Transformations thermal conversion

The most reasonable mechanism for this transformation, in accord with that suggested by van Tamelen et al. for the dilute acid photolysis, is initial photoisomerization to 2 followed in this case by thermal conversion of the Dewar tropylium ion to 7. The isomerization of 2 to 7 has been reported to be very rapid at temperatures below —60°, and it has been shown, in addition that, in nucleophilic solvents, capture of 2 competes very efficiently with isomerization (Lustgarten et al., 1967). 

Differential thermal analysis (DTA) consists of the monitoring of the differences in temperature existing between a solid sample and a reference as a function of temperature. Differences in temperature between the sample and reference are observed when a process takes place that requires a finite heat of reaction. Typical solid state changes of this type include phase transformations, structural conversions, decomposition reactions, and desolvation processes. These processes may require either the input or release of energy in the form of heat, which in turn translates into events that affect the temperature of the sample relative to a nonreactive reference. 

Abstract. The subject of this research are the regularities of the particles motion in the electric and thermoelectric fields with distributed potential and the influence of temperature field to the particle motion trajectories in aggregate electric and thermal fields. The analytical solution of the problem of particle motion in thermoelectric field with distributed potential is produced. Common regularities of particle motion and trajectory changes in such fields are derived. It is shown that nonlinear curves give a nonconsiderable part of the trajectory within the macrostructures and so the trajectory shape doesn t considerably influence the electron flow transformation process. Conversely, the trajectory shape does influence the aforesaid processes in micro- and nanostructures defining the specific ways of transformation. 

Of additional concern is the thermal conversion of PCBs to polychlorinated dibenzofurans, especially when PCB—filled electrical transformers are involved (16). Further, PCB isomers with no chlorine atoms substituted in the ortho. ortho -biphenvl positions are particularly potent as inducers of aryl hydrocarbon hydroxylase activity. The potency of certain dibenzofurans and non-ortho, ortho chlorine substituted PCBs in inducing activity of these enzymes is similar to that of the highly toxic 2,3,7,8-tetrachloro-dibenzo- -dioxin (15. 17., 18). 

Thioamides of 3-oxoacids 118 are transformed into 1,2,4-dithiazolidines 29 by treatment with cerium ammonium nitrate (CAN) in MeOH or with CF3SC1 in CH2CI2 (Equation 16) <1996SC4165, 2001SC189>. The thermal conversion of 6/7-1,3,5-oxathiazine A-oxides 119 in refluxing benzene results in 1,2,4-oxathiazolines 20 with extrusion of R CHO. This reaction involves the heterodiene intermediate 120, which can be independently trapped by the reaction with EtOH (Scheme 32) <2003TL2517, 2004HAC175>. 

The synthesis of a number of pyrrole derivatives has been effected by the thermal conversion of 3-vinyl-2H-aziiines to butadienylnitrenes followed by 1,5-electrocyclization (75JA4682). For example, the thermal transformations observed on thermolysis of 2H-azirine 28 were rationalized in terms of an equilibration of the 2H-azirine with a butadienylnitrene, which subsequently rearranged to the final products. The rearrangement of 28 to pyrrole 30 was envisaged as occurring by an electrocyclic reaction followed by a 1,5-sigma tropic ethoxycarbonyl shift and subsequent tautomerization... 

From a thermodynamic standpmnt, one can expect that for the thermal conversion of (1) to (2) and related derivatives, unless the temperature is sufficiently high or strain factors become predominant, cycloreversion will not be observed. A more complete discussion of the factors affecting the thermal equilibration of strained hexatrienes and cyclohexadienes will be discussed in Section 6.2.2.2.I. A kinetic study of the pericyclic transformation of the parent triene (1) to 1,3-cyclohexadiene (2) provided an activation energy of 29.9 kcal mol. Taking into account the heats of formation of reactant and product (40.6 kcal mol for (Z)-l,3,5-hexatriene and 25.4 kcal mol" for 1,3-cyclohexadiene), the... 

This type of electrocyclization is illustrated by the formation of (35) and the related formation of (46) and (47) (see also Section 6.2.3) discussed earlier. Another example is the thermal conversion of trienone (157) to ketone (158). A similar transformation of a related triene intermediate has been postulated to account for the formation of (162) from (161) by pyrolysis of pyrethrin-I (159), which initially produces (160). ... 

Thermal conversion to propene was one of the first known reactions of cyclopropane. Remarkably, however, the mechanism of this transformation is still a matter of some considerable uncertainty. 

If biomass is subjected to the ASTM D 3172 procedure for determination of fixed carbon, chemical transformation of a portion of the organic carbon in biomass into carbonaceous material occurs as described here. All of the fixed carbon determined by the ASTM procedure is therefore generated by the analytical method. Furthermore, the amount of fixed carbon generated depends on the heating rate used to reach biomass pyrolysis temperatures and the time the sample is subjected to these temperatures. Nevertheless, such analyses are valuable for the development of thermal conversion processes for biomass feedstocks. But application of the ASTM procedures to biomass might more properly be called a method for determination of pyrolytic carbon or coking yields. In the petroleum industry, the Conradson carbon (ASTM D 189, differ-... 

Transformations of Sulfur-Containing Compounds During Thermal Conversion of Coal... 

Depending on the voliune filHng factor of the matrix material, substantial shrinkage of the porous network accompanied by crack formation may occur for low filHng fractions during template removal. Furthermore, annealing the repHca material at elevated temperatures may lead to a transformation from one modification or crystal phase to another that is thermodynamically more stable at these temperatures, as shown for the thermal conversion of amorphous titania or its anatase phase to the rutile structure [79]. 

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