Study of the oxidation of ethylenediaminetetra-acetic acid with lead dioxide suspension in sulphuric acid

The stoichiometry of the reaction between lead dioxide suspension and EDTA was studied by derivative polarographic titration and determination of the products. Four moles of Pb(IV) are reduced per mole of EDTA with moderate speed at room temperature in sulphuric acid solutions. Four moles of carbon dioxide and 3 moles of formaldehyde are the products of the oxidation of 1 mole of EDTA. One mole of N-hydroxymethylethylenediamine is also thought to be produced. The overall reaction may be written as 4Pb(IV) + EDTA + 4H(2)O-->4Pb(II) + 4CO(2) + 3HCHO + H(2)NCH(2)CH(2)NHCH(2)OH + 8H(+). Ethylenediamine is also partly produced if a large excess of lead dioxide is used.     

Influence of electronic and steric effects on stability constants and electrochemical reversibility of divalent ion complexes with glycine and sarcosine. A glass electrode potentiometric, sampled direct current polarographic, virtual potentiometric, and molecular modelling study

Cd^II complexes with glycine (gly) and sarcosine (sar) were studied by glass electrode potentiometry, direct current polarography, virtual potentiometry, and molecular modelling. The electrochemically reversible Cd^II–glycine–OH labile system was best described by a model consisting of M(HL), ML, ML₂, ML₃, ML(OH) and ML₂(OH) (M = Cd^II, L = gly) with the overall stability constants, as log β, determined to be 10.30 ± 0.05, 4.21 ± 0.03, 7.30 ± 0.05, 9.84 ± 0.04, 8.9 ± 0.1, and 10.75 ± 0.10, respectively. In case of the electrochemically quasi-reversible Cd^II–sarcosine–OH labile system, only ML, ML₂ and ML₃ (M = Cd^II, L = sar) were found and their stability constants, as log β, were determined to be 3.80 ± 0.03, 6.91 ± 0.07, and 8.9 ± 0.4, respectively. Stability constants for the ML complexes, the prime focus of this work, were thus established with an uncertainty smaller than 0.05 log units. The observed departure from electrochemical reversibility for the Cd–sarcosine–OH system was attributed mainly to the decrease in the transfer coefficient . The MM2 force field, supplemented by additional parameters, reproduced the reported crystal structures of diaqua-bis(glycinato-O,N)nickel(II) and fac-tri(glycinato)-nickelate(II) very well. These parameters were used to predict structures of all possible isomers of (i) [Ni(H₂O)₄(gly)]⁺ and [Ni(H₂O)₄(sar)]⁺; and (ii) [Ni(H₂O)₃(IDA)] and [Ni(H₂O)₃(MIDA)] (IDA = iminodiacetic acid, MIDA = N-methyl iminodiacetic acid) by molecular mechanics/simulated annealing methods. The change in strain energy, ΔU_str, that accompanies the substitution of one ligand by another (ML + L′ → ML′ + L), was computed and a strain energy ΔU_str = +0.28 kcal mol⁻¹ for the reaction [Ni(H₂O)₄(gly)]⁺ + sar → [Ni(H₂O)₄(sar)]⁺ + gly was found. This predicts the monoglycine complex to be marginally more stable. By contrast, for the reaction [Ni(H₂O)₃IDA] + MIDA → [Ni(H₂O)₃MIDA] + IDA, ΔU_str = −0.64 kcal mol⁻¹, and the monoMIDA complex is predicted to be more stable. This correlates well with (i) stability constants for Cd–gly and Cd–sar reported here; and (ii) known stability constants of ML complex for glycine, sarcosine, IDA, and MIDA.     

Superoxometal-catalyzed co-oxidation of alcohols and nitrous acid with molecular oxygen

