The rates of oxidation of phenylthioacetic acid (PTAA) and several substituted phenylthioacetic acids by potassium peroxodiphosphate (PP) in 50% (v/v) aqueous acetic acid have been studied in detail. The rate of oxidation is expressed as 








An analysis of the dependence of the rate on [H+] reveals that H3P2O is the active oxidizing species in the oxidation. The effect of ring substituents on the rate gives a ρ+ value of -0.45 ± 0.03 (r = 0.998, s = 0.02 at 40°C), pointing to the development of an electron-deficient center in the transition state. The results are discussed in terms of a mechanism involving the rate-determining formation of an intermediate between PP and phenylthioacetic acids, followed by the decomposition of the intermediate. These kinetic results are compared with those obtained in the oxidation of phenylthioacetic acids by peroxodisulfate.

Mechanism of oxidation of phenylthioacetic acids by potassium peroxodiphosphate

The photooxidation of caffeine in presence of peroxydiphosphate (PDP) in aqueous solution at natural pH (∼7.5) has been carried out in a quantum yield reactor using a high-pressure mercury lamp. The reactions were followed spectrophotometrically by measuring the absorbance of caffeine at λmax (272 nm). The rates of reaction were calculated under different experimental conditions. The quantum yields were calculated from the rates of oxidation of caffeine and the intensity of light at 254 nm which was measured by using peroxydisulphate solution as a standard chemical actinometer. The reaction rates of oxidation of caffeine by PDP increase with increase in [PDP] as well as with increase in light intensity, while they are independent of [caffeine]. The quantum yields of oxidation of caffeine by PDP are independent of [PDP] as well as light intensity. However, quantum yields of oxidation of caffeine by PDP increase with increase in caffeine concentration. On the basis of these experimental results and product analysis, a probable mechanism has been suggested in which PDP is activated to phosphate radical anions (PO4
 ·2−) by direct photolysis of PDP and also by the sensitizing effect of caffeine. The phosphate radical anions thus produced react with caffeine by electron transfer reaction, resulting in the formation of caffeine radical cation, which deprotonates in a fast step to produce C8-OH adduct radicals. These radicals might react with PDP to give final product 1,3,7-trimethyluric acid and PO4
 ·2− radicals, the latter propagates the chain reaction.

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Oxidation of caffeine by phosphate radical anion in aqueous solution under anoxic conditions

Graft copolymerization onto textile fibers is a challenging field of research with unlimited future prospects [1–6]. This is attractive to chemists as a means of chemical modification of natural macromolecules since, in general, degradation could be minimized. Thus it is hoped to retain the desirable properties of the natural material and give it additional properties through the added polymer. Means of forming copolymers with natural macromolecules are now well understood because the techniques of polymer chemists are usually applicable. A vast number of combinations of composition and conformation is possible for each copolymer, and the properties of each copolymer may vary with the mode of formation employed.

Grafting of Vinyl Monomers onto Silk Fibers

Perborates are mild oxidants with a wide range of actual and potential uses. Sodium perborate is widely and extensively utilized, with applications in bleaching, stain removal, oral hygiene, decontamination, synthetic organic chemistry, and several other areas. Perborates are largely dissociated into borate and hydrogen peroxide on dissolving in water and are often regarded simply as a convenient source of the latter. This chapter is centered on the question as to whether borate can catalyze or activate hydrogen peroxide as oxidant, in other words whether perborates offer any advantage over hydrogen peroxide beyond ease of transport. In order to put this question into context, we review the applications, structures, and properties of both perborates and several peroxoanions with similar chemistry and uses. The main comparisons are with percarbonates, peroxosulfates, and peroxophosphates, with briefer treatment of peroxonitrites and peroxocarboxylates Comparisons are also drawn with hydrogen peroxide and, in view of its importance as a bleaching agent, hypochlorite. As perborates and other peroxoanions have been in use for more than a century, we include some historical background to show how applications and an understanding of their chemistry have developed, as well as indicating areas of current and possible future uses—and areas where solution properties and reaction mechanisms are still less than perfectly established and understood.

Catalysis or Convenience? Perborate in Context

Oxidation of Hydrazine in Aqueous Solution

Iodometric determination of peroxydiphosphate in the presence of copper(II) or iron(II) as catalyst.

Kinetics and mechanism of oxidations by peroxodiphosphate—IV: Stoichiometry and kinetics of oxidations of antimony(III), hydrazine and nitrite in aqueous perchloric acid medium

Peroxodiphosphate, [P2O8]4–, oxidises arsenious acid in perchloric acid medium according to equation (i). H4P2O8+ H3AsO3+ H2O → 2H3PO4+ H3AsO4(i) The mechanism essentially involves hydrolysis of the species [H2P2O8]2–, [H3P2O8]–, and H4P2O8, and the rate of the redox reaction is independent of the arsenic (III) concentration. The rate law when 2.5 > [HClO4] > 0.1 mol dm–3 is as in (ii), and the values of k2 and k3 are (2.7 ± 0.2)× 10–4 and (8.65 ± 0.3)× 10–3 s–1 respectively at 45 °C. –d[P2O8]/dt=k2[H3P2O8–]+k3[H4P2O8](ii) The rate of reaction is independent of the ionic strength. Acrylamide, F–, Cu2+, Mn2+, Fe2+, and phosphate have no effect on the reaction, but Ag+ catalyzes the reaction.

Kinetics and mechanism of oxidations by peroxodiphosphate ions. Part I. Oxidation of arsenic(III) in aqueous perchloric acid

Oxidation of hypophosphite by peroxodiphosphate in perchloric acid solution is a consecutive reaction, (i) and (ii), H4P2O8+ H2O [graphic omitted] H3PO5+ H3PO4(i), H3PO5+ H3PO2 [graphic omitted] H3PO4+ H3PO3(ii) and a plot of [H3PO5] against time for the reaction exhibits a maximum. In a separate study, the rate law for reaction (ii) has been found to be (iii), where K1 and K2 are the acid-ionization constants of H3PO2 and H3PO5–d[H3PO5]/dt=k2[H3PO5]T[H3PO2]T[H+]2/([H+]+K1)([H+]+K2)(iii) respectively; k2 was (1.2 ± 0.08)× 10–2 dm3 mol–1 s–1 at [H+]= 0.50 mol dm–3, I= 1.0 mol dm–3, and 45 °C. An estimated value of K2 is 0.15 mol dm–3 at 35 °C and I= 1.0 mol dm–3. Maximum concentrations of H3PO5 and the times at which they are built up have been calculated using the values of kh and k2, and these are in good agreement with the observed values.

Kinetics and mechanism of oxidations by peroxodiphosphate ions. Part 3. Oxidation of hypophosphite in aquous perchloric acid by the hydrolytic product peroxomonophosphate in a consecutive reaction

Surinder Kapoor

Papers

Iodometric determination of peroxydiphosphate in the presence of copper(II) or iron(II) as catalyst.

Kinetics and mechanism of oxidations by peroxodiphosphate—IV: Stoichiometry and kinetics of oxidations of antimony(III), hydrazine and nitrite in aqueous perchloric acid medium

Kinetics and mechanism of oxidations by peroxodiphosphate ions. Part I. Oxidation of arsenic(III) in aqueous perchloric acid

Kinetics and mechanism of oxidations by peroxodiphosphate ions. Part 3. Oxidation of hypophosphite in aquous perchloric acid by the hydrolytic product peroxomonophosphate in a consecutive reaction

Kinetics and mechanism of oxidations by peroxodiphosphate ions. part i. oxidation of arsenic(iii) in aqueous perchloric acid