Topochemistry

While the topochemistry of interface advance can be observed, the chemistry of reactions proceeding within that interface, localized inside the bulk of reactant particles, is less easily investigated. Intermediates cannot be isolated without destruction of the specialized environment in the strained region at the juxtaposition of two phases where these are generated. Identification of those species which are the necessary participants in a chemical transformation can be difficult since the total quantity... 

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. 

Miyafuji, H. and Saka, S. (1997). Fire-resisting properties in several Ti02 wood-inorganic composites and their topochemistry. Wood Science and Technology, 31(6), 449 55. 

West, H. and Banks W.B. (1986). Topochemistry of the wood isocyanate reaction. An analysis of reaction profiles. Journal of Wood Chemistry and Technology, 6(3), 411-425. 

Besides the above differentiation, restricted-access media can be further subdivided on the basis of the topochemistry of the bonded phase. Packings with a uniform surface topochemistry show a homogenous ligand coverage, whereas packings with a dual topochemistry show a different chemical modification of the pore internal surface and the particle external surface (114). Restricted-access media of the former type are divided into mixed-mode and mixed-function phases, bonded-micellar phases, biomatrix, binary-layered phases, shielded hydrophobic phases, and polymer-coated mixed-function phases. Restricted-access media of the latter type include the Pinkerton s internal surface reversed-phase, Haginaka s internal surface reversed-phase diol, alkyl-diol silica, Kimata s restricted-access media, dual-zone phase, tris-modified Styrosorb, Svec s restricted-access media, diphil sorbents, Ultrabiosep phases. Bio Trap phases, and semipermeable surface phases. 

Based on some interesting reactions in certain inorganic crystalline compounds, Kohlschutter [9,10] proposed that the nature and properties of the products obtained take place on the surface or within the solid state. Indeed, he coined the term topochemistry for such reactions in the solid state. However, systematic investigations of photoinduced reactions in crystals began from 1964 onward by Schmidt and Cohen [11], Their studies on the 2tt + 2tt photoreaction of cinnamic acid derivatives in the crystalline state and correlation with the molecular organization in these crystals led to what are now known as Topochemical Principles. The most important conclusions reached by them are as follows (1) The necessary conditions for the reactions to take place are that the reactive double bonds are parallel to one another and the center-to-center distance be within 4.1 A (2) there is one-to-one correspondence between the stereochemistry of the photoproduct and the symmetry relationship between the reactants. The centrosymmet-ric relationship (called the a-form) leads to centrosymmetric cyclobutane (anti-HT), whereas the mirror symmetric arrangements (called the (5-form) produce mirror symmetric dimer (yy -HH). 

Recent work by Len MacGillivray of the University of Iowa, USA, has used topochemistry to produce an impressive range of new solid compounds by the addition of hydrogen bonded templates in order to bring about the designer orientations of photochemically reactive molecules in the solid state.34 A simple example is the use of resorcinol (1,3-dihydroxybenzene) to position two molecules of trans 1,2 bis (4-pyridyl) ethylene with their double bonds overlapping at ca. 4 A as required by the topochemical postulate. Upon photolysis the product rcfHetrakis(4-pyridyl)cyclobutane is formed stereospecifically and in 100 % yield, Scheme 8.2. In the absence of the resorcinol template trans-l,2-bis(4-pyridyl) ethylene is... 

Laue M. and Steinbrecht R. A. (1997) Topochemistry of moth olfactory sensilla. Int. J. Insect Morph. Embryol. 26, 217-228. 

Lumsden, R. D., Voge, M. Sogandares-Bemal, F. (1982). The metacestode tegument fine structure, development, topochemistry, and interactions with the host. In Cysticercosis present state of knowledge and perspectives, ed. A. Flisser, K. Willms, J. P. Laclette, C. Larralde, C. Ridaura, F. Beltran M. W. Vogt, pp. 307-61. Academic Press New York. 

Reasons for the Differences in Reactivity Ratios Between the Dissolved and Crystalline "Phase (Topochemistry of Chain Propagation)... 

Paszner, L. and Behera, N. C., Topochemistry of softwood delignification by alkali earth metal salt catalyzed organosolv pulping. Holzforschung 1989,43 (3), 159-168. 

Montanari, S., Rountani, M., Heux, L., and Vignon, M. R., Topochemistry of carboxylated cellulose nanocrystals resulting from TEMPO-mediated oxidation. Macromolecules 2005, 38 (5), 1665-1671. 

In addition to UV microscopy, there are other microscopic techniques for investigating the topochemistry of lignin in wood. These methods include fluorescence and electron microscopy The combination of these techniques with UV microscopy should give the best results However, when a composite technique is employed, precautions must be taken. For example, in measurements of lignin concentration by bromination/UV microscopy, a correction factor is needed to account for the difference in the reactivities of middle lamella and secondary wall lignins toward bromine (Saka et al, 1982) (see Chap, 4.4). 

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