Yugul K. Gupta

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

Peroxydiphosphate can be determined iodometrically in the presence of a large excess of potassium iodide with copper(II) or iron(II) as catalyst through the operation of the Cu(II)/Cu(I) or Fe(II)/Fe(III) cycle. The method is applicable in HClO(4), H(2)SO(4), HCl and CH(3)COOH acid media in the range 0.1-1.0M studied. Nickel, manganese(II), cobalt(II), silver, chloride and phosphate are without effect.

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

Abstract Oxidations of antimony(III), hydrazine and nitrite by peroxodiphosphate in perchloric acid medium occur as, Sb(III) + H 2 P 2 O 8 2− → Sb(V) +2 HPO 4 2 N 2 H 4 +2 H 2 P 2 O 8 2 → N 2 +4 H 2 PO 4 2 HNO 2 + N 2 P 2 O 8 2− + N 2 O → HNO 3 +2 H 2 PO 4 2− The rate does not depend on the concentration of the reducing substance and the mechanism is essentially a hydrolytic one. A white precipitate of antimony(III) phosphate with absorbed antimony(V) is formed.

Determination of sulphide, sulphite and thiosulphate with thallic perchlorate or sulphate

Sulphide, sulphite and thiosulphate can be determined separately or in admixture, with thallic perchlorate or sulphate in acid medium. A sample solution is rendered approximately 0.5 M in acid, 5 ml of 0.05 M KI are added and the solution is titrated to a starch end-point with thallium(III) solution. In another method an acid sample solution is titrated with thallium(III) or iodine solution in the presence of indigo carmine indicator. The end-point is improved in the presence of Co(II).

Kinetics and mechanism of electron-transfer reactions of aqueous and co-ordinated thallium(III). Part X. Kinetics of reduction of hexa-aquathallium(III) by hydrogen peroxide and induction of the reaction by cerium(IV) and iron(II) ions.

Thallium(III) and H2O2 react in aqueous perchloric acid solution as in equation (i). The kinetics of reaction have TlIII+ H2O2→ Tl I+ 2H++ O2(i) been followed by estimating TlIII iodometrically and the rate law for [HClO4]= 0·5–2·0M and I= 0·5–2·5M is –d[TlIII]/dt=k′[TlIII][H2O2]2/(Kh+[H+]). Here k′ is the apparent rate constant, which probably includes a formation constant also, and Kh is the acid dissociation constant of Tl3+(aq); k′ has the value 6·7 ± 0·5 l mol–1 s–1 at I= 2·0M and 30 °C, and the energy of activation is 10·3 ± 0·7 kcal mol–1. The reaction is independent of ionic strength in the range 0·5–2·5M(LiClO4). The reaction is induced by cerium(IV) ions through the intermediate radicals H2O2+ and/or HO2˙, and the induction factor is unity. Iron(II) ions act as a strong initiator for the reaction, and hydrogen peroxide can be determined in their presence using thallium(III) as a primary standard.

Kinetics and mechanism of electron-transfer reactions of aqueous and co-ordinated thallium(III). Part IX. Stoicheiometry and kinetics of reduction of hexa-aquathallium(III) by hydroxylamine

The Stoicheiometry of the reaction between TlIII and NH3OH+ depends on the relative concentrations of the reactants, and measurements under different conditions have indicated that the products may be formed by transfer of two, four, and six electrons in stages from hydroxylamine to produce NI, HNO2, or NO3–, respectively. In the presence of excess of NH3OH+, the Stoicheiometry of the reaction is as in (i) with the corresponding rate law TlIII+ NH2OH+→ TlI+ NI+ 3H+(i)–d[TlIII]/dt=KA[TlIII][NH2OH+]; a mechanism is proposed which relates the observed effect of acidity to the entity KA=kKh/([H+]+Kh), where k is the rate constant for reaction of [Tl(OH)]2+(aq) with NH3OH+ and Kh is the acid-dissociation constant of Tl3+(aq). These parameters are 154 ± 8 l mol–1 s–1 and 0·078 ± 0·008 respectively at 25 °C and ionic strength 1M. The energy and entropy of activation for the rate-determining step were found to be 10·0 ± 1·0 kcal mol–1 and –17 ± 4 cal K–1 mol–1 respectively; ΔH and ΔS associated with Kh were found to be 16·6 ± 3·3 kcal mol–1 and 51 ± 14 cal K–1 mol–1 respectively. Addition of TlI, oxygen, and sulphate or nitrate ions has no observable effect on the rate, but chloride ions strongly inhibit the reaction, which is also inhibited by an increase in ionic strength. Comparison of the observed enthalpy of activation with those for other oxidations by TlIII and the observation of chloride inhibition suggest that the reaction proceeds via an intermediate complex.

Kinetics and mechanism of oxidation of hypophosphite by hexacyanoferrate(III) ion in alkaline solution

Hypophosphite is oxidised to phosphite by hexacyanoferrate(III) in alkaline solution according to equation (i). [H2PO2]–+ 2[Fe(CN)6]3–+ OH–→ H3PO3+ 2[Fe(CN)6]4–(i) The rate law at 55.7 °C is (ii) where k′=(2.80 ± 0.08)× 10–4 l2 mol–2 s–1 at I= 4.7M. The ionic-strength –d[Fe(CN)63–]/dt=k′[Fe(CN)63–][H2PO2–][OH–](ii) dependence and entropy of activation show that ion-pair species are more reactive in this reaction.

Kinetics and mechanism of the osmium(VIII)-catalyzed oxidation of phosphite by hexacyanoferrate(III) ion in aqueous alkaline media

The oxidation of phosphite by alkaline [Fe(CN)6]3– occurs with a measurable rate at 35 °C in the presence of OsVIII according to equation (i) and rate law (ii), where k is the rate constant and K3 is the equilibrium constant for 2[Fe(CN)6]3–+[HPO3]2–+ 2[OH]–→ 2[Fe(CN)6]4–+[HPO4]2–+ H2O (i), –d[Fe(CN)63–]/dt=2kK3[OsVIII][OH–][HPO32–]//1 +K3[OH–](ii) the complex formation between OsVIII and [OH]–; k and K3 are 1.0 ± 0.05 dm6 mol–2s–1 and 32 ± 3 dm3 mol–1 respectively at 35 °C and I= 1.0 mol dm–3. A spectrophotometric value of K3 is 30 ± 6 dm3 mol–1. A mechanism consistent with the above facts has been suggested.

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

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.

Determination of peroxydiphosphate in acid medium with oxalate (i) with silver(I) as catalyst and (ii) in the presence of excess of manganese(II).

Peroxydiphosphate can be determined with oxalate in acid medium in the presence of silver(I). Excess of oxalic acid along with the sample and silver (I) is heated to boiling and the excess of oxalic acid is titrated against standard permanganate. Another method involves boiling for 2 min a mixture consisting of the sample and excess of manganese(II), followed by titration of the resulting Mn(III) or MnO(2) with standard oxalic acid solution.

Iron(II)-Induced oxidation of hypophosphite by peroxydiphosphate in acid medium.

It is shown that when peroxydiphosphate reacts with excess of iron(II) an induced oxidation of hypophosphite occurs if any is present.