A facile method for the N-formylation of primary and secondary amines by liquid phase oxidation of methanol in the presence of hydrogen peroxide over basic copper hydroxyl salts

N-formylation reactions by catalytic oxidation of methanol in the presence of primary or secondary amines and hydrogen peroxide has been investigated using a liquid phase reaction system over basic copper hydroxyl salts. A series of basic copper hydroxyl salts was prepared by the conventional precipitation method using aqueous ammonia and sodium hydroxide as precipitating agents. PXRD, SEM, FT-IR, BET were employed for physical characterization of the prepared basic copper hydroxyl salts. The composition of the catalytic material obtained was found dependent on the nature of the anion associated with the copper salt precursor. The copper hydroxyl chloride catalyst has shown the best catalytic performance in terms of the reaction rate and product selectivity whereas for the copper oxide catalyst the reaction rate was extremely slow. It is interesting to observe that 4-piperidone protected with acid-sensitive functional groups such as N-acetyl piperazine and ethylene glycol can also be formylated from moderate to good yields by these catalysts.     

Relationship between the reactions of hydrogen sorption/desorption and methanol oxidation on bifunctional Ni/Pd electrode in alkaline solution

The present paper is aimed at studying the influence of the hydrogen sorption/desorption process occurring on the layered nickel–palladium (Ni/Pd) electrode on the kinetics of the reaction of methanol oxidation in strong alkaline KOH solution. The electrodes were prepared by chemical deposition of a thin layer of porous palladium on a nickel foam support. A scanning electron microscope was used for studying the morphology of both the nickel support and the porous palladium layer. The mechanism of the anodic desorption of hydrogen changes depending on whether or not 6 M KOH electrolyte is admixed with methanol. It was shown that, in the first cycle of the cyclic voltammetry (CV) measurements, the anodic peak current and peak charge related to the oxidative desorption of hydrogen significantly decrease due to the presence of methanol in KOH. This effect is attributed to the obstacles in hydrogen sorption due to the formation of a passivating layer on the Pd surface composed of both adsorbed methanol molecules and the intermediate products involving adsorbed CO. On the other hand, hydrogen desorbing from Pd electrode exerts influence on the kinetics of the reaction of methanol oxidation. Ni/Pd electrode undergoes considerable reactivation due to the potentiostatic saturation with hydrogen at ?1.1 V, followed by the ease in hydrogen desorption. The CV measurements proved that, after such a treatment, the peak of hydrogen desorption partially overlaps the double peak of methanol oxidation and, in consequence, the rate of methanol oxidation is enhanced. The positive effect of hydrogen releasing from the electrode on the kinetics of the reaction of methanol oxidation is ascribed to the anti-poison behavior consisting in the reaction of hydrogen radicals with intermediates adsorbed on the Pd surface.     

A study of gas-phase reactions of radical cations of mono- and dihaloethenes with alcohols by FT-ICR spectrometry and molecular orbital calculations: substitution versus oxidation

The ion-molecule reactions of the radical cations of vinyl chloride (1), vinyl bromide (2), 1,2-dichloroethene (3), 1,2-dibromoethene (4), 1,1-dichloroethene (5), and 1,1-dibromoethene (6) with methanol (MeOH) and ethanol (EtOH) have been studied by FT-ICR spectrometry. In the case of EtOH as reactant the oxidation of the alcohol to protonated acetaldehyde by a formal hydride transfer to the haloethene radical cation is the main process if not only reaction observed with the exception of the 1,2-dibromoethene radical cation which exhibits slow substitution. In secondary reactions the protonated acetaldehyde transfers the proton to EtOH which subsequently undergoes a well known condensation reaction of EtOH to form protonated diethyl ether. With MeOH as reactant, the 1,2-dihaloethene radical cations of 3.+ and 4.+ exhibit no reaction, while the other haloethene radical cations undergo the analogous reaction sequence of oxidation yielding protonated formaldehyde. Generally, bromo derivatives of haloethene radical cations react predominantly by substitution and chloro derivatives by oxidation. This selectivity can be understood by the thermochemistry of the competing processes which favors substitution of Br while the effect of the halogen substituent on the formal hydride transfer is small. However, the bimolecular rate constants and reaction efficiencies of the total reactions of the haloethene radical cations with both alcohols exhibit distinct differences, which do not follow the exothermicity of the reactions. It is suggested that the substitution reaction as well as the oxidation by formal hydride transfer proceeds by mechanisms which include fast and reversible addition of the alcohol to the ionized double bond of the haloethene radical cation which generates a beta-distonic oxonium ion as the crucial intermediate. This intermediate is energetically excited by the exothermic addition and fragments either directly by elimination of a halogen substituent to complete the substitution process or rearranges by hydrogen migration before dissociation into the protonated aldehyde and a beta-haloethyl radical. Reversible addition and hydrogen migrations within a long lived intermediate is proven experimentally by H/D exchange accompanying the reaction of the radical cations of vinyl chloride (1) and 1,1-dichloroethene (5) with CD3OH. The suggested mechanisms are substantiated by ab initio molecular orbital calculations.     

