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.     

Bestimmung der Stabilit?tskonstanten von mehrkernigen Komplexen mit Hilfe einer spektrophotometrischen Methode

Zusammenfassung Es wurde eine allgemeine Gleichung für die Berechnung der Stabilitätskonstante von Komplexen L _mH_iM_nZ_j (Z=OH^–, usw.) abgeleitet und für Maximumbedingungen der Jobschen Kurve die Schwarzenbachsche graphische Methode so modifiziert, daß sie die allgemeine Bestimmung der Zusammensetzung und Stabilität von Komplexen L _mH_iM_nZ_j ermöglicht.

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Summary A general equation has been derived for the calculation of stability constants of complexes L _mH_iM_nZ_j (Z=OH^–, etc.). The graphic method of Schwarzenbach has been modified for maximum conditions of Job's curve in order to make possible the general determination of the composition and stability of complexes L _mH_iM_nZ_j.

     

Magnetische Untersuchungen an Komplexen von La(III), Pr(III) und Nd(III) mitSchiffschen Basen

Specific magnetic susceptibilities (_s) of several newly synthesized chelates of some of the lanthanons [La(III), Pr(III) and Nd(III)] are reported. These derivatives are of the general type,Ln(O-i-C₃H₇)_3–n (C₆H₅CHNRO) _n [where,Ln=La(III), Pr(III) or Nd(III);n=1 or 2 and R=CH₂CH₂, CH₂CHCH₃ or C₆H₄] and have been prepared by the reaction of the alkoxides of the lanthanons withSchiff bases such as benzylidene-2-hydroxyethylamine (C₆H₅CHNCH₂CH₂OH), benzylidene-2-hydroxy-n-propylamine (C₆H₅CHNCH₂CHOHCH₃) and benzylidene-o-aminophenol (C₆H₅CHNC₆H₄OH) in different molar relations in dry benzene.The resulting crystalline derivatives are non-volatile, light to deep yellow or blackish in colour. These tend to polymerize on keeping as shown by their insoluble nature and higher melting points, the polymerisation possibly occurring by the intermolecular coordination through oxygen atoms as reported earlier¹.UsingGouy method², the bis-isopropoxy mono-Schiff base and mono-isopropoxy bis-Schiff base complexes of La(III) have been shown to be diamagnetic, with _s values being in the range of –0.32 to –0.45×10^–6 and –0.39 to –0.55×10^–6 c.g.s. units at 305 K respectively.In the remaining derivatives, Pr(O-i-C₃H₇)_3–n (C₆H₅CH NRO) _n and Nd(O-i-C₃H₇)_3–n (C₆H₅CHNRO) _n (where,n=1 or 2 and R=CH₂CH₂, CH₂CHCH₃ or C₆H₄) the magnetic moment values range between 3.25 to 3.32 and 3.30 to 3.33 _B respectively indicating their paramagnetic nature.     

A di-μ-oxomolybdenum(V) complex of 6-acetonylisoxanthopterin,undergoing oxygen atom transfer with dimethyl sulphoxide

The new compound, Na[(Mo₂ ^VO₄)(pte)(OMe)(MeOH)₂] (pte = anion of 6-acetonylisoxanthopterin), has been prepared using the redox non-innocent title ligand in MeOH–H₂O, and characterized by elemental analysis and physico-chemical methods including e.s.m.s., i.r., u.v.–vis. and ¹H-n.m.r. spectra. Rate constants data (1.4 × 10^–3 s^–1 at 300 K) for its oxygen atom transfer with dimethyl sulphoxide tally with those of synthetic analogue systems reported earlier by different authors. The negative activation entropy (–206.3 J mol^–1 deg^–1) is consistent with an associative mechanism for this reaction.     

