Mechanism of the oxidation of ferrocene and its derivatives with hydrogen peroxide: A new effect

A new effect was recorded during the studies of the mechanism of ferrocene oxidation with hydrogen peroxide, namely, a shift of λ_max of the absorption band of the ferricinium cation (ABFC) toward the long-wave region and its broadening during the reaction. The shiftΔλ_max increased with the excess of the H₂O₂ concentration with respect to the ferrocene concentration and reached 90 nm and more at H₂O₂/Fc ≈ 80–100. Similar changes in ABFC took place during the oxidation of a series of ferrocene derivatives. A shift of ABFC was not revealed at comparable concentrations of the metal complex and H₂O₂. During the oxidation of ferrocene with other peroxides (t-C₄H₉OOH or (PhCOO)₂), there were no changes in the spectrum of the ferricinium cation at any ratios of reagent concentrations. The observed effect is based on the formation of a {ferricinium cation + ^.OH} radical pair during the primary interaction of the metallocomplex with H₂O₂ and subsequent reaction between the radicals of the radical pair according to the radical substitution mechanism, which leads to the formation of the hydroxy derivatives of ferrocene and their cations. Sequential accumulation of OH substituents in the metallocomplex and the corresponding ferricinium cations caused a continuous shift of ABFC toward the long-wave region.     

Theoretical Study on Reactivity of Electron Transfer in Model—System of Oxidation of α—Amino Carbon—centered Radical by O2

Electron transfer reaction between a simplified model model molecule of α－amino carbon-centered radical and O2 has studied with ab initio calculations at the MP2/6-31 G^**//UHF/6-31 G^** level,The reactant complex and the ion pair complex have been optimized and employed to perform calculation of the reaction heat and the reorganization energy,Solvent effects have been considered by applyning the conductor-like screening model,Theoretical results show that the highly endothermic charge separation process ,in which one electron transfers from the α－amino carbon-centered radical to O2,so as to form an ion pair complex,is difficult to occur in gas-phase,By apply-ing an external electronic field to prepare the charge-locallized molecular orbitals,the charge-separated state has been obtained using the initial-guess-induced self-consistent field technique,The theoretical investigations indicate that the solvent effect in the process of the oxidation of α-animo carbon-centered radical by O2 is remarkable.From the rate constant estima-tion ,it can be predicted that the oxidation of the model donor molecule by O2 can proceed,but not very fast.A peroxyl radi-cal compound has been found to be a competitive intermediate in the oxidation process.     

Kinetics of heat release during the reaction ofn-decane with nitrogen dioxide in the liquid phase

The rates of heat release in the nitrogen dioxide—n-decane system at a molar ratio of nitrogen oxides ton-decane (β) from 2.4·10⁻³ to 3.1 and gaseous volumes per mole ofn-decane (V(g)) equal to 0.05–4.5 were studied in the 55.2–92.8 °C temperature range. The initial rate of the process is determined by the interaction of NO₂ withn-decane. The equilibrium constants of dissociation of N₂O₄ inn-decane and Henry's constants of NO₂ and N₂O₄ in ann-decane solution were determined by complex analysis of the thermodynamic equilibrium in the NO₂—n-decane system and dependences of the initial rates onV(g) and β. The experimentally observed self-acceleration of the process in the region of high β and lowT values was suggested to be due to the reaction of N₂O₄ with intermediate oxidation products. The rate constants of the reaction of NO₂ withn-decane were compared with analogous values determined in its mixtures with HNO₃ solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1789–1794, October, 1997.     

Disupersilylperoxo Radical Anion [tBu3SiOOSitBu3]⋅−: An Intermediate of Supersilanide Oxidation

In the oxidative process of the supersilanide anion [SitBu₃]^?, radical species are generated. The continuous wave (cw)‐EPR spectrum of the reaction solution of Na[SitBu₃] with O₂ revealed a signal, which could be characterized as disupersilylperoxo radical anion [tBu₃SiOOSitBu₃]^?? affected by sodium ions though ion‐pair formation. A mechanism is suggested for the oxidative process of supersilanide, which in a further step can be helpful in a better understanding of the oxidation process of isoelectronic phosphanes.     

