A kinetic study of reactions between polymers

A study has been made of the rate of reaction of polymers containing different reactive groups. Poly(ethylene oxide) with isocyanate end-groups has been reacted with poly(ethylene oxide) with hydroxyl end-groups. Polymers with higher molecular weights were found to give lower rates of reaction. It was not possible to find an analogous low molecular weight compound which gives a reasonable rate of reaction compared to the polymers. This suggests that the rate of reaction is very dependent on the environment of the reacting groups and brings a possibility of ambiguity into the conclusions.     

Substitution reactions in ionic liquids. A kinetic study

The rate of the substitution reaction of (R)-3-chloro-3,7-dimethyloctane (1) with either methanol or benzyl alcohol in mixtures containing the ionic liquid [Bmim][N(CF₃SO₂)₂] was monitored using ³⁵Cl NMR spectroscopy. The enantiomeric excess of the product, (S)-3-methoxy-3,7-dimethyloctane (2a), was analyzed using chiral gas chromatography. This product showed a decreasing enantiomeric excess with increasing concentration of ionic liquid. The rate of reaction of substrate 1 in each case varied with the concentration of the ionic liquid. Polarity measurements of the solvent mixtures were undertaken by standard methods, which are compared both to each other and to the observed rates. Solvent reorganization and selective solvation are also each proposed as contributing to the difference in the observed rates of reaction.     

A generalized kinetic model for heterogeneous gas-solid reactions

We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used.     

Geometric description of chemical reactions

We use the formalism of Geometrothermodynamics to describe chemical reactions in the context of equilibrium thermodynamics. Any chemical reaction in a closed system is shown to be described by a geodesic in a 2-dimensional manifold that can be interpreted as the equilibrium space of the reaction. We first show this in the particular cases of a reaction with only two species corresponding to either two ideal gases or two van der Waals gases. We then consider the case of a reaction with an arbitrary number of species. The initial equilibrium state of the geodesic is determined by the initial conditions of the reaction. The final equilibrium state, which follows from a thermodynamic analysis of the reaction, is shown to correspond to a coordinate singularity of the thermodynamic metric which describes the equilibrium manifold.     

On the description of reactions in solution

A formulation for diffusion-influenced reactions in solution is given in which reactive and translational contributions are separated, steady state rate-limiting step formulations are generalized to the dynamical case and the influence of different experimental initial conditions is isolated.     

Redox reactions: inconsistencies in their description

The paper is aimed at defining reduction, oxidation, and redox reactions based both on the oxidation number and charge changes in reacting species. It is rationalized that the processes of oxidation and reduction, usually occurring simultaneously, can occur also as independent processes. It is explained that in balancing chemical equations of redox reactions the “gain” or “loss” of electrons should be understood as changes in oxidation number. A formal expressions “+n e^?” and “?n e^?” represent in reality a decrease and increase in oxidation number by n units, respectively.     

A simple kinetic model of antigen-antibody reactions in particle-enhanced light scattering immunoassays

Polymer colloids coated by antibodies are used in diagnostic tests for the detection of antigens in biological fluids. We present in this paper a simple kinetic model for the optical monitoring of the formation of specific complexes between antigen and antibody with amplification by latex beads. The antibodies are physical or chemically adsorbed onto sulphonate polystyrene or chloromethylstyrene particles respectively. This is a very simple model combining the La Mer idea of optimum surface coverage with Langmuir adsorption of antigen molecules. The kinetic model explains reasonably well the optical response of immunolatex prepared by both methods of immobilization of antibodies on polymer carriers. According to the results obtained with this model the percentage of active IgG on latex particles is extremely low, with a maximum of a 5%.     

Using vortex layer devices to accelerate chemical reactions in low-speed systems

This work shows the effectiveness of applying vortex layer devices to accelerate chemical reactions in low-speed systems, using the production of dioctylphthalate as an example. The influence of production conditions on the product properties is evaluated.     

CRTA: A mathematical description of reversible thermal dissociation reactions in the Q-derivatograph

For the analysis of experimental data, an elemental process model is suggested, which considers the kinetic and thermodynamic parameters of the reaction, its topochemical mechanism, and the mass exchange between the reaction zone and the external medium. The proposed model is fully based on the principal assumption that the duration of the experiment is much greater than the relaxation time for all the heat transfer processes in the sample volume.     

Monte Carlo simulation of equilibrium reactions at vapor-liquid interfaces

Chemical reactions are known to behave differently, depending upon their local environment. While the interactions with neighboring molecules may alter both the kinetics of chemical reactions and the overall equilibrium conversion, we have performed simulations of the latter. The particular environment that we address is the vapor-liquid interface, since only a few, limited studies have explored the influence of an interface on equilibrium reaction behavior. Simple dimerization reactions are modeled, as well as more complex multicomponent reactions, using the reactive Monte Carlo (RxMC) simulation technique. We find that the conversion of a reaction can be markedly different at an interface as compared to the bulk vapor and liquid phases, and these trends are analyzed with respect to specific intermolecular interactions. In conjunction, we calculate the surface tension of the reacting fluids at the interface, which is found to have unusual scaling behavior, with respect to the system temperature.     

A kinetic study of reactions of Et3ZnLi and di-tert-butyl ketone

An organozincate of composition Et3ZnLi and di-tert-butyl ketone react in toluene to form (after hydrolysis) ethyl-di-tert-butylmethanol. The rate is proportional to approximately [Et3ZnLi](-0.5)[ketone](1) when the initial concentration of Et3ZnLi is greater than that of the ketone but proportional to [Et3ZnLi](1)[ketone](-1) when the initial concentration of ketone is greater than that of Et3ZnLi. The rate of addition of Et3ZnK to di-tert-butyl ketone is <10(-4) that of Et3ZnLi.