Solid-state topochemical reaction

The expansion mechanism has been the subject of numerous studies for mai r years. It is caused by the known contradiction consisting in the lowering of absolute volume of the system, due to ettringite or other hydrates formation this problem is discussed in Chap. 5. The oldest hypothesis was presented by Lafuma [60], which already in 1929 suggested that the formation of ettringite as a result of reaction in the solid state (topochemical reaction) will cause expansion, while occurring... 

Thus, the basic contents of the theory on solid-state topochemical reaction occurring on the phase boundary are as follows ... 

Fang G, Javier M-R, Zhigang P, Colan EH, Kenneth DMH (2008) Direct structural understanding of a topochemical solid state photopolymerization reaction. J Phys Chem C 112 19793-19796... 

When I was young, solid-state phase changes and chemical reactions were regarded more as a nuisance than as an area worthy of serious study and attention. It was the topochemical approach to solid-state chemical reactions, pioneered by Gerhard Schmidt, that transformed the subject for me and for many others. The textbook example is the photochemical dimerization of (fj-cinnamic acids in solution such compounds yield mixtures of the various possible stereoisomeric products, but irradiation of a particular crystal leads to a single product, or to no reaction, depending on the crystal structure [40]. Thus, one can determine the relative positions of the atoms before the reaction and after it, and haice deduce the metrical relationships that needed to be satisfied for reaction to proceed. In the meantime we have learned that not all chemical reactions in solids are topochemical. Some proceed not in the ordered bulk of the crystal but at defects, on the surface, or at other irregularities. 

Changes in the FT-Raman spectmm of 1,4-bis(3-quinolyl)buta-l,3-diyne as a function of gamma-ray dosage are used to monitor the degree of monomer to polymer conversion in a solid-state topochemical polymerisation reaction (i.e., polymerisation directed by the solid-state structure) (315). 

Topotactic processes are described more comprehensively in Mechanical Preparation of Crystalline Materials. An Oxymoron and Templated [2 + 2] Photodimerizations in the Solid State, Supramolecular Materials Chemistry. Since its original definition in 1959, the term topotaxy has evolved " to mean a solid-state chemical reaction (not necessarily reversible) that completely transforms a single crystal such that the product resembles that of the initial material both in terms of its three-dimensional structure and the orientation thereof. Topotactic is synonymous with topochemical... 

The term crystal engineering was first used by Schmidt [1] in coimection with the research on solid state photodimerization reactions on the basis of topochemical principle, which correlated the solid state reactivity of monomers with their crystal... 

Shortly after, Doetschman and Hutchison reported the first example of a reactive carbene in the crystalline solid state, by preparing diphenylcarbene from diphenyldi-azomethane in mixed crystals with 1,1-diphenylethylene 84 (Scheme 7.23). When the mixed crystals were irradiated, carbene 85 was detected by electron paramagnetic resonance (EPR) and the disappearance of the signal was monitored to determine its kinetic behavior. Two reactions were shown to take place under topochemical... 

When the course taken by a given solid-state reaction is determined by geometrical details of the crystal lattice, the reaction type falls under the general category of topochemistry. In a topochemical reaction, the reaction takes place in the solid state with a minimum amount of molecular motion. For example, bimolecular reactions are expected to take place between nearest neighbors, which then suggests that the product of the reaction would be a function of the geometric relation in the crystal structure of the reactant molecules. 

Photodimerization of cinnamic acids and its derivatives generally proceeds with high efficiency in the crystal (176), but very inefficiently in fluid phases (177). This low efficiency in the latter phases is apparently due to the rapid deactivation of excited monomers in such phases. However, in systems in which pairs of molecules are constrained so that potentially reactive double bonds are close to one another, the reaction may proceed in reasonable yield even in fluid and disordered states. The major practical application has been for production of photoresists, that is, insoluble photoformed polymers used for image-transfer systems (printed circuits, lithography, etc.) (178). Another application, of more interest here, is the use that has been made of mono- and dicinnamates for asymmetric synthesis (179), in studies of molecular association (180), and in the mapping of the geometry of complex molecules in fluid phases (181). In all of these it is tacitly assumed that there is quasi-topochemical control in other words, that the stereochemistry of the cyclobutane dimer is related to the prereaction geometry of the monomers in the same way as for the solid-state processes. 

McBride and co-workers have studied extensively the reactions of such free-radical precursors as azoalkanes and diacyl peroxides (246). By employing a variety of techniques, including X-ray structure analysis, electron paramagnetic resonance (EPR), and product studies, and comparing reactions in the crystal and in fluid and rigid solvents, they have been able to obtain extremely detailed pictures of the solid-state processes. We will describe here some of the types of lattice control they have elucidated, and the mechanisms that they suggest limit the efficacy of topochemical control. 

Eq. 2-248) [Braun and Wegner, 1983 Hasegawa et al., 1988, 1998]. This polymerization is a solid-state reaction involving irradiation of crystalline monomer with ultraviolet or ionizing radiation. The reaction is a topochemical or lattice-controlled polymerization in which reaction proceeds either inside the monomer crystal or at defect sites where the product structure and symmetry are controlled by the packing of monomer in the lattice or at defect sites, respectively. 

The oxidation and hydrolysis of Fe leads to Fe " oxides either directly or via soluble green rust complexes, solid green rusts or Fe(OH)2. The latter convert to the oxides either by a solid state reaction or a via solution (reconstructive) transformation. Generally, where there is a difference between the structure of the precursor and that of the final oxide, a via solution process seems more likely, but internal rearrangement during topochemical oxidation to the new phase, may also take place. 

The prototypes of intra-solid reactions are the [2-1-2] photochemically activated cycloaddition reactions that constitute the basis of Schmidt s work on topochemical reactions [36]. It is now clear, however, that the topochemical postulate, though correct and of wide applicability, cannot account for many solid-state processes, in particular those implying high molecular or ionic mo-... 

Keywords Crystal engineering Solid-state photoreaction Topochemical polymerization Controlled radical polymerization Dimerization Isomerization Topotactic reaction... 

The polymerization proceeds under photo- [49,50],X-ray [51], and y-ray [52] irradiation in the dark in vacuo, in air, or even in water or organic solvent as the dispersant (nonsolvent) for the crystals, similar to the solid-state polymerization of diacetylene compounds [ 12]. The process of topochemical polymerization of 1,3-diene monomers is also independent of the environment surrounding the crystals. Recently, the thermally induced topochemical polymerization of several monomers with a high decomposition and melting point was confirmed [53]. The polymer yield increases as the reaction temperature increases during the thermal polymerization. IR and NMR spectroscopies certified that the polymers obtained from the thermally induced polymerization in the dark have a stereoregular repeating structure identical to those of the photopolymers produced by UV or y-ray irradiation. 

Thus, the solid-state photoisomerization of 10 proceeds via a topotactic reaction mechanism, while some (Z,Z)-muconic esters (e.g., 13 and 15) can pho-toisomerize to the corresponding ( , )-muconic esters (14 and 16) without any change in the space group, i.e., proceed via topochemical EZ isomerization (Scheme 13, Fig. 15) [115]. 

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