Reactions in solids

Katz A I, Schiferl D and Mills R L 1981 New phases and chemical reactions in solid carbon monoxide under pressure J. Phys. Chem. 88 3176... 

Cyclobutadiene itself is not stable at room temperature. Several derivatives with stabilizing groups have been prepared by the acid-catalyzed dimerization of alkjmes (R. Gompper, 1975). Less substituted cyclobutadienes could be obtained by photolytic reactions in solid matrix at low temperatures (G. Maier, 1973, 1974). 

That this is not always the case should be expected. In fact, if it was not for heterogeneous localization of some flow phenomena, it would be very diflicult to initiate secondary explosives, or to effect shock-induced chemical reactions in solids. Heterogeneous shear deformation in metals has also been invoked as an explanation for a reduction in shear strength in shock compression as compared to quasi-isentropic loading. We present here a brief discussion of some aspects of heterogeneous deformation in shock-loaded solids. 

In most cases of interest, shock-induced chemical reactions in solids are studied in mixtures of powders of the potential reactants. In the earlier description of conceptual models it was emphasized that the pores provide space in which the potential reactants can be more intimately mixed in order... 

F.P. Bowden A.D. Yoffe, Fast Reactions in Solids , Academic Press, NY (1958)... 

P.V. Phung, Propagation of Gasless Reactions in Solids , Combustion Flame 21, No 1... 

Propagation of Gasless Reactions in Solids , Combustion Flame 21, No 1 (1973), 91-97 69) B.E. Douda, Radiative Transfer Model of a Pyrotechnic Flare , NAD-RDTR No 258... 

C.G. Vayenas, Catalytic and Electrocatalytic Reactions in Solid Oxide Fuel Cells, Solid State Ionics 28-30, 1521-1539 (1988). 

P J. Gellings, H.S.A. Koopmans, and A.J, Burgraaf, Electrocatalytic Phenomena in Gas Phase Reactions in Solid Electrolyte Electrochemical Cells, Appl. Catal. 39, 1-24 (1988). 

The Szilard-Chambers Reactions in Solids Carman Harhotlle and Norman Sutin... 

Harbottle, G., Sutin, N. The Szilard-Chalmers Reaction in Solids. Advan. Inorg. Chem. Radiochem. /, 267—314 (1959). 

A few methods produce reactive molecules by reactions in solid matrices. The most widely used consists of irradiating already isolated precursors with UV light (including vacuum UV light at A < 200 nm), y- or X-rays. In this case, the fragments which are formed as products of the precursor s dissociation must not recombine in the matrix site. To achieve this effect, one of the fragments should be either chemically inactive [e.g. N2, CO2 see (la)] or able to diffuse easily from the site [e.g. hydrogen atoms as in (lb)]. 

Having Introduced these examples, let us now examine a method of symbolism useful in characterizing defect reactions in solids. 

K. Hauffe, Reactions in Solids and their Surface, Foreign Literature Publ., Moscow, 1963... 

V.A. Radtsig, Kinetics and Mechanism of Chemical Reactions in Solids, Chemogolovka, 1981 (in Russian)... 

DMAP has been found to improve the coupling reaction in solid phase peptide synthesis (4). Polypeptides synthesized via the DMAP-DCC method were found to be of higher purity compared to other methods of synthesis. In polymer chemistry, DMAP has been used for hardening of resins and in the synthesis of polyurethanes, (5) polycarbonates, (6) and polyphenyleneoxides (7) ... 

Development of the quantum mechanical theory of charge transfer processes in polar media began more than 20 years ago. The theory led to a rather profound understanding of the physical mechanisms of elementary chemical processes in solutions. At present, it is a good tool for semiquantitative and, in some cases, quantitative description of chemical reactions in solids and solutions. Interest in these problems remains strong, and many new results have been obtained in recent years which have led to the development of new areas in the theory. The aim of this paper is to describe the most important results of the fundamental character of the results obtained during approximately the past nine years. For earlier work, we refer the reader to several review articles.1 4... 

