Solid state reactions isomerization

This distinction is, however, only practical. Several reaction types are not easily encompassed in the above description. For instance, Scheffer (see within this book) has provided ample examples of stereocontrolled solid-state reactions [11], while solid-state isomerizations have been studied by Coville and Levendis [12]. These processes can be explained with the reaction cavity concept, i.e. reactivity takes place in a constrained environment generated by the surrounding molecules. Relevant contributions to the field have also derived from the studies of Eckhardt [13] and those of Ohashi and collaborators [14]. 

Solid-state reactions are known from thermal intracrystalline conversions (isomerizations or loss of volatile fragments), photoreactions, gas-solid reactions, and solid-solid reactions. As all of these relate strictly to the crystal packing (unifying solid-state mechanism) and are not separated in the various sections. Also, nontopotactic (normal) and topotactic (very rare) reactions are not separated in different sections. 

The irradiation of the optically active dibenzbarrelene (72) in solution affords the four isomeric products (73 a-d). The ratio of products formed (73)(a+b) (73)(c+d) is 55 45. Irradiation of a single crystal affords the same four products but in a ratio of 90 10 when the conversion was kept to < 25 %. The results obtained show that there is no chiral selectivity in the solution phase conversion but that there is a preference for the formation of one of the regio isomers (73 a.b). The solid state reaction is considerably different and affords the regio isomer (73a) in high optical purity (80 % enantiomeric excess). ... 

There have been studies of polyanion unit isomerization in the solid state but such isomerizations are more problematical to quantify and unequivocal inferences from them are harder to come by than from the analogous studies in solution. The difficulty derives in part because high-quality kinetics data are hard to obtain for reactions in the solid state. Nonetheless, some reports on solid-state POM isomerization in the time period of this review afford valuable insights. 

In this chapter, we describe the isomerization, dimerization, and topochemical polymerization of benzyl muconates with various kinds of substituents on the benzyl ester group (Scheme 24.1), in order to reveal the solid-state reaction mechanism by the direct observation of crystal structures which change during the reactions. 

Eslami studied the solid-state thermal isomerization of [Co(NH3)5(ONO)]Cl2 (nitrito isomer) to [Co(NH3)5(N02)]Cl2 (nitro isomer) and the reverse reaction, using DSC [134], The isomerization was shown to be essentially an equilibrium process and the interconversions are accelerated at above 65 °C, to reach the equilibrium state at about 155 C. After establishment of the equilibrium, the relative amounts of the two isomers at any temperature are governed by a Gibbs energy relationship. 

The solid-state facile isomerization of the [(dppe)Ni( / -N02)C1] complex to its nitrito isomer (Figure 24A), Raithby noted, was possible due to the use of the bulky phosphine ligands which allowed the nitro group to sit in a sterically sheltered reaction cavity so that the interconversion could occur... 

The reactivity of butadiene and -diyne derivatives in layer perovskites demonstrates the suitability of these complex salts to act as templates for solid state reactions. Besides the polyaddition also other chemical reactions should be able to occur with a high stereoselectivity, as for example isomerizations, or addition reactions, such as hydrations, halogenations, oxidations, or polycondensations. In any case it will... 

As mentioned above, an example where lattice control over the course of an organic solid state reaction is explicit is provided by the solid state photodimerization of trans-cinnamic acid and many of its derivatives.When irradiated in the melt or in solution, cinnamic acid derivatives do not dimerize — the presumed singlet photoexcited state being too short-lived for reaction in such mobile phases. The only consequence of irradiation is trans cis isomerization. Irradiation of crystalline solids, however, was found to result in one of three distinct events — and that which occurs found to depend upon the solvent of crystallization— see Scheme 6.1. The contribution of Schmidt, Cohen, and co-workers at the Weizmarm Institute in Israel was first to appreciate the importance of polymorphism and then to establish a direct correlation between the molecular packing within a particular polymorphic phase and the nature of the photodimer which results. ... 

Roessner et al. [134] found that Zn,H-ZSM-5 or Zn-ZSM-5 obtained via SSIE possessed catalytic activities in n-hexane isomerization similar to those exhibited by Zn,H-ZSM-5 catalysts that had been prepared by conventional methods, i. e., either through ion exchange in aqueous solutions of ZnfNOjlj or by the incipient-wetness technique. The latter method seemed to be in between exchange in aqueous solution and a solid-state reaction (cf. Sect 6.1). Also, Zn-ZSM-5 produced via SSIE proved to be almost as equally active in ethane arom-atization as conventionally modified Zn-ZSM-5 prepared by exchange in aqueous Zn(N03)2 solution [135]. Finally, as was shown by Rojasova et al. [143], incorporation of zinc into NH4-Y by solid-state reaction with, e.g., ZnO yielded catalysts active in n-hexane aromatization. Under equal conditions, ZnO alone did not catalyze this reaction. 

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