Kinetics of the aromatic hydroxylation with permonophosphoric acid

Oxidation of phenol, anisole and toluene with permonophosphoric acid in acetonitrile or water gives the corresponding ortho and para hydroxylated aromatics (HO-C₆H₄-X, X = OH, OMe, Me). The observed ortho :para ratio in a solvent acetonitrile are as follows: 5·0 with phenol, 3·5 with anisole and 2·0 with toluene. The oxidation rates for phenol and anisole in acetonitrile are expressed as: v = k″[ArH][H₃PO₅]²h_o, where h_o is the Hammett's acidity function and ArH is phenol or anisole. A mechanism involving a rate-determining attack of protonated dimeric perphosphoric acid 4 on aromatic carbon is presented and discussed.     

Kinetics and mechanism of aromatic electrophilic substitution reactions: VII. Temperature dependence of substrate selectivity of methylbenzene hydroxylation in the system H2O2-H2SO4

The relative rates of the hydroxylation of toluene,ortho-, meta-, andpara-xylenes, mesitylene, and pseudocumene are measured by the kinetic distribution method in the H₂O₂-H₂SO₄ (70.0 wt %) system at 15 to 55°C. The activation entropies correlate with the basicities of arenes and the activation enthalpies correlate with both the basicities and ionization potentials of ArH. Substrate selectivity is described with a high accuracy by the general equation with three variables (basicity, ionization potentials, and temperature) and implies the compensation effect between changes in standard entropies and enthalpies for the basicity constants of ArH. The structure of the transition state of the slow step of hydroxylation is intermediate between the structure of a charge-transfer complex and that of a σ-complex.     

Kinetics and reaction mechanism of phenol hydroxylation catalyzed by La-Cu<Subscript>4</Subscript>FeAlCO<Subscript>3</Subscript>

The present work synthesizes La-Cu₄FeAICO₃ catalyst under microwave irradiation and characterizes its structure using XRD and IR techniques. The results show that the obtained La-Cu₄FeAICO₃ has a hydrotalcite structure. In the phenol hydroxylation with H₂O₂ catalyzed by La-Cu₄FeAICO₃, the effects of reaction time and phenol/H₂O₂ molar ratio on the phenol hydroxylation, and relationships between the initial hydroxylation rate with concentration of the catalyst, phenol, H₂O₂ and reaction temperature are also investigated in details. It is shown the phenol conversion can reach 50.09% (mol percent) in the phenol hydroxylation catalyzed by La-Cu₄FeAICO₃, under the reaction conditions of the molar ratio of phenol/H₂O₂1/2, the amount ratio of phenol/catalyst 20, reaction temperature 343 K, reaction time 120 min, 10 ml_ distilled water as solvent. Moreover, a kinetic equation of v = k[La-Cu₄FeAlCO₃][C₆H₅OH][H₂O₂]. and the activation energy of E _a=58.37 kJ/mol are obtained according to the kinetic studies. Due to the fact that the HO-Cu⁺-OH species are detected in La-Cu₄FeAICO₃/H₂O₂ system by XPS, the new mechanism about the generation of hydroxyl free radicals in the phenol hydroxylation is proposed, which is supposed that HO-Cu⁺-OH species are transition state in this reaction.     

First steps of the reactions of alkanes and arenes with adamantyl cations in sulfuric acid in comparison with other reagents