The dependence of the proton resonance integral J for the unexcited vibrational states on the vibrations of the crystal lattice was taken into account recently in Ref. 47 for proton transfer reactions in solids. The dependence of J on the nuclear coordinates was chosen phenomenologically as an exponential Gaussian function. 

Most mechanistic work has focused on chemical reactions in solution or extremely simple processes in the gas phase. There is increasing interest in reactions in solids or on solid surfaces, such as the surfaces of solid catalysts in contact with reacting gases. Some such catalysts act inside pores of defined size, such as those in zeolites. In these cases only certain molecules can penetrate the pores to get to the reactive surface, and they are held in defined positions when they react. In fact, the Mobil process for converting methanol to gasoline depends on zeolite-catalyzed reactions. 

There are several ways to induce reactions in solids. The application of heat, electromagnetic radiation, pressure, ultrasound or some other form of energy may induce a transformation in a solid. For centuries, it has been a common practice to subject solid materials to heat in order to determine their thermal stability, to study their physical properties, or to convert one material into another. One important commercial reaction, that producing lime,... 

Reactions in solids are often vastly different from those that take place in solutions. Because many of the reactions in the solid state involve inorganic materials, an introduction to this important topic is presented in this chapter to show some of the principles that are applicable to this area of inorganic chemistry. The emphasis is on showing several types of reactions, but no attempt is made to present comprehensive coverage of the hundreds of reactions that take place in the solid state. Although some 255... 

A rate law that shows some of the peculiarities of reactions in solids arises in the following way. A solid particle having a spherical shape is assumed to react only on the surface. This rate law has been found to model the shrinking of solid particles in aerosols as well as other reactions that take place on the surface of solid particles. 

Methods of data analysis for reactions in solids are somewhat different from those used in other types of kinetic studies. Therefore, the analysis of data for an Avrami type rate law will be illustrated by an numerical example. The data to be used are shown in Table 8.1, and they consist of (a,t) pairs that were calculated assuming the A3 rate law and k = 0.025 min-1. 

The kinetic models just described are only a few of those that have been found to represent reactions in solids. Moreover, it is sometimes observed that a reaction may follow one rate law in the early stages of the reaction, but a different rate law may apply in the later stages. Because many of the rate laws that apply to reactions in solids are quite different from those encountered in the study of reactions... 

Table 8.2 Some Common Rate Laws for Reactions in Solids.

From the discussion presented of reactions in solids, it should be apparent that it is not practical in most cases to determine the concentration of some species during a kinetic study. In fact, it may be necessary to perform the analysis in a continuous way as the sample reacts with no separation necessary or even possible. Experimental methods that allow measurement of the progress of the reaction, especially as the temperature is increased, are particularly valuable. Two such techniques are thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). These techniques have become widely used to characterize solids, determine thermal stability, study phase changes, and so forth. Because they are so versatile in studies on solids, these techniques will be described briefly. 

Gomes, W. (1961). "Definition of Rate Constant and Activation Energy in Solid State Reactions," Nature (London) 192, 965. An article discussing the difficulties associated with interpreting activation energies for reactions in solids. 

House, J. E. (1980). "A Proposed Mechanism for the Thermal Reactions in Solid Complexes." Thermochim. Acta 38, 59-66. A discussion of reactions in solids and the role of free space and diffusion. 

In proposed mechanism I, the loss of water from the complex is the rate-determining step, but removal of water from the coordination sphere of the metal ion should be independent of the nature of the anion that is not part of the coordination sphere of the metal ion. On the other hand, if mechanism II is correct, the entry of X into the coordination sphere of the metal would be dependent on the nature of the anion, because different anions would be expected to enter the coordination sphere at different rates. Because there is an observed anion effect, it was concluded that the anation reaction must be an Sn2 process. However, it is not clear how a process can be "second-order" when both the complex cation and the anion are parts of the same formula. As discussed in Chapter 8, it is not always appropriate to try to model reactions in solids by the same kinetic schemes that apply to reactions in solutions. 

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