Properties of Adsorbed Oxygen Forms on a Defective Ag(111) Surface. DFT Analysis

A cluster model of an Ag12–3O (AS_V) adsorption center using layered silver oxide as a prototype is proposed. The model includes a cation vacancy V on the Ag(111) surface and oxide type subsurface oxygen atoms O_ox. Density functional theory (DFT) (B3LYP/LANL1MB approximation) is used to analyze the electronic structure of AS_V and oxygen adsorption on this center, AS_V+O AS–O. As shown by the calculations, the adsorbed oxygen is associated with the subsurface oxygen atoms O_ss to form structures similar to metal ozonides — Ag–O_ss–O_ep–O_ss–Ag–O_ox–Ag, containing electrophilic oxygen O_ep along with the oxide oxygen O_ox. The optical spectra of the AS_V and AS–O centers were calculated by the configuration interaction method with single excitations (CIS). For AS_V, the most intense absorption bands were obtained in the region 500-700 nm. Oxygen association is accompanied by a sharp decrease in spectrum intensity in the range 600-700 nm and an increase in the intensity of the peak at 500 nm. Vibration frequencies and (IR) intensities were determined for the AS_V and AS–O centers. The AS_V center exhibits a characteristic spectrum in the region 350-500 cm^–1, which corresponds to the frequency spectrum of the surface oxide Ag₂O. For associated oxygen forms (AS–O center), the calculations predict additional peaks around 980, 640 and 230 cm^–1. These peaks are due to the vibrations of the O_ss–O_ep–O_ss structural unit, stabilized at the cation vacancy.     

Synthesis and Properties of the Mixed Hydrated Oxides V2?yWyO5 + δ < eqid2 > nH2O

Compounds of the general formula V_{2 − y}W_yO_{5 + δ} < eqid3 > nH₂O (0 < y ≤ 0.25) with the layered structure of polyvanadic acid V₂O₅ < eqid4 > nH₂O (H₂V₁₂O_{31 − δ} < eqid5 > nH₂O) have been prepared from peroxide solutions using the sol–gel process. The samples contain up to 5–8 wt% vanadium (IV). The water content changes within the range of 0.7 ≤ n ≤ 1.5 in depending on tungsten concentration. The V_{2 − y}W_yO_{5 + δ} < eqid6 > nH₂O (y ≤ 0.125) form the thin films described an interlayer distance of 11.60 ± 0.05 Å. The thermal properties, IR, and X-ray photoelectron spectra of the compounds synthesized have been studied. The thermal stability of the phases increases with the rising of tungsten content. The dehydration finishes with the forming solid solution V_2−yW_yO₅ and WO₃. The electrical conductivity of V_2−yW_yO_{5 + δ} < eqid7 > nH₂O (0 < y ≤ 0.25) powders was measured between 293 and 473 K at a relative humidity of 12%. The activation energy of conduction is independent upon the W content and equals 0.22–0.24 eV. Partial substitution of vanadium for tungsten was found to reduce the conductivity of the phases. The conductivity of the films increases with the increasing of relative air humidity and is governed by proton diffusion across the V-O-W layers.     

Effect of adding H2SO4 and NaCl TO palladium-containing catalysts on the results of methane oxidation at 220°C

A study has been made of the interaction of methane at 220°C with silica gel-supported complexes of palladium(II), Na_n H_9-n[PMo₆V₆O₄₀], H₉[PMo₆V₆O₄₀], H₃[PMo₁₂O₄₀], NaCl, and with added sulfuric acid. Competition between electrophilic and chloride pathways is examined. Additions of Na⁺ and Cl^– direct the reaction along the chloride pathway, leading to the formation of CH₃Cl. Without NaCl, the electrophilic mechanism is realized, the main product of which is CO₂.L. M. Litvinenko Institute of Physical-Organic Chemistry and Coal Tar Chemistry, National Academy of Sciences of the Ukraine, 70 R. Luxembourg Street, Donetsk 340114, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 2, pp. 92–96, March–April, 1996. Original article submitted June 30, 1995.     

Electromigration of carrier-free radionuclides

Dependences of La(III) overall ion mobilities on concentrations of ox^2– and tart^2– anions of oxalic and tartaric acid in aqueous solutions of 0.01 overall ionic strength and temperature 298.1 K were obtained by direct measurements of electromigration of carrierfree¹⁴⁰La-lanthanum(III). Concentration stability constants K_n and individual ion mobilities u _i ^o of oxalate and tartrate complexes of La(III) have been calculated for nitrate and perchlorate electrolytes, respectively: [La(ox)]⁺, lg K₁=5.63(9), u⁰[La(ox)]⁺=1.95(15)·10^–4 cm²·s^–1·V^–1; [la(ox)₂]^–, lg K₂=4.05(19) u⁰[La(ox)₂]^–=–1.76(20)·10^–4 cm²·s^–1·V^–1; [La(tart)]⁺, lg K₁=4.40(5), u⁰[La(tart)]⁺=+1.99(18)·10^–4 cm²·s^–1·V^–1.Results are compared with literature data. Additional, limiting individual La³⁺ ion mobility was calculated: =+6.9(1)·10^–4 cm²·s^–1·V^–1 for pure water at 298.1 K.     

