] hexacyanoferrate. Prussian blue-modified electrodes allowed sulfite determination in wine products [64], which is important for the wine industry. 

X.Y. Zhou, S.F. Wang, Z.P. Wang, and M. Jiang, Electrocatalytic oxidation of thiosulfate on a modified nickel hexacyanoferrate-film electrode. Fresenius J. Anal. Chem. 345, 424-427 (1993). 

The approach to pyrazino[2,3-, ]quinoxalines shown in Equation (114) has now been used to prepare pyrazino[2,3-, ]pyrazines <2007EJ01237>, whose nickel complexes have also been prepared. The same publication also describes the formation of 172 by treatment of conjugated system 173 with sodium thiosulfate. The former is reconverted to the latter on exposure to air and, on further aerial oxidation at 130 °C, 173 eventually forms the highly condensed system 174. Detailed studies of the formation of the tetrahydropyrazinopyrazine 101 have been reported, along with theoretical studies, and structural data for the trans isomer <2007T6915>. 

We can now make sensible guesses as to the order of rate constant for water replacement from coordination complexes of the metals tabulated. (With the formation of fused rings these relationships may no longer apply. Consider, for example, the slow reactions of metal ions with porphyrine derivatives (20) or with tetrasulfonated phthalocyanine, where the rate determining step in the incorporation of metal ion is the dissociation of the pyrrole N-H bond (164).) The reason for many earlier (mostly qualitative) observations on the behavior of complex ions can now be understood. The relative reaction rates of cations with the anion of thenoyltrifluoroacetone (113) and metal-aqua water exchange data from NMR studies (69) are much as expected. The rapid exchange of CN " with Hg(CN)4 2 or Zn(CN)4-2 or the very slow Hg(CN)+, Hg+2 isotopic exchange can be understood, when the dissociative rate constants are estimated. Reactions of the type M+a + L b = ML+(a "b) can be justifiably assumed rapid in the proposed mechanisms for the redox reactions of iron(III) with iodide (47) or thiosulfate (93) ions or when copper(II) reacts with cyanide ions (9). Finally relations between kinetic and thermodynamic parameters are shown by a variety of complex ions since the dissociation rate constant dominates the thermodynamic stability constant of the complex (127). A recently observed linear relation between the rate constant for dissociation of nickel complexes with a variety of pyridine bases and the acidity constant of the base arises from the constancy of the formation rate constant for these complexes (87). 

Compound Name Ammonium Hydroxide Hexamethylenetetramine Ammonium Acetate Ammonium Bifluoride Ammonium Sulfamate Ammonium Sulfamate Ammonium Benzoate Ammonium Bicarbonate Ammonium Dichromate Ammonium Bifluoride Ammonium Carbonate Ammonium Chloride Ammonium Citrate Ammonium Citrate Ammonium Pentaborate Ammonium Dichromate Nickel Ammonium Sulfate Ferric Ammonium Citrate Ferric Ammonium Oxalate Ferrous Ammonium Sulfate Ammonium Fluoride Ammonium Silicofluoride Ammonium Formate Ammonium Gluconate Ammonium Bicarbonate Ammonium Bifluoride Ammonium Sulfide Ammonium Hydroxide Ammonium Thiosulfate Ammonium Thiosulfate Ammonium Iodide Ferrous Ammonium Sulfate Ammonium Lactate Ammonium Lactate Ammonium Lauryl Sulfate Ammonium Molybdate Ammonium Chloride Nickel Ammonium Sulfate Ammonium Nitrate Ammonium Nitrate-Urea Solution Ammonium Oleate... 

A thiosulfate group coordinated as a chelate has been found in the complex [Ni(S203)(thiourea)4]H20 (224).1692 Actually, the Ni—S(S203) bond distance is significantly longer than the Ni—S bonds usually found in six-coordinate nickel(II) and consequently the nickel coordination can be viewed as an intermediate one between octahedral and square pyramidal. 

This compound may be prepared in solution by dissolving 4.5g of nickel sulfate 7-hydrate in 25ml of water and adding 5g of barium thiosulfate monohydrate. 

Sulfur can be effectively removed from a compound, organic or inorganic, by contact with Raney nickel. The action has been described by Aubry (118) as being noncatalytic in nature. One atom of sulfur is removed from sodium thiosulfate in the cold, yielding sodium sulfite from which the sulfur can be completely removed at 100°. Although sulfur can be completely removed from stannous sulfide, it can be only partially removed from antimony sulfide. Following are some of the inorganic compounds from which sulfur removal by use of Raney nickel has been observed (119). 

The reaction of a strong solution of aqueous ammonia with the sulfide concentrate in a strongly agitated pressure vessel at a temperature between 160 and 190°F under an oxygen partial pressure of about 10 psi, either as pure oxygen or as compressed air, fulfills the optimal conditions for the above requirements. The iron present in the concentrate is oxidized to hydrated ferric oxide which, together with the silicates is insoluble in aqueous ammonia. The copper, nickel, and cobalt form their amines, while the sulfides are oxidized to sulfates, thiosulfates, and polythionates. 

The temperature and NHj coneentrations in the leach liquor have the most influence on the rate of leaching, followed by oxygen partial pressure and amount of agitation. A pregnant solution with sufficient thiosulfate and polythionate content must be produced to react with the copper present in the subsequent boiling stage. It must also be regulated to produce an iron oxide residue with very little absorbed nickel. 

From a practical viewpoint, the significance of the thiosulfate bath lies in the fact that it is a noncyanide, near-neutral pH system, and that it is not sensitive to nickel... 

Pregnant solution from the leaching circuit contains typically 40-50 g/L nickel, 0.7-1.0 g/L cobalt, 5-]0g/L copper, 120-180 g/L ammonium sulfate. 5-10 g/L sulfor as thiosulfate and polythionates. and 85-100 g/L Tree ammonia.1 Copper removal requires inilia] reseoval of ammonia followed by ptacipilation of copper in the form of coppar sulfides. The unoxidized sulfur in solution assists in the precipitation process. Removal of ammonia by steam injection releases cupric ions to react with these sulfur compounds, as shown by the reactions ... 

MUR/KUR] Murai, R., Kurakane, K., Sekine, T., The stability constants of nickel(Il) complexes with chloride, thiocyanate, sulfate, thiosulfate and oxalate ions, as determined by a solvent extraction method. Bull. Chem. Soc. Jpn., 49, (1976), 335-336. Cited on pages 146, 148, 234, 377. 

All sulfur is shown to convert to sulfate ions in solution. Under the conditions of leaching, much of the sulflir remains in solution as metastable soluble intermediates. Oxidation of sulfur occurs in the sequence thiosulfate ions, 203 thionate ions, S 0 sulfamate ions, SO3NH3 and sulfate ions. SOl. The partially oxidized sulfur ions in solution must be converted to sulfate ions prior to nickel reduction to maintain nickel purity. One of the important features of the pressure-leaching process is the concurrent... 

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