Theoretical study of acridane oxidation reactions

The interactions of acridanes with oxidants were modeled using combined methods of quantum chemistry (DFT B3LYP/6-311G(d,p)), molecular mechanics, MERA model, and MOPS algorithm. The results of simulation are compared with XRD data, oxidation potentials of acridanes, and the reduction potentials of the products of the oxidation reaction. It is shown that elimination of the hydride anion by the reactions of acridanes with oxidants is a consequence of a two-step process; the first step is the transfer of electron density from the HOMO of acridane to the LUMO of the oxidant; the second step is hydrogen elimination from the acridane molecule due to hydrogen bonding with the oxygen atom of the oxidant. The details of the mechanism were established by modeling the acridane-oxidant complexes using the MOPS algorithm including the continuum model of the solvent. The logarithms of the rate constants of the processes depend on the structure parameters of the model complexes with correlation coefficients of at least 0.93.     

Iridicycle‐Catalysed Imine Reduction: An Experimental and Computational Study of the Mechanism

The mechanism of imine reduction by formic acid with a single‐site iridicycle catalyst has been investigated by density functional theory (DFT), NMR spectroscopy, and kinetic measurements. The NMR and kinetic studies suggest that the transfer hydrogenation is turnover‐limited by the hydride formation step. The calculations reveal that, amongst a number of possibilities, hydride formation from the iridicycle and formate probably proceeds by an ion‐pair mechanism, whereas the hydride transfer to the imino bond occurs in an outer‐sphere manner. In the gas phase, in the most favourable pathway, the activation energies in the hydride formation and transfer steps are 26–28 and 7–8 kcal mol^?1, respectively. Introducing one explicit methanol molecule into the modelling alters the energy barrier significantly, reducing the energies to around 18 and 2 kcal mol^?1 for the two steps, respectively. The DFT investigation further shows that methanol participates in the transition state of the turnover‐limiting hydride formation step by hydrogen‐bonding to the formate anion and thereby stabilising the ion pair.     

Electroinitiated oligomerization of methyl acrylate in methanol solution

The electroinitiated oligomerization of methyl acrylate in methanol solution in the presence of lithium acetate was studied. It was found that in this system the initiator is the methyl radical (obtained from anodic oxidation of acetate ion), and the major termination step is the abstraction of hydrogen radical from methanol by the growing oligomer chain. Eleven compounds were found to be formed in the reaction. A reaction sequence for their formation together with an electric balance for the reactions is given.     

Experimental investigation on the mechanism of chelation-assisted, copper(II) acetate-accelerated azide-alkyne cycloaddition

