Reactions in the Solid Phase

1 Aldol Reactions Using Pol3tmer-Supported Silyl Enol Ethers 

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In addition to chemical reactions, the isokinetic relationship can be applied to various physical processes accompanied by enthalpy change. Correlations of this kind were found between enthalpies and entropies of solution (20, 83-92), vaporization (86, 91), sublimation (93, 94), desorption (95), and diffusion (96, 97) and between the two parameters characterizing the temperature dependence of thermochromic transitions (98). A kind of isokinetic relationship was claimed even for enthalpy and entropy of pure substances when relative values referred to those at 298° K are used (99). Enthalpies and entropies of intermolecular interaction were correlated for solutions, pure liquids, and crystals (6). Quite generally, for any temperature-dependent physical quantity, the activation parameters can be computed in a formal way, and correlations between them have been observed for dielectric absorption (100) and resistance of semiconductors (101-105) or fluidity (40, 106). On the other hand, the isokinetic relationship seems to hold in reactions of widely different kinds, starting from elementary processes in the gas phase (107) and including recombination reactions in the solid phase (108), polymerization reactions (109), and inorganic complex formation (110-112), up to such biochemical reactions as denaturation of proteins (113) and even such biological processes as hemolysis of erythrocytes (114). 

II) Solid-phase reaction zone Nitrogen dioxide and aldehydes are produced in the thermal degradation process. This reaction process occurs endothermically in the solid phase and/or at the burning surface. The interface between the solid phase and the burning surface is composed of a solid/gas and/or soUd/Uquid/gas thin layer. The nitrogen dioxide fraction exothermically oxidizes the aldehydes at the interface layer. Thus, the overall reaction in the solid-phase reaction zone appears to be exothermic. The thickness of the solid-phase reaction zone is very small, and so the temperature is approximately equal to the burning surface temperature, T. ... 

A general procedure for the iodine reaction in the solid phase is shown in Scheme 9. Both Boc and Fmoc chemistry can be used to assemble the linear S-protected bis-cysteine peptides and for thiol protection the well-established Acm and Trt groups are usually used. Suitable solvents for the thiol-deprotection/oxidation step by iodine to form the disulfide are CH2C12, DMF, or aqueous AcOH. The final deblocking and cleavage from the resin is carried out under standard conditions. Modification at sensitive amino acid residues caused... 

All these mechanisms along with any reaction in the solid phase are considered to be processes in series (Smith, 1981). In three-phase systems, three interface concentrations, two in the gas-liquid interface CG i and CLi, and one in the liquid-solid interface Cs, have to be eliminated. If equilibrium exists at the bubble-liquid interface, CG>i and CLi are related by Henry s law ... 

For a long time attempts have been made to explain why three non-explosive substances, viz. potassium nitrate, charcoal and sulphur, when combined together should form an explosive mixture. It was particularly incomprehensible that binary mixtures of potassium nitrate with charcoal or with sulphur should be non-explosive or only poorly so. The problem was the more difficult to elucidate since it involves a reaction in the solid phase. 

Not all reactions in the solid phase convert bisphthalonitrile derivatives into ball-type Pcs. One example of such reactions is the conversion of the bisphthalonitrile derivative of phenolphthalein into ball-type Pc [50], As can be seen in Fig. 13, when a solid mixture of bisphthalonitrile 48 and metal salt was heated in a sealed tube at 320° C for 5 min, only mono Pcs 49 and 50 were formed. Further reaction of 49 or 50 with an excess of the corresponding metal salt in a refluxing solvent for 24 h resulted in the formation of ball-type Pcs 51 or 52. 

A major limitation of the present work is that it deals only with well-defined (and mostly unidirectional) flow fields and simple homogeneous and catalytic reactor models. In addition, it ignores the coupling between the flow field and the species and energy balances which may be due to physical property variations or dependence of transport coefficients on state variables. Thus, a major and useful extension of the present work is to consider two- or three-dimensional flow fields (through simplified Navier-Stokes or Reynolds averaged equations), include physical property variations and derive lowdimensional models for various types of multi-phase reactors such as gas-liquid, fluid-solid (with diffusion and reaction in the solid phase) and gas-liquid-solid reactors. 

