Pyrolysis stabilization

The alkanes have low reactivities as compared to other hydrocarbons. Much alkane chemistry involves free-radical chain reactions that occur under vigorous conditions, eg, combustion and pyrolysis. Isobutane exhibits a different chemical behavior than / -butane, owing in part to the presence of a tertiary carbon atom and to the stability of the associated free radical. 

Thermal Stability. The saturated C —C 2 ketones are thermally stable up to pyrolysis temperatures (500—700°C). At these high temperatures, decomposition can be controlled to produce useful ketene derivatives. Ketene itself is produced commercially by pyrolysis of acetone at temperatures just below 550°C (see Ketenes, ketene dil rs, and related substances). 

Perhaps the most firmly based report for the formation of an azete involves flash pyrolysis of tris(dimethylamino)triazine (303). This gave a red pyrolysate believed to contain the highly stabilized azete (304) on the basis of spectroscopic data. The putative azete decomposed only slowly at room temperature, but all attempts to trap it failed (73AG(E)847). Flash pyrolysis of other 1,2,3-triazines gives only acetylenes and nitriles and it is not possible to tell whether these are formed by direct <,2-l-<,2-l-<,2 fragmentation of the triazine or by prior extrusion of nitrogen and collapse to an azete (81JCR(S)162). 

H-1,2-Oxazine, 3,6-dihydro-6-(2-pyridyl)-mass spectra, 2, 529 2H-1,2-Oxazine, tetrahydro-synthesis, 2, 92 4H-l,2-Oxazine, 5,6-dihydro-pyrolysis, 3, 999 synthesis, 3, 1017 tautomerism, 3, 999 4H-1,2-Oxazine, 5,6-dihydro-3-methyl-metallation, 1, 484 4H-l,2-Oxazine, 5,6-dihydro-3-nitro-reactions, 3, 1000 6H-l,2-Oxazine, 3,5-diphenyl-stability, 3, 997 synthesis, 3, 1014... 

Oxetane, 3,3,4,4-tetramethyl-2,2-diphenyl-pyrolysis, 7, 372-373 Oxetane, vinyl-thermal stability, 7, 370 Oxetane-3-carboxylic acid, 3-hydroxy-2,2,4,4-tetramethyl-synthesis, 7, 394... 

Several methods ean be employed to eonvert eoal into liquids, with or without the addition of a solvent or vehiele. Those methods which rely on simple pyrolysis or carbonization produce some liquids, but the mam produet is eoke or char Extraction yields can be dramatically increased by heating the coal over 350°C in heavy solvents sueh as anthraeene or eoal-tar oils, sometimes with applied hydrogen pressure, or the addition of a eatalyst Solvent eomponents whieh are espeeially benefieial to the dissolution and stability of the produets eontain saturated aromatic structures, for example, as found in 1,2,3,4 tctrahydronaphthalene Ilydroaromatie eompounds are known to transfer hydrogen atoms to the coal molecules and, thus, prevent polymerization... 

The efficacy of RF in stabilizing small rings is well illustrated by the fact that the azete from trifluoro-l,2,3-triazine is considerably more reactive. Trapping experiments were unsuccessful and a polymer was isolated at room temperature. The dimer (41) forms an observable anion with CsF, which confirmed the endo structure [87CC1699 90JCS(P1)975, 90JCS(P1)983], In contrast, trifluoro-l,2,4,-triazine is resistant to vapor phase photoysis and flow pyrolysis [87JCS(P1) 1251]. 

The Dewar benzene of hexafluorobenzene formed an adduct with pheny-lazide that gave a polyfluoro-l//-azepine on pyrolysis. R=C02Et (47) was obtained when ethylazidoformate was decomposed in C6F6 [82JCS(P1)2101]. Photolysis of (47) yielded a 2-aza-bicyclo(3.2.0.)hepta-3,6-diene, which, in contrast to its nonfluorinated analogue, showed excellent thermal stability (3 h, 200°C, 88% recovered) [82JCS(P1 )2105]. 

This reaction provides a third indication of the usefulness of a radiofrequency discharge in the synthesis of compounds of low thermal stability. The more-stable (CFaljTej had been prepared by the interaction of CFj radicals, formed in the pyrolysis of (CF3)2CO, with a tellurium mirror (19). The less-stable (CFsljTe was not, however, observed in that experiment. 

In contrast to this behavior stabilized sulfonyl ylides 125 lose PhjP under flash vacuum pyrolysis conditions to give sulfonyl carbenes 127 which evolve to the formation of various products among which the alkenes 129, observed in all the cases (Scheme 35) [129]. 

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