Solutions of 1-adamantanol in sulfuric acid at T < 100 °C interact with alkanes (RH, [H₂SO₄] > 85%) and arenes (ArH, [H₂SO₄] > 59%). The data on the kinetics, kinetic isotope effect (KIE), effects of the structure of RH and ArH and acidity of the medium, and the observation of 1,4-cis-dimethylcyclohexane isomerization indicate that adamanyl cations (Ad⁺) serve as reactive species. In the reactions with alkanes, the Ad⁺ cation abstracts the hydride ion from RH in the rate-determining step. Compensation dependences appear between the activaion parameters for the KIE and “effect 5/6” (ratio of the rate constants for the C–H bond cleavage in cyclopentane and cyclohexane) in the reactions of cycloalkanes with Ad⁺ and other electrophilic reagents, such as “anthracene” (An₂)H⁺ and hydroxymethyl (CH₂OH)⁺ cations and Hg^II ions, including the points of the lower selectivity limit (k _H/k _D) = 1.4, (“5/6”) = 1. In the reactions with the Ad⁺ cation, the bond selectivity 3⁰: 2⁰ of alkanes is higher, while 2⁰: 2⁰ is lower compared to other reagents. In the first case, the selectivity is probably determined predominantly by the energies of the cleaved C–H bonds, whereas in the second case it is determined by steric hindrances. Judging by the kinetic and selectivity data in the series benzene—toluene—o-xylene—m-xylene and the absence of the reaction with p-xylene, mesitylene, and pseudocumene, it can be concluded that the main contribution to the Ad⁺ + ArH interaction is made by adamantylation to the para- and meta-positions of the benzene ring, whereas the ortho-positions are inaccessible to the attack because of steric hindrances. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1581–1596, August, 2008.     

Steric mode of enzymic hydroxylation at primary carbon atoms: Hydroxylation of (1R)- and (1S)-[1-3H, 2H, 1H][1-14C]-octanes by Pseudomonas Oleovorans

(1R)- and (1S) [1-³H, ²H, ¹H]-octanes and mixed with [1-¹⁴C]-octane, were synthesized. The mixed samples were incubated with homogenats of P. oleovorans strain TF4-1L and the biosynthesized mixtures of octanols isolated. It was shown that mainly the achiral termini [-C¹H₃] were hydroxylated and that chiral methyls were oxygenated to the extent of 20–30%. In all instances the products derived from hydroxylation at the chiral methyls [-C-³H, ²H, ¹H] were mixtures of (1R)- and (1S)-octanols, the major component of which was the alcohol obtained by displacement of ¹H. The results indicate that hydroxylation proceeded with a normal isotope effect k_h>k_d>k_t. The amount of (1R)-octanol in the mixtures of octanols derived from (1R)- and (1S)-octane was determined. It was found that the C-1 hydroxylation of octane proceeded with retention, i.e. the incoming hydroxyl assumed the orientation of the displaced hydrogen (or isotopic hydrogen) atom.     

Electrochemical Hydroxylation of Arenes Catalyzed by a Keggin Polyoxometalate with a Cobalt(IV) Heteroatom

The sustainable, selective direct hydroxylation of arenes, such as benzene to phenol, is an important research challenge. An electrocatalytic transformation using formic acid to oxidize benzene and its halogenated derivatives to selectively yield aryl formates, which are easily hydrolyzed by water to yield the corresponding phenols, is presented. The formylation reaction occurs on a Pt anode in the presence of [Co^IIIW₁₂O₄₀]^5? as a catalyst and lithium formate as an electrolyte via formation of a formyloxyl radical as the reactive species, which was trapped by a BMPO spin trap and identified by EPR. Hydrogen was formed at the Pt cathode. The sum transformation is ArH+H₂O→ArOH+H₂. Non‐optimized reaction conditions showed a Faradaic efficiency of 75 % and selective formation of the mono‐oxidized product in a 35 % yield. Decomposition of formic acid into CO₂ and H₂ is a side‐reaction.     

