Kinetics of oxidation of ethylene to vinyl acetate using a homogeneous palladium complex catalyst

A kinetic study of the oxidation of ethylene to vinyl acetate using a palladium complex catalyst is reported. The effects of the ethylene partial press concentration and temperature on the rate of ethylene absorption were studied. The solubility of ethylene in acetic acid was determined at various sodi order with respect to the catalyst (PdCl₂) concentration and zero order with respect to the benzoquinone concentration. The dependence of the react basis of these data and the kinetic parameters were evaluated. The activation energy was found to be 14.6 kcal mol⁻¹.The effect of sodium acetate on the reaction rate was found to be complex, and an optimum sodium acetate concentration exists for a given set of condit increased with increase in temperature.     

Kinetics of hydroformylation of 1-decene using carbon-supported ossified HRh(CO)(TPPTS)3 catalyst

The kinetics of hydroformylation of 1-decene has been investigated using a carbon-supported ossified HRh(CO)(TPPTS)₃/Ba catalyst in a temperature range of 343–363 K. The effect of concentration of 1-decene, catalyst loading, partial pressure of H₂ and CO, and stirring speed on the reaction rate has been investigated. A first-order dependence was observed for catalyst concentration and hydrogen partial pressure. The rate showed a typical case of substrate inhibition for high 1-decene concentration. The rate varied with a linear dependence on P_CO up to a CO partial pressure of 5–6 MPa in contrast to the general trends; for most of the rhodium-phosphine catalyzed hydroformylation reactions, severe inhibition of rate is observed with an increase in CO pressure. A rate equation has been proposed, which was found to be in good agreement with the observed rate data within the limit of experimental errors. The kinetic parameters and activation energy values have been reported.     

Kinetics of hydroformylation of camphene using rhodium-phosphite catalyst

Kinetics of hydroformylation of camphene was investigated in the presence of [Rh(CO)₂(acac)]/P(OPh)₃ catalyst in a temperature range of 363–383 K. The influence of parameters such as stirring speed, camphene, catalyst, ligand concentrations, and partial pressures of H₂ and CO on the activity and selectivity of the catalyst has been studied. The rate showed a first-order dependence with respect to catalyst and camphene concentrations. The effect of partial pressure of hydrogen showed fractional order dependence. The plots of rate versus excess ligand, that is, (P(OPh)₃) concentration and rate versus CO partial pressure passed through maxima and showed typical substrate/ligand inhibited kinetics. An empirical rate equation has been proposed and found to be in good agreement with the observed rate data. The kinetic parameters and activation energy were also evaluated.     

Catalytic hydrogenation of styrene-g-natural rubber (ST-g-NR) in the presence of OsHCl(CO)(O2)(PCy3)2

OsHCl(CO)(O₂)(PCy₃)₂, was used as a catalyst for hydrogenation of styrene-g-natural rubber copolymer (ST-g-NR). Univariate experiments were conducted to explore the effect of variables on the rate of hydrogenation by measuring the hydrogen consumption as a function of time using a gas-uptake apparatus. From the kinetic results, the hydrogenation of ST-g-NR was observed to exhibit a first-order dependence on [CC]. The rate of hydrogenation showed a first-order dependence on the catalyst concentration and a first-order shift to zero-order dependence on hydrogen pressure with increasing hydrogen pressure. The rate of hydrogenation was also found to decrease with an increase in rubber concentration. The addition of a small amount of acid provided a beneficial effect on the hydrogenation rate of the grafted natural rubber. The hydrogenation rate of ST-g-NR was dependent on the reaction temperature and the apparent activation energy over the range of 120-160 °C was found to be 83.3 kJ/mol.     

