Interaction of Phosphate with Iron(III) in Acidic Medium,Equilibrium and Kinetic Studies

Equilibrium reactions of iron(III) with phosphate were studied spectrophotometrically by UV-Vis in the pH range of ～ 1.0-2.20. The STAR-94 Program was used to determine the number of absorbing species as well as the stoichiometries and formation constants of the complex species. Some literature values were further confirmed and new values of different stoichiometries were obtained. The kinetics and mechanism of Fe(III) with phosphate were studied in acidic medium. The reactive phosphate species were found to be only H₃PO₄ and H₂PO^? ₄ and for Fe(III) were only Fe³⁺, FeOH²⁺ and Fe(OH)⁺ ₂. The observed rate constants were pH as well as T_phos (total concentration of phosphate) dependent, i.e. K_obs,i = A _i + B _i T_phos + C _i T² _phos (at a given pH).     

Kinetics and mechanism of the reduction of diaquotetrakis (2,2′-bipyridine)-µ-oxodiruthenium(III) ion by hypophosphorous acid in acidic medium

The kinetics and mechanism of the reduction of diaquotetrakis(2,2′-bipyridine)-µ-oxodiruthenium(III), [(H₂O)₂(bipy)₄Ru₂O]⁴⁺, by H₃PO₂ has been studied in aqueous acid at ionic strength = 0.5 mol dm^?3 (NaClO₄), [H⁺] = 5.0 × 10^?2 mol dm^?3 and temperature = 31 ± 1 °C. Measurement of the stoichiometry showed that 1 mole of [(H₂O)₂(bipy)₄Ru₂O]⁴⁺ was reduced by 1 mole of H₃PO₂. The reaction was found to be first order with respect to both [(H₂O)₂(bipy)₄Ru₂O⁴⁺] and [H₃PO₂], hence second order overall. Variations in the ionic strength and dielectric constant of the reaction medium had no effect on the rate. Also, addition of various ions to the reaction medium did not significantly alter the rate. Free radicals were identified during the course of the reaction by a polymerisation test. Spectroscopic information and Michaelis–Menten plots suggested the absence of an intermediate complex prior to electron transfer. [(H₂O)₂(bipy)₂Ru]²⁺, the reduction product of [(H₂O)₂(bipy)₄Ru₂O]⁴⁺, plus H₃PO₃, the oxidation product of H₃PO₂, were identified in the product solutions. It is suggested that the reaction proceeds through the outer sphere pathway. A mechanism for the reaction is proposed.     

Correlation of the extraction constants of the system Cd(II)–H3PO4/Cyanex 302–kerosene at different ionic strengths

Bromley's theory for calculating activity coefficients in order to correlate the values of cadmium extraction constant by Cyanex 302 from phosphoric acid solutions at different ionic strengths has been applied. A chemical model for the aqueous phase including the species H₃PO₄, H₂PO₄⁻, H₅P₂O₈⁻, H₆P₂O₈, CdHPO₄ and CdH₂PO₄⁺ has been considered. The increase observed for the extraction constant value when increasing the phosphoric acid concentration is probably due to the significant increase of the cadmium activity coefficient. A reaction extraction including water as a component has been proposed, and the value of the thermodynamic extraction constant of log K⁰=7.02 for the formation of CdR₂(HR) species, HR being the major component of Cyanex 302, has been obtained.     

1,15-Diferrocenyl-2,5,8,11,14-pentaazapentadecane,an Open-Chain Redox-Active Ferrocene-Functionalized Polyazaalkane Ligand for Anions

The interaction of the ferrocene-functionalized open-chain polyazaalkane 1,15-diferrocenyl-2,5,8,11,14-pentaazapentadecane (L¹) with the sulfate, phosphate, and ATP anions has been studied by potentiometric methods in THF/H₂O 70 : 30 (v/v) (containing 0.1M (Bu₄N)ClO₄ at 25°). Additionally, the electrochemical response of L¹ in the presence of H⁺, HSO^-₄, H₂PO^-₄, Br⁻, and Cl⁻ in a non-aqueous solvent such as MeCN has been studied. A remarkable cathodic shift of the ferrocene oxidation potential was induced for phosphate (198 mV) and sulfate (145 mV) showing an EC mechanistic response. Competitive electrochemical studies showed that L¹ is able to electrochemically and selectively recognize HSO^-₄ vs. H₂PO^-₄ in a mixture of both anions in MeCN.     

