Pyrazine

{{Short description|Chemical compound}} {{chembox | Watchedfields = changed | verifiedrevid = 417947419 | ImageFileL1 = Pyrazine 2D aromatic full.svg | ImageFileR1 = Pyrazine 2D numbers.svg | ImageFileL2 = Pyrazine-3D-balls-2.png | ImageAltL2 = Pyrazine molecule | ImageFileR2 = Pyrazine-3D-spacefill.png | ImageAltR2 = Pyrazine molecule | PIN = Pyrazine<ref>{{cite book |author=International Union of Pure and Applied Chemistry |date=2014 |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 |publisher=The Royal Society of Chemistry |pages=141 |doi=10.1039/9781849733069 |isbn=978-0-85404-182-4}}</ref> | OtherNames = 1,4-Diazabenzene, p-Diazine, 1,4-Diazine, Paradiazine, Piazine, UN 1325 |Section1={{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 8904 | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 15797 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C4H4N2/c1-2-6-4-3-5-1/h1-4H | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = KYQCOXFCLRTKLS-UHFFFAOYSA-N | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 290-37-9 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 2JKE371789 | EINECS = 206-027-6 | PubChem = 9261 | SMILES = c1cnccn1 | InChI = 1/C4H4N2/c1-2-6-4-3-5-1/h1-4H | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 30953 }} |Section2={{Chembox Properties | Formula = C4H4N2 | MolarMass = 80.09 g/mol | Appearance = White crystals | Density = 1.031 g/cm3 | MeltingPtC = 52 | BoilingPtC = 115 | Solubility = Soluble | pKa =0.37<ref>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.</ref> (protonated pyrazine) | MagSus = −37.6·10−6 cm3/mol }} |Section3={{Chembox Hazards | MainHazards = | FlashPtC = 55 | FlashPt_notes = c.c. | AutoignitionPt = | NFPA-H = 2 | NFPA-F = 2 | NFPA-R = 0 | NFPA-S = | GHSPictograms = {{GHS05}}{{GHS07}} | GHSSignalWord = Danger | HPhrases = {{H-phrases|228|315|319|335}} | PPhrases = {{P-phrases|210|261|305+351+338}} }} }}

'''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. It is a ''"deliquescent crystal or wax-like solid with a pungent, sweet, corn-like, nutty odour"''.<ref>{{cite web |title=Pyrazine {{!}} C4H4N2 {{!}} ChemSpider |url=https://www.chemspider.com/Chemical-Structure.8904.html?rid=e2532a2c-d5cb-457e-884b-ca9e4c8bd96b |website=www.chemspider.com |access-date=4 January 2022}}</ref>

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.<ref>{{cite journal | doi = 10.1016/S0024-3205(03)00139-5 | title=Tetramethylpyrazine scavenges superoxide anion and decreases nitric oxide production in human polymorphonuclear leukocytes | journal=Life Sciences | date=2003 | volume=72 | issue=22 | pages=2465–2472 | first1=Zhaohui | last1=Zhang|last2=Wei|first2=Taotao|last3=Hou|first3=Jingwu|last4=Li|first4=Gengshan|last5=Yu|first5=Shaozu|last6=Xin|first6=Wenjuan|pmid=12650854}}</ref>

== 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.<ref>{{cite journal | doi = 10.1002/cber.187600901174 | title = Ueber die Einwirkung von Ammoniak auf Chloracetylbenzol | date = 1876 | last1 = Staedel | first1 = W. | last2 = Rügheimer | first2 = L. | journal = Berichte der Deutschen Chemischen Gesellschaft | volume = 9 | pages = 563–564 }}</ref> A variation is the '''Gutknecht pyrazine synthesis''' (1879) also based on this selfcondensation, but differing in the way the alpha-ketoamine is synthesised.<ref>{{cite journal | doi = 10.1002/cber.187901202284 | title = Ueber Nitrosoäthylmethylketon | journal = Berichte der Deutschen Chemischen Gesellschaft | date = 1879 | volume = 12 | issue = 2 | pages = 2290–2292 }}</ref><ref>''Heterocyclic chemistry'' T.L. Gilchrist {{ISBN|0-582-01421-