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Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2.

Pyrazine 2D aromatic full.svg
Pyrazine 2D numbers.svg
Pyrazine molecule
Pyrazine molecule
IUPAC name
Other names
1,4-Diazabenzene, p-Diazine, 1,4-Diazine, Paradiazine, Piazine, UN 1325
3D model (JSmol)
ECHA InfoCard 100.005.480
EC Number 206-027-6
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)
Acidity (pKa) 0.37[1] (protonated pyrazine)
-37.6·10−6 cm3/mol
R-phrases (outdated) R11, R36/37/38
S-phrases (outdated) S16, S26, S36
NFPA 704
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 codeNFPA 704 four-colored diamond
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 is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine.

Derivatives such as phenazine are well known for their antitumor, antibiotic and diuretic activities.[citation needed]

Tetramethylpyrazine (also known as ligustrazine) is reported to scavenge superoxide anion and decrease nitric oxide production in human polymorphonuclear leukocytes.[2]


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]


See alsoEdit


  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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