Pyrazine

Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine.

Pyrazine
Pyrazine molecule
Pyrazine molecule
Names
IUPAC name
Pyrazine
Other names
1,4-Diazabenzene, p-Diazine, 1,4-Diazine, Paradiazine, Piazine, UN 1325
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.005.480
EC Number
  • 206-027-6
UNII
Properties
C4H4N2
Molar mass 80.09 g/mol
Appearance White crystals
Density 1.031 g/cm3
Melting point 52 °C (126 °F; 325 K)
Boiling point 115 °C (239 °F; 388 K)
Soluble
Acidity (pKa) 0.37[1] (protonated pyrazine)
-37.6·10−6 cm3/mol
Hazards
R-phrases (outdated) R11, R36/37/38
S-phrases (outdated) S16, S26, S36
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
2
0
Flash point 55 °C (131 °F; 328 K) c.c.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Pyrazine and a variety of alkylpyrazines are flavor and aroma compounds found in baked and roasted goods. Tetramethylpyrazine (also known as ligustrazine) is reported to scavenge superoxide anion and decrease nitric oxide production in human polymorphonuclear leukocytes.[2]

Synthesis

Many methods exist for the organic synthesis of pyrazine and its derivatives. Some of these are among the oldest synthesis reactions still in use.

In the Staedel–Rugheimer pyrazine synthesis (1876) 2-chloroacetophenone is reacted with ammonia to the amino ketone, then condensed and then oxidized to a pyrazine.[3] A variation is the Gutknecht pyrazine synthesis (1879) also based on this selfcondensation, but differing in the way the alpha-ketoamine is synthesised.[4][5]

The Gastaldi synthesis (1921) is another variation:[6][7]

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See also

References
  1. Brown, H.C., et al., in Baude, E.A. and Nachod, F.C., Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955.
  2. Zhang, Zhaohui (2003). "Tetramethylpyrazine scavenges superoxide anion and decreases nitric oxide production in human polymorphonuclear leukocytes". Life Sciences. 72 (22): 2465–2472. doi:10.1016/S0024-3205(03)00139-5.
  3. Ueber die Einwirkung von Ammoniak auf Chloracetylbenzol (pp. 563–564) W. Staedel, L. Rügheimer doi:10.1002/cber.187600901174 Berichte der deutschen chemischen Gesellschaft Volume 9, Issue 1, pp. 563–564, 1876
  4. Mittheilungen Ueber Nitrosoäthylmethylketon H. Gutknecht Berichte der deutschen chemischen Gesellschaft Volume 12, Issue 2 , pp. 2290–2292, 1879 doi:10.1002/cber.187901202284
  5. Heterocyclic chemistry T.L. Gilchrist ISBN 0-582-01421-2
  6. G. Gastaldi, Gazz. Chim. Ital. 51, (1921) 233
  7. Amines: Synthesis, Properties and Applications Stephen A. Lawrence 2004 Cambridge University Press ISBN 0-521-78284-8
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