Pyrazine

Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C₄H₄N₂. It is a symmetrical molecule with point group D_2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a "deliquescent crystal or wax-like solid with a pungent, sweet, corn-like, nutty odour".^[3]

Pyrazine

Names
Preferred IUPAC name Pyrazine[1]
Other names 1,4-Diazabenzene, p-Diazine, 1,4-Diazine, Paradiazine, Piazine, UN 1325
Identifiers
CAS Number	290-37-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30953 Y
ChEMBL	ChEMBL15797 Y
ChemSpider	8904 Y
ECHA InfoCard	100.005.480
EC Number	206-027-6
PubChem CID	9261
UNII	2JKE371789 Y
CompTox Dashboard (EPA)	DTXSID8049410
InChI InChI=1S/C4H4N2/c1-2-6-4-3-5-1/h1-4H Y Key: KYQCOXFCLRTKLS-UHFFFAOYSA-N Y InChI=1/C4H4N2/c1-2-6-4-3-5-1/h1-4H
SMILES c1cnccn1
Properties
Chemical formula	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)
Solubility in water	Soluble
Acidity (pKa)	0.37[2] (protonated pyrazine)
Magnetic susceptibility (χ)	-37.6·10−6 cm3/mol
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H228, H315, H319, H335
Precautionary statements	P210, P261, P305+P351+P338
NFPA 704 (fire diamond)	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). Y verify (what is YN ?) 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 anions and decrease nitric oxide production in human granulocytes.^[4]

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.^[5] A variation is the Gutknecht pyrazine synthesis (1879) also based on this selfcondensation, but differing in the way the alpha-ketoamine is synthesised.^[6][7]

The Gastaldi synthesis (1921) is another variation:^[8][9]

See also

• Alkylpyrazines
• Methoxypyrazines
• Simple aromatic rings
• Benzene, an analog without the nitrogen atoms
• Pyridazine, an analog with the second nitrogen atom in position 2
• Pyridine, an analog with only one nitrogen atom
• Pyrimidine, an analog with the second nitrogen atom in position 3
• Piperazine, the saturated analog

References

1. International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 141. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
2. 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.
3. "Pyrazine | C4H4N2 | ChemSpider". www.chemspider.com. Retrieved 4 January 2022.
4. Zhang, Zhaohui; Wei, Taotao; Hou, Jingwu; Li, Gengshan; Yu, Shaozu; Xin, Wenjuan (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. PMID 12650854.
5. Staedel, W.; Rügheimer, L. (1876). "Ueber die Einwirkung von Ammoniak auf Chloracetylbenzol". Berichte der Deutschen Chemischen Gesellschaft. 9: 563–564. doi:10.1002/cber.187600901174.
6. "Ueber Nitrosoäthylmethylketon". Berichte der Deutschen Chemischen Gesellschaft. 12 (2): 2290–2292. 1879. doi:10.1002/cber.187901202284.
7. Heterocyclic chemistry T.L. Gilchrist ISBN 0-582-01421-2
8. G. Gastaldi, Gazz. Chim. Ital. 51, (1921) 233
9. Amines: Synthesis, Properties and Applications Stephen A. Lawrence 2004 Cambridge University Press ISBN 0-521-78284-8

External links

• Safety evaluation of food additives – pyrazine derivatives