Rhodium/tris-binaphthyl chiral monophosphite complexes: Efficient catalysts for the hydroformylation of disubstituted aryl olefins

A family of threefold symmetry phosphite ligands, P(O–BIN–OR)₃ (BIN = 2,2′-binaphthyl; R = Me, Bn, CHPh₂, 1-adamantyl), derived from enantiomerically pure (R)-BINOL, was developed. Cone angles within the range 240–270° were calculated for the phosphite ligands, using the computational PM6 Hamiltonian. Their rhodium complexes formed in situ showed remarkable catalytic activity in the hydroformylation of hindered phenylpropenes, under relatively mild reaction conditions, with full chemoselectivity for aldehydes, high regioselectivity, however with low enantioselectivity. The ether substituents at the ligand affected considerably the catalytic activity on the hydroformylation of 1,1- and 1,2-disubstituted aryl olefins. The kinetics of the hydroformylation of trans-1-phenyl-1-propene, using tris[(R)-2′-benzyloxy-1,1′-binaphthyl-2-yl]phosphite as model ligand, was investigated. A first order dependence in the hydroformylation initial rate with respect to substrate and catalyst concentrations was found, as well as a positive order with respect to the partial pressure of H₂, and a slightly negative order with respect to phosphite concentration and CO partial pressure.     

Regularities of adsorption of zinc acetate from aqueous solutions onto the surface of modified activated carbons

The dependence of the characteristics of Zn(OAc)₂/C catalysts for vinyl acetate synthesis on the solution circulation rate, on the temperature and initial concentration of zinc acetate solution, and on the procedures for modification of activated carbons with oxidants was studied with the aim to achieve uniform distribution of the supported active component (zinc acetate). Oxidation of activated carbons with hydrogen peroxide and nitric acid increases the adsorption rate and the amount of adsorbed zinc acetate. Treatment of the support with acetic acid leads to an increase in the adsorption capacity for zinc acetate, to more uniform distribution of the active component over the surface, and to enhancement of the catalyst activity. The hydrodynamic regime of stirring in the two-phase system consisting of the support and zinc acetate solution is an important factor determining the activity and stability of the zinc acetate catalyst for vinyl acetate synthesis.     

Ceric Ion Initiated Graft Polymerization onto Poly(vinyl Alcohol)

This paper describes the kinetics of the ceric ion-initiated graft co-polymerization of vinyl acetate-acrylonitrile to poly(vinyl alcohol). The graft copolymerization rate R_p was found to be first order with respect to the total concentration of the comonomer mixture [M], the concentration of vinyl alcohol repeating units [PVA], and the mole fraction of vinyl acetate in the comonomer feed mixture. R_p was independent of cerous ion. The grafting rate was independent of ceric ion above a ceric concentration of 0.0020 M but first order in ceric ion below that concentration. Rp initially increased rapidly with [H⁺] to a maximum and then decreased and levelled off at hgher [H⁺]. The rate of ceric ion disappearance was first order in [PVA], independent of [MI, and increased with increasing [H⁺] with a leveling off at high [H⁺]. A reaction mechanism.     

Asymmetric hydroformylation of vinyl acetate with BINAP–rhodium(I) complexes

Complexes of (R)-BINAP (BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) derived from the available rhodium precursors Rh(acac)(CO)₂ and [Rh(μ-OMe)(cod)]₂ are used for the asymmetric hydroformylation of vinyl acetate. Enantiomeric excesses of up to 60% are achieved with regioselectivities of up to 99%. Only a BINAP/Rh ratio of 2 is required. Effects of pressure and temperature on catalyst stability, enantio- and chemoselectivity are discussed.     

The Polymerization of Free Enols with Electron-Deficient Comonomers

Abstract

The balance between kinetics and thermodynamics is illustrated herein by the first direct polymerization of vinyl alcohol, the thermodynamically unstable tautomer of acetaldehyde, at a rate faster than it can tautomerize. Vinyl alcohol was formed through the acid catalyzed hydrolysis of ketene methyl vinyl acetal. With excess water present, the kinetics of tautomerization first order dependence upon vinyl alcohol (k_obs = 2.73 × 10^?4 s^?1). Under water starved conditions, however, the kinetics now show a zero order dependence upon the concentration of vinyl alcohol (k_obs = 3.5 × 10^?6 M/s). Under these latter conditions, the half life of vinyl alcohol is nearly 24 hours at room temperature. Although cationic and homo free radical polymerization of vinyl alcohol failed, we found that this meta-stable species could be quantitatively polymerized in a copolymerization (AIBN, hυ, -10 to 25°C) with maleic anhydride. The k_obs for copolymerization was found to be 4.41 × 10^?4 sec^?1 at ?10°C. Since the rate of polymerization is far greater than that of tautomerization under these conditions (ca. 30 times faster at ?10°C), there is no significant increase in acetaldehyde concentration during polymerization.     