掺Ni钒磷氧化物催化剂的合成和表征

以VOPO4.2H2O为原料制备了钒磷氧化物催化剂,考察了镍掺杂(1%,2%和5%)对该催化剂的影响.低掺杂量的Ni明显提高了活性晶格氧物种O-的数量,降低了V5 和V4 相的还原峰温.粉末X射线衍射、程序升温还原和化学分析结果表明,高掺杂量的Ni促使V5 物相生成并抑制V4 物相出现.高含量与V5 相关的氧物种会降低正丁烷的转化率,但会提高马来酸酐的选择性.     

Interaction between a Decahydro-closo-Decaborate(2–) Anion and Aliphatic Carboxylic Acids

Interaction between a closo-decaborate anion B₁₀H^2– ₁₀and carboxylic acids RCOOH (R = H, CH₃, C₂H₅, iso-C₃H₇, C₄H₉) is studied. The mono-, di- tri- and tetrasubstituted products B₁₀H_{10 – n} (OCOR)^2– _n are formed in sequence with the temperature growth. The reaction follows an essentially regioselective mechanism: only one of all possible isomers forms at every stage of the process. The respective hydroxy-closo-decaborates B₁₀H_{10 – n} (OH)^2– _n were prepared by alkaline hydrolysis in aqueous and nonaqueous solutions. All the compounds were identified by chemical analysis and ¹¹B NMR and IR spectroscopy. The crystal structure of [Pb(Bipy)(DMF)(B₁₀H₉OH)] · DMF was determined by X-ray diffraction.     

Surface and Subsurface Oxygen on Platinum in a 0.5 M H2SO4 Solution

The oxidation of polycrystalline platinum in 0.5 M H₂SO₄ is studied by cyclic voltammetry at potential scan rates of 5–500 mV s^–1 while varying the potential cycling range. The scheme, which is proposed for explaining the observed acceleration and deceleration of oxygen sorption at 0.75–1.0 V, accounts for the presence of oxygen in the subsurface layers of platinum (O_ss) and the formation of a barrier layer comprising complexes O_ss–Pt _n –SO₄. Cycling platinum secures certain steady-state contents of O_ss at 0.01–1.35 V. In an anodic scan, O_ss accumulates at E > 0.85 V (slow post-electrochemical stage) due to exchange of platinum and oxygen atom sites. In a cathodic scan, the desorption of most oxygen gives way to the adsorption of anions, which prevent residual O_ss from appearing on the surface. The residual O_ss disappears at E < 0.1 V after a sufficiently complete desorption of anions and the destruction of stable complexes O_ss–Pt _n –SO₄. Varying the potential cyclic limit leads, after a delay, to other steady-state O_ss contents.     

Thermodynamic study of perfluorohexane + ether mixtures: VLE, LLE, and H

Vapour–liquid equilibria (VLE), liquid–liquid equilibria (LLE), and excess enthalpies (H^E) of binary mixtures of perfluoro-n-hexane plus an ether (diethyl, dipropyl, dibutyl, butyl methyl, and butyl ethyl ether), have been determined using a head-space gas-chromatographic technique, a turbidimetric apparatus, and a heat-flow calorimeter, respectively. A recently designed titration technique and calculation procedure have been used to obtain H^E from heats of solution. The observed liquid–liquid coexistence curves have been compared with those predicted by the activity coefficients γ_i and their temperature dependence. All mixtures are strongly endothermic (H^E > 0) and show large positive deviations from ideality (G^E > 0), which increase with the size of the ether. Molecular interactions have been examined by calculating and discussing solvation functions and Kirkwood–Buff (KB) integrals. Perfluorohexane proved to be an inert molecule that interacts with ethers more weakly than hexane.     

The EDTA complexes of astatine

Using the electromigration method the monopositive astatine ion has been shown to form EDTA [H₄L] complexes in 0.1M NaClO₄ solution at pH=3–10. The ion mobility of the AtL^3– complex is 5.60/23/x10^–4 cm².V^–1.s^–1.     

