THERMAL STABILITY OF REACTION MIXTURES AND SYSTEMS

THERMAL STABILITY OF REACTION MIXTURES AND SYSTEMS THERMOCHEMISTRY AND EXOTHERMIC DECOMPOSITION... 

Textile clothing static charges, 394 Theory without detailed thought, 394 Thermal explosions, 394 Thermal stability of reaction mixtures and systems, 394 Thermite reactions, 395 Thermochemistry and exothermic decomposition, 396 Thiatriazoles, 400 Thionoesters, 401 Thiophenoxides, 401 Thorium furnace residues, 401 Tollens reagent, 401 Toxic hazards, 402 Trialkylaluminiums, 402 Trialkylantimony halides, 403 Trialkylbismuths, 403... 

Catalytic reactions can take place in either the liquid or vapor phase. Liquid phase reactions can be run in either a continuous manner or as a batch process while vapor phase reactions are run only in a continuous mode. In a batch reaction the catalyst, reactants, and other components of the reaction mixture are placed in an appropriate reaction vessel, the reaction is run and the products removed from the vessel and separated from the catalyst. In a continuous system the reactants are passed through the catalyst and the products removed at the same rate as the reactants are added. The applicability of vapor phase processes is limited by the volatility and thermal stability of the reactants and products so such processes are not commonly involved in the preparation of even moderately complex molecules. Because of this, primary attention will be placed here on liquid phase processes with vapor phase systems of secondary importance. A discussion of the different types of reactors used for each of these processes is found in the following chapter. The present discussion is concerned with the effect that the different reaction parameters can have on the outcome of a catalytic reaction. 

In Table 2 the results on the synthesis of BEA zeolite type are reported. First of all, when the reaction temperature increased from 140 to 170 C the crystallization time was shortened, but the thermal stability of the product decreased. As a matter of fact, from the reaction system B2 the BEA type zeohte was obtained after 7 days at 140 °C and after 4 days at 170 °C, but if the reaction time was prolonged up to 8 days at 170 °C, the products were BEA and quartz. On the contrary, at 140 °C only the BEA phase formed even after 18 days. The BEA type zeolite was obtained also in presence of a mixture of TEIAOH and TEABr, but the preliminary experiments carried out with this mixture showed that for a complete crystallization it is necessary to prolong twice the crystallization time. 

The advantages of the heterogeneous catalysts are self-evident first there is the possibility to use these systems in continuous processes (important for the industrial applicability), secondly we have the ease of separation of the catalyst from the reaction mixture and last there is the better (thermal) stability of these heterogeneous systems. 

Thermal cycloadditions of butadiene to 3-bromo- 133 and 3-methoxy-5-methylene-2(5//)-furanones 220 were studied (95TL749). These systems contain substituents at C3 capable of stabilizing also a possible radical intermediate, influencing hereby the rate and/or the course of the reaction. Thus, the reaction of 133 and 220, respectively, with butadiene at 155°C afforded mixtures of the expected 1,4-cycloadducts 221 and 222, respectively, and of the cyclobutane derivatives... 

Mn(II) > Mg(II).270 It should be underlined that titanium and zirconium alkoxides are efficient catalysts for both stages of reaction. Lanthanide compounds such as 2,2/-bipyridyl, acetylacetonate, and o-formyl phenolate complexes of Eu(III), La(III), Sm(III), Er(III), and Tb(III) appear to be even more efficient than titanium alkoxides, Ca or Mn acetates, Sb203, and their mixtures.273 Moreover, PET produced with lanthanides has been reported to exhibit better thermal and hydrolytic stability as compared to PET synthesized with the conventional Ca acetate -Sb203 catalytic system.273... 

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