Ferrofluid catalyzed water gas shift reaction to give carbon-dioxide and hydrogen

A ferrofluid consisting of colloidally dispersed magnetite particles in water was found to be an efficient selective catalyst for water gas shift reaction at 15–25 atmosphere of CO pressure in the temperature range of 423–553 K where the products obtained were only CO₂ and H₂. The reaction was studied as a function of variation of the concentration of catalyst, pressure of CO gas and temperature. Kinetic parameters suggested a mechanism involving first order dependence in CO and catalyst concentrations.     

The mechanism and kinetics of energy transfer processes in Xe–CCl4–M (M=CO,CO2) mixtures irradiated by xenon resonance light

The mechanism and kinetics of energy transfer from the Xe(6s[3/2]₁) resonance state to CO and CO₂ molecules have been investigated by XeCl(B–X) (λ_max=308 nm) fluorescence intensity measurements at stationary conditions in Xe–CCl₄–M systems. Steady-state analysis of the fluorescence intensity dependence on the xenon and M pressure at constant CCl₄ concentration shows that these processes occur in two- and three-body reactions: Xe(6s[3/2]₁⁰)+M→products; Xe(6s[3/2]₁⁰)+M+Xe→products. The two-body rate constants for above reactions have been found to be (0.7±0.2)×10⁻¹⁰ and (4.9±0.4)×10⁻¹⁰ cm³ s⁻¹ for CO and CO₂, respectively. The three-body rate constants have been found to be (3±1)×10⁻²⁹ and (2.4±0.3)×10⁻²⁸ cm⁶ s⁻¹ for CO and CO₂, respectively. It has been shown that the third order reaction is a very effective channel of xenon excited atoms decay at high xenon pressures (P(Xe)>50 Torr).     

Kinetics and mechanistic aspects on electron‐transfer process for permanganate oxidation of poly(ethylene glycol) in aqueous acidic solutions in the presence and absence of Ru(III) catalyst

The kinetics and mechanism of oxidation of poly(ethylene glycol) (PEG) by the permanganate ion as a multiequivalent oxidant in aqueous perchlorate solutions at an ionic strength of 2.0 mol dm⁻³ has been investigated spectrophotometrically. The reaction kinetics was found to be of complex in nature. The pseudo–first‐order plots showed curves of inverted S‐shape, consisting of two distinct stages throughout the entire course of reaction. The first stage was relatively slow, followed by a fast reaction rate at longer time periods. The first‐order dependence in [MnO₄⁻], fractional first‐order dependence in [H⁺], and fractional first‐order kinetics in the PEG concentration for the first stage have been revealed in the absence of the Ru(III) catalyst. The influence of the Ru(III) catalyst on the oxidation kinetics has been examined. The oxidation was found to be catalyzed by the added Ru(III) catalyst. The First‐order dependence on the catalyst and zero order with respect to the oxidant concentrations have been observed. The kinetic parameters have been evaluated, and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.     

The influence of the supramolecular structure of water on the kinetics of vaporization

The kinetics of water vaporization was studied gravimetrically using a Q-1500 D derivatograph with an accuracy of ±5 × 10^?5 g under atmospheric conditions. Various supramolecular structures were created in liquid water using solutions of K, Na, Ba, and Zn chlorides with various concentrations. The kinetic dependences of weight P loss caused by the vaporization of solutions were compared with the data on pure water used to prepare the solutions. The dependence of the rate of vaporization V on the concentration of hydrated ions in solutions was used to show that the rate V is the sum of the rates of vaporization of particles of two types, (a) H₂O molecules and (b) supramolecular formations (H₂O clusters) with H-bonds. As a consequence, a nonlinear (piecewise linear) dependence of the kinetics of vaporization P = f(τ) of water and solutions is observed. The rate of vaporization (V ₁) along the initial P = f(τ) curve portions is substantially (by ～30%) higher than its stationary value (V).     

