Kinetic study of resin catalyzed hydrolysis of ethyl propionate in aqueous-organic systems

A kinetic study of solvent effect on sulfonated resin catalyzed hydrolysis of ethyl propionate has been made in water-acetone, water-dioxane, water-DMF and water-DMSO solvent mixtures of varying compositions, at different temperatures. Specific rate constants (k_r) were found to be a first order and decreased with increasing amount of organic co-solvent in the media. The variation in rates as well as the activation parameters have been interpreted on the basis of specific solvation ion and dielectric properties of the medium.

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Kinetic study on acid‐base catalyzed hydrolysis of azimsulfuron,a sulfonylurea herbicide

Pseudo‐first‐order rate constants (k_obs) for hydrolysis of a sulfonylurea herbicide, azimsulfuron, AZIM®, {N‐[[(4,6‐dimethoxy‐2‐pyrimidinyl)amino]carbony]‐1‐methyl‐4‐(2‐methyl‐2H‐tetrazol‐5‐yl)‐1H‐pyrazole‐5‐sulfonamide} (AZS) follow an empirical relationship: k_obs =α₁ + α₂[⁻OH] + α₃[⁻OH]² within the [NaOH] range of 0.1–2.0 M at different temperatures ranging from 40 to 55°C. The contribution of α₃[⁻OH]² term is small compared with α₂[⁻OH] term and this turns out to be zero at 60°C. Pseudo‐first‐order rate constants (k_obs) for hydrolysis of AZS within the [H⁺] range from 2.5 × 10⁻⁶ to 1.4 M follow the relationship: k_obs = (α₁K _a + B₁[H⁺] + B₂[H⁺]²)/([H⁺] + K_a) where pK_a = 4.37 at 50°C. The value of B₁ is nearly 25 times larger than that of α₁. The rate of alkaline hydrolysis of AZIM is weakly sensitive to ionic strength. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 253–260, 1999     

希夫碱型大环多胺锌配合物对α-吡啶甲酸对硝基苯酚酯催化水解的研究

酶是具有催化活性中心的复杂蛋白质,酶催化反应以其高效性、专一性及反应条件温和而引起人们的极大兴趣.自然界中存在着多种水解金属酶如羧肽酶、碱性磷酸酯酶、碳酸酯酶等,它们能水解蛋白质、磷酯、DNA、RNA等生命物质,是生命过程中不可缺少的重要物质,其催化活性中心由金属离子和若干有机功能团构成.     

聚醚桥连二异羟肟酸配合物催化羧酸酯水解的动力学研究

研究羧酸酯和磷酸酯的水解在环境和生物应用等方面具有越来越重要的意义。为实现对环境友好、高经济效益的生产过程,许多研究者致力于研发反应条件温和、催化效率高和高度专一性的催化剂。因而,仿酶研究倍受人们的关注,其中,水解金属酶是被研究得较为广泛的一类。我们曾报道过异羟肟酸过渡金属配合物仿生催化氧化性能和二氧亲合性能。本文我们将4种聚醚桥连二异羟肟酸过渡金属铜（Ⅱ）、锌（Ⅱ）、钴（Ⅱ）和锰（Ⅱ）配合物（见图1）作为仿水解酶模型,在底物浓度高于催化剂浓度10倍以上的条件下,研究了配合物在缓冲溶液中催化α-吡啶甲酸对硝基苯酯（PNPP）的水解反应的机理,并建立了相应的动力学数学模型;考查了配合物中心金属离子、溶液酸度和反应温度等对催化PNPP水解反应性能的影响。     

Kinetics of gas-phase hydrolysis of ethyl acetate catalyzed by immobilized lipase

Reactions catalyzed by supported enzymes present important advantages when compared with those in aqueous media or organic solvents: separation of enzymes from substrate is easily accomplished, enzyme stability may be improved, and control of the reaction products is more accurate. We present the experimental results of the kinetic study of ethyl acetate hydrolysis in gaseous phase catalyzed by a commercial immobilized lipase (Lipozyme IM; Novo Nordisk). The hydrolysis reaction was studied as a function of ethyl ester and water partial pressure at a constant temperature of 318 K. The amount of biocatalyst used was varied between 100 and 300 mg, and the reaction was studied in a flow-through glass microreactor. Under the conditions used, water was an important parameter in the gas-phase reaction. Activation energy was 24.8 kJ/mol and the overall order of reaction was one. Finally a Bi-Bi reaction mechanism is proposed.     