Ligation reaction in the solid phase is different from that in the liquid phase, since factors such as the surface characteristics of the support may influence the ligation. The advantage of ligation in the solid state is that the products can be detected directly on solid supports without further separation. 

Many decomposition reactions in the solid phase (section 4.3) or in suspensions apparently follow zero-order kinetics. Figure 4.1 shows the hydrolysis of a suspension of acetyl-salicylic acid. 

Dipolar cycloaddition of polyethylene glycol-supported azide with various dipolarophiles followed by acidic cleavage afforded 4- and 5-substituted-1,2,3-triazoles 05T4983>. Trimethylsilyl-directed 1,3-dipolar cycloaddition reactions in the solid-phase synthesis of 1,2,3-triazoles have been developed <05OL1469>. 

In combinatorial synthesis the reactions must operate with reliable yield on a structurally broad set of building blocks to provide a multitude of almost pure final compounds under identical conditions. In the most time- and labor-intensive step, selected building blocks are rehearsed individually through reactions in the solid-phase format, under conditions mimicking those that will be used faithfully in the final combinatorial synthesis. As it will often be impracticable to examine every member of the desired library to confirm its presence, building block combinations that are anticipated to represent worst-case scenarios (e.g., with respect to steric and/or electronic factors) are studied and optimized, with problematic building blocks being excluded from the library construction. 

Triallyl cyanurate is made from cyanuric chloride and allyl alcohol. Triallyl cyanurate is used as a comonomer to impart higher temperature resistance to polyesters. It also is used as an organic catalyst for polymer grafting reactions in the solid phase, including polypropylene-g-maleic anhydride (a polypropylene-graft copolymer) [184],... 

Nucleophilic displacement reactions in the solid phase using a reverse approach (e.g. the carboxy acid derivative on resin, and target product as the leaving group) has been undertaken to prepare alcohols and phenols by alcoholysis, saponification, aminolysis or ammonolysis (Figure 15.7). 

As discussed in chapter 5, diffusion through catalyst pores represents a resistance to mass and heat transfer, which gives rise to concentration and temperature gradients within the catalyst pellet. This causes the rate of reaction in the solid phase to be different from that if the bulk phase conditions prevail inside the particle, and the rate of reaction should be integrated along the radius of the pellet to get the actual rate of reaction. 

First, some high-pressure Diels-Alder reactions in the solid phase will be described in the following paragraphs. The main part of this chapter will be devoted to high-pressure multicomponent domino cycloaddition reactions in the liquid phase and on the sohd phase. 

Heat the product to 260°-280° for 6 hours as described in the preceding section. During this annealing, a reaction in the solid phase takes place the mixture of pyrophosphate and metaphosphate is transformed to a single salt, sodium tripolyphosphate. If the molten mass is cooled quickly, the individual particles of pyrophosphate and metaphosphate are very small and intimately mixed, so that the solid phase reaction proceeds relatively quickly but if the melt is cooled slowly, considerable segregation of the two salts takes place and the solid-phase reaction hardly has a chance. 

Kinetic experiments show the char thickness progressively increases following the same rate as the weight loss (41.43.44) and this fact causes the rate and nature of further degradation reactions in the solid phase to be quite different from those occurring simultaneously in the gas phase for three reasons ... 

These reactions can be carried out in solution or in dispersion or by reaction in the solid phase (Cunneen and Porter, 1965) in the last case it is again dilHcult to differentiate the Prins reaction from mechanochemical reactions initiated by chain rupture during mastication. 

Several studies have been reported on solid-liquid reactions, some of which are listed in Table 15.2. However, there are only a few that have attempted to model these reactions along the lines just outlined. Where the authors have indicated whether the solid is slightly soluble or insoluble, this fact is mentioned in the table but in many cases such information is also not available. It is a reasonable conclusion from these observations that solid-liquid reactions, particularly those involving reaction in the solid phase, need to be studied more rigorously. 

Scheme 18 Trimethylsilyl-directed 1,3-dipolar cydoaddition reactions in the solid-phase synthesis of 1,2,3-triazoles [57]...

The solvent selected for a particular reaction should not cause any environmental pollution and health hazard. The use of liquid or supercritical liquid CO2 should be explored. If possible, the reaction should be carried out in aqueous phase or without the use a of solvent (solventless reactions). A better method is to carry out reactions in the solid phase (for details see Chapter 13). 

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