On a possible radical-cation mechanism of the biomimetic oxidation of the saturated hydrocarbon 1,3-dimethyladamantane in a Gif-type system containing a Fe2+ salt, picolinic acid, and pyridine

Based on an analysis of the ratio between the final products of the oxidation of 1,3-dimethyladamantane (1,3-DMA) with hydrogen peroxide under new catalytic conditions, an EPR-spectroscopic study of the 1,3-DMA radical cation under model radiation-chemical conditions, and the results of PM3 quantum-chemical calculations, a new mechanism was proposed for the biomimetic oxidation of the saturated hydrocarbon. This mechanism involves the intermediate formation of the 1,3-DMA radical cation, in which a tertiary C-H bond is selectively activated. Next, oxene (oxygen atom) is inserted into this C-H bond to form a tertiary alcohol. It was found that a comparison of the composition of final products in the oxidation of saturated hydrocarbons under conditions of a real chemical experiment with the structure and reactivity of their radical cations under model radiation-chemical conditions can be a methodologically new general technique for the analysis and prediction of the reactivity of saturated hydrocarbons under oxidative conditions.     

Catalytic oxidation of ascorbic acid by molecular oxygen in aqueous pyridine in the presence of Co2+, Ni2+, Mn2+ and Zn2+ ions

In aqueous pyridine solutions, Co²⁺, Ni²⁺, Mn²⁺ and Zn²⁺ effectively catalyze the oxidation of ascorbic acid by molecular oxygen. A kinetic expression consistent with the experimental data is given and a possible mechanism proposed.

---

- , , . , . .

     

Fe2OCl6(2-) salt formed by electrochemical oxidation of ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolemethide in the presence of FeCl4- ion with a silicon wafer electrode

Electrochemical oxidation of a bent donor molecule, ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolmethide ( 2), in chlorobenzene (PhCl)/ethanol containing NBu 4FeCl 4 as a supporting electrolyte is performed using an undoped silicon wafer electrode. Black crystals of 2 6.Fe 2OCl 6.2PhCl are obtained that have a different molecular formula from that of 2 2.FeCl 4 crystals obtained previously using a platinum rod electrode. The new crystal has a structure composed of alternately stacked layers of 2 molecules and Fe 2OCl 6 (2-) ions, whose Fe-O-Fe bond is completely linear and for which the geometry around the Fe atom is almost tetrahedral. The electrical resistivity decreases with temperature until ca. 200 K, but below this temperature, it gently increases. The magnetic susceptibility (chi p) observed can be described by the sum of chi p obeying a Curie-Weiss law for the impurity spins and of chi p obeying a dimer model with a spin-exchange integral ( J approximately -180 K) in each Fe 2OCl 6 (2-) ion, which is also weakly coupled to neighboring Fe 2OCl 6 (2-) ions through an additional exchange interaction.     

Mechanism of ascorbic acid oxidation by molecular oxygen in aqueous pyridine catalyzed by CO2+, Ni2+, Mn2+ and Zn2+

Data on the radical non-chain mechanism of ascorbic acid oxidation by molecular oxygen catalyzed by Co²⁺, Ni²⁺, Mn²⁺ and Zn²⁺ ions are reported.

---

Co²⁺, Ni²⁺, Mn²⁺ Zn²⁺.

     

Coagulation of bitumen with kaolinite in aqueous solutions containing Ca2+, Mg2+ and Fe3+: effect of citric acid

Heterocoagulation experiments of kaolinite with solvent-diluted-bitumen were carried out to investigate the effect of hydrolyzable metal cations and citric acid on the liberation of bitumen from kaolinite. The adsorption of Ca(2+) and Mg(2+) on kaolinite, and zeta potentials of kaolinite and bitumen droplets in solutions containing 10(-3)mol/L of Ca(2+), Mg(2+) and Fe(3+) with or without citric acid were also measured. It was found that the heterocoagulation of bitumen with kaolinite was enhanced in the presence of the metal cations from pH 7 to pH 10.5, accompanied by a decrease in the magnitude of the zeta potentials and an increase in the adsorption of the metal cations on kaolinite and possibly on bitumen droplets. The addition of 5 x 10(-4)mol/L citric acid reduced the degree of coagulation from 90% to less than 40% in the presence of 10(-3)mol/L Ca(2+) and Mg(2+) cations at pH approximately 10, and at pH approximately 8 for Fe(3+). It was found that hydrolyzable metal cations enhanced bitumen-kaolinite interactions through electrical double layer compression and specific adsorption of the metal hydrolysis species on the surface of kaolinite. The effect of metal cations was removed by citric acid through formation of metal-citrate complexes and/or the adsorption of citrate anions, which restored the zeta potentials of both kaolinite and bitumen. Therefore, electrostatic attraction or repulsion was responsible for the coagulation or dispersion of kaolinite particles from bitumen droplets in the tested system.     