A superoxochromium(III) ion, Cr_aqOO²⁺, acts as a catalyst for the co-oxidation of alcohols and nitrous acid with molecular oxygen according to the stoichiometry: CH₃OH+HNO₂+O₂→CH₂O + NO₃⁻ + H₂O+H⁺. The kinetics are second order in [HNO₂] and independent of the concentrations of the superoxochromium catalyst, substrate, and O₂. The proposed mechanism features the disproportionation of HNO₂ to NO and NO₂, both of which react rapidly with Cr_aqOO²⁺. The Cr_aqOO²⁺/NO reaction generates another equivalent of NO₂ and a mole of Cr_aqO²⁺, the active oxidant. The two-electron oxidation of the alcohol by Cr_aqO²⁺ produces Cr_aq²⁺, which reacts rapidly with O₂ to regenerate the catalyst, Cr_aqOO²⁺. The NO₂/Cr_aqOO²⁺ reaction yields the peroxynitrato complex, Cr_aqOONO₂²⁺, in a dead-end equilibrium process that has no effect on the catalytic reaction. The disproportionation of NO₂ yields the final nitrogen-containing product, NO₃⁻, and regenerates an equivalent of HNO₂. Under a fixed set of conditions, the relative catalytic efficiency (CE) of Cr_aqOO²⁺ decreases as its concentration increases owing to the competition between O₂ and Cr_aqOO²⁺ for the intermediate Cr_aq²⁺.     

Flash photolysis/temperature jump study of the vibrational relaxation of N2O(010) by O(P) and NO

This survey begins with the photochemistry at 254 nm and 298 K in the system H₂O₂COO₂RH, the primary objective of which is to determine the rate constants for the reaction OH + RH → H₂O + R relative to the well-known rate constant for the reaction OH + CO → CO₂ + H. Inherent in the scheme is that the reaction HO₂+CO→OH+CO₂ is negligible compared with the OH reaction, and a literature consensus gives k_HO2 < 10⁻¹⁹ cm³ molecule⁻¹ s⁻¹, or some 10⁶ less than k_OH at 298 K. Theoretical calculations establish that the first stage in the HO₂ reaction is the formation of a free radical intermediate HO₂ + CO → HOOCO (perhydroxooxomethyl) which decomposes to yield the products, and that the rate of formation of the intermediate is equal to the rate of formation of the products. The structure of the intermediate and a reaction profile are shown.

High temperature rate data reported subsequent to the data in the consensus and theoretical calculations lead here to a recommendation that, in the range 250–800 K, k_HO2 = 3.45 × 10⁻¹²T^1/2 exp(1.15 × 10⁴/T) cm³ molecule⁻¹ s⁻¹, the hard-sphere-collision Arrhenius modification. This yields k_HO2(298) = 1.0 × 10⁻²⁷ cm³ molecule⁻¹ s⁻¹ or some 10¹⁴ slower than k_OH(298).     

The oxidative decarboxylation of polyaminocarboxylic acids with lead dioxide suspension in neutral medium

The reaction between a suspension of lead dioxide and polyaminocarboxylic adds in neutral medium at 80° has been examined titrimetrically and found to involve decarboxylation in which 3 moles of PbO₂ oxidize 1 mole of the acid, the products being 3 moles of CO₂, 3 moles of HCHO, 1 mole of ethylenediaminemonoacetic acid and 3 moles of Pb(II) followed by chelation of the 3 moles of Pb(II) by an additional 3 moles of EDTA.     

Treatment of protonic delocalisation in water by the complex scaling method: theory and experimental results

Recently the complex scaling method has been extended to large systems (e.g. a liquid) by use of quantum statistics. The main tool for its extension is the theory of fermionic second-order density matrices as developed by Coleman. After proper treatment based on the complex scaling method the second-order density matrix reveals a new kind of off-diagonal long range order in the form of Jordan blocks. We call this kind of “order” coherent dissipative structures. To test the new theory, contact with experiment was sought and found in the form of protonic delocalisation effects in liquid H₂O. Two relations could be derived from first principles concerning (i) the limiting excess conductivity of mixtures of H⁺/D⁺ in H₂0/D₂0 and (ii) the proton exchange rate in the reaction H₂O+H₃O⁺ → H₃O⁺+H₂0 in relation to that in the reaction H₂0+OH⁻ → OH⁻+H₂O, which are in marked contrast to the results expected by conventional (i.e. classical) theories. The experiments have since been carried out and the theory was confirmed by both of them. Here we present briefly the theoretical predictions as well as the experimental results. Work on other fields (ionic conductance of molten alkali chlorides, the size of magnetic clusters in Gd far above the Curie temperature) illustrate that quantum interference or delocalisation effects (e.g. coherent dissipative structures) are important for the physics of condensed matter.     