Synthesis and study of binuclear vanadyl complexes with acyldihydrazones of salicylaldehyde and dicarboxylic acids

The binuclear vanadyl(ii) complexes [(VO)₂·2Py·2EtOH]·mH₂O with acyldihydrazones of salicylaldehyde (H₄L) and dicarboxylic acids were synthesized and studied. In these complexes, two chelate vanadyl(ii) complexes with the tridentate bicyclic ligands are linked to each other by the polymethylene bridges —(CH₂) _n — of different lengths varying from one to four units. The ESR spectra of solutions of these complexes, unlike those of analogous copper(ii) complexes, have an isotropic signal with an eight-line hyperfine structure (g = 1.972, a _V = 93·10^–4 cm^–1) typical of monomeric vanadyl complexes, which indicates that no exchange interactions occur between the paramagnetic centers through the polymethylene chain.     

Diffuse reflectance spectra of iron(III) vanadates

The electronic spectra of solid iron(III) vanadates FeVO₄ and Fe₂V₄O₁₃ were investigated by the diffuse reflectance technique in the spectral range 12 500–50 000 cm⁻¹. The spectra of investigated vanadates contain 2–3 intensive CT bands in the UV region and two lowest energy d–d bands in the 12 000–22 000 cm⁻¹ range. The presence of the weak bands for FeVO₄ and Fe₂V₄O₁₃ at 16 500 cm⁻¹ and 20 500 cm⁻¹ points to the lattice deffects (oxygen deficiency and the presence of the V⁴⁺ ions) in the structure of investigated vanadates.     

The interpretation of the stability of aromatic hydrocarbon ions by valence bond theory

Hückel theory predicts the experimentally observed stabilities of the cyclic polyene ions C _nH_n ^–, C_nH_n ⁺, n=3, 5, 7 (C ₃H₃ ^–stable, C ₃H₃ ^–unstable, etc.) correctly. This result can also be obtained by a simple valence bond calculation which takes into account only the lowest energy resonance structures. E. g. it turns out that C ₃H₃ ⁺should be a singlet ground state while C ₃H₃ ^– should be a triplet ground state. However, the stability cannot be explained by just counting the number of resonance structures.

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Zusammenfassung Es wird gezeigt, daß die Stabilitätsverhältnisse der Cyclopolyenionen C _nH_n ^–, C _nH_n ⁺, n=3, 5, 7 (C ₃H₃ ⁺stabil, C ₃H₃ ^– instabil, usw.), die nach der Hückeltheorie richtig erklärt werden, auch nach der VB-Methode vorhergesagt werden können. Dabei ist es ausreichend, nur die energetisch niedrigsten Resonanzstrukturen mit zu berücksichtigen. Es ergibt sich dann z. B., daß C ₃H₃ ⁺einen Singulett-Grundzustand besitzt, C ₃H₃ ^–dagegen einen Triplett-Grundzustand. Die Anzahl der möglichen Resonanzstrukturen erlaubt jedoch keinen Rückschluß auf die Stabilitätsverhältnisse.

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Résumé La théorie de Hückel prédit correctement les stabilités expérimentales des ions des cyciopolyènes C _nH_n ^–, C _nH_n ⁺, n=3, 5, 7 (C ₃H₃ ⁺stable, C ₃H₃ ^–instable, etc.). Ce résultat peut être obtenu aussi par un simple calcul au cadre de la méthode de la mésomérie, ne comprenant que les formules de plus basse énergie. Il en résulte, par exemple, que l'état fondamental du C ₃H₃ ⁺devrait être un singulet, celui de C ₃H₃ ^–un triplet. Cependant, on ne peut pas expliquer la stabilité en comptant le nombre des formules mésomères.

     

Hydrogenation of β-Keto Sulfones to β-Hydroxy Sulfones with Alkyl Aluminum Compounds: Structure of Intermediate Hydroalumination Products

β-Hydroxy sulfones are important in organic synthesis. The simplest method of β-hydroxy sulfones synthesis is the hydrogenation of β-keto sulfones. Herein, we report the reducing properties of alkyl aluminum compounds R₃Al (R = Et, i-Bu, n-Bu, t-Bu and n-Hex); i-Bu₂AlH; Et₂AlCl and EtAlCl₂ in the hydrogenation of β-keto sulfones. The compounds i-Bu₂AlH, i-Bu₃Al and Et₃Al are the at best reducing agents of β-keto sulfones to β-hydroxy sulfones. In reactions of β-keto sulfones with aluminum trialkyls, hydroalumination products with β-hydroxy sulfone ligands [R₂AlOC(C₆H₅)CH₂S(O)₂(p-R¹C₆H₄]_n [where n = 1,2; 2aa: R = i-Bu, R¹ = CH₃; 2ab: R = i-Bu, R¹ = Cl; 2ba: R = Et, R¹ = CH₃; 2bb: R = Et, R¹ = Cl] and {[Et₂AlOC(C₆H₅)CH₂S(O)₂(p-ClC₆H₄]∙Et₃Al}_n 3bb were obtained. These complexes in the solid state have a dimeric structure, while in solutions, they appear as equilibrium monomer–dimer mixtures. The hydrolysis of both the isolated 2aa, 2ab, 2ba, 2bb and 3bb and the postreaction mixtures quantitatively leads to pure racemic β-hydroxy sulfones. Hydroalumination reaction of β-keto sulfones with alkyl aluminum compounds and subsequent hydrolysis of the complexes is a simple and very efficient method of β-hydroxy sulfones synthesis.     