Fe2+-catalyzed heterolytic RO-OH bond cleavage and substrate oxidation: a functional synthetic non-heme iron monooxygenase system

The reaction of [Fe22+(H2Hbamb)2(N-MeIm)2], [1], a binuclear, non-heme iron complex, with 2-methyl-1-phenylprop-2-yl hydroperoxide (MPPH) shows that [1] induces heterolytic cleavage of the peroxy O-O bond. Catalytic atom transfer reactions (1:MPPH:PhSMe 1:596:6011) resulted in the highly efficient (99 +/- 1%), catalytic oxidation of phenyl methyl sulfide to phenyl methyl sulfoxide/sulfone (T.N. = 500/11 respectively) and cyclohexane to cyclohexanol/cyclohexanone (T.N. = 230/5 respectively) showing the highly efficient, catalytic capacity of [1] to carry out oxygen insertion chemistry.     

New reaction of the sodium salt of 2-nitroethanol. X-ray analysis of the sodium salt of 2-oxo-3-hydroxypropionic acid oxime, 2-bromo-2-nitropropane-1,3-diol,and the model 2,2-dinitropropane-1,3-diol

A novel reaction of the sodium salt of 2-nitroethanol in aqueous ammonia resulted in the sodium salt of 2-oxo-3-hydroxypropionic acid oxime (1) has been found. Bromination of1 affords 2-bromo-2-nitropropane-1,3-diol (2) with a previously unknown molecular conformation. The formation mechanisms of compounds1 and2 were suggested. X-ray analysis of products1,2 and that of the model compound, 2,2-dinitropropane-1,3-diol, was performed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1217–1221, May, 1996.     

Second chemiluminescence behavior of Fe2+, Fe3+ and Cr3+ in the luminal-KMnO4 system.

A novel flow injection chemiluminescence (CL) method has been developed for the determination of three metal ions, namely Fe2+, Fe3+ and Cr3+, based on the second CL (SCL) signal of the mixture of luminal with KMnO4 in a sodium hydroxide medium by the catalysis of Fe2+, Fe3+ or Cr3+. The possible CL mechanism of the systems, the influencing factors, and the optimum conditions for the reactions were investigated based upon the kinetic curve of the CL reaction, CL spectra, UV-visible spectra and some other experiments. Under the optimum conditions, the SCL intensity was directly proportional to the concentration of these metal ions in solution in the range of 0.10 - 100.00 mg l(-1) for Fe(2+), 0.50 - 7.50 and 7.50 - 200.00 mg l(-1) for Fe3+, 0.01 - 0.25 and 0.25 - 10.00 mg l(-1) for Cr3+. The detection limits (3 sigma/s) were 9.87 x 10(-6) g l(-1), 2.71 x 10(-6) g l(-1) and 5.25 x 10(-7) g l(-1) for Fe2+, Fe3+ and Cr3+, respectively.     

Interaction-induced enhancement in the activity and selectivity of a titania-supported ammonium salt of a 12-molybdophosphoric acid catalyst during ammoxidation of 2-methylpyrazine

A titania-supported ammonium salt of 12-molybdophosphoric acid has been synthesized, and the salt-support interaction, which enhanced the reaction rate, has been correlated with the activity of the catalyst in the ammoxidation of 2-methylpyrazine.     

Isotope exchange in reactions between D2O and size-selected ionic water clusters containing pyridine, H+ (pyridine)m(H2O)n

Pyridine containing water clusters, H(+)(pyridine)(m)(H(2)O)(n), have been studied both experimentally by a quadrupole time-of-flight mass spectrometer and by quantum chemical calculations. In the experiments, H(+)(pyridine)(m)(H(2)O)(n) with m = 1-4 and n = 0-80 are observed. For the cluster distributions observed, there are no magic numbers, neither in the abundance spectra, nor in the evaporation spectra from size selected clusters. Experiments with size-selected clusters H(+)(pyridine)(m)(H(2)O)(n), with m = 0-3, reacting with D(2)O at a center-of-mass energy of 0.1 eV were also performed. The cross-sections for H/D isotope exchange depend mainly on the number of water molecules in the cluster and not on the number of pyridine molecules. Clusters having only one pyridine molecule undergo D(2)O/H(2)O ligand exchange, while H(+)(pyridine)(m)(H(2)O)(n), with m = 2, 3, exhibit significant H/D scrambling. These results are rationalized by quantum chemical calculations (B3LYP and MP2) for H(+)(pyridine)(1)(H(2)O)(n) and H(+)(pyridine)(2)(H(2)O)(n), with n = 1-6. In clusters containing one pyridine, the water molecules form an interconnected network of hydrogen bonds associated with the pyridinium ion via a single hydrogen bond. For clusters containing two pyridines, the two pyridine molecules are completely separated by the water molecules, with each pyridine being positioned diametrically opposite within the cluster. In agreement with experimental observations, these calculations suggest a "see-saw mechanism" for pendular proton transfer between the two pyridines in H(+)(pyridine)(2)(H(2)O)(n) clusters.     