Substituent effects on the kinetics of the cerium(IV) oxidation of mandelic acids in sulfate media. Anomalous kinetic behavior of the methoxy derivative

The kinetics of the cerium(IV) oxidation of p-nitro and p-methoxymandelic acids have been investigated in H₂SO₄-MHSO₄ (M⁺ = Li⁺, Na⁺, K⁺) and H₂SO₄-MClO₄ (M⁺ = H⁺, Na⁺) mixtures at a constant total electrolyte concentration of 2.00 mol/dm³. The oxidation of p+nitromandelic acid proceeds through two [H⁺]-independent paths, as was also observed for some substituted mandelic acids studied previously. The kinetic behavior of the p-methoxy derivative differs from that of the other mandelic acids in that (1) the oxidation occurs via two [H⁺]-dependent paths, (2) the reaction rate is anomalously high, (3) the activation enthalpy and entropy of the overall process are markedly lower. It provides strong support to the suggestion that a different mechanism is operative. The substituent effects and the reaction mechanism are discussed.     

Thermodynamics of electrolytes. VI. Weak electrolytes including H3PO4

Equations previously developed and widely applied to the thermodynamic properties of strong electrolytes are extended to solutions involving a dissociation equilibrium. Excellent agreement is obtained with the data for pure phosphoric acid to 6M and for phosphate buffer solutions. The parameters of the strong electrolyte components of the buffer solutions are taken from other work, and the remaining parameters for H⁺, H₂PO ₄ ^– , and H₃PO₄ are evaluated, including a pK of 2.146. The present method avoids ambiguities which formerly arose in treating weak acids with as small pK as this.     

Coupled diffusion produced by hydrolysis of aqueous potassium phosphate

Conductimetric and diaphragm cell techniques have been used to measure diffusion of aqueous potassium phosphate solutions at 25°C from 0.01 to 0.10 mol-dm^–3 (M). A significant portion of the aqueous K₃PO₄ component diffuses as equimolar amounts of potassium hydrogen phosphate and potassium hydroxide produced by hydrolysis: K₃PO₄+H₂O=K₂HPO₄+KOH. Because OH^– diffuses more rapidly than HPO ₄ ^2– , the total flow of KOH exceeds the flow of K₂HPO₄. The extra flow of KOH constitutes coupled transport of a second solute component. Ternary diffusion coefficients that describe interacting flows of K₃PO₄ and KOH components are reported. At low concentrations where phosphate is strongly hydrolyzed, the molar flux of the KOH component produced by diffusion of K₃PO₄ is six times larger than the flux of the K₃PO₄ component. Binary diffusion coefficients for aqueous K₂HPO₄ solutions are also reported. It is shown that ternary transport coefficients for K₃PO₄ solutions can be estimated from the properties of binary solutions of K₂HPO₄ and KOH.     

