Solid phase reactions

Despite the relative infancy in the development of solid phase reactions, a wide range of functionalised resins are commercially available. The main uses of these functionalised resins can be roughly classified as follows ... 

The experimental studies of a large number of low-temperature solid-phase reactions undertaken by many groups in 70s and 80s have confirmed the two basic consequences of the Goldanskii model, the existence of the low-temperature limit and the cross-over temperature. The aforementioned difference between quantum-chemical and classical reactions has also been established, namely, the values of k turned out to vary over many orders of magnitude even for reactions with similar values of Vq and hence with similar Arrhenius dependence. For illustration, fig. 1 presents a number of typical experimental examples of k T) dependence. 

A considerable amount of research has been conducted on the decomposition and deflagration of ammonium perchlorate with and without additives. The normal thermal decomposition of pure ammonium perchlorate involves, simultaneously, an endothermic dissociative sublimation of the mosaic crystals to gaseous perchloric acid and ammonia and an exothermic solid-phase decomposition of the intermosaic material. Although not much is presently known about the nature of the solid-phase reactions, investigations at subatmospheric and atmospheric pressures have provided some information on possible mechanisms. When ammonium perchlorate is heated, there are three competing reactions which can be defined (1) the low-temperature reaction, (2) the high-temperature reaction, and (3) sublimation (B9). 

Based on this approach, an approximate energy balance around the solid-phase reaction zone is given as... 

The most notable theoretical analysis of the instability problem has been presented by McClure and Hart (M5). These investigators postulated a generalized combustion zone that includes a temperature-dependent and pressure-independent solid-phase reaction zone, and a temperature- and pressure-dependent gas-phase reaction zone. From this general model, Hart... 

These studies have indicated that the independent parameters controlling the postulated solid-phase reactions significantly affect the resulting acoustic admittance of the combustion zone, even though these reactions were assumed to be independent of the pressure in the combustion zone. In this combustion model, the pressure oscillations cause the flame zone to move with respect to the solid surface. This effect, in turn, causes oscillations in the rate of heat transfer from the gaseous-combustion zone back to the solid surface, and hence produces oscillations in the temperature of the solid surface. The solid-phase reactions respond to these temperature oscillations, producing significant contributions to the acoustical response of the combustion zone. 

Williams (W2) has recently modified the analysis of Hart and McClure by considering in more detail the effect of diffusional processes on the gas-phase reaction zone. The results of his study show that the diffusional processes tend to stabilize the gas-phase combustion process, indicating that the postulated solid-phase reactions are probably the underlying cause of the instability. 

The concentrations of reactants are of little significance in the theoretical treatment of the kinetics of solid phase reactions, since this parameter does not usually vary in a manner which is readily related to changes in the quantity of undecomposed reactant remaining. The inhomogeneity inherent in solid state rate processes makes it necessary to consider always both numbers and local spatial distributions of the participants in a chemical change, rather than the total numbers present in the volume of reactant studied. This is in sharp contrast with methods used to analyse rate data for homogeneous reactions in the liquid or gas phases. 

Surface features can also be revealed by etching, which permits identification of points of intersection of line dislocations with the surface, and this is valuable in determining the role of these imperfections in chemical processes [45,214] and, in particular, nucleus formation. Smaller topographical details can be rendered visible by the evaporation of a thin (<0.5 nm) film of gold onto the surface [215,216]. Heights and depths of surface features can be determined by interferometry [203—205]. Microcinematography has also been used [217] to record the progress of solid phase reactions. 

The several distinct derivations of eqn. (6) originally provided [30] by Avrami [436], by Erofe ev [437,448] and by Mampel [447] and developed by others, is a consequence of the importance to be attached to this expression for the kinetic analysis of solid phase reactions. Written in general form... 

Rate equations which have found application in kinetic studies of solid phase reactions a... 

Green [491] has given a general account of the applications of statistical methods to kinetic analyses and, without mentioning specific examples, suggests the approach could be of value in rate studies of solid phase reactions. The steps in his treatment are given below [492,493],... 

No single criterion has been recognized as constituting a satisfactory basis for the systematic classification of the kinetics of solid-phase reactions (Chapt. 1, Sect. 3). A classification based on the anion is preferred here since it is this constituent which undergoes breakdown in most reactions of interest and proposed reaction mechanisms for substances containing a common anion often include similar features. 

Lorsbach B. A., Kurth M. J. Carhon-Carhon Bond Forming Solid-Phase Reactions Chem. Rev. (Washington, D. C.) 1999 99 1549-1581... 

Journal of Applied Polymer Science 81, No.9, 29th August 2001, p.2249-52 MECHANOCHEMICAL SOLID-PHASE REACTION BETWEEN POLYVINYLIDENE FLUORIDE AND SODIUM HYDROXIDE Qiwu Zhang Jinfeng Lu Saito F Baron M Tohoku,University Eeole des Mines d Albi Carmaux... 

Knowledge of such fine differences between the compositions of the octachloroditechnetates (+2.5) is useful mainly for studying certain solid-phase reactions, since the dissolution of these compounds leads to their dissociation into the M+, H+, 0+, and [Tc2Cl8]3- ions and the properties of the solutions are then determined by the concentration of the octachloroditechnetate ions. The simplified formula of these complexes M3 [Tc2C18] H20 was therefore used in subsequent studies [9,11,15,42,43,48,49]. 

The diffusion coefficient (D) of ferf-butyloxycarbonyl-L-phenylalanine (Boc-Phe) was determined in a Merrifield network of polystyrene (PS) gels used as a solid phase reaction field.108 When probe molecules have multicomponents in diffusion on the measurement time scale, the total echo attenuation is given by a superposition of contributions from the individual components ... 

For general solid-phase reactions in a dedicated multimode instrument, an adaptable filtration unit is available from Anton Paar (see Fig. 3.18). This tool is connected to the appropriate reaction vessel by a simple screw cap and after turning over the vessel, the resin is filtered by applying a slight pressure of up to 5 bar. The resin can then be used for further reaction sequences or cleavage steps in the same reaction vessel without any material loss. However, at the time of writing, no applications of this system for solid-phase synthesis had been reported. 

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