Theoretical investigation of the Fe+-catalyzed oxidation of acetylene by N2O

The gas-phase Fe(+)-mediated oxidation of acetylene by N2O on both sextet and quartet potential energy surfaces (PESs) is theoretically investigated using density functional theory. Geometries and energies of all the stationary points involved in the catalytic reaction are located. For the catalytic cycles, the crucial step is the initial N2O reduction by Fe(+) to form FeO(+), in which a direct O-abstraction mechanism is located on the sextet PES, whereas the quartet pathway favors a N-O insertion mechanism. Spin inversion moves the energy barrier for this process downward to a position below the ground-state entrance channel. The second step of the catalytic cycles involves two mechanisms corresponding to direct hydrogen abstraction and cyclization. The former mechanism accounts for the ethynol formation with the upmost activation barrier below the entrance channel by about 5 kcal/mol. The other mechanism involves a "metallaoxacyclobutene" structure, followed by four possible pathways, i.e., direct dissociation, C-C insertion, C-to-O hydrogen shift, and/or C-to-C hydrogen shift. Among these pathways, strong exothermicities as well as energetically low location of the intermediates suggest oxidation to ketene and carbon monoxide along the C-to-C hydrogen shift pathway is the most favorable. Reduction of the CO loss partner FeCH2(+) by another N2O molecule constitutes the third step of the catalytic cycles, which contains direct abstraction of O from N2O giving OFeCH2(+), intramolecular rearrangement to form Fe(+)-OCH2, and nonreactive dissociation. This reaction is also energetically favored considering the energy acquired from the initial reactants.     

胭脂红酸褪色光度法检测H2O2-Fe2+产生的羟自由基

提出了Fe2 H2O2 胭脂红酸分析新体系,并用于羟自由基的测定。该法用Fenton反应产生羟自由基,并加入胭脂红酸显色剂,使胭脂红酸褪色,采用分光光度计测定其ΔA值的变化,可间接测定羟自由基的产生量。通过测定条件的研究,得出最佳实验条件,并对抗坏血酸等7种抗氧化剂的抗羟自由基氧化性能进行了比较。     

Kinetics and mechanism of aqueous oxidation of H2S by Fe+3

The reaction kinetics of aqueous oxidation of H₂S by Fe⁺³ is investigated at 25°C by spectrophotometric method. The study conducted at various reactant concentrations and pH revealed that the reaction proceeds according to complex‐series reactions involving polysulfides as intermediates. The reaction of each step is first order with respect to Fe⁺³ and hydrogen sulfide or polysulfide. A mechanism is proposed, involving sulfido and polysulfido radicals. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 331–335, 1999     

维生素C氧化反应的研究: H2O2-Cu^2^+-磷酸体系中的反应动力学

研究了在铜离子存在时的弱酸性条件下, 用过氧化氢氧化维生素C, 并用直接分光光度法测定未变化的酸, 表明维生素C的催化氧化是以链式反应机制进行的.     

Substrate selectivity of Gluconobacter oxydans for production of 2,5-diketo-D-gluconic acid and synthesis of 2-keto-L-gulonic acid in a multienzyme system

Substrate selectivity of Gluconobacter oxydans (ATCC 9937) for 2,5-diketo-d-gluconic acid (2,5-DKG) production was investigated with glucose, gluconic acid, and gluconolactone in different concentrations using a resting-cell system. The results show that gluconic acid was utilized favorably by G. oxydans as substrate to produce 2,5-DKG. The strain was coupled with glucose dehydrogenase (GDH) and 2,5-DKG reductase for synthesis of 2-keto-l-gulonic acid (2-KLG), a direct precursor of l-ascorbic acid, from glucose. NADP and NADPH were regenerated between GDH and 2,5-DKG reductase. The mole yield of 2-KLG of this multienzyme system was 16.8%. There are three advantages for using the resting cells of G. oxydans to connect GDH with 2,5-DKG reductase for production of 2-KLG: gluconate produced by GDH may immediately be transformed into 2,5-DKG so that a series of problems generally caused by the accumulation of gluconate would be avoided; 2,5-DKG is supplied directly and continuously for 2,5-DKG reductase, so it is unnecessary to take special measures to deal with this unstable substrate as it was in Sonoyama’s tandem fermentation process; and NADP(H) was regenerated within the system without any other components or systems.     