Radiochemical oxidation of hydrazine in aqueous solutions containing oxygen

The chain mechanism of oxidation of hydrazine in aqueous solutions saturated with oxygen at pH > 7.5 was established. The yields of radiochemical decomposition of hydrazine increase with a decrease in the absorbed dose rate, an increase in the concentration of hydrazine, and the pH of the solution and attains hundreds of molecules per 100 eV of absorbed energy. It is hypothesized that the chain process includes a stage of formation of the N₂H₃ radical, its reaction with O₂, and the formation of O₂ ^– or N₂H₃O₂. The chain propagation reaction is due to the reaction of molecules of N₂H₄ with N₂H₃O₂ or O₂ ^–.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2450–2453, November, 1989.     

Kinetics, substrate selectivity, and mechanisms of alkane and alkylbenzene reactions with peroxynitrous acid in the gas phase and solution

Specific features of the kinetics of alkane and alkylbenzene oxidation with HOONO formed in the H₂O₂-NaNO₂ system (pH 4.27) are quantitatively explained assuming the simultaneous occurrence of reactions in the gas and liquid phases. A model of the kinetic distribution method is developed and verified that accounts for the equilibrium distribution of a substrate and a reagent between phases and their interaction in both phases. Relative rate constants for the oxidation ofn-alkanes (C₃-C₈), isobutane, cyclopentane, cyclohexane, benzene, and alkylbenzenes are measured over a wide range of the volume ratios of the gas and liquid phases (λ = V_g/V₁). Relative rate constants for the oxidation of alkanes in the gas phase and alkylbenzenes in gas and solution were determined. Similarity in substrate selectivities and kinetic isotope effects of the gasphase reactions of alkanes and arenes with peroxynitrous acid and^•OH radicals suggest that hydroxyl radical or the ˙OH...NO₂ radical pair is an active species in the gas phase. In solution, alkylbenzenes react nonselectively with HOONO, as well as with ˙OH radicals. In contrast to the liquid-phase oxidation of arenes, the liquidphase oxidation of all alkanes under study insignificantly contribute (5–15%) to the overall rate of the substrate consumption.     

Adduct ion formation by metal complexes under methane negative chemical ionization conditions

Negative chemical ionization mass spectrometry is used as a probe to examine reactions between hydrocarbon radicals and metal complexes in the gas phase. The methane negative chemical ionization mass spectra of 27 complexes of cobalt(II ), nickel(II ) and copper(II ) in the presence of O₄, O₂N₂ and N₄ donor atom sets are characterized by two dominant series of adduct ions of the form [M + C_nH_2n]^? and [M + C_nH_2n+1]^? at m/z values above the molecular ion, [M]^?. Insertion of the CH radical into the ligand followed by radical/radical recombination and electron capture is proposed as the major mechanism leading to the formation of [M + C_nH_2n]^? adduct ions. A second pathway involves ligand substitution by C_nH_2n+1 radicals concomitant with H elimination and electron capture. Oxidative addition at the metal followed by ionization is suggested as the principal pathway for the formation of [M + C_nH_2n+1]^? adduct ions.     

The Reaction of Peroxynitrite with Morpholine (Secondary Amines) Revisited: The Overlooked Hydroxylamine Formation

