Search results for "reaction rate constant"

A study of the enolization of some alkyl ketones in lyomesophases formed by alkylammonium surfactants

1988

The kinetics of enolization of acetone, 3-pentanone, and 6-undecanone have been studied in lyotropic systems in the isotropic, nematic, and lamellar phases. The data, analysed in terms of spontaneous and acid-catalyzed rate constants, do not show any relevant influence of the physical nature of the phase. Effects are instead observed in relation to the length of the alkyl chains of the ketones and the type of the amphiphilic molecule. 6-undecanone has a surprising effect in stabilizing ordered mesophases.

The effect of TMEDA on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran using lithium as counterion

2000

The kinetics of the anionic polymerization of methyl methacrylate in presence of N,N,N', -tetramethylethylenediamine (TMEDA) in THF are investigated using 1,1-diphenyl-hexyllithium as initiator in a temperature range between -20°C and 0°C in a flow-tube reactor. The rate constants of propagation determined in the presence of TMEDA are compared to those obtained in the absence of a chelating agent. For propagation, the reaction order with respect to active centers is found to be 0.5 in both cases which indicates that the chelation of the lithium cation does not effectively perturb the aggregation of the enolate ion pair. Both the rate constants of propagation via non-aggregated ion pairs, k …

Basic kinetic model for the reaction yielding linear polyurethanes. II

1995

On the basis of the gradual polyaddition kinetic model developed earlier, an attempt was made to provide a generalized mathematical model for the set of reactions yielding linear polyurethanes. The model is a system of first-order ordinary differential equations. It was assumed at the present stage of this model that the rate constants for the reaction considered do not change. The model developed was then solved numerically. Average molecular weight of the polymer and composition data for oligomers were calculated for a constant volume batch reactor and varied process parameters. The GPC method, which was tested for model urethane oligomers, was employed to verify the model developed. The …

Molecular Parameters of Hyperbranched Copolymers Obtained by Self-Condensing Vinyl Copolymerization, 2. Non-Equal Rate Constants

2001

The kinetics, molecular weight averages, and the average degree of branching, DB, are calculated for the self-condensing vinyl copolymerization (SCVCP) of a vinyl monomer M with an "inimer" AB* in the case of different reactivities of active species. Emphasis is given to two limiting cases: formation of "macroinimers" occurs if the monomer M is more reactive than the vinyl groups of inimers or polymer, and "hyperstars" are formed in the opposite case. It is shown that the kinetics, the molecular weight averages, and the average degree of branching strongly depend on the relative reactivities of monomer and inimer. Comparison with experimental data shows that consistent fits of the reactivit…

A new experimental protocol for intrazeolite photooxidations. The first product-based estimate of an upper limit for the intrazeolite singlet oxygen …

2002

The intrazeolite photooxidations of several alkenes have been examined in hexane and in perfluorohexane slurries. The ability of perfluorohexane to increase the affinity of alkenes for the interior of the zeolite was documented. The nearly identical reaction rates in the two slurry solvents are attributed to a leveling of the singlet oxygen lifetime by the zeolite framework. A consideration of the rates of the various intrazeolite processes was used to estimate an upper limit for the intrazeolite lifetime of singlet oxygen.

Cu2+ Coordination Properties of a 2-Pyridine Heptaamine Tripod: Characterization and Binding Mechanism

2009

The synthesis, protonation, and Cu(2+) coordination chemistry of a tripodal heptaamine ligand (L(1)) functionalized with 2-pyridine fragments at the ends of its three branches are reported. L(1) presents six relatively high protonation constants followed by much more reduced constant that as indicated by the UV-vis and NMR data, occur on the pyridine fragments. p[H]-metric, ESI/MS(+), EPR and UV-vis data show that L(1) is able to form mono-, di-, and trinuclear Cu(2+) complexes. Slippage movements and molecular reorganizations have been observed to occur as a function of p[H] in the 1:1 Cu(2+) complexes. The kinetic studies showed that the complex formation is fast and proceeds through a di…

Kinetics in a Double Antibody Radioimmunoassay (RIA): Diffussion Control

2012

Competitive protein binding radioimmunoassay (CPB-RIA) is a principal method for quantifying serum C Peptide concentration. The accuracy of this method is critically dependent on factors that influence the reaction between anti-C Peptide antibody (P) with 125I-C Peptide (M). We studied the influence of initial concentration of M, ionic strength, and viscosity on the reaction between M and P. A kinetic model for the the reaction between. Such model adjusts satisfac- torily to the results. Bi-exponential and irreversible kinetics is determined. The results of the viscosity analysis show clear negative influence on the direct reaction rate. The ionic strength shows scarce influence on equilibr…

1977

Methacryloyloxyalkyltrimethylammonium chlorides (1a–c) with different alkyl chain lengths were synthesized and polymerized radically with 4,4′-azobis(4-cyanovalerianic acid) and K2S2O8 as initiators. With K2S2O8 as initiator, reaction orders of 0,5 and 1 with respect to initiator and monomer, were found. For the ionic monomers with longer alkyl chains the ratio of rate constants kp(2fkd/kt)0,5 was determined over a wide concentration range. It was found that with decreasing monomer concentration the ratio of rate constants increases, which is caused by a diminished termination rate because of an increased electrostatic repulsion of the ionic polymer radicals in dilute solution (increase of …

Kinetische untersuchungen zur reaktionsfähighkeit von chlormethylgruppen in methylendiphenolen

1984

The chloromethyl derivatives of 16 differently substituted methylenediphenols were synthesized for the first time. To compare their reactivity, the solvolysis in methanol and the animolysis with an excess of p-nitroaniline in dimethyl sulfoxide were studied kinetically at 25°C. The rate constants for the methanolysis do not differ very much, beside of the fact that para-chloromethyl derivatives react about 100 times faster than ortho-chloromethyl derivatives. However, for the aminolysis a large acceleration up to 103 was found for compounds having both hydroxyl groups in ortho-position to the methylene bridge. Obviously, the cleavage of the OH bond, which occurs in the rate determining step…

Influence of hydrogen peroxide on the kinetics of phenol photodegradation in aqueous titanium dioxide dispersion

1990

Abstract The influence of hydrogen peroxide on the phenol photodegradation rate under near UV radiation was investigated in homogeneous and heterogeneous systems: the heterogeneous systems were aqueous dispersions of titanium dioxide (anatase). The hydrogen peroxide photodecomposition reaction was also investigated for all the systems used. The highest rate of phenol photodegradation was observed in the heterogeneous system for the contemporary presence of hydrogen peroxide and oxygen. The rate equations for phenol photodegradation and hydrogen peroxide photodecomposition for both systems were obtained. A mechanistic model able to explain the main experimental results is also proposed.