Pyrazines pyrolysis

Didehydropyrazine is believed to be an intermediate in the pyrolysis of pyrazine-2,3-dicarboxylic anhydride. According to DFT calculations, this molecule has a triplet ground state with a singlet state about 10 kcal/mol higher in... 

Acid chlorides in pyridine convert 91 to the tetraamides 96, which, when heated, cleanly extrude 2 mol acid to give the diimidazo[4,5-h 4, 5 -e]-pyrazines (97) in good yield. The temperatures required for the pyrolysis can be readily determined by thermogravimetric analysis, and range from 285°C (97, R = Me) to 420°C (97, R = p-chlorophenyl). Under these conditions, the acid distills leaving analytically pure 97 in most cases (Scheme 35). 

The pyrolysis of pyrazine at 1000°C/2mmHg gives pyrimidine in 3% yield (68TL3115). The photolysis of pyrazine at 254 nm gives a little pyrimidine in addition, 2-methylpyrazine gives both 4- and 5-methylpyrimidine, 2,6-dimethylpyrazine gives 4,5-dimethylpyrimidine, and 2,5-dimethylpyrazine gives both 4,6- and 2,5-dimethylpyrimidine, all in minute yield... 

Photolysis sometimes gives the same products as pyrolysis An example is photolysis of perfluorooxazeudines [/] Frequently, however, the results of photolysis and pyrolysis are different Thermal rearrangement of fluonnated pyndazmes at 300 °C yields a mixture of fluonnated pyrimidines and pyrazines [/20,121,122,123]... 

A paper reporting the pyrolysis of pyrazine, pyrimidine, and pyridine combined with laser-Schlieren densitometry and TOF mass spectrometry proposes decomposition via a... 

The a-aminocarbonyls are not only precursors of pyrazines, but can also lead to pyrroles,242 as well as imidazoles and oxazoles.243 Pyrolysis-GC-MS is relatively readily available and provides a productive technique. As mentioned previously, Wnorowski and Yaylayan212 had shown that, although more products are formed on pyrolysis than in aqueous media, most of the products identified in aqueous systems are present in pyrolysates with identical label distribution, even though the proportions may differ. Pyrolysates (250 °C, 20 s) of model systems of carbonyl and [2-13C]Gly or Ala were analysed. In the butanedione-Gly system, acetaldehyde and formaldehyde formed by decomposition of the carbonyl are unlabelled, but formaldehyde by Strecker degradation is labelled. 2,4,5-Trimethyloxazole was found to be unlabelled, being formed from acetaldehyde, but 4,5-dimethyloxazole was 15% mono-labelled, i.e., 15% of the precursor formaldehyde had been derived by Strecker degradation. 

Reference has already been made to the partial decarboxylation of pyrazinedicarboxylic acids.219 Both pyrazine itself,232 and 2,3-dimethylpyrazine,207 are conveniently prepared by decarboxylation of the appropriate dicarboxylic acids. The decarboxylation of pyrazine-2,3-dicarboxylic acid is carried out by heating in din-butyl phthalate and gives pyrazine in 90% yield. The 2,3-dicarboxylic acid forms an anhydride in the normal way. Pyrolysis of the anhydride at 800°/0.05 mm through a silica tube gives in 80% yield an approximately 1 1 mixture of maleonitrile and fumaronitrile (Scheme 19). 2,3-Dehydropyrazine is thought to be an intermediate in this reaction and a strong peak of m/e 78, corresponding to the dehydropyrazine ion, is observed in the mass spectrum of the anhydride.233... 

PTV PU PVA PVAC PVAL PVC PVDC PVDF PVE PVF PXRD py Py PY Py-GC-MS pyr pyrr pz programmed-temperature vaporizer polyurethane poly (vinyl alcohol) poly(vinyl acetate) poly (vinyl alcohol) poly (vinyl chloride) poly(vinylidene dichloride) poly(vinylidene difluoride) poly (vinyl ether) poly(vinyl fluoride) powder X-ray diffraction pyridine (ligand) pyridine pyramidal (coordination compounds) pyrolysis-gas chromatography-mass spectrometry pyrazine (ligand) pyrrolidine (ligand) pyrazole (ligand)... 

Flash pyrolysis of 5,7-diphenyl-2,3-dihydro-1/7-1,4-diazepine (34, R = H) at 700°C in a vacuum afforded 2-phenylpyrazine (35) in 21% yield, after separation from a pyrimidine the methyl substrate (34, R = Me) also gave a small yield of the same product (35) and 6-phenyl-2,3-dihydro-17/-l,4-diazcpine gave some unsubstituted pyrazine.176,1698... 

Thermolytic conversions of aromatic pyridines into pyrazines have been reported, albeit in minute yield. Thus vacuum pyrolysis of 4-dichloroamino-2,3,5,6-tetrafluoropyridine (69) at 550°C gave at least 12 products in which 2,3,5,6-tetrafluoropyrazine (70) could be identified 1320 and flow thermolysis of 4-azido-2,3,5,6-tetrafluoropyridine in nitrogen at 300°C gave l,2-difluoro-l,2-bis(3,5,6-trifluoropyrazin-2-yl)ethylene (71), isolated in 0.1% yield.1322... 

Apart from the pyrolysis of 2-tert-butylsulfonylpyrazine to afford pyrazine (1) [in 49% yield with loss of sulfur dioxide and unsaturated ( ) hydrocarbon]239 and the reduction of pyrazine to piperazine (2) (in 76% yield by treatment of an alkaline solution with Ni—A1 alloy),479 no new or improved routes to pyrazine or piperazine appear to have been reported in recent years nor has any di- or tetrahy-dropyrazine been prepared. Both pyrazine and piperazine are now available commercially at modest cost. 

Nitrogen derivatives A remarkable series of transformations has been discovered with fluorinated pyridazines, giving pyrimidines and small amounts of pyrazines on pyrolysis [262, 263] and pyrazines on photolysis [264]. Highly specific substituent labelling occurs on pyrolysis and diazabenzvalenes, or vibrationally excited species approaching these,... 

Cyclization of 2-hydrazinoquinoxalines occurs very readily with carboxylic acids and esters and ortho esters. This is in contrast to the pyrazines which could only be cyclized with ortho esters (60JA4044,68JHC485). Pyrolysis of the hydrazones derived from 2-hydrazinoquinoxalipe have led to various compounds of this series (60JA4044>. 

---