K3[Fe3.26V0.74(OH)O(PO4)4(H2O)2]·2H2O: a synthetic leucophosphite

A new iron(III)/vanadium(III) phosphate, K₃[Fe_3.26V_0.74(OH)O(PO₄)₄(H₂O)₂]·2H₂O (1), has been obtained by hydrothermal synthesis and characterized by single crystal X-ray diffraction, Scanning electron microscopy–energy dispersive X-ray spectroscopy, Inductively coupled plasma atomic emission spectroscopy (ICP), thermogravimetric analysis, and FTIR spectroscopy. Single crystal X-ray diffraction reveals a 3D open framework (monoclinic, space group P2₁/n, a?=?9.6391(7)?Å, b?=?9.8063(7)?Å, c?=?9.7268(7)?Å, β?=?100.71(1)°, and V?=?903.38(11)?ų). This structure presents Fe^III and V^III in a 4.4?:?1?M ratio with the metal ions in two different crystallographic sites. Both metallic centers have distorted octahedral environments, linked by PO₄ tetrahedra, forming channels along the a-axis. The asymmetric unit of K₃[Fe_3.26V_0.74(OH)O(PO₄)₄(H₂O)₂]·2H₂O presents a {M₄(OH)O(PO₄)₄(H₂O)₂}^3? anionic entity, charge balanced by three K⁺, which are located within the channels. It is also possible to distinguish M₄O₂ units whose M^III polyhedra are linked by vertex and edges.     

Tripotassium Trichrome (III) Tetraphosphate K3Cr3(PO4)4: Synthèse, Étude Structurale,Caractérisation et Conductivité Ionique

The potassium chromium (III) phosphate K₃Cr₃(PO₄)₄ is prepared by a solid state reaction at 1173 K from a mixture of K₂CO₃, NH₄H₂PO₄, and (NH₄)Cr₂O₇. It is structurally characterized by single-crystal X-ray diffraction. It crystallizes in the Cmca (n°64) space group with a = 10.524(4) Åi, b = 20.466(6) Åi, c = 6.374(2) Åi, V = 1372.9(8) Åi³, Z = 4, R(F²) = 0.0452, and R _W (F²) = 0.1184 for 790 reflections with I > 2σ(I). The structure consists of CrO₆ octahedra and PO₄ tetrahedra sharing corners and edges to form a two-dimensional framework. The K⁺ cations are located in the interlayer space. Conductivity measurement leads to σ = 47.32 10^?5 Ω^?1 m^?1 at 729 K. K₃Cr₃(PO₄)₄ is a better ionic conductor than K₃Cr₃(AsO₄)₄ at the same temperature.     

Kinetics and mechanism of pyrogallol autoxidation: Calibration of the dynamic response of an oxygen electrode

The kinetics of the reaction between 1,2,3-trihydroxybenzene (pyrogallol) and O₂ (autoxidation) have been determined by monitoring the concentration of dissolved dioxygen with a polarographic oxygen electrode. The reaction is carried out in pseudo-first-order excess pyrogallol, 25°C, 0.08 M NaCl, and 0.04 M phosphate buffer in the pH range 6.9–10.5. Data collection precedes reaction initiation, but only the data recorded after the estimated 3.2 s dead time are used in kinetics calculations. Observed rate constants are corrected for incomplete mixing, which is treated as a first-order process that has an experimentally determined mixing rate constant of 4.0 s^?1. The rate law for the reaction is ?d[O₂]/dt=k_app[PYR]_tot[O₂], in which [PYR]_tot is the total stoichiometric pyrogallol concentration. A mechanism is presented which explains the increase in rate with increasing [OH^?] by postulating that H₂PYR^? (k₂) has greater reactivity with dissolved dioxygen than does H₃PYR (k₁). The data best fit the equation k_app=(k₁ + k₂K_H[OH^?])/(1 + K_H[OH^?]) when the value of the hydrolysis constant K_H (the quotient of the pyrogallol acid dissociation and water autoprotolysis constants) for this medium equals 3.1×10⁴ M^?1. The resulting values of k₁ and k₂, respectively, equal (0.13 + 0.01) M^?1 s^?1 and (3.5 plusmn; 0.1) M^?1 s^?1. This reaction is recommended as a test reaction for calibrating the dynamic response of an O₂-electrode. © 1993 John Wiley & Sons, Inc.     