Studies on the polymerization of ethyl acrylate. I. Kinetic studies

Kinetic studies on the polymerization of ethyl acrylate have been carried out and the various rate constants and their corresponding activation energies determined.     

Intramolecular general base catalyzed ester hydrolysis. The hydrolysis of 2-aminobenzoate esters

Rate constants have been obtained for the hydrolysis of the trifluoroethyl, phenyl, and p-nitrophenyl esters of 2-aminobenzoic acid at 50 degrees C in H(2)O. The pseudo-first-order rate constants, k(obsd), are pH independent from pH 8 to pH 4 (the pK(a) of the amine group conjugate acid). The 2-aminobenzoate esters hydrolyze with similar rate constants in the pH-independent reactions, and these water reactions are approximately 2-fold slower in D(2)O than in H(2)O. The most likely mechanism involves intramolecular general base catalysis by the neighboring amine group. The rate enhancements in the pH-independent reaction in comparison with the pH-independent hydrolysis of the corresponding para substituted esters or the benzoate esters are 50-100-fold. In comparison with the hydroxide ion catalyzed reaction, the enhancement in k(obsd) at pH 4 with the phenyl ester is 10(5)-fold. Intramolecular general base catalyzed reactions are assessed in respect to their relative advantages and disadvantages in enzyme catalysis. A general base catalyzed reaction can be more rapid at low pH than a nucleophilic reaction that has a marked dependence on pH and the leaving group.     

Stereoelectronic control in the base catalyzed hydrolysis of five-membered ring cyclic phosphonamidates

The base catalyzed hydrolysis of 2-phenyl-2-oxo-3-(2,6-dimethylphenyl)-1,3,2-oxazaphospholidine, $\text{6}$, and 2-phenyl-2-oxo-3-(2,6-diisopropylphenyl)-1,3,2-oxazaphospholidine, $\text{7}$, yields ring opened products involving 95% and 100% P-O cleavage, respectively.     

Medium effects in the acid catalyzed hydrolysis of benzohydroxamic acid in binary aqueous mixtures

Hydrochloric acid catalyzed hydrolysis of benzohydroxamic acid (C₆H₅CONHOH) has been studied in dioxane, acetone, DMSO, DMF, methanol, ethanol and isopropanol of varying compositions (10–70 vol.%) at 55°C. The anomalous behavior has been explained on the basis of solvent properties, solvation of the transition state and dielectric constant.     

Tandem three-component reactions of aldehyde, alkyl acrylate, and dialkylmalonate catalyzed by ethyl diphenylphosphine

A new highly efficient three-component reaction of alkyl acrylate, aldehyde and dialkyl malonate using ethyl diphenylphosphine as organocatalyst has been described. Various highly functional compounds bearing hydroxyl groups and the ester functions can be easily prepared in moderate to good yields according to our one-step procedure. The reactions are believed to proceed via Morita-Baylis-Hillman reactions of alkyl acrylate and aldehydes, followed by the Michael addition reactions of dialkyl malonates. Our reactions indicated that the intermediate species formed in the phosphine-catalyzed MBH reaction are an effective organic base to catalyze the Michael addition reactions of dialkyl malonates to the preformed MBH adducts.     