具有Dawson结构的钼钒磷杂多酸氧化还原性质的研究

通过SnCl₂电位滴定、极谱和循环伏安方法,详细研究了2:18系列钼钒磷杂多酸H_(6+n)[P₂Mo^13-nV_nO₆₂]·xH₂O(n=1～3)和H^_4+n[P₂Mo_18-nV_nO₆₂H₂]·xH₂O(n=4,5)在溶液中的氧化还原性质,证实它们的还原为三步分别加合n,2,2个电子,同时加合n,2,2个质子的过程,总结了循环伏安峰电位与pH的关系,提出了还原机理。     

On the existence of the protonated hydronium dication H4O in sulfolane solution

The enthalpy of solvation in sulfolane of the gaseous protonated hydronium dication is estimated as −628 kcal/mol at 298 K. Using literature data, a value ΔH^o = −212 kcal/mol is calculated for the reaction H₃O⁺ + H⁺→ H₄O²⁺ (in sulfolane), supporting the thermodynamic existence of H₄O²⁺ in sulfolane solution, as characterized previously by potentiometric and conductometric titrations. Some aspects of these results are discussed.     

Determination of pK(a)'s for thymol blue in aqueous medium: evidence of dimer formation

Formation constants for recrystallized thymol blue were determined in water, using the SQUAD and SUPERQUAD programs. The best model correlating spectrophotometric, potentiometric and conductimetric data was fitted with the dissociation of HL⁻=L²⁻+H⁺−log K=8.918±0.070 and H₃L₂⁻=2L²⁻+3H⁺−log K=29.806±0.133 with the SUPERQUAD program at variable low ionic strength (1.5×10⁻⁴–3.0×10⁻⁴ M); and HL=L²⁻+H⁺−log K=8.9±0.000, H₃L₂⁻ =2L²⁻+3H⁺−log K=30.730±0.032, H₄L₂=2L²⁻+4H⁺−log K=32.106±0.033 with SQUAD at 1.1 M ionic strength.     

Cobalt(III) complexes of ethylenediamine-N,N′-di-S-isobutylacetic acid

A new optically active ONNO-type tetradentate ligand, ethylenediamine-N,N′- di-S-isobutylacetate (SS-eniba), has been synthesized. During the preparation of diaqua cobalt(III) complexes of SS-eniba, [Co(SS-eniba)(H₂O)₂]⁺, the title ligand has coordinated stereospecifically to the cobalt(III) ion to give three isomers, Δ-s-cis, Δ-uns-cis and Λ-uns-cis, which have been isolated and characterized via electronic absorption, circular dichroism (CD), and ¹H NMR spectroscopy, along with elemental analysis data. The preparation of Δ-s-cis-[Co(SS-eniba)Cl₂]⁺ and Δ-s-cis-[Co(SS-eniba)CO₃]⁺ are also reported.     

Kinetics of formation and dissociation of the ternary complex ion (pentane-2,4-dionato)(nitrilotriacetato)chromate(III) in aqueous media

Synthesis of solid [Cr(nta)(H₂O)₂] 1, kinetics and equilibrium of ots reaction with pentane-2,4-dione (Hpd) to form [Cr(nta)(pd)]⁻ 2 (H₃nta is nitrilotriacetic acid), aquation of 2 into 1, and some related reactions have been described. Parallel proton-independent and inverse proton-dependent paths lead from 1 to 2. The [H⁺]⁻¹ path arises from metal assisted deprotonation of HE, the enol form of Hpd. Aquation of 2 into 1 involves [Cr(Hnta)(pd)(H₂O]⁺ 2H (Hnta is tridentate nta) in addition to 2. The nta comples 1 is considerably more labile and a weaker acid than [Cr(H₂O)₆]³⁺.     

新型磷-钒-氧层状化合物[H2en]2[H3O]6[Co(H2O)2(VO)8(OH)4(PO4)8]的水热合成与晶体结构

金属磷酸盐材料在吸附、离子交换、离子传导和催化剂方面有潜在的应用前景[1～5]. 近年来, 通过水热反应合成了一些A-V-P-O化合物. 在这些化合物中, A一般为碱金属或有机阳离子, 如层状结构的[H2N(C4H8)2NH2][(VO)4(OH)4(PO4)2][6] 和[H2N(C2H4)3NH2][(VO)8(HPO4)3(PO4)4*(OH)2]*2H2O[6], 一维链状结构的 [H2NCH2CH2NH3(VO)(PO4)][7], 手性双螺旋结构的 [(CH3)2NH2]K4[(VO)10(H2O)2(OH)4(PO4)7]*H2O[8]以及具有三维骨架结构的化合物 [H3N(CH2)3NH3K(VO)3(PO4)3][9], [H3N(CH2)3NH3]2[V(H2O)2(VO)6(OH)2(HPO4)3(PO4)5]*3H2O[10]和[H3N(CH2)2NH3][(VO)3(H2O)2(PO4)2(HPO4)4][11].     