Recombination of tert-butyl radicals: the role of weak van der Waals interactions

A mechanism for the recombination of tert-butyl radicals is postulated to involve the loosely bonded intermediates tert-C₄H₉⋯tert-C₄H₉. Three processes contribute to the overall recombination rate constant: tert-C₄H₉+ tert-C₄H ⇆ tert-C₄H₉⋯tert-C₄H₉ characterized by the equilibrium constant K ₁ and tert-C₄H₉⋯tert-C₄H₉ → C₈H₁₈* characterized by the rate constant k ₂, k _rec,∞(T) ≈ K ₁ k ₂. This recombination rate constant exhibits a negative temperature dependence and is proportional to T ^−3/2. The agreement with experiment is very good. Received: 2 October 2000 / Accepted: 2 May 2002 / Published online: 7 August 2002     

On the mechanism of reaction of tert-butoxyl radicals with dialkylphosphites

It has been shown by ESR spectroscopy that the title reaction involves abstraction of hydrogen from the phosphite, since at ?10°C the reaction has a kinetic deuterium isotope effect, k_H/k_D, or ～3. The rate constant for hydrogen abstraction is c. 2 × 10⁴ M^?1 s^?1. There is no significant addition of alkoxyl radicals to the phosphite.     

Characteristics of oxygen exchange in phosphoric acid

The oxygen exchange between phosphoric acid and water at various temperatures and concentrations has been investigated in the presence and absence of K₂HPO₄. The minimum rate of exchange is observed for a solution concentration of 2–2.5 mole/l. It has been shown that in concentrated solutions of phosphoric acid the formation of H₄PO ₄ ⁺ is possible, and the true rate constant of the acid-catalytic conversion and the basicity constant of H₃PO₄ has been calculated. It has been found that in a solution where the mobility of the oxygen atom towards the anion increases, the value of the limiting current on the anodic dissolution of copper diminishes.     

Synthese und Kristallstruktur von K2(HSO4)(H2PO4), K4(HSO4)3(H2PO4) und Na(HSO4)(H3PO4)

Synthesis and Crystal Structure of K₂(HSO₄)(H₂PO₄), K₄(HSO₄)₃(H₂PO₄), and Na(HSO₄)(H₃PO₄) Mixed hydrogen sulfate phosphates K₂(HSO₄)(H₂PO₄), K₄(HSO₄)₃(H₂PO₄) and Na(HSO₄)(H₃PO₄) were synthesized and characterized by X‐ray single crystal analysis. In case of K₂(HSO₄)(H₂PO₄) neutron powder diffraction was used additionally. For this compound an unknown supercell was found. According to X‐ray crystal structure analysis, the compounds have the following crystal data: K₂(HSO₄)(H₂PO₄) (T = 298 K), monoclinic, space group P 2₁/c, a = 11.150(4) Å, b = 7.371(2) Å, c = 9.436(3) Å, β = 92.29(3)°, V = 774.9(4) ų, Z = 4, R₁ = 0.039; K₄(HSO₄)₃(H₂PO₄) (T = 298 K), triclinic, space group P 1, a = 7.217(8) Å, b = 7.521(9) Å, c = 7.574(8) Å, α = 71.52(1)°, β = 88.28(1)°, γ = 86.20(1)°, V = 389.1(8)ų, Z = 1, R₁ = 0.031; Na(HSO₄)(H₃PO₄) (T = 298 K), monoclinic, space group P 2₁, a = 5.449(1) Å, b = 6.832(1) Å, c = 8.718(2) Å, β = 95.88(3)°, V = 322.8(1) ų, Z = 2, R₁ = 0,032. The metal atoms are coordinated by 8 or 9 oxygen atoms. The structure of K₂(HSO₄)(H₂PO₄) is characterized by hydrogen bonded chains of mixed H_nS/PO₄^– tetrahedra. In the structure of K₄(HSO₄)₃(H₂PO₄), there are dimers of H_nS/PO₄^– tetrahedra, which are further connected to chains. Additional HSO₄^– tetrahedra are linked to these chains. In the structure of Na(HSO₄)(H₃PO₄) the HSO₄^– tetrahedra and H₃PO₄ molecules form layers by hydrogen bonds.     

