Reaction between two solids

This study was prompted by a report that phthalimidoacetic acid (R = CH2C02H, see also Scheme 4.11, vide supra) could be synthesized by the reaction of phthalic anhydride with glycine in the absence of solvent, which involves the reaction between two solids [56], However, in this study [45], it was established that the synthesis of phthalimides under solvent-free reactions requires at least one liquid reactant in order to occur. This was possible when reacting a liquid amine (e.g. R = CH2Ph) or a solid with a sufficiently low melting point to melt rapidly under MW (e.g. R = (CH2)6OH, m.p. 56-58). In these cases, the reaction temperature was typically over 135 °C after 2 or 3 min of MW heating resulting in dissolution of phthalic anhydride in the molten... 

Solvent-free microwave reactions between phthalic anhydride and amino compounds were carefully re-examined by Gedye et al. [93], who showed that the reaction needs at least one liquid phase. The reaction occurs after melting of the phthalic anhydride and subsequent solubilization in the amine. It was concluded that reactions between two solids might not occur and that a high-boiling joint solvent might be necessary. Excellent yields (>90%) were always obtained within short reaction times (5-10 min) (Scheme 8.67). 

Although we have shown several kinetic models for reacting solids, none specifically applies to a reaction between two solids. A rate law that was developed many years ago to model reacting powders is known as the Jander equation, and it is written as... 

This equation has the same form as that for three-dimensional diffusion (see Table 8.2). The Jander equation was found to model the process shown in Eq. (8.27) quite well. The reaction between two solids requires the reaction to begin on the surface of the particles and progress inward. For solids in which there is no anisotropy in the structures, diffusion should take place equally in all directions, so a three-dimensional diffusion model would seem to be appropriate. 

Reaction between two solid phases in the presence of a fluid phase... 

As far as we are aware, the only examples of reactions between two solids in a solvent-free and catalyst-free environment were performed with neat 5 or 8-oxobenzopyran-2(lH)-ones, with a variety of aromatic and heteroaromatic hydrazines, providing rapid access to several synthetically useful heterocyclic hydrazones (Scheme 16) [71]. 

Lawrence Stamper Darken (1909-1978) subsequently showed (Darken, 1948) how, in such a marker experiment, values for the intrinsic diffusion coefficients (e.g., Dqu and >zn) could be obtained from a measurement of the marker velocity and a single diffusion coefficient, called the interdiffusion coefficient (e.g., D = A ciiD/n + NznDca, where N are the molar fractions of species z), representative of the interdiffusion of the two species into one another. This quantity, sometimes called the mutual or chemical diffusion coefficient, is a more useful quantity than the more fundamental intrinsic diffusion coefficients from the standpoint of obtaining analytical solutions to real engineering diffusion problems. Interdiffusion, for example, is of obvious importance to the study of the chemical reaction kinetics. Indeed, studies have shown that interdiffusion is the rate-controlling step in the reaction between two solids. 

C. Conducting Composites Formed by Direct Charge-Transfer Reaction Between Two Solid Components... 

In heterogeneous reactions, either the reaction at the phase boundary or the transport to or from the reaction zone can be rate-determining. In the case of a reaction between two solid phases, the diffusion of one reactant determines, in general, the rate of the reaction. Diffusion is considered in more detail in section 18.5. 

Emanation techniques are also used for the study of reactions between two solids, for instance the formation of PbSiOs (as in the preparation of lead glass) by the reaction... 

Reactions between Metals. These are essentially phase-boundary reactions between two solids and are of the simplest type. The reaction between copper and... 

The hydrazone was subsequently treated with KOH under the action of MW irradiation to undergo Wolff-Kishner reduction (leading to PhCH2Ph) within 25-30 min in excellent yield (95%). As an extension, the reaction of neat 5- or 8-oxoben-zopyran-2(li-f)-ones with a variety of aromatic and heteroaromatic hydrazines is remarkably accelerated by irradiation in the absence of any catalyst, solid support, or solvent [105] (Eq. 21). Kinetic considerations for the reaction between two solids below their melting points have been explained by the formation of a eutectic melt during the reaction ... 

