Vacuum pyrolysis conditions

PTFE decomposes to TFE with first-order kinetics and a 347.4-kJ/mol activation energy under vacuum pyrolysis conditions It is extremely flame resistant and does not bum in air Its limiting oxygen mdex (LOR, the muumum oxygen content of an atmosphere under ambient conditions that sustams combustion, is 96%, which means that it requires almost pure oxygen for combustion... 

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]. 

In contrast to carbenes of the AX2 type, which contain three atoms, generation of carbenes with a more complex structure under photolysis or vacuum pyrolysis conditions may be accompanied by intramolecular rearrangements. Thus, the matrix isolation study of the vacuum pyrolysis... 

The Diels-Alder adduct of sulpholene and cyclopentadiene is a useful starting material for substituted diene synthesis121. The diene moiety is unmasked by retro-Diels-Alder reaction and sulphur dioxide extrusion under flash vacuum pyrolysis conditions (equations 74 and 75)122,123. 

Alder-Rickert cleavage has not been widely used for cycloproparene synthesis, since the preparation of the precursors is often tedious, except for the simple cases like 7,7-difluorobenzocyclopropene (21). The approach offers, however, decisive advantages in special situations. If the Alder-Rickert cleavage is carried out under flash-vacuum pyrolysis conditions, the products may be isolated under neutral conditions and at low temperature. Thus the synthesis of the highly reactive li/-cyclopropa[a]naphthalene (56) by pyrolysis of 68 has been achieved by this approach. Several other approaches to 56 failed. 

The sulfone 80 undergoes clean extrusion of sulfur dioxide on exposure to flash vacuum pyrolysis conditions to produce divinyl compound 81 (Equation 18) <1999J(P1)605>. 

Under flash vacuum pyrolysis conditions 1- and 2-(l-adamantyl)indazoles as well as 1-, 2- and 3-tritylindazoles are mutually interconverted (91BSF592, 89BSB349). 

Oxadiazoles undergo thermal and photochemical ring cleavage at the 0(1)-N(2) and C(3)-C(4) bonds to yield nitrile and nitrile oxide fragments, and products derived therefrom. Thus, diphenylfurazan (30, X = 0) decomposes under flash vacuum pyrolysis conditions (600°C, 10-3 mm... 

There is less evidence for the participation of azomethine ylides 88 in the early examples of the thermal cyclization reactions of Meldrum s acid derivatives 86. This reaction, conducted under flash vacuum pyrolysis conditions, may proceed via the methyleneketene 87. Hydrogen transfer from this highly unstable species may lead to the dipolar intermediate 88, which could cyclize either in a 6zr, to give 89, or 8tt, to give 90, manner (Scheme 27) [83JCS(CC)988 85TL833 87JCS(CC)140]. 

The hexyl derivative 7 was pyrolyzed26 in the gas phase (Flash Vacuum Pyrolysis conditions)27 with the hope of losing CO to produce 17.28 Little or no 17 was produced, but a reasonable yield of several products including two isomers of 7, always in a ratio of 4 1, was obtained. We have determined (using... 

The simplest pentalene yet known, the 1-methyl derivative, has been prepared by making recourse to a retro-Diels-Alder degradation as the generative step under flash vacuum pyrolysis conditions (Scheme 27).234 Addition of 4-bromo-3-buten-2-... 

In refluxing xylene (160 °C), fused Dewar s thiophene 40 mainly desulfurized to give cyclobutene 41 but under flash vacuum pyrolysis conditions, a mixture of isomeric dihydrothiophenes 42, 43, and 5H-benzocycloheptatriene 44 was formed (Scheme 9). Evidently the latter product derived from a formal electrocyclic ring opening of the cyclobutene intermediate 41 <1990H(31)1769>. 

Similarly, no free spiro[2.5]octa-5,7-dien-4-one was obtained under flash-vacuum pyrolysis conditions applied to its complex 51. ... 

Stereoisomeric vinylcyclopropanes 36 under flash-vacuum-pyrolysis conditions yield mixtures of cis- and trans- isomers of cyclopentenes 37 and 38 in good yield (see table below). 

The thermal rearrangement of 3-hydroxyindoxazene to benzoxazolin-2-one is temperature-dependent. The indoxazene is inert at 250°C but rearranges quantitatively at 450°C.78 3-Phenylindoxazene under flash vacuum pyrolysis conditions (800°C, 0.1-1 torr) rearranges to 3-phenylbenzoxazole in 80% yield.79 In both reactions a spiroazirine intermediate [59 or 60 (R = Ph)], analogous to those isolated in some isoxazole-oxazole rearrangements,80 is considered likely. 

Phosphaalkynes without sterically demanding substituents can also be manipulated either in solution or by freezing out at low temperatures. They are often generated by thermal P-elimination of hydrogen halide under vacuum pyrolysis conditions [10]. 

The Diels-Alder reaction of cyclohexa-1,3-diene (17) with the phosphaalkyne 9a only proceeds under drastic conditions in a pressure Schlenk tube but then does provide the 2-phos-phabicyclooctadiene 18 [23] in quantitative yield (Scheme 6-4). This compound represents the first member of the previously unknown class of polycyclic phosphaallrenes. From a thermal point of view, 18 is unexpectedly stable cycloreversion only occurs under flash vacuum pyrolysis conditions (520°C/10 mbar) but then it does not give rise to the starting materials 9a and 17 instead it proceeds by cleavage of ethylene to furnish the 2-terr-butyl-X -phosphinine [23]. 

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