Persulphate ion

The reactions of this species with Ag(I) and Cu(II) are, of course, oxidations of these ions and are discussed in the appropriate section. 

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In aqueous solutions the persulphate ion is known as a strong oxidizing agent, either alone or with activators. Thus, it has been extensively used as the initiator of vinyl polymerization [43-47]. However, only later, Kulkarni et al. [48] reported the graft copolymerization of AN onto cellulose using the Na2S203/K2S20s redox system. 

The reaction proceeds by a free radical mechanism. The mechanism involves the decomposition of persulphate ions to sulphate radical ions either when heated alone or in the presence of a reducing agent as described below ... 

Both Ag(ll) and Ag(III) have been considered to be the active species in the Ag(I)-catalysed oxidation of many compounds by persulphate ion. Salts of Ag(III) have been prepared but only a single kinetic study (of the decomposition of water by the ethylene dibiguanide nitrate) has been reported (p. 366). 

Oxidations by persulphate ion have been reviewed by House . Silver-ion catalysed reactions normally obey the rate expression... 

The two steps are considered to be an oxidation of Ag(I) to Ag(II) followed by an oxidation of the latter to Ag(III). The stoichiometry is unexpected in that one Ag(I) species consumes two persulphate ions. The release of -804 would be expected to result in oxidation of further Ag(enbig) the existence of two stages rules out a two-equivalent oxidation directly to Ag(enbig). ... 

The reduction of persulphate by tris-[a-(2-pyridyl)-benzylideneaniline] iron(II) is, by contrast, independent of persulphate ion concentration , and the rates of reaction of several ring-substituted complexes of this type correspond exactly to the rates of acid-catalysed separation of one ligand. Clearly oxidation of the ligand... 

Oxidation of carboxylate ions in homogeneous solution using some one-electron transfer agents gives in varying proportions the Kolbe dimer and the product from hydrogen atom abstraction from the solvent by the intermediate alkyl radical. Persulphate ion [109], hexachloco-osmate(v) [110] and the radical-cation from tris(4-bromophenyl)amine [111] all have been used to promote this reaction. 

While most studies on CD have been on snlphides and selenides, considerable work has also been carried ont on oxide films. The fdms are most often formed by reaction of hydroxide ions with a metal salt. While it might be expected that the prodnct is a hydroxide rather than an oxide, in many reported cases oxides are directly formed. This is probably dne to two factors Many of the metal ions nsed (e.g., Pb, Sn, Tl,) do not readily, if at all, form simple hydroxides others (Ag, Cu, Mn) are very readily oxidized even in aqueous solutions. Ni(II) hydroxide is fairly readily dehydrated, particnlarly in the presence of the persulphate ion used to deposit the oxides in some cases. Zn(OH)2, Cd(OH)2 and In(OH)3 are reasonably stable Zn(OH)2 can be easily dehydrated while the other two require annealing to form the oxide. 

Kolthoff, and Miller (21) have shown that persulphate ions decompose when heated in aqueous solution forming sulphate radicals... 

As early as 1903 Marie and Bunel (22) have shown that alcohols accelerate the persulphate decomposition. Kolthoff, Meehan, and Carr (23) confirmed this and proved that this reaction is not between persulphate ion and alcohol, but between the sulphate ion radical and the alcohol (VI). 

Surface modification of LDPE film can also be brought about by chemical treatment [118] with an aqueous solution of ammoniacal ammonium persulphate in the presence of Ni+2 ions under variable reaction conditions. The investigation of treated surface showed the presence of polar groups (viz. carbonyl and hydroxyl) in the infrared (IR) spectroscopy, with characteristic bands at 1700, 1622 and 3450 cm-1. It is known that the persulphate ion attacks the double-bond-producing epoxy or diol group. However, the destructive oxidation of saturated hydrocarbons does not occur with persulphate alone, but requires the presence of the nickel (II) ion. The authors have proposed the following mechanism of chemical treatment ... 

The polymerization of anions is a special type of irreversible anodic processes. Of these the oxidation of sulphate to persulphate ions has been studied in the deepest detail. In the production of pcrsulphuric acid the yield is increased to a certain limit by a higher concentration of the initial sulphuric acid and an increased current density at the anode of smooth platinum. In too concentrated sulphuric acid the pcrsulphuric acid is already hydrolysed to a considerable extent to monopersulphuric acid (Caro s acid), which then acts as a depolarizer and lowers the required high potential at the anode. Electrolysis of sulphate solutions also gives persulphates and in this reaction the current efficiency will depend on the nature of the cation the efficiency increasing in the order of Na+, K+ and NHj. 

The liberation of oxygen can, however, be supressed considerably if sulphuric acid is used as the electrolyte, which is anodically oxidized into persulphuric acid. From what has been said about the formation of persulphate ions (see theoretical section) it is clear that the anodic process can be expressed by the following overall equation ... 

Other current losses may be caused by the reduction of persulphate ions at the cathode. In order to prevent this the anode and cathode must be separated by a diaphragm. 

From what has been said about the influence of the cations it follows that the highest current efficiency is obtained when electrolysis is carried out with a neutral solution of ammonium sulphate. With such a solution the formation of harmful Caro s acid is almost entirely avoided. Another advantage of a neutral solution is that no diaphragm is needed to prevent the reduction of persulphate at the cathode. The addition of a small amount of alkali chromate to the solution will suppress reduction as a thin film of chromium hydroxide is formed on the cathode surface which prevents the persulphate ions coming into contact with the electrode. 

Luminescence may also arise as a consequence of electrode reactions at semiconductors that result in injection of minority carriers under accumulation conditions (see references in Kelly et al., 1999). An interesting example is the efficient red electroluminescence observed during the reduction of persulphate ions at a porous silicon layer on n-Si (Meulenkamp et al, 1995). Here the luminescence arises from electron/hole recombination, and the holes are injected by the persulphate radical ion according to the scheme... 

The product of the reaction of e"q with the permanganate ion is the manganate ion and with the persulphate ion is the sulphate ion radical, both of which have been identified from pulse radiolysis studies, viz. 

Free radicals can be produced by the thermal or photochemical decomposition of an azo or peroxy componnd examples given below are benzoyl peroxide and persulphate ion. 

Chemical synthesis of a soluble polymer in the presence of nano-objects and subsequent deposition by drop casting or spin coating Chemical polymerization of pyrrole in the presence of CNTs in acidic aqueous solution containing an oxidizing species, namely persulphate ions [175]... 

Kolthoff, I. and Miller, I.K., The chemistry of persulphate. I. The kinetics and mechanism of the decomposition of the persulphate ion in aqueous medium. Journal of the American Chemical Society 73, 3055, 1951. 

Elbs oxidation of 2- and 3-hydroxypyridine gives in each case mainly 2,5-dihydroxypyridine. In the first case some 2,3-dihydroxypyridine, and in the second, some 2,3- and 3,4-dihydroxypyridine are also formed. The kinetics and mechanism of the oxidation of 2-hydroxypyridine have been examined, and the reaction could involve attack by the anion of the hydroxy compound upon the peroxy bond of the persulphate ion, with the displacement of sulphate ioni sa, 2-Aminopyridine gives hydrogen 2-amino-3-pyridyl sulphate but 4-aminopyridine behaves differently (p. 359). 

The rate constant of the reaction between persulphate ion and iodide ion varies with ionic strength I as follows ... 

On electrolysing a cool solution of potassium hydrogen sulphate, the discharged anions combine to form peroxodisulphate (persulphate) ions. 

Kinetics and mechanism of the oxidation of iodide ions by persulphate ions... 

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