The reaction of peroxynitrite/peroxynitrous acid with morpholine as a model compound for secondary amines is reinvestigated in the absence and presence of carbon dioxide. The concentration‐ and pH‐dependent formation of N‐nitrosomorpholine and N‐nitromorpholine as reported in three previous papers ([25] [26] [14]) is basically confirmed. However, ¹³C‐NMR spectroscopic product analysis shows that, in the absence of CO₂, N‐hydroxymorpholine is, at pH ≥ 7, the major product of this reaction, even under anaerobic conditions. The formation of N‐hydroxymorpholine has been overlooked in the three cited papers. Additional (ring‐opened) oxidation products of morpholine are also detected. The data account for radical pathways for the formation of these products via intermediate morpholine‐derived aminyl and α‐aminoalkyl radicals. This is further supported by EPR‐spectrometric detection of morpholine‐derived nitroxide radicals, i.e., morpholin‐4‐yloxy radicals. N‐Nitrosomorpholine, however, is very likely formed by electrophilic attack of peroxynitrite‐derived N₂O₄. ¹⁵N‐CIDNP Experiments establish that, in the presence of CO₂, N‐nitro‐ and C‐nitromorpholine are generated by radical recombination. The present results are in full accord with a fractional (28 ± 2%) homolytic decay of peroxynitrite/peroxynitrous acid with release of free hydroxyl and nitrogen dioxide radicals.     

Isothermal soot oxidation experiments with intermediate gas change in a Perkin-Elmer TGA6

Two isothermal soot oxidation protocols were tested in a Perkin-Elmer TGA6: (1) the sample was heated under N₂ and then the reaction gas was introduced and (2) the sample was introduced after the empty furnace was heated under the reaction gas. The first protocol is common in soot oxidation studies, it gives a measure of the volatiles and is easier to handle, but as it is shown the determined reaction rate may be falsified by the O₂ concentration. Using gas analysis it was found that ∼2000 s are necessary for the complete gas change in the instrument. An instrument specific correction function involving the O₂ concentration and reaction order n with respect to O₂ was developed which allowed the correlation of the rates measured with both protocols.     

Kinetics of the formation of N2O in the catalytic oxidation of NH3 on Pt-Rh filament

The kinetics of the reactions involving the formation of N₂O in the catalytic oxidation of NH₃ have been studied over polycrystalline Pt-10% Rh filament in a static system, using a Fourier transform infrared spectrometer to monitor the partial pressures of NH₃ and N₂O. The sole formation of N₂O proceeds over the filament temperatures range of 250～350°C The reaction rate is of first order in NH₃ pressure and half order in O₂ pressure, and the rate equation can be written as v = K_app· PNH₃· PO₂^1/2. The apparent activation energy of the N₂O formation reaction from the temperature coefficient of the rate constants is found to be 25 kcal/mol. The interpretation of these results in terms of Eley-Rideal type mechanism has been presented. The rate-controlling step might be the reaction between gaseous ammonia molecules and the chemisorped oxygen atoms on the surface.     

Phenol Photonitration and Photonitrosation upon Nitrite Photolysis in basic solution

Nitrophenols have been detected in some Antarctic lakes, the water of which is basic and rich in nitrate, nitrite and other nutrients. Nitrate or nitrite photolysis could be a possible reaction to explain the presence of these compounds. This work presents evidence for the formation of 2-nitrophenol (2NP), 4-nitrophenol (4NP) and 4-nitrosophenol (4NOP) upon UV irradiation of phenol and nitrite in aerated basic solutions.

The pH dependence of the 2NP initial formation rate is different from those of 4NP and 4NOP. The dependence of the first mainly reflects the phenol/phenolate equilibrium, with phenol yielding 2NP at a higher rate than phenolate. In the case of 4NOP, the initial formation rate vs pH has a maximum at pH 9.5. The pH dependence of 4NOP formation rate suggests that three pathways are likely to operate: nitrosation of undissociated phenol by N₂O₃, prevailing at pH<8.7, nitrosation of phenolate by N₂O₃, prevailing in the pH interval 8.7–10.8, and reaction between phenoxyl radical and ^?NO, prevailing at pH>10.8. Phenol nitrosation by N₂O₃ is favoured when phenol is negatively charged (phenolate), but it is also disfavoured at alkaline pH values, owing to the depletion of N₂O₃ (the nitrosating agent) by basic hydrolysis. Differently from 2NP, the initial formation rate vs pH of 4NP is very similar to that of 4NOP, suggesting that 4NP may originate from the oxidation of 4NOP. Moreover, while in neutral and acidic solutions the formation rate of 2NP is slightly higher than that of 4NP, in the pH interval 8–12 the formation of 4NP is much more rapid than that of 2NP. This indicates that the pH of natural waters influences the ratio of nitroisomers.     