Tetrahedral intermediates 4. The effect of chloro-substituents on the kinetics of the breakdown of hemiorthoesters

1-Hydroxy-2-chloromethyl-1,3-dioxolane (4) and 1-hydroxy-2-dichloromethyl-1, 3-dioxolane (5) have been detected as intermediates by¹H NMR spectroscopy in the hydration of respectively 2-chloromethylene-1, 3-dioxolane and 2-dichloromethylene-1, 3-dioxolane in aqueous acetonitrile. The kinetics of the breakdown of (4) and (5) into ethylene glycol monochloroacetate and monodichloroacetate have been studied by uv spectroscopy and values ofk_H+,k_HO-, andk_H2O evaluated. It was found that the introduction of chlorosubstituents into 2-hydroxy-2-methyl-1, 3-dioxolane caused a decrease ink_H+ and increase ink_H2O- and little change ink_H2Ofor its breakdown. The mechanisms of these reactions are discussed. Present     

Catalysis by HBr in the bromination of o-xylene in acetic acid

Hydrogen bromide is known to inhibit the bromination of aromatic substrates (ArH), either by fixing up bromine as HBr₃ or ArH as ArH · HBr. However, there is catalysis by HBr in the bromination of mesitylene in acetic acid. The bromination of o-xylene in acetic acid in the dark is found to be autocatalytic, and the reaction is overall third order, first order in o-xylene with the orders in Br₂ and HBr depending on the concentrations. A composite rate expression involving Br₂ and HBr as electrophiles has been proposed and verified using iodine bromide as a catalyst where the orders are one in each of the reactants, irrespective of the concentrations used.     

Über die Si-N-bindung: XLI. Kinetische untersuchungen zur hydrolyse von trimethylsilylurethanen des typs Me3Si(p-XC6H4)NCOOEt

Hydrolysis reactions of silylurethanes Me₃Si(p-XC₆H₄)NCOOEt (I) with X = Cl, H or Me in aqueous buffer solutions, with pH values from 1.94 to 10.00 were studied.The catalytic rate constants for the acid and base catalysed reactions and for the “non-catalysed” reaction k(H₃O⁺), k(CH₃COO^?), k(H₂PO₄^?), k(HPO₄^2?), k(NH₃), k(OH^?) and k₀ were evaluated from the pseudo first-order rate constants k_exp determined by UV spectroscopy.The Brönsted coefficients for the base-catalysed reactions were obtained from the catalytic rate constants found and the known constants of dissociation K(HB⁺).The ρ values of the reactions could be derived from the σ constants given by Jaffé.The kientical results obtained are interpreted mechanistically and are believed to also have model character for other nucleophilic substitution reactions with silicon compounds.     

Iron Incorporated Mesoporous Molecular Sieves Synthesized by a Microwave-Hydrothermal Process and Their Application in Catalytic Oxidation

Fe-FSM-16 and Fe-containing mesoporous materials (Fe-JLU-15) prepared by using semifluorinated surfactant as a template, have been synthesized by microwave-hydrothermal (M-H) process and characterized by several spectroscopic techniques. The catalytic activity of these materials was tested for the phenol hydroxylation and wet phenol oxidation with H₂O₂ under mild reaction conditions. The effect of pH, H₂O₂/PhOH molar ratio and stability of the catalyst on the oxidation process was also investigated. Phenol oxidation and H₂O₂ decomposition show that the Fe-JLU-15 is more active than Fe-FSM-16 and more stable in aqueous solution. The total amount of dissolved iron is less than 5 wt% of the iron initially contained in the catalyst. In phenol hydroxylation, these two solids can effectively catalyze the phenol hydroxylation. Catechol and hydroquinone were observed as the major products, with a difference in the product distribution for these solids. The Fe-JLU-15 has a high selectivity for catechol (63.5 % phenol conversion, CAT/HQ = 2.7) while the Fe-FSM-16 shows a high selectivity for hydroquinone (56.8 % phenol conversion, CAT/HQ < 1) under the same reaction conditions.     