Kinetics and mechanism of protection of thymine from phosphate radical anion under anoxic conditions

The rates of photooxidation of thymine in the presence of peroxydiphosphate (PDP) have been determined by measuring the absorbance of thymine at 264 nm spectrophotometrically. The rates and the quantum yields (φ) of oxidation of thymine by phosphate radical anion have been determined in the presence of different concentrations of dithiothreitol (DTT). An increase in DTT is found to decrease the rate of oxidation of thymine, suggesting that DTT acts as an efficient scavenger of PO₄^·2? and protects thymine from it. Phosphate radical anion competes for thymine as well as DTT; the rate constant for the phosphate radical anion with DTT has been calculated to be 2.21 × 10⁹ dm³ mol^?1 s^?1, assuming the rate constant of phosphate radical anion reaction with thymine as 9.6 × 10⁷ dm³ mol^?1 s^?1. The quantum yields of photooxidation of thymine have been calculated from the rates of oxidation of thymine and the light intensity absorbed by PDP at 254 nm, the wavelength at which PDP is activated to phosphate radical anion. From the results of experimentally determined quantum yields (φ_exptl) and the quantum yields calculated (φ_cl), assuming DTT acts only as a scavenger of PO₄^·2? radicals, show that φ_exptl values are lower than φ_cl values. The φ′ values, which are experimentally found quantum yield values at each DTT concentration and corrected for PO₄^·2? scavenging by DTT, are also found to be greater than φ_exptl values. These observations suggest that the thymine radicals are repaired by DTT in addition to scavenging of phosphate radical anions. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 271–275, 2001     

A kinetic study of the oxidation of L-ascorbic acid by chromium(VI)

The reaction between chromium(VI) and L-ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69–7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is where K_p is the equilibrium constant for protonation of chromate ion and k_r is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L-hydrogenascorbate ion). The activation parameters associated with rate constant k_r are E_a = 20.4 ± 0.9 kJ mol^?1, ΔH^≠ = 17.9 ± 0.9 kJ mol^?1, and ΔS^≠=?152 ± 3 J K^?1 mol^?1. The reaction thermodynamic magnitudes associated with equilibrium constant K_p are ΔH⁰ = 16.5 ± 1.1 kJ mol^?1 and ΔS⁰ = 167 ± 4 J K^?1 mol^?1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.     

MZn2HPO4PO4 (M=Na+, K+)的合成、表征和标准摩尔生成焓

采用低温固相法和水热法制备MZn2HPO4PO4 (M=Na+, K+) 并用XRD, FT-IR, TG and SEM对其进行表征,用等温量热计测定热化学性质。按照Hess’s定律,设计一新的热化学循环。结果表明,所合成的物质是等结构三斜晶系的目标产物,具有片层结构,分解温度分别为： 415 ℃和430 ℃。从测定的溶解焓和其他的标准热化学数据,计算出MZn2HPO4PO4 (M=Na+, K+) 的标准摩尔生成焓分别为：ΔfHm [NaZn2HPO4PO4, s]=-3042.38±0.31 kJ·mol-1; ΔfHm [KZn2HPO4PO4,s]=-3093.46 ±0.27 kJ·mol-1。     

Solubility of (UO2)3(PO4)2?4H2O in H+-Na+-OH?-H2PO?4-HPO2?4-PO3?4-H2O and Its Comparison to the Analogous PuO2 +2 System

