Organic reactions endothermic

The influence of the temperature distribution on selectivity varies according to the reaction scheme. Among such schemes, the ccmsecutive reaction (A —B — C) qualitatively represents many organic reactions with by-products. As shown in the previous section, the use of dilute phase is recommended for endothermic reactions, but prohibited for exothermic reactions. This conclusion agrees with the development of fluid bed reactors for partial oxidations (exothermic) and cracking (endothermic). This knowledge may help one to design or develop new fluid bed contactors. 

In addition, transition metal compounds have the ability to donate additional electrons or accept electrons from organic substrates and can change both their valence and their coordination number reversibly. These properties play an important role in organic synthesis, especially in catalytic processes. The ability to serve as catalysts in organic reactions is the most important property of the transition metal compounds. Reaction mechanisms involving intermediate organic structures, which are prohibitively endothermic in the absence of transition metal catalysts, are made feasible in their presence. 

The applications of DTA and DSC to inorganic compounds are similar to those discussed for organic compounds. Endothermic and exothermic peaks are caused by phase transitions (melting, boiling, polymorphic changes), dehydration, dissociation, isomerization, oxidation-reduction reactions, and so on. These applications are summarized in Figure 7.19. A... 

Thermal decomposition of spent acids, eg, sulfuric acid, is required as an intermediate step at temperatures sufficientiy high to completely consume the organic contaminants by combustion temperatures above 1000°C are required. Concentrated acid can be made from the sulfur oxides. Spent acid is sprayed into a vertical combustion chamber, where the energy required to heat and vaporize the feed and support these endothermic reactions is suppHed by complete combustion of fuel oil plus added sulfur, if further acid production is desired. High feed rates of up to 30 t/d of uniform spent acid droplets are attained with a single rotary atomizer and decomposition rates of ca 400 t/d are possible (98). 

Spent acid burning is actually a misnomer, for such acids are decomposed to SO2 and H2O at high temperatures in an endothermic reaction. Excess water in the acid is also vaporized. Acid decomposition and water vaporization require considerable heat. Any organic compounds present in the spent acid oxidize to produce some of the required heat. To supply the additional heat required, auxiUary fuels, eg, oil or gas, must be burned. When available, sulfur and H2S are excellent auxiUary fuels. 

The reaction is endothermic. Energy from sunlight is stored in the form of high-energy C-C bonds (e.g., organic biomass) and O2, the raw materials for the support of hetero-trophic organisms dependent upon the food source. 

The acid dissociation of neutral molecules is such a highly endothermic reaction that the acid dissociation of nitromethane can hardly take place. The results of the calculations presented here provide a theoretical support for nitromethane as an ideal model of aprotic solvent in the acid-base theory of organic molecules. 

The nature of dangerous reactions involving organic chemicals depends on the saturated, unsaturated or aromatic structures of a particular compound. Saturated hydrocarbons are hardly reactive, especially when they are linear. Branched or cyclic hydrocarbons (especially polycyclic condensed ones) are more reactive, in particular as with oxidation reactions. With ethylenic or acetylenic unsaturated compounds, the products are endothermic . 

Similarly, Ervin and co-workers have measured acidities of organic molecules by measuring the energy for endothermic proton transfer reactions between acids and anionic bases." " Alternatively, it is possible to use competitive CID of proton-bound dimer ions." Nominally, these are relative approaches for measuring acidities, as the measured acidities depend on the properties of the reference acids or bases. However, it is usually possible to select references with very accurately known acidities (such as HE, HCN, or HCl), such that the accuracy of the final measurement depends predominantly on the accuracy of the threshold energy determination. 

At present, waste heat exhausted from the ICE is removed with any efficient radiator system through direct apparent heat exchanging. On the contrary, organic chemical hydrides can recuperate the chemical energy of endothermic reaction heat during exhausted heat removal. Heat transfers accompanying the phase change of evaporation and condensation of aromatic products and unconverted reactants will certainly facilitate the removal of heat from the ICE parts, with adoption of any new radiator system compelled. 

Heat flow from any external thermo-source into the dehydrogenation reactor should take the role of affording the endothermic reaction heat and the evaporation heat of both reactant and product in addition to the apparent heat for raising their temperatures from the ambient up to the external heating one. Under assumptions of the sufficient amounts of active catalyst and the adequate feed rates of organic chemical hydride, the minimum required heat is obtained as shown in the example of methylcyclohexane at 285°C on the basis of 100% conversion of methylcyclohexane to toluene and hydrogen (Table 13.5). 

One of the important problems of the chain oxidation of organic compounds was the problem of chain generation in the absence of hydroperoxide and other initiating agents. These reactions should be very slow due to their endothermicity. Two most probable reactions were predicted [56,57] ... 

This is a strongly endothermic process, but it becomes possible at high temperature due to a favorable entropy change - formation of the random vapor state from solid reactants. Such reactions provide another reason for the lower flame temperatures achieved when organic binders are added to oxidizer/metal mixtures [3]. 

Carbon Suboxide Photoiysis. In principle, carbon suboxide (1) can be used as a precursor to atomic carbon and two molecules of carbon monoxide as shown in Eq. 2. However, this reaction is endothermic by 141 kcal/mol and can only be realized in the vacuum ultraviolet (UV) at wavelengths that destroy most organic substrates. However, photolysis of 1 at 1470 A produces C atoms in a low-temperature matrix. The short wavelength flash photolysis of 1 coupled with atomic absorption has been used to measure the rate constants for various spin states of carbon with simple substrates. 

There has been much discussion of the possibility of converting C02 emissions to useful organic compounds, but most proposals involve endothermic reactions that would require input of heat, probably generated at the expense of yet more C02 emissions. The proposed formation of liquid acetic acid AH = —485.76 kJ mol-1, S° = 178.7 J K-1 mol-1) from C02 and methane has been claimed to be exothermic. Is this reaction feasible in the industrial context, assuming an appropriate catalyst can be found (Use the data of Appendix C.)... 

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