Synthesis and anhydrous proton conductivity of poly(5-vinyltetrazole) prepared by free radical polymerization

5-Vinyltetrazole (VT)-based polymer is mainly produced by ‘click chemistry’ from polyacrylonitrile due to the unavailability of 5-vinyltetrazole monomer, which usually produces copolymers of VT and acrylonitrile rather than pure poly(5-vinyltetrazole) (PVT). In present work, VT was synthesized from 5-(2-chloroethyl)tetrazole via dehydrochlorination. A series of PVT with different molecular weight were synthesized by normal free radical polymerization. The chemical structures of VT and PVT were characterized by ¹H NMR and FTIR. PVT without any doped acid exhibits certain proton conductivity at higher temperature and anhydrous state. The proton conductivity of PVT decreases at least 2 orders of magnitude after methylation of tetrazole. PVT and PVT/H₃PO₄ composite membranes are thermally stable up to 200 °C. The glass transition temperature (T_g) of PVT/xH₃PO₄ composite membranes is shifted from 90 °C for x = 0.5 to 55 °C for x = 1. The temperature dependence of DC conductivity for pure PVT exhibits a simple Arrhenius behavior in the temperature range of 90–160 °C, while PVT/xH₃PO₄ composite membranes with higher H₃PO₄ concentration can be fitted by Vogel–Tamman–Fulcher (VTF) equation. PVT/1.0H₃PO₄ exhibits an anhydrous proton conductivity of 3.05 × 10⁻³ at 110 °C. The transmission of the PVT/xH₃PO₄ composite membrane is above 85% in the wavelength of visible light and changes little with acid contents. Thus, PVT/xH₃PO₄ composite membranes have potential applications not only in intermediate temperature fuel cells but also in solid electrochromic device.     

Synthesis and characterization of new strontium 4-carboxyphenylphosphonates

Several new strontium 4-carboxyphenylphosphonates, i.e., two modifications of Sr(HOOCC₆H₄PO₃H)₂, SrH(OOCC₆H₄PO₃)·H₂O, Sr₃(OOCC₆H₄PO₃)₂·4H₂O and Sr₃(OOCC₆H₄PO₃)₂·5.7H₂O were prepared and characterized by elemental analysis, thermogravimetry, X-ray powder diffraction and infrared spectroscopy. It was found that the compositions of these compounds depend on the acidity of the reaction medium. In addition, the presented compounds are interconvertible in dependence on pH. The position of the acid hydrogen atom in SrH(OOCC₆H₄PO₃)·H₂O was determined from the IR spectra of the studied compounds.The structure of the β modification of Sr(HOOCC₆H₄PO₃H)₂ was solved from its X-ray powder diffraction pattern using an ab initio method (the FOX program) with subsequent Rietveld refinement in the FULLPROF program. The compound is monoclinic, with the space group P2₁/c (No. 14), a=49.88(2), b=7.867(2), c=5.602(3) Å, β=128.68(2)°, and Z=4. It has a one-dimensional structure with an inorganic part built of SrO₈ distorted tetragonal antiprisms.     

Triethylamine-modified Keggin heteropolyacid: a novel phase-transfer catalyst for hydroxylation of benzene with H2O2

The Keggin-structured heteropolyacid H₄PMo₁₁VO₄₀ and its triethylamine-modified derivative [(C₂H₅)₃NH]₄PMo₁₁VO₄₀ were prepared and characterized by FT-IR and UV–visible spectrometry, and elemental analysis. Direct hydroxylation of benzene to phenol by H₂O₂ over these two catalysts was then compared. The effect of the triethylamine in [(C₂H₅)₃NH]₄PMo₁₁VO₄₀ on the catalytic hydroxylation of benzene was investigated in detail. The results showed that although the triethylamine-modified catalyst is not significantly more active than the parent heteropolyacid catalyst, its reaction-controlled phase-transfer characteristics enable easy separation of the catalyst from the reaction medium, and its reuse, suggesting its potential for application to the hydroxylation of benzene to phenol with H₂O₂.     

