Flash vapor pyrolysis

Flash vapor pyrolysis of chloroform has been used to effect the... 

Flash vapor pyrolysis of the rf -thiophene l,l-dioxide)cobalt complexes results in extrusion of SO2 to generate (cyclobutadiene)cobalt complexes (Scheme 63)229. The absence of ligand crossover products indicates that this reaction occurs in a unimolecular fashion. Pyrolysis of the diastereomerically pure complex 240 gave the cyclobutadiene complex as an equimolar mixture of diastereomers 241a and 241b. In addition, the recovered starting material (37%) was shown to have ca 40% scramble of the diastereomeric... 

Many rDA reactions are carried out at temperatures of 150 C or more in solution phase and often at temperatures of 400-600 C using the flash vapor pyrolysis (FVP) method individual conditions are referenced throughout the text. However, an accelerating effect by anionic, cationic and radical substimtion on either the dienophile or at the termini of the diene fragments has been predicted by Carpenter.Experimentally, this prediction has been substantiated only for anionic substitution. In 1967, Hart reported what is likely the first example of an oxyanion-accelerated rDA reaction. Both oxyanionic " and car-banionic substituents accelerate the cycloreversion reaction such that they proceed rapidly at room temperature (for example, equation 3). In addition, acid-catalyzed rDA reactions have been reported in which protonation effectively makes the dienophile fragment of the adduct more electron deficient. Grieco has utilized a room temperature retro aza DA reactitm useful for the N-methylation of dipeptides and amino acid derivatives (equatitm 4). ... 

In contrast with the relatively facile thermal rearrangement of sulfinates to sulfones discussed in the preceding section, the reverse process is relatively, rarely encountered and is usually observed only at elevated temperatures. One of the first thermal sulfone to sulfinate isomerizations has been invoked by Fields and Meyerson to occur during the pyrolysis of dibenzothiophene S, S-dioxide (26) to dibenzofuran, through elimination of sulfur monoxide from the sultine intermediate 27 (equation 27). More recently, the flash vapor-phase pyrolysis of various 2,5-dialkyl and diaryl thiophene-S, S-dioxides has also been shown to involve SO extrusion and formation of the corresponding furans in good yields . 

Similarly, flash vapor-phase pyrolysis of 4-(allyloxy)trifluoropyrimidine (39) results in migration to nitrogen, giving 3-allyltrifluoropyrimidin-4(37/)-one (40) in 53% yield.29... 

Vapor phase pyrolysis of two unsymmetrically substituted 1,2,3-triazole isomers, like (75) and (76), involves the antiaromatic l//-azirine derivative (77) which rearranges to two isomeric 2//-azirines (78) and (79) (71CC1519, 73JCS(Pi)555> and other products. Iminocar-benes (80) are most likely involved as intermediates. Furthermore, nitrogen has been extruded from several IH- 1,2,3-triazoles by flash vacuum pyrolysis. 1-Alkyl-1,2,3-triazoles (81) give nitriles (82) and (83) (via Wolff rearrangement) and (hydroxy)isoquinolines (84) and (85) (by [1,4-H] transfer in the iminocarbene) (75JCS(P1)1). 

Lagow et al. during these experiments in addition made the most important discovery, that polylithioalkanes prior to pyrolysis are stable in the gas phase for a short period of time. In this way for the first time mass spectra have been achieved of those compounds which have no observable vapor pressure below 650 °C even in the highest possible vacuum. A temperature of 1500 °C has been reached in less than three seconds by a special flash-vaporization apparatus, whereby e.g. dilithio-... 

Flash vapor-phase pyrolysis of benzo[f>]thiophene 1,1-dioxide gives benzothiete (60 X = Y = H) (45%).566 Other significant reactions have been mentioned in the appropriate Sections. 

The decomposition of Ti(OR)4 in the vapor phase was performed using flash vacuum pyrolysis technique [20] at a pressure of approx. 10 mm of Hg. Pyrolysis at 550°C and 700°C were carried out in glass and quartz tubes, respectively. The inorganic product obtained was amorphous Ti02 containing small amounts of carbon... 

The most interesting process is, therefore, the flash pyrolysis, because it leads to the maximum yield of the most valuable product, the oil. For this process, the key parameters are the char separation and the vapor residence time (determined by the quenching method). 

The extraction of environmental or geological particulate matter with solvents, solvent mixtures or supercritical carbon dioxide is the preferred method, because it results in minimum alteration of its polar components, avoids hydrolysis of anhydrides, esters, etc. and is highly efficient for most organic compounds (even sugars). Other workers have reported the direct vaporization by thermal desorption or flash pyrolysis of organic compounds from particulate matter into GC, MS, or GC-MS instruments. Those methods work fine for neutral compounds (e.g. hydrocarbons) but should be used with caution when analyzing polar or labile compounds. 

Vapor-phase flash pyrolysis of 4-phenyl-1,2,3-benzotriazine (8, R = Ph) at 420°-450° gives a mixture of biphenylene, 9-phenylacridine, unchanged triazine, and the 2-phenylbenzazete (158). Compound 158, which is stable at -80°, dimerizes when warmed to room temperature and reacts readily with nucleophiles and 1,3-dienes. The thermally more... 

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