Li+- and Ag+-cationized per-O-acetyl- and Per-O-benzyl-α-D-thioglycosides: a collision-induced decomposition study

The collision-induced decompositions of the [M + Li]⁺ and [M + Ag]⁺ ions of per-O-acetyl- and per-O-benzyl-α-D -thioglycosides having phenyl sulphide, phenyl sulphoxide and phenyl sulphone as the aglycone moieties were studied. The [M + Li]⁺ ion of the acetyl derivative of the phenylthioglucoside shows loss of AcOLi, whereas its [M + Ag]⁺ ion shows elimination of PhSAg. Their sulphoxide and sulphone derivatives lose the C(1) and C(2) substituents to form the glucal under both Li⁺ and Ag⁺ cationization conditions. The corresponding benzyl derivatives do not show the loss of metal. The formation of glucal leads to ring fragmentation by retro-Diels-Alder reaction in the ring-activated benzyl derivatives.     

Estimation of the R-H bond energy from the activation energy for the reaction RH + O2 → R· + HO2·

Since the activation energy for the reaction RH + O₂ → R· + HO₂. is very close to its endothermicity, the R-H bond energy can be calculated from the activation energy for free radical formation by the reaction RH + O₂. The relation between E_i and Q_R–H was found empirically after measuring E_i by the method of inhibitors for the oxidation of cyclohexane, n? heptane, and toluene: The values of Q_R–H are calculated from these and earlier experimental data for five hydrocarbons, five phenols, and four aromatic amines.     

Effect of acetonitrile on the catalytic decomposition of hydrogen peroxide by vanadium ions and conjugated oxidation of alkanes

The rate of hydrogen peroxide decomposition in acetonitrile in the presence of a vanadate anion and pyrazine-2-carboxylic acid decreases remarkably when alkane (cyclohexane, n-heptane, isooctane) is added to the reaction solution. The alkane added is oxidized by this system to alkyl hydroperoxide. This is explained by the fact that much more hydrogen peroxide molecules are consumed to acetonitrile oxidation with formation of the final products, which is suppressed considerably by additives of necessary amounts of alkane, than those consumed to the oxidation of cyclohexane to form cyclohexyl hydroperoxide. In an organic solvent, H₂O₂ decomposes in a non-chain radical process.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2231–2234, October, 2004     

Si-Containing Amides of Phosphoric Acid

The first representative of the N-silylmethylamides of phosphoric acid O=P[NMe(CH₂SiMe _n (OEt)_3-n ]₃ have been synthesized by interaction of MeNHCH₂SiMe _n (OEt)_3-n (n = 2, 3) with POCl₃. The interaction of the N,N′,N″-trimethyl-N,N′,N″-tris[(ethoxydimethyl- silyl)methyl]triamide phosphoric acid with BF₃·Et₂O or BCl₃ results in the formation of the N,N′,N″-trimethyl-N,N′,N″-tris[(fluorodimethyl-silyl)methyl]triamide phosphoric acid or N,N′,N″-trimethyl-N,N′,N″-tris[(chlorodimethylsilyl)methyl]triamide phosphoric acid. NMR data show on the tetracoordinate state of silicon in these products.     