A mechanistic model is formulated to account for the high reactivity of chelating azides (organic azides capable of chelation-assisted metal coordination at the alkylated azido nitrogen position) and copper(II) acetate (Cu(OAc)(2)) in copper(II)-mediated azide-alkyne cycloaddition (AAC) reactions. Fluorescence and (1)H NMR assays are developed for monitoring the reaction progress in two different solvents, methanol and acetonitrile. Solvent kinetic isotopic effect and premixing experiments give credence to the proposed different induction reactions for converting copper(II) to catalytic copper(I) species in methanol (methanol oxidation) and acetonitrile (alkyne oxidative homocoupling), respectively. The kinetic orders of individual components in a chelation-assisted, copper(II)-accelerated AAC reaction are determined in both methanol and acetonitrile. Key conclusions resulting from the kinetic studies include (1) the interaction between copper ion (either in +1 or +2 oxidation state) and a chelating azide occurs in a fast, pre-equilibrium step prior to the formation of the in-cycle copper(I)-acetylide, (2) alkyne deprotonation is involved in several kinetically significant steps, and (3) consistent with prior experimental and computational results by other groups, two copper centers are involved in the catalysis. The X-ray crystal structures of chelating azides with Cu(OAc)(2) suggest a mechanistic synergy between alkyne oxidative homocoupling and copper(II)-accelerated AAC reactions, in which both a bimetallic catalytic pathway and a base are involved. The different roles of the two copper centers (a Lewis acid to enhance the electrophilicity of the azido group and a two-electron reducing agent in oxidative metallacycle formation, respectively) in the proposed catalytic cycle suggest that a mixed valency (+2 and +1) dinuclear copper species be a highly efficient catalyst. This proposition is supported by the higher activity of the partially reduced Cu(OAc)(2) in mediating a 2-picolylazide-involved AAC reaction than the fully reduced Cu(OAc)(2). Finally, the discontinuous kinetic behavior that has been observed by us and others in copper(I/II)-mediated AAC reactions is explained by the likely catalyst disintegration during the course of a relatively slow reaction. Complementing the prior mechanistic conclusions drawn by other investigators, which primarily focus on the copper(I)/alkyne interactions, we emphasize the kinetic significance of copper(I/II)/azide interaction. This work not only provides a mechanism accounting for the fast Cu(OAc)(2)-mediated AAC reactions involving chelating azides, which has apparent practical implications, but suggests the significance of mixed-valency dinuclear copper species in catalytic reactions where two copper centers carry different functions.     

Total oxidation of methanol on Cu(110): a density functional theory study

The partial and total oxidation of methanol on clean and oxygen-precovered Cu(110) has been studied by periodic density functional theory calculations within the generalized gradient approximation. Reaction paths including the geometry and the energetics of several reaction intermediates and the activation barriers between them have been determined, thus creating a complete scheme for methanol oxidation on copper. The calculations demonstrate that the specific structure of oxygen on copper plays an important role in both the partial and the total oxidation of methanol. For lower oxygen concentrations on the surface, the partial oxidation of methanol to formaldehyde is promoted by the presence of oxygen on the surface through the removal of hydrogen in the form of water, which prevents the recombinative desorption of methanol. At larger oxygen concentrations, the presence of isolated oxygen atoms reduces the C-H bond breaking barrier of adsorbed methoxy considerably, thus accelerating the formation of formaldehyde. Furthermore, oxygen also promotes the formation of dioxymethylene from formaldehyde, which then easily decays to formate. Formate is the most stable reaction intermediate in the total oxidation. Thus the formate decomposition represents the rate-limiting step in the total oxidation of methanol on copper.     

Thermodynamic and electron-transfer properties of copper(II/I) polyaminothiaether complexes

In electron-transfer reactions, the change in the oxidation states of the reactants is generally accompanied by structural changes, which influence the electron-transfer kinetics. Previous studies on the systems of Cu(II)/(I) complexes involving cyclic tetrathiaether ligands indicated that inversion of coordinated donor atoms is a major geometric change during the overall electron-transfer process. Complex formation and isomerization studies on complexes with the 1,4,8,11-tetraazacyclotetradecane ligand have demonstrated that a necessary condition for conformational change is deprotonation followed by inversion of coordinated N atoms. When one or more nitrogen donor atoms in a ligand are replaced with sulfur, there is a choice of N or S inversion. It has been hypothesized that donor atom inversion (N or S donors) is a major factor that can lead to conformationally limited electron-transfer kinetics of copper systems. In the current study, the thermodynamic properties, electron-transfer kinetics and conformational changes in copper(II)[1,4,8-trithia-11-azacyclotetradecane], copper(II)[1,8-dithia-4,11-diazacyclotetradecane] and copper(II)[1,11,-dithia-4,8-diazacyclotetradecane] were determined in order to determine the effect of inversion of coordinated N atoms on electron-transfer rates as a function of low concentrations of water in an aprotic solvent (acetonitrile). By using controlled amounts of water as a hydrogen ion acceptor, deprotonation of amine nitrogen and nitrogen donor inversion was followed by comparing self-exchange rate constants for reduction and oxidation of the copper complexes. Data on thermodynamic properties and electron-transfer kinetics are presented. Possible conformational changes and kinetic pathways for complexes with ligands having mixed N and S donor sets are presented.     