The objectives of this study were to address uncertainties in the solubility product of (UO₂)₃(PO₄)₂⋅4H₂O(c) and in the phosphate complexes of U(VI), and more importantly to develop needed thermodynamic data for the Pu(VI)-phosphate system in order to ascertain the extent to which U(VI) and Pu(VI) behave in an analogous fashion. Thus studies were conducted on (UO₂)₃(PO₄)₂⋅4H₂O(c) and (PuO₂)₃(PO₄)₂⋅4H₂O(am) solubilities for long-equilibration periods (up to 870 days) in a wide range of pH values (2.5 to 10.5) at fixed phosphate concentrations of 0.001 and 0.01 M, and in a range of phosphate concentrations (0.0001–1.0 M) at fixed pH values of about 3.5. A combination of techniques (XRD, DTA/TG, XAS, and thermodynamic analyses) was used to characterize the reaction products. The U(VI)-phosphate data for the most part agree closely with thermodynamic data presented in Guillaumont et al.,⁽¹⁾ although we cannot verify the existence of several U(VI) hydrolyses and phosphate species and we find the reported value for formation constant of UO₂PO⁻₄ is in error by more than two orders of magnitude. A comprehensive thermodynamic model for (PuO₂)₃(PO₄)₂⋅4H₂O(am) solubility in the H⁺-Na⁺-OH⁻-Cl⁻-H₂PO⁻₄-HPO²⁻₄-PO³⁻₄-H₂O system, previously unavailable, is presented and the data shows that the U(VI)-phosphate system is an excellent analog for the Pu(VI)-phosphate system.     

Étude de la solubilité et des phases en équilibre dans le système quaternaire réciproque K+, Mn2+/Br−, (H2PO2)−//H2O

Study of solubility and of phases at equilibrium in the K⁺, Mn²⁺/Br⁻, (H₂PO₂)⁻//H₂O system. To elaborate a new method of synthesis of manganese hypophosphite Mn(H₂PO₂)₂·H₂O based on an exchange reaction, the solubility of the phases at equilibrium in the K⁺, Mn²⁺/Br⁻, (H₂PO₂)⁻//H₂O system has been investigated by the isothermal method at 25 °C. For the system under investigation, the two invariants quartets points have been determined, of which compositions are: E₁ – KBr 10.21, MnBr₂ 57.37, Mn(H₂PO₂)₂ 1.35 and H₂O 31.07; E₂ – KBr 3.12, KH₂PO₂ 72.22, Mn(H₂PO₂)₂ 0.12 and H₂O 24.54. The crystallization field of the Mn(H₂PO₂)₂ occupies 91.6% of the total area.     

Preparation,Single Crystal Structure Analysis,and Thermal Behaviour of the Acidic Mercury(I) Phosphate (Hg2)2(H2PO4)(PO4)

Yellowish single crystals of acidic mercury(I) phosphate (Hg₂)₂(H₂PO₄)(PO₄) were obtained at 200 °C under hydrothermal conditions in 32% HF from a starting complex of microcrystalline (Hg₂)₂P₂O₇. Refinement of single crystal data converged at a conventional residual R[F² > 2σ(F²)] = 3.8% (C2/c, Z = 8, a = 9.597(2) Å, b = 12.673(2) Å, c = 7.976(1) Å, β = 110.91(1)°, V = 906.2(2) ų, 1426 independent reflections > 2σ out of 4147 reflections, 66 variables). The crystal structure consists of Hg₂²⁺‐dumbbells and discrete phosphate groups H₂PO₄^– and PO₄^3–. The Hg₂²⁺ pairs are built of two crystallographically independent Hg atoms with a distance d(Hg1–Hg2) = 2.5240(6) Å. The oxygen coordination sphere around the mercury atoms is asymmetric with three O atoms for Hg1 and four O atoms for Hg2. The oxygen atoms belong to the different PO₄ tetrahedra, which in case of H₂PO₄‐groups are connected by hydrogen bonding. Upon heating over 230 °C, (Hg₂)₂(H₂PO₄)(PO₄) condenses to (Hg₂)₂P₂O₇, which in turn disproportionates at higher temperatures into Hg₂P₂O₇ and elemental mercury.