Hydroxylation of phenol over MeAPO molecular sieves synthesized by vapor phase transport

In this study, MeAPO-25 (Me = Fe, Cu, Mn) molecular sieves were first synthesized by a vapor phase transport method using tetramethyl guanidine as the template and applied to hydroxylation of phenol. The zeolites were characterized by XRD, SEM, FT-IR, and DR UV–Vis. As a result, MeAPO-21 and MeAPO-15 were synthesized by changing the Me/Al ratio. UV–Visible diffuse reflectance study suggested incorporation of heteroatoms into the framework and FT-IR study also supported these data. Effects of heteroatoms, contents of Me in MeAPO-25, reaction temperature, phenol/H₂O₂ mole ratios, reaction time and concentration of catalyst on the conversion of phenol, as well as on the selectivity were studied. FeAPO-25 exhibited a high catalytic activity at the mole ratio of FeO and Al₂O₃ equal to 0.1 in the synthesis gel, giving the phenol conversion of 88.75% and diphenols selectivity of 66.23% at 60°C within 3 h [n(phenol)/n(H₂O₂) = 0.75, m(FeAPO-25)/m(phenol) = 7.5%]. Experimental results indicated that the FeAPO-25 molecular sieve was a fairly promising candidate for the application in hydroxylation of phenol.     

一维双链镉(Ⅱ)配合物[Cd(C5H5N)CH2C(OH)(PO3)(PO3H)·3H2O]n的合成与晶体结构

A new cadmium complex [Cd(C₅H₅N)CH₂C(OH)(PO₃)(PO₃H)·3H₂O]_n((C₅H₄N)CH₂C(OH)(PO₃H₂)₂=1-hydroxy-2-(2-pyridyl)ethylidene-1,1-diphosphonate acid) has been synthesized under hydrothermal conditions. Single crystal structure determination reveals that the compound has a ladder-like chain structure in which the edge-shared {CdO₆} octahedra are linked by {CPO₃} tetrahedra through corner-sharing. The chains of {Cd(C₅H₅N)CH₂C(OH)(PO₃)(PO₃H)}_n are linked by inter-chain hydrogen bonds, forming a supramolecular layer. CCDC: 722396.     

A Minimalist Approach to C?H Activation by Copper

The complex [Cu₂( 1 )₂]²⁺ ( 1 = 1,3‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)benzene) undergoes slow oxidation by dioxygen in DMF solution to give the hydroxylated product [Cu₂( 2 ‐H)₂]²⁺ ( 2 = 2,6‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)phenol) characterized by an X‐ray crystal‐structure analysis. The oxidation occurs much faster when Cu^II is mixed with 1 in the presence of H₂O₂, with 80% hydroxylation observed within a few minutes. The mononuclear complex formed with 1‐methyl‐2‐phenyl‐1H‐benzimidazole ( 3 ) shows no hydroxylation under these conditions. It is concluded that the hydroxylation requires the presence of a ligand capable of stabilizing a binuclear species, but no special coordinative activation of the copper is required.     

Analytical applications of the reaction of thorium with benzenephosphonic acid

Benzenephosphonic acid quantitatively precipitates thorium as Th(C₆H₅PO₃)₂·3H₂O at pH values as low as 0.5. The compound may be dried at 140° to 180° C and weighed, as a gravimetric means of determining thorium. On ignition, Th (C₂H₅PO₃)₂ 3 H₂O undergoes decomposition at 240° to 300° C to form Th(C₆H₅PO₃)₂·2H₂O, at 450° to 650° C to form Th(HPO₄)₂·2H₂O and finally at 800° to 1000° C to form Th(HPO₄)₂. The latter compound is stable to 1200° C.Potentiometrically (pK₁' = 0.91, pK₂' = 6.41) and spectrophotometrically (pK₁' = 0.96, pK₂' = 6.51) determined pK' values are reported. Absorption spectra of C₆H₅PO₃H₂, C₆H₅PO₃H^- and C₆H₅PO₃^-2 are reported. The solubility of Th (C₆H₅PO₃)₂·3H₂O was studied as a function of pH and the average value of the solubility product (K_sp = 4s³) was found to be 3.24·10^-31.     