Kinetics-Based Approach to Developing Electrocatalytic Variants of Slow Oxidations: Application to Hydride Abstraction-Initiated Cyclization Reactions

Electrochemical oxidant regeneration is challenging in reactions that have a slow redox step because the steady-state concentration of the reduced oxidant is low, causing difficulties in maintaining sufficient current or preventing potential spikes. This work shows that applying an understanding of the relationship between intermediate cation stability, oxidant strength, overpotential, and concentration on reaction kinetics delivers a method for electrochemical oxoammonium ion regeneration in hydride abstraction-initiated cyclization reactions, resulting in the development of an electrocatalytic variant of a process that has a high oxidation transition state free energy. This approach should be applicable to expanding the scope of electrocatalysis to include additional slow redox processes.     

Kinetics of oxidation of ketoglutaric acids by alkaline chloramine-t solution

Kinetics of the oxidation of α-ketoglutaric and β-ketoglutaric acids by chloramine-T (CAT) have been investigated in highly alkaline media. The reactions show first order dependence in chloramine-T and fractional order in substrates. The order in hydroxide ions has been found to be second but shows a slight decrease at high concentration of alkali. No effect of p-toluene-sulphonamide was evident. Observed stoichiometry, positive effects of ionic strength and dielectric constant point to a mechanism involving formation of an intermediate in a termolecular rate determining slowest step among hypochlorite ion, hydroxide ion and enolic anion of keto acids followed by a fast step leading to products. Activation parameters have been computed and formaldehyde and formic acid were Identified as end-products.     

Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

 The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism.     

Influence of copper(II) catalyst on the oxidation of l-histidine by platinum(IV) in alkaline medium: a kinetic and mechanistic study

The kinetics of oxidation of l-histidine (His) by platinum(IV) in the absence and presence of copper(II) catalyst was studied using spectrophotometry in alkaline medium at a constant ionic strength of 0.1 mol dm^?3 and at 25 °C. In both cases, the reactions exhibit a 1:1 stoichiometry ([His]:[Pt^IV]). The rate of the uncatalyzed reaction is dependent on the first power of each of the concentrations of oxidant, substrate and alkali. The catalyzed path shows a first-order dependence on both [Pt^IV] and [Cu^II], but the order with respect to both [His] and [OH^?] is less than unity. The rate constants increase with increasing ionic strength and dielectric constant of the medium. The catalyzed reaction has been shown to proceed via formation of a copper(II)^_histidine intermediate complex, which reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. Platinum(IV) is reduced to platinum(II) by the substrate in a one-step two-electron transfer process. This is followed by other fast steps, giving rise to the oxidation products which were identified as 2-imidazole acetaldehyde, ammonia and carbon dioxide. A tentative reaction mechanism is suggested, and the associated rate laws are deduced. The activation parameters with respect to the slow step of the mechanism are reported and discussed.     

Association of Formaldehyde in Aqueous-Alcoholic Systems

In the neutral systems formaldehyde-water-alcohol (methanol, ethanol, ethylene glycol) at 25°C, formaldehyde is preferentially present as hemiacetals. The mean equilibrium constants of step polycondensation of formaldehyde are calculated.     

Kinetics and mechanisms of the oxidation of phenols by a trans-dioxoruthenium(VI) complex