The speciation of rhodium(III) in hydrochloric acid media by capillary zone electrophoresis

A fast and effective method to study the aquation of rhodium(III) chlorocomplex in hydrochloric solutions using capillary zone electrophoresis (CZE) is developed. At least five species, some of which seem to be oligomeric, are formed in solution during the aquation process at pH>1. The fast hydration of RhCl₆³⁻ makes this species impossible to detect. The first species detected in the optimised conditions is RhCl₅(H₂O)²⁻ although RhCl₄(H₂O)₂⁻ is the main species during the first stage of the aquation process. When equilibrium is reached either RhCl₃(H₂O)₃ or a cationic complex, RhCl₂(H₂O)₄⁺, is formed as the main species. Matrix Assisted Laser Desorption Ionisation Time of Flight Mass Spectrometry (MALDI-TOF MS) is used as a novel technique to elucidate the structure of the rhodium aqua/chloro complexes formed in solution. Results obtained by CZE are confirmed by spectrophotometry.     

Strahlenchemie von alkoholen—IX Die UV-photolyse (λ = 185 nm) von methanol in flüssiger phase

The UV photolysis (λ = 185 nm) of liquid methanol yields hydrogen, glycol, formaldehyde, methane and traces of ethane in quantum yields of 0·83, 0·78, 0·058, 0·05 and 0·002 resp. (related to φ(H₂) = 0·4 of the ethanol-actinometer (5 mole/1 in water)). The isotopic distribution of the hydrogen (85% HD) formed in the photolysis of CH₃OD shows, that as in the gasphase² the scission of the O---H-bond (1) is the major process. CH₃OH + hv (λ = 185 nm) → CH₃O^• + H^• (1)

In methanoi-water mixtures (nearly all the light of the wavelength λ = 185 nm is absorbed by methanol) the quantum yields of hydrogen, glycol, methane and ethane are greatly reduced, while the formaldehyde yield remains unaffected. In 1 molar solution φ(H₂) = 0·42, φ(glycol) = 0·32 and φ(CH₄) = 6 x 10⁻⁴ is obtained. Ethane cannot be detected.     

Kinetics and mechanisms of the redox reaction of hexaaquotitanium(III) and the ethylenediamine tetraacetato titanium(III) complex by aqueous solutions of bromine

At 25°C, I = 1.0 M (CF₃SO₃⁻Li⁺+CF₃SO₃H), [H⁺] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H₂O), ₆³⁺ by bromine was found to be: −d/[Br₂]T/dt=kK/[Br₂][Ti^III]/[H⁺]+K+kK/[Br₃⁻][Ti^III]/[H⁺+K, where k = 9.2 × 10⁻³ M ⁻¹ s ⁻¹ and K = 4.5 × 10⁻³ M. At [H⁺] = 1.0 M, [Br⁻] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br⁻] increases.

The pH-dependence of the oxidation of Ti^III-edta by bromine is interpreted in terms of the change in identity of the Ti^III-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k₀^edta)² weighting into an equation of the form: k₀^edta =k₁+k₂K₁[H⁺]⁻¹+k₃K₁K₂[H⁺]^−2/1+K₁[H⁺[H⁺⁻¹+K₁K₂[H⁺]⁻², with K₁ and K₂ fixed as earlier determined at 9.55 × 10⁻³ and 2.29 × 10⁻⁹ M, respectively, for the oxidation of bromine. k₁=k₂=(3.1±0.32)×10³M⁻¹s⁻¹ k₃=(2.3±0.45)×10⁶N⁻¹s⁻¹.

It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br₂^.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for Ti^III-edta+Ti^IV-edta is estimated at 32 M⁻¹ s⁻¹.     