Structural and mechanistic information on the nitrosation of model Fe(II) complexes containing a biomimetic S4N chelate

In order to provide insight into the reaction pathways of nitrogen oxide redox species with [Fe-S] models that may parallel those existing in biology, the reactivity of the iron-sulfur species, {[Fe(II)(S(4)NEt(2)N)]}(2) (1) and [Fe(II)(CH(3)CN)(S(4)NEt(2)N)] (2), where (S(4)NEt(2)N)(2-) = 2,6-bis(2-mercaptophenylthiomethyl)-4-diethylaminopyridine(2-), towards NO(+) (nitrosation) has been studied mechanistically in acetonitrile and compared with the corresponding reactions with NO (nitrosylation). For the nitrosation of 1, the reaction takes place in two steps that correspond to the nitrosation of the mononuclear (2) and dinuclear (1) complexes, respectively. For the corresponding carbonyl complex [Fe(II)(CO)(S(4)NEt(2)N)] (3), the nitrosation reaction occurs in a single step. The relative reactivity of the iron-sulfur species is approximately (1)/(2)/(3) = 1/20/10. Activation parameters for the nitrosation of 1 (ΔH(#) = 27 ± 1 kJ mol(-1), ΔS(#) = -111 ± 2 J K(-1) mol(-1), and ΔV(#) = -19 ± 2 cm(3) mol(-1)), 2 (ΔH(#) = 46 ± 2 kJ mol(-1), ΔS(#) = -22 ± 7 J K(-1) mol(-1), and ΔV(#) = -9.7 ± 0.4 cm(3) mol(-1)) and 3 (ΔH(#) = 38 ± 1 kJ mol(-1), ΔS(#) = -44 ± 4 J K(-1) mol(-1), and ΔV(#) = -7.8 ± 0.3 cm(3) mol(-1)) were determined from variable temperature and pressure studies. The significantly negative ΔS(#) and ΔV(#) values found for the nitrosation reactions are consistent with an associative mechanism. A comparative study of the reactivity of the iron-sulfur species 1 to 3 towards NO(+) and NO is presented.     

The solubility of magnetite and the hydrolysis and oxidation of Fe2+ in water to 300°C

The solubility of carefully characterized magnetite, Fe₃O₄, in dilute aqueous solutions saturated with H₂ has been measured at temperatures from 100 to 300°C in a flow apparatus. Solution compositions included either HCl or NaOH molalities of up to 1 and 40 mmole-kg^?1, respectively, and H₂ molalities of 0.0779, 0.779, and 8.57 mmole-kg^?1. The dependence of the equilibrium solubility on the pH and reduction potential were fitted to a scheme of soluble ferrous and ferric species consisting of Fe²⁺, FeOH⁺, Fe(OH)₂, Fe(OH) ₃ ^? , Fe(OH)₃, and Fe(OH) ₄ ^? . Solubility products from the fit, corresponding to the reactions $$\tfrac{1}{3}Fe_3 O_4 + (2 - b)H^ + + \tfrac{1}{3}H_2 \rightleftharpoons Fe(OH)_b^{2 - b} + (4/3 - b)H_2 O$$ and $$\tfrac{1}{3}Fe_3 O_4 + (3 - b)H^ + \rightleftharpoons Fe(OH)_b^{3 - b} + \tfrac{1}{6}H_2 + (4/3 - b)H_2 O$$ were used to derive thermodynamic constants for each species. The extrapolared value for the Gibbs energy of formation of Fe²⁺ at 25°C is ?88.92±2.0 kJ-mole^?1, consistent with standard reduction potentials in the range E^o(Fe²⁺)=?0.47±0.01 V. The temperature coefficient of the equilibrium Fe molality, (?m(Fe, sat.)/?T)_{m(H2).m(NaOH)}, changes from negative to positive as the NaOH molality is increased to the point where Fe(OH) ₃ ^? and Fe(OH) ₄ ^? predominate.     

Germanium phthalocyanine, GePc, and the reduced complexes SiPc(pyridine)(2) and GePc(pyridine)(2) containing antiaromatic pi-electron circuits

The reaction of GeCl2(dioxane) with K2Pc(DMF)4 yields germanium phthalocyanine, GePc. GePc dissolves in pyridine to form GePc(py)2. The 1H NMR spectrum of GePc(py)2 and nucleus-independent chemical shift (NICS) calculations on GePc(NMe3)2 both show the presence of a strong paratropic ring current. That ring current, along with the bond-length alternation in the crystal structure of GePc(tBuPy)2, indicates the presence of an antiaromatic pi-electron circuit in GePc(py)2. SiPc(py)2 was synthesized, and its electronic structure is similar to that of GePc(py)2.