Liquid-state reactions

The chemical methods can be divided into three types, in accord with three aggregate states of the matter (i) gas phase reactions, (ii) liquid state reactions, and (iii) solid state reactions. 

Gas phase reactions are not so common in producing solid oxides and will not be considered here. As far as liquid state reactions are concerned, these can be performed in aqueous and non-aqueous solvents and can be subdivided into (i) precipitation and co-precipitation, including the so-called template synthesis, (ii) evaporation, and (iii) sol-gel methods. 

Diffusion of molecules in rigid glasses is negligible within the lifetimes of excited molecules, so that the main reactions are unimolecular dissociations and isomerization. These are rather similar to liquid state reactions, but the fragments cannot separate through diffusion and often recombine to restore the reactants. There are exceptions when the photoproducts are in fact more stable than the reactants, as in the case of photoeliminations. 

In the last decade, instrumental techniques have advanced to the point where many of these limitations can be removed. Quantitative solution-phase studies, making use of, IC- and 2vSi-NMR on high-field instruments, can now include direct measurement of low concentrations of multifunctional intermediates on a time scale appropriate for kinetic studies [25-31], Studies of reactions with surfaces at submonolayer concentrations are now becoming feasible [32]. Both solid-state and liquid-state reactions can be measured simultaneously [32],... 

The kinetics of the liquid-state reaction are also first order. For both the solid and liquid the activation enthalpies and entropies are the same, AS = 8 J deg1, indicating that the rate-determining step is the breaking of a Cl-O bond, with the formation of atomic oxygen... 

Polymerization is influenced by the physical structure and phase of the monomer and polymer. It proceeds in the monomer, and the chemical configuration of the macromolecules formed depends on whether the monomer is a liquid, vapor, or solid at the moment of polymerization. The influence of structural phenomena is evident in the polymerization of acrylic monomer either as liquids or liquid crystals. Supermolecular structures are formed in solid- and liquid-state reactions during and simultaneously with polymerization. Structural effects can be studied by investigating the nucleation effect of the solid phase of the newly formed polymer as a nucleation reaction by itself and as nuclei for a specific supermolecular structure of a polymer. Structural effects are demonstrated also using macromo-lecular initiators which influence the polymerization kinetics and mechanism. 

Komljenovic M.M., Radakovic A., Zivanovic B.M. et al. An investigation of solid- and liquid-state reactions in CaO-SiOj system. Science of Sintering 1994 26 185-93. 

At least two points should be especially emphasized, (i) From the solvent part, the parent radical cations exist in a non polar surrounding. Hence, the cations have practically no solvation shell which makes the electron jump easier in respect to more polar solvents. In a rough approximation the kinetic conditions of FET stand between those of gas phase and liquid state reactions, exhibiting critical properties such as collision kinetics, no solvation shell, relaxed species, etc. (ii) The primary species derived from the donor molecules are two types of radical cations with very different spin and charge distribution. One of the donor radical cations is dissociative, i.e. it dissociates within some femtoseconds, before relaxing to a stable species. The other one is metastable and overcomes to the nanosecond time range. This is the typical behavior needed for (macroscopic) identification of FET ... 

David W. Oxtoby is a physical chemist who studies the statistical mechanics of liquids, including nucleation, phase transitions, and liquid-state reaction and relaxation. He received his B.A. (Chemistry and Physics) from Harvard University and his Ph.D. (Chemistry) from the University of California at Berkeley. After a postdoctoral position at the University of Paris, he joined the faculty at The University of Chicago, where he taught general chemistry, thermodynamics, and statistical mechanics and served as Dean of Physical Sciences. Since 2003 he has been President and Professor of Chemistry at Pomona College in Claremont, California. 

The photoisomerization dynamics of diphenylbutadiene in both liquid and solid alkane environments has been analyzed in paper which is one contribution to the complete journal issue on the role of solvents in liquid state reactions. Several related topics of photophysical interest are discussed in this collection of papers. 

Before presenting the mathematical formulation of the theory, it is useful to describe the types of dynamic event that are likely to be important for the description of liquid-state reactions this discussion shows why current theories of the dynamics of simple liquids are relevant for this problem. 

The dynamic process that enter into the rate kemal expression [(9.46) or (8.9)] are, of course, those that have been included in the kinetic equation, as discussed briefly in Section VII. We discuss now the specific processes, which are relevant for the rate kernel, in more detail. The kinetic theory expression contains all the collision events that one might anticipate would be important for liquid state reactions. The analysis of the rate kernel in the limit where velocity relaxation effects are neglected bears a strong similarity to the derivation of Stokes law from kinetic theory, and we also explore this relationship. 

There is still a gap between our models of liquid-state reactions and the often bewildering complexity of real chemical systems. Progress in shortening the gap will probably come only from the application of a variety of methods to this problem. The full promise of picosecond spectroscopy techniques for studying the details of the dynamics of reactive events in liquids has yet to be realized. How deeply can these methods probe the dynamics Computer simulations, another source of experimental information in reacting systems, are only beginning to be exploited. "" The description by direct computer simulation of both primary and secondary recombination dynamics, for example, would yield a wealth of information that could be used to test theories. 

Y. S. Li and K. R. Wilson, /. Am. Chem. Soc., submitted for publication. Fluctuation, Regression and Liquid State Reaction Dynamics. 

Komljenovic, M.M., Zivanovic, B.M., and Rosie, A. (1997) -dicalcium silicate synthesis by liquid state reaction, in Proceedings 10th ICCC Goteborg, paper li017. 

P.J. Stiles, D.F. Fletcher, I. Morris, The effect of gravity on the rate of a simple liquid-state reaction in a small unstirred cylindrical vessel (II), Phys. Chem. Chem. Phys., 2001, 3, 3651-3655. 

An EPR study on and Cr ions introduced by solid- and liquid-state reactions with synthetic zeolites 3 A, 4A, 5 A, and the natural clinoptilolite was reported [96K2]. The coordination stracture around the Cu ions was found to be square pyramidal when solid-state reactions were used, whereas it is octahedral when the ions were introduced by the liquid-state reaction. In the above zeolites, Cr was oxidized to Cr, which coordination is square pyramidal. 

If collisions were the only factor, however, most gaseous and liquid state reactions would take place almost instantaneously if every collision resulted in a reaction. Such high reaction rates are not observed, a fact that brings us to assumptions 2 and 3. 

The rapidity of some liquid-state reactions at first seems surprising since ordinary diffusion processes in liquids take hours or days to occur. The difference is that in an ordinary diffusion process the root-mean-square distance traveled by molecules might be several centimeters, whereas the mean distance between reacting molecules in a solution reaction might be a few nanometers. 

The temperature dependence of rate constants for both gaseous and liquid-state reactions is usually well described by the Arrhenius formula, Eq. (12.3-2). For activation-limited reactions, the activation energies are roughly equal to those for gas-phase reactions. This is as expected, since the collisional activation is very similar to that of gaseous reactions. In the case of diffusion-limited reactions, the temperature dependence of the rate constant is governed by the diffusion coefficients. Diffusion coefficients in liquids commonly have a temperature dependence given by Eq. (10.4-5), which is also of the same form as the Arrhenius formula ... 

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