Homogeneous catalysis of the water gas shift reaction by iridium carbonyl in alkaline solution

The water gas shift reaction, H₂O + CO ? H₂ + CO₂, catalyzed homogeneously by a system based on tetrairidiumdodecacarbonyl (Ir₄(CO)₁₂) in alkaline 2-ethoxyethanol/water solution was examined at moderate temperatures (90–130°C) and pressures (P_CO 0.5–2.0 atm). The catalytic reaction showed an approximate first-order dependence on base concentration and on the concentration of iridium. The catalytic cycle was shown to have a zero order dependence on the partial pressure of CO. An apparent activation energy of 10.7 kcal mol^?1 was obtained from a linear Arrhenius plot based on hydrogen production over the temperature range 90–130°C. The predominant pathway of the reaction can be explained by a mechanism in which activation of CO by nucleophilic attack of hydroxide on the metal hydride species HIr₄(CO)₁₁^? produces the dihydride species, H₂Ir₄(CO)₁₀^2? in the rate-limiting step. Subsequent reaction of this anion with H₂O gives H₂ plus HIr₄(CO)₁₁^? again. The complex Ir₈(CO)₂₀^2? is shown to be a catalytically poor component of the solution. The system has also been shown to be active toward the decomposition of formate. This pathway however, is concluded to make an insignificant contribution to the catalysis rate under water gas shift reaction conditions.     

Mononuclear ruthenium complexes containing two different phosphines in trans position: II. Catalytic hydrogenation of CC and CO bonds

Bis(acetate) ruthenium(II) complexes of the general formula Ru(CO)₂(OAc)₂(PⁿBu₃)[P(p-XC₆H₄)₃] (OAc = acetate, X = CH₃O, CH₃, H, F or Cl), containing different phosphine ligands trans to PⁿBu₃, have been employed as catalyst precursors for the hydrogenation of 1-hexene, acetophenone, 2-butanone and benzylideneacetone. For comparative purposes, analogous reactions have been performed using the homodiphosphine precursors Ru(CO)₂(OAc)₂(PⁿBu₃)₂ and Ru(CO)₂(OAc)₂(PPh₃)₂. The catalytic activity of the heterodiphosphine complexes depends on the basicity of the triarylphosphine trans to PⁿBu₃ as this factor controls, inter alia, the rate of formation of hydride(acetate), Ru(CO)₂(H)(OAc)(PⁿBu₃)[P(p-XC₆H₄)₃], or dihydride, Ru(CO)₂(H)₂(PⁿBu₃)[(p-XC₆H₄)₃], complexes, by hydrogenation of the bis(OAc) precursors. The catalytic hydrogenation of the CC double bond is best accomplished by homodiphosphine dihydride catalysts, while heterodiphosphine monohydrides are more efficient catalysts than the homo- and heterodiphosphine dihydrides for the reduction of the keto CO bond.     

Mechanistic investigations of the reaction network in chemo-bio catalyzed synthesis of R-1-phenylethyl acetate

The kinetics and reaction network of the one-pot synthesis of R-1-phenylethyl acetate was investigated at 70°C in toluene over a combination of three different catalysts: PdZn/Al₂O₃ as a catalyst for acetophenone hydrogenation, lipase as an enzymatic catalyst for R-1-phenylethanol acylation with ethyl acetate and Ru/Al₂O₃ as a racemization catalyst for S-1-phenylethanol. In addition to the desired reactions, other reactions, namely hydrogenolysis and dehydration of (R, S)-1-phenylethanol and debenzylation of (R, S)-1-phenylethyl acetate also occurred. The kinetic results revealed that ethylbenzene formation was enhanced with higher amounts of PdZn/Al₂O₃, whereas lipase did not catalyze ethylbenzene formation. Furthermore, ethylbenzene was formed in the hydrogenolysis of (R, S)-phenylethanol and in the debenzylation of (R, S)-1-phenyl-ethylacetate over Pd/Al₂O₃ catalyst. The presence of Ru/Al₂O₃ catalyst, in which Ru was in the oxidation state of 3⁺, enhanced the formation of R-1-phenylethyl acetate, although no clear racemization of S-1-phenylethanol during the one-pot synthesis of R-1-phenylethyl acetate was observed. Dynamic kinetic resolution of (R, S)-1-phenylethanol in toluene, was, however, demonstrated over Ru/Al₂O₃ and lipase.     