The first example of a reaction between two solids, under solvent-free and catalyst-free conditions, was demonstrated [41] when the reaction of neat 5- or 8-oxobenzo-... 

The question arises as to what type of rate law can be used to model reactions between two solids. Probably the most widely employed rate law is that known as the Jander equation. 

Although causing a reaction between two solids by heating them is a common practice, a reaction between two solids using ultrasound as the energy source was studied by Kassel (1994). This work was carried out to assess the feasibility using this technique as a basis for kinetic studies. One... 

Reactions between two solids are analogous to the oxidation of a metal, because the product of the reaction separates the two reactants. Further reaction is dependent on the transport of material across this barrier. As with oxidation, cracking, porosity and volume mismatch can all help in this. In this section, the case when a coherent layer forms between the two reactants will be considered. The mechanism of the reaction may depend on whether electron transport is possible in the intermediate phase, and the rate of reaction will be controlled by the rate of diffusion of the slowest species. To illustrate the problems encountered a typical solid-state reaction, the formation of oxide spinels, is described. 

A parabolic rate constant is characteristic of a reaction between two solids which is controlled by ... 

The immobilization of the metal complex can be achieved by adding the metallic derivative to the already formed polymer, via reactions at the ligand functional groups in the polymer chains. When the metal complexes to be anchored are soluble, reaction with the coordinating polymer (soluble or insoluble) may be carried out by conventional synthetic methods. It is highly desirable that the metallic precursor is soluble. Otherwise the metal-polymer reaction between two solids suspended in a solvent leads to conditions not favorable to a high yield of product. 

Reaction between two solids There are two types, addition and displacement reactions ... 

Another example of the use of percolation in inorganic chemistry is the SHS reaction as described in Chapter 6. The reaction between two solid powders (such as the reaction between titanium and boron particles) can propagate after local ignition only if the heat of reaction is high enough and loss of heat low enough. 

The simplest system involves the reaction between two solid phases, A and B, to produce a solid solution C. A and B are commonly elements for metallic systems, while for ceramics they are commonly crystalline compounds. After the initiation of the reaction, A and B are separated by the solid reaction product C (Fig. 2.13). Further reaction involves the transport of atoms, ions, or molecules by several possible mechanisms through the phase boundaries and the reaction product. Reactions between mixed powders are technologically important for powder synthesis. However, the study of reaction mechanisms is greatly facilitated by the use of single crystals because of the simplified geometry and boundary conditions. 

Tammann Temperature. The temperature at which reaction between two solids (or sintering within powder composed of a single solid) becomes appreciable. As originally defined by G. Tammann (Z. angew. Chem., 39,869, 1926) this temperature lies between the two values obtained by multiplying the m.p. K) of each reactant by 0.57. The temperature is only approximate and different multiplying factors have been proposed. 

The majority of the chemical reactions discussed in this chapter take place in solution. This is because the reaction between two solid reactants often proceeds very slowly or not at all. In a solid, the molecules or ions in a crystal tend to occupy approximately fixed positions, so that the chance of two molecules or ions coming together to react is small. In liquid solutions, reactant molecules are free to move throughout the liquid therefore, reaction is much faster. When you run reactions in liquid solutions, it is convenient to dispense the amounts of reactants by measuring out volumes of reactant solutions. In the next two sections, we will discuss calculations involved in making up solutions, and in Section 4.10 we will describe stoichiometric calculations involving such solutions. 

The processes discussed in this chapter belong to the class of solid-state reactions in which the reaction between two solid compounds results in the formation of a third. The compounds in question are divalent metal oxides reacting with ferric oxide to form ferrites. The interaction between the sintering process and that of compound formation complicates the interpretation of the experimental results. 

The structure of a mechanism depends on the nature of the reaction (decomposition of a solid, reaction between a gas and a solid, reaction between two solids, etc.). However, in all the cases that require transport of matter from one area to another, we will introduce the phenomena of diffusion and will then envisage the formation of the diffusing particles at the border lines of the diffusion zones (except if they exist in the initial state such as caibon in steel during decaiburization) and their consumption (except if they exist in the finished products such as a gas produced by the reaction and diffusing through pores). 

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