Limiting Partial Molar Volumes of Electrolytes in 2-Methyl-2-Butanol <Emphasis Type="Bold">+</Emphasis> Water Mixtures at 298.15 K

Partial molar volumes at infinite dilution, V⁰₂, of alkali–metal halides (LiCl, NaCl KCl RbCl CsCl, NaBr, KBr, KI), tetra-n-alkylammonium bromides, R₄NBr (R=Me, Et, n-Pr, n-Bu, n-Pen), NaBPh₄, and Ph₄PCl have been determined in binary solvent mixtures of water with 2-methyl-2-butanol covering the water-rich region and the alcohol-rich region at 298.15 K. V⁰₂ for alkali–metal halides show relatively little dependence on the solvent composition. However, in the case of hydrophobic electrolytes the observed effects are more pronounced. A good linear dependence between V⁰₂(R₄NBr) and the molecular weight of the tetra-n-alkylammonium cation is found. Limiting single-ion volumes have been obtained using the assumption that V⁰(Ph₄P⁺)–V⁰(BPh^–₄)=2.0 cm³-mol^–1. The trends in the single-ion volumes are discussed in both solvent regions.     

The Complexes of Holmium with Methylenediphosphonate and 1-Hydroxyethylidenephosphonate

The composition and stability of holmium methylenediphosphonate (MDP) and 1-hydroxyethylidenephosphonate (HEDP) complexes were studied by potentiometric titration methods in 0.1M NaCl at 25 °C. It was found that besides L^4– anions the protonated H _n L^(4–n)– species (n = 1–3 for MDP and n = 1–4 for HEDP) are present in the pH region 3 to 10. The presence of the undissociated acids (H₄L) has not been unambiguously proved for MDP. The complexes of the composition HoH _n L (n varies from 1 to –2 for MDP and from 1 to –1 for HEDP) have been found if the concentration of the ligand is higher than the concentration of holmium. The protonation constants of both acids and the stability constants of the complexes discussed were determined and the comparison with literature data of analogical complexes of other lanthanides was performed.     

Cyclopalladation of mono-, di- and tribenzylamine by palladium(II) acetate: Influence of bulkiness around the nitrogen atom of benzylamine upon internal metallation

Cyclopalladation of mono-, di- and tribenzylamine has been investigated by reacting the corresponding amines with an equimolar amount of palladium(II) acetate (reaction i), or by heating the corresponding bis-amine complexes [Pd(O₂CMe)₂{(PhCH₂)_nNH_3−n}₂] (n=1, 2) (reaction ii). By the reaction i, all the three amines undergo cyclopalladation. However, in the case of the reaction ii, only the dibenzylamine complex [Pd(O₂CMe)₂{(PhCH₂)₂NH}₂] has been converted into a cyclopalladated complex. The reactivity of the three benzylamines towards cyclopalladation has been discussed in terms of the co-ordinating ability influenced by the bulkiness around the nitrogen atom. Temperature-dependent ¹H-NMR spectra are observed for mononuclear cyclopalladated complexes [Pd(O₂CMe){C₆H₄CH₂N(CH₂Ph)₂–C¹, N}L] (L=PPh₃, AsPh₃) and are attributed to the dissociation of the nitrogen atom in the cyclopalladated chelate ring. A heteroleptic bis-cyclopalladated complex [Pd[C₆H₄CH₂N(CH₂Ph)₂–C¹, N](C₆H₄CH₂NMe₂–C¹, N)] has also been prepared. X-ray crystallographic studies on [{Pd(O₂CMe)[C₆H₄CH₂N(CH₂Ph)₂–C¹, N]}₂] and [Pd[C₆H₄CH₂N(CH₂Ph)₂–C¹, N](C₆H₄CH₂NMe₂–C¹, N)] have been reported.