Studies on the synergetic effect of group viii transition metal carbonyls on homogeneous catalysis of the water-gas shift reaction

Homogeneous catalysis of the water-gas shift reaction by Group VIII mixed metal carbonyls and by mixtures of Group VIII metal carbonyls in pyridine solution was examined under mild conditions (T= 100°C, P_co = 0.42–0.60 atm).A weak synergetic effect of Group VIII metals was observed between iron and iridium carbonyls. A stronger synergetic behaviour of mixed metal Fe/Ru catalyst precursors (Fe₂Ru(CO)₁₂ and FeRu₂(CO)₁₂) was noted. The effect of phosphine and phosphite substitution on Fe₂Ru(CO)₁₂ and FeRu₂(CO)₁₂ was examined. Only monosubstitution on Fe₂Ru(CO)₁₂ was found to have an enhancing effect on catalytic activity.Rhodium carbonyls, which were found to produce the most active catalyst solution under homogeneous water-gas shift conditions, did not show a synergetic behaviour with other Group VIII metals.     

Synthesis and properties of a CO oxidation catalyst based on plasma-chemical silicon carbide,titanium dioxide,and palladium

A catalyst based on plasma-chemical β-SiC and TiO₂ with a palladium content of 10 wt % has been synthesized. The dependence of the rate of the CO oxidation reaction at room temperature and low CO concentrations (less than 100 mg/m³) on the β-SiC content has been studied. It has been found that with a β-SiC content of 8 to 10 wt %, the catalyst has a maximum reaction rate, which is three times that on a catalyst based on pure TiO₂ including palladium clusters. The catalysts are promising for use in catalytic and photocatalytic air purification systems.     

The initial oxidative polymerization kinetics of 2,6-dimethylphenol with a Cu-EDTA complex in water

The initial oxidative polymerization kinetics of 2,6-dimethylphenol (DMP) catalyzed by a Cu(II)-EDTA complex in water was studied. The initial polymerization rate of DMP (R₀) increases with an increase in concentrations of DMP and catalyst. R₀ firstly increases with the molar ratio of N/Cu and then decreases. The reaction order with respect to oxygen is 0.1. R₀ increases with NaOH concentration and reaches its maximum value at a concentration of 0.50 mol/L. 1/R₀ is in direct proportion to 1/[DMP]₀, which indicates that the initial polymerization kinetics of DMP in water obeys Michaelis-Menten model. The dissociation rate constant of the intermediate complex (k₂) and Michaelis-Menten constant (K_m) at various temperatures are calculated. It is found that both k₂ and K_m increase with an increase in temperature.     

Lifetime of living polymers in cationic polymerization. III. Living polymerization of isobutyl vinyl ether initiated by a cationogen/etalcl2 system in the presence of 1,4-dioxane as an added base

The concentration ([P^*]) and lifetime (half-life) of the propagating species were measured in the living cationic polymerization of isobutyl vinyl either initiated by the 1-(isobutoxy) ethyl acetate [CH₃COOCH (OiBu) CH₃]/ethylaluminum dichloride (EtAlCl₂) system in the presence of excess 1,4-dioxane in n-hexane at 0 to +70°C; the acetate serves as a cationogen that forms an initiating vinyl ether-type carbocation. The measurements were based on the end-capping reaction with sodiomalonic ester [Na^⊕?CH (COOEt)₂], which was shown to react rapidly and quantitatively with the living growing end. From the terminal malonate group of the quenched polymers, [P^*] was determined by ¹H-NMR spectroscopy. In contrast to its constancy during the polymerization, [P^*] progressively decreased with time after the complete consumption of monomer. The postpolymerization decay was first order in [P^*], and the lifetime (half-life) of the living end was determined from the decay rate constant. The lifetime increased on lowering polymerization temperature, decreasing EtAlCl₂ concentration, and increasing dioxane concentration. In particular, the “base-stabilized” living ends, generated by the CH₃COOCH (OiBu) CH₃/EtAlCl₂/dioxane system, turned out extremely stable at 0°C (half-life > 5 days in the absence of monomer).