Specific Enhancement of Catalytic Activity by a Dicopper Core: Selective Hydroxylation of Benzene to Phenol with Hydrogen Peroxide

A dicopper(II) complex, stabilized by the bis(tpa) ligand 1,2‐bis[2‐[bis(2‐pyridylmethyl)aminomethyl]‐6‐pyridyl]ethane (6‐hpa), [Cu₂(μ‐OH)(6‐hpa)]³⁺, was synthesized and structurally characterized. This complex catalyzed selective hydroxylation of benzene to phenol using H₂O₂, thus attaining large turnover numbers (TONs) and high H₂O₂ efficiency. The TON after 40 hours for the phenol production exceeded 12000 in MeCN at 50 °C under N₂, the highest value reported for benzene hydroxylation with H₂O₂ catalyzed by homogeneous complexes. At 22 % benzene conversion, phenol (95.2 %) and p ‐benzoquinone (4.8 %) were produced. The mechanism of H₂O₂ activation and benzene hydroxylation is proposed.     

Hydrothermal Synthesis, Single-Crystal Structure Analysis, and Solid-State NMR Characterization of Zn2(OH)0.14(3)F0.86(3)(PO4)

The zinc fluoro phosphate Zn₂F(PO₄) has been produced by hydrothermal synthesis employing hydrofluoric acid as a mineralizer in a H₂O or D₂O medium. A single-crystal X-ray synchrotron diffraction analysis of Zn₂F(PO₄) shows that the zinc fluoro phosphate is monoclinic, a=9.690(1), b=12.793(1), and c=11.972(1) Å, β=108.265(1)°, space group P2₁/c, No. 14, Z=16. Reflections hkl with k=2n+1 are weak but significant and the structure shows pseudosymmetry. Zn₂F(PO₄) has the wagnerite-type M₂F(XO₄) structure with four Zn atoms each coordinated to four O atoms and one F atom while four other Zn atoms are coordinated to four O atoms and two F atoms. A difference Fourier map, calculated from the single-crystal X-ray data, shows additional electron density close to the four fluorine atoms, indicating a possible partial substitution of F⁻ by OH⁻ ions. This is unambiguously confirmed by ³¹P-{¹H} cross-polarization magic-angle spinning (MAS) and by ¹H/²H MAS NMR spectroscopy. The narrow line width observed for the ¹H resonance and the unique set of ²H quadrupole coupling parameters (obtained for the Zn₂F(PO₄) sample using D₂O as medium) show that ¹H/²H is present as OH(D) groups rather than as water of crystallization in the structure. Quantitative ¹H MAS NMR analysis shows that the composition of the sample is Zn₂(OH)_0.14(3)F_0.86(3)(PO₄). The high-speed ¹⁹F MAS NMR spectrum exhibits two resolved resonances with equal intensity, which are ascribed to an overlap of resonances from the four distinct fluorine sites in Zn₂(OH)_0.14(3)F_0.86(3)(PO₄).     

Efficient hydroxylation of aromatic compounds catalyzed by an iron(II) complex with H2O2

A mononuclear iron(II) complex, Et₄N[Fe(C₁₀H₆NO₂)₃], coordinated by three 1‐nitroso‐2‐naphtholate ligands in a fac‐N₃O₃ geometry, was initiated to catalyze the direct hydroxylation of aromatic compounds to phenols in the presence of H₂O₂ under mild conditions. Various reaction parameters, including the catalyst dosage, temperature, mole ratio of H₂O₂ to benzene, reaction time and solvents which could affect the hydroxylation activity of the catalyst, were investigated systematically for benzene hydroxylation to obtain ideal benzene conversion and high phenol distribution. Under the optimum conditions, the benzene conversion was 10.2% and only phenol was detected. The catalyst was also found to be active towards hydroxylation of other aromatic compounds with high substrate conversions. The hydroxyl radical formed due to the reaction of the catalyst and H₂O₂ was determined to be the crucial active intermediate in the hydroxylation. A rational pathway for the formation of the hydroxyl radical was proposed and justified by the density functional theory calculations. Copyright © 2014 John Wiley & Sons, Ltd.