Kinetic Monte Carlo study of binary diffusion in silicalite

We report a Kinetic Monte Carlo (KMC) study of the diffusion of linear n-hexane (nC6) and 2,2-dimethylbutane (22DMB) mixture in zeolite silicalite. We first investigated the loading dependences of single component self- and corrected diffusivities of nC6 at 300 K. Anisotropic transition rates are implemented to account for the distribution of the molecules within the zeolite framework. Repulsive guest-guest interactions are modeled using the parameter introduced by Reed and Ehrlich (Surf. Sci. 102:588–601, 1981). The results are in good agreement with recent experimental Quasi Elastic Neutron Scattering data of Jobic et al. (J. Phys. Chem. B 110:2195–2201, 2006), although the influence of the adsorption isotherm inflection is not reproduced. The binary diffusion study of nC6/22DMB mixtures was performed by implementing the nC6 transition rates used for the single component study while 22DMB molecules propagate via intersection-intersection hops. This KMC model allows for different saturation capacities and accounts for interactions between molecules by introducing f _ij parameters. Results show the large impact of guest-guest interactions between nC6 and 22DMB on both self- and corrected diffusivities of the two components. Molecule-size effects are found to be predominant near 22DMB saturation capacity. Acceleration/deceleration effects already described in the literature are confirmed.     

Photochemical polymerization of gaseous ethyl acrylate

Exposure of gaseous ethyl acrylate to ultraviolet radiation causes deposition of poly(ethyl acrylate) at a rate depending on a number of parameters, including the wave-length of the radiation, its intensity, and exposure time. The rate also depends upon the monomer pressure and the presence of contaminants, most notably moisture and oxygen.     

Exceptional efficiency of palladium nanoparticle catalyzed Heck cross-coupling in binary task specific ionic liquids

The utilization of the task specific onium salt supported substrates in ionic liquids as solvents (i.e., binary task specific ionic liquids) for palladium nanoparticle catalyzed Heck cross-coupling reactions is presented. Adequate substrates have been prepared and used leading to expected products in very high yields. Exceptionally high turnover (TON = 940,000, TOF = 208,000) can be achieved taking advantages of this combination. Additional advantages of this technology reside in the monitoring of the reaction and purification of products after degrafting which are simplified to the extreme.     

Calorimetric study of the kinetics of the bulk polymerization of ethyl acrylate

The bulk polymerization of ethyl acrylate using 1-1′-azobisisobutyronitrile as initiator at several temperatures has been studied by DTA. The order with respect to the monomer and the apparent activation energy of the polymerization process have been determined.     

Reactivity ratios of ethyl acrylate,n-butyl methacrylate copolymer system by 1H-NMR

Ethyl acrylate (EA) and n-butyl methacrylate (n-BMA) copolymers were prepared in solution and the composition of the copolymer samples was estimated by ¹H-NMR spectroscopic techniques. Because the characteristic signals, which vary with the composition of the copolymer, were absent, the ratio of intensities of down-field protons to that of the total protons was used for the estimation of copolymer composition. Reactivity ratios were calculated from these values by using the Kelen-Tudos differential linear equation.     

Efficiencies of some ethyl acrylate chain terminators

A group of substituted phenols, quinone, and tropone were used to retard AIBN-initiated ethyl acrylate polymerization in ethyl propionate solution at 44.7°C. in the absence of oxygen. It was concluded that the efficiency of retardation depended upon the ability of the terminator to stabilize a positive charge on its reaction site in the transition state. Tropone was found to be a particularly good retarder. The radical-trapping efficiency of 2,2-diphenyl-1-picrylhydrazyl in this system was found to be 50–60%.     

Kinetic study of high-conversion copolymerization of butyl acrylate with methyl methacrylate in solution

Butyl acrylate (BA) and methyl methacrylate (MMA) have been copolymerized in a 3 mol/L benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator over a wide composition and conversion range. The overall copolymerization parameter k_p/k_t^1/2 and the composition of the copolymer formed have been measured as a function of conversion. Theoretical values of the coupled parameter k_p/k_t^1/2 calculated from the implicit penultimate unit model and those of cumulative copolymer composition, determined from the Mayo—Lewis terminal model, have been correlated with those experimentally obtained. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1961–1965, 1997     

双Schiff碱过渡金属配合物在胶束溶液中催化BNPP水解的研究

双Schiff碱过渡金属配合物和胶束形成的金属胶束作为模拟磷酸二酯水解酶用于催化BNPP水解，探讨了催化作用机理；提出了一种金属胶束催化BNPP水解的动力学数学模型。研究表明，本文所用的金属胶束在适当酸度、温度、介质的条件下对催化BNPP水解具有较高的活性。