The kinetics of the oxidation of phenols by trans-[Ru(VI)(L)(O)(2)](2+) (L = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) have been studied in aqueous acidic solutions and in acetonitrile. In H(2)O the oxidation of phenol produces the unstable 4,4'- biphenoquinone, as evidenced by a rapid increase and then a slow decrease in absorbance at 398 nm. The first step is first-order in both Ru(VI) and phenol, and rate constants are dependent on [H(+)] according to the relationship k(f) = k(x) + (k(y)K(a)/[H(+)]), where k(x) and k(y) are the rate constants for the oxidation of PhOH and PhO(-), respectively. At 298 K and I = 0.1 M, k(x) = 12.5 M(-1) s(-1) and k(y) = 8.0 x 10(8) M(-1) s(-1). At I = 0.1 M and pH = 2.98, the kinetic isotope effects are k(H(2)O)/k(D(2)O) = 4.8 and 0.74 for k(x) and k(y), respectively, and k(f)(C(6)H(5)OH)/k(f)(C(6)D(5)OH) = 1.1. It is proposed that the k(x) step occurs by a hydrogen atom abstraction mechanism, while the k(y) step occurs by an electron-transfer mechanism. In both steps the phenoxy radical is produced, which then undergoes two rapid concurrent reactions. The first is a further three-electron oxidation by Ru(VI) and Ru(V) to give p-benzoquinone and other organic products. The second is a coupling and oxidation process to give 4,4'-biphenoquinone, followed by the decay step, k(s). A similar mechanism is proposed for reactions in CH(3)CN. A plot of log k(x) vs O-H bond dissociation enthalpies (BDE) of the phenols separates those phenols with bulky tert-butyl substituents in the ortho positions from those with no 2,6-di-tert-butyl groups into two separate lines. This arises because there is steric crowding of the hydroxylic groups in 2,6-di-tert-butyl phenols, which react more slowly than phenols of similar O-H BDE but no 2,6-tert-butyl groups. This is as expected if hydrogen atom abstraction but not electron transfer is occurring.     

Removal of copper from aqueous solution by aminated and protonated mesoporous aluminas: kinetics and equilibrium

A novel adsorbent, aminated and protonated mesoporous alumina, was prepared and employed for the removal of copper from aqueous solution at concentrations between 5 and 30 mg/l, in batch equilibrium experiments, in order to determine its adsorption properties. The removal of copper by the adsorbents increases with increasing adsorbent dosages. The adsorption mechanism is assumed to be an ion exchange between copper and the hydrogen ions present on the surface of the mesoporous alumina. The adsorbent was characterized by XRD, TEM, SEM, and BET methods. The sorption data have been analyzed and fitted to linearized adsorption isotherm of the Freundlich, Langmuir, and Redlich-Peterson models. The batch sorption kinetics have been tested for first-order, pseudo-first-order, and pseudo-second-order kinetic reaction models. The rate constants of adsorption for all these kinetic models have been calculated. Results also showed that the intraparticle diffusion of Cu(II) on the mesoporous catalyst was the main rate-limiting step.     

Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

Summary.  The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism. Received December 30, 1999. Accepted (revised) March 6, 2000     

Mechanism of anodic dissolution of copper in aqueous acidified solutions of different anions

The potentials of copper anodes were measured as a function of current density in aqueous acidified solutions of different anions. Tafel lines were obtained, whose slopes depend on the nature of the anion. This denoted the participation of the anion in the anodic dissolution of the metal. Hence, mechanisms were suggested based on the formation of intermediate cuprous compounds, which are further oxidized electrochemically, or undergo chemical disproportionation to cupric salts.The results in phosphate solutions indicated that the second electrochemical oxidation is the rate determining step. In chloride, nitrate and sulphate solutions, both the second electrochemical step and the disproportionation reaction govern the overall reaction rate.Measurements in acidified copper salt solutions showed that Cu²⁺ ions affect the reaction mechanism. Thus, in chloride and sulphate solutions, the disproportionation reaction becomes predominating, whereas in nitrate solutions the intermediate is mainly oxidized electrochemically. An interpretation is provided, based on the adsorption of Cu²⁺ ions.     

Sonochemical synthesis of copper hydride (CuH)

We report the sonochemical synthesis of copper(I) hydride (CuH) by the ultrasonic irradiation of a copper(II) aqueous solution. A reaction mechanism based on the reduction of copper(II) by the ultrasound-generated hydrogen atoms is discussed. To the best of our knowledge, this is the first time that a metal hydride has been synthesized through sonochemistry.     

Reaction mechanism and structure of products in photochemical transformations of copper(ii) heptafluorobutyrate in methanol

The mechanism of photochemical transformations of copper(II) heptafluorobutyrate in methanol is studied. The structure of products and intermediate compounds is investigated. Photolysis occurs as a two- step process. The first step involves changes in the coordination sphere of the Cu(II) ion. The second step is photoreduction of Cu(II) forming metallic copper and Cu(II) fluoride as a complex with methanol. In the presence of oxygen, the first step is reversible. A scheme of these processes is suggested. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 4, pp. 662–668, July–August, 1997.