Hydroperoxide Oxidation of Difficult-to-Oxidize Substrates: An Unprecedented C–C Bond Cleavage in Alkanes and the Oxidation of Molecular Nitrogen

In the V^(V)H₂O₂/AcOH system, C₅–C₂₀ n-alkanes, isooctane, and neohexane undergo oxidation to ketones and alcohols; the oxidation products of branched alkanes are indicative of a C–C bond cleavage in these substrates. A concept is developed, according to which the peroxo complexes of vanadium(V) are responsible for alkane oxidation. These complexes can transfer the oxygen atom or the O^+· radical cation to a substrate. The formation of nitrous oxide was found in the oxidation of molecular nitrogen in the H₂O₂/V^(V)/CF₃COOH system.     

Evaluation of dipole moment of hydrogen bonded complexes of long-chain alcohols with acetic acid and chlorobenzene

The formation of 1 : 1 complexes involving n-pentanol-acetic acid, n-hexanol-chlorobenzene and n-heptanol-chlorobenzene in a non-polar solvent tetrachlormethane have been studied at the frequency of 455 kHz and at the temperature of 303.16 K. The dipole moment of 1 : 1 complex μ _ab , molar polarisation P_ab , and interaction dipole moment Δμ in all these ternary mixtures have been evaluated. The results indicate that complexation is due to polarisation effect.     

Formation of a promazine radical and promazine 5‐oxide in the reaction of promazine with hydrogen peroxide: Mechanistic insight from kinetic and EPR measurements

The kinetics of the oxidation of promazine (PMZ) by hydrogen peroxide was studied in the presence of a large excess of H₂O₂ in acidic chloride media using UV–vis spectroscopy. The reaction proceeds via two consecutive steps. In the first step, oxidation leads to formation of a promazine radical. In the second step, the promazine radical is oxidized to promazine 5‐oxide. Electron paramagnetic resonance spectroscopy (EPR) results provide clear evidence for the formation of an intermediate promazine radical. Linear dependences of the pseudo‐first‐order rate constants (k₁ and k₂) on [H₂O₂] with a nonzero intercept were established for the first and the second process, respectively. The rate of the first stage of the reaction increased slightly with increasing concentration of O₂, indicating the role of the OH^? radicals on the redox process, which are transformed into the Cl radicals. The mechanism of the overall reaction is discussed on the basis of all these kinetic measurements. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 1–9, 2010     

Quenching of Singlet Oxygen by Tertiary Aliphatic Amines. Structural Effects on Rates and Products

A kinetic and product study of the reaction of a series of α‐methyl‐substituted N‐methylpiperidines with thermally generated ¹O₂ in MeCN was carried out. It was found that as the number of α‐methyl groups (Me in α‐position relative to the N‐atom) increases, the rate of ¹O₂ quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N‐demethylation products and N‐formyl derivatives. The same trend was observed for the ratio between N‐demethylation and formation of the N‐formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme 1 where an exciplex is first formed that by a H‐atom transfer process produces an α‐amino‐substituted C‐radical. The latter forms the product of N‐demethylation by one electron oxidation, or affords the N‐formyl derivative by radical coupling (Scheme 1). Similar results were obtained with N,N‐dimethylcyclohexanamine. However, this ‘acyclic’ amine exhibited behaviors quite distinct from those of the N‐methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio.     

Si-Containing Amides of Phosphoric Acid

Summary. The first representative of the N-silylmethylamides of phosphoric acid O=P[NMe(CH₂SiMe _n (OEt)_3-n ]₃ have been synthesized by interaction of MeNHCH₂SiMe _n (OEt)_3-n (n = 2, 3) with POCl₃. The interaction of the N,N′,N″-trimethyl-N,N′,N″-tris[(ethoxydimethyl- silyl)methyl]triamide phosphoric acid with BF₃·Et₂O or BCl₃ results in the formation of the N,N′,N″-trimethyl-N,N′,N″-tris[(fluorodimethyl-silyl)methyl]triamide phosphoric acid or N,N′,N″-trimethyl-N,N′,N″-tris[(chlorodimethylsilyl)methyl]triamide phosphoric acid. NMR data show on the tetracoordinate state of silicon in these products. Professor Vadim Aleksandrovich Pestunovich, our chief, teacher and friend died on July 4^th, 2004