OH (A Σ) fragment emission from reaction of electronically excited Xe(6p) with H2O under free jet and bulb conditions

The state-selective energy transfer from two-photon excited Xe(6p) to H₂O and the subsequent reaction has been studied by measured of emission spectra of OH (A ²Σ⁺ → X ²Π). The vibrational population ratios, N_v=1/N_v=0, are 0.52 ± 0.01 in a free jet and 0.37 ± 0.02 in a bulb. This reveals the difference in dissociation dynamics following the intra-complex and the intermolecular electronic energy transfers from Xe(6p) to H₂O.     

在MA(甲基胺)-SiO2-H2O凝胶中ZSM-39单晶的生长

ZSM-39合成专利首次发表于1981年。1982年Schleker和Meier等通过拟合X射线粉末衍射数据推测出ZSM-39晶体具有氧化硅12面体及16面体的笼形包络物结构(ClathrateStructure),与天然矿物硫方晶石(Melanophlogite)的结构类型相近。1983年Bibhy等研究了ZSM-39的性质并用包络物结构进行解释。目前,这类材料的合成与结构研究已成为沸石科学家和矿物学家感兴趣的问题之一。     

A novel photosynthetic mimic reaction catalysed by K[Ru(H-EDTA)Cl] · 2H2O; reduction of carbon dioxide to formate and formaldehyde in the presence of an aqueous suspension of Pt—CdS—RuO2

An efficient photocatalytic reduction of carbon dioxide to HCOOH and HCHO is reported using K[Ru(H-EDTA)Cl] · 2H₂O (1) as homogeneous catalyst and particulate Pt—CdS—RuO₂ as photon absorber at 505 nm. This system produces 0.22 M of HCOOH and 0.10 M of HCHO in 6 h of photolysis at rates of 3.05 × 10⁻² M h⁻¹ and 2.0 × 10⁻² M h⁻¹ respectively. Trace amounts of CH₃OH, CH₄ and CO are detected in the reaction vessel. The rates of formation of HCOOH and HCHO exhibit a first-order dependence on the catalyst and dissolved CO₂ concentrations. The reaction shows deuterium isotope effects (k_H/k_D) of 1.5 and 2.00 for the formation of HCOOH and HCHO respectively. Under identical experimental conditions, the rate of decomposition of formate was studied. The rate of decomposition of formate is slower (by two orders of magnitude compared with the formation of formate) even at high formate concentrations. A mechanism for the formation of HCOOH and HCHO is proposed.     

Effect of the nature of mendiaxon–X interactions (X= Na, Cu, H) and the hydrogen bonding on the ν(C=O) behavior: theoretical and spectroscopic study

Theoretical and spectroscopic (IR and Raman) study of different 7-hydroxy-4-methylcoumarin (mendiaxon) systems (mend⁻, mendNa, mendCu, mendH and mendH · 2H₂O) were performed at B3LYP/6-31G(d) and B3LYP/6-31++G(d,p) levels of theory. The geometric and electronic structures as well as the vibrational behavior of the systems studied were discussed: (1) as to the changes that occurred in the anion coumarin ring upon the mend⁻–X⁺ (X⁺ =Na⁺, Cu⁺, H⁺) interactions and (2) as to the changes that occurred in mendH due to hydrogen bondings in mendH · 2H₂O. The largest bond length changes in the anion coumarin ring were obtained for mendH and the smallest ones for mendNa. The bond length changes were mainly produced from the electrostatic effect of the positive charge of X. The induced polarization of the C=O bond upon the mend⁻–X⁺ interactions was found to be opposite to the basic one and it led to shorter C=O bond lengths (higher ν(C=O) frequencies) in the order: mendNa, mendCu and mendH. Conversely, upon the hydrogen bonding the induced polarization of the C=O bond was found in the same direction as the basic one and it produced elongation to the C=O bond length (lower ν(C=O) frequency). On the basis of the correlations found, the ν(C=O) positions in mendNa, mendCu, mendH and mendH · 2H₂O were explained.     

Can chlorine anion catalyze the reaction of HOCl with HCl?

The reaction of HOCl + HCl → Cl₂ + H₂O in the presence of chlorine anion Cl⁻ has been studied using ab initio methods. The overall exothermicity is 15.5 kcal mol⁻¹ and this reaction has been shown to have a high activation barrier of 46.5 kcal mol⁻¹. Cl⁻ is found to catalyze the reaction via the formation of HOCl·Cl⁻, ClH·HOCl·Cl⁻ and Cl⁻·H₂) intermediate ion-molecule complexes or by interacting with a concerted four-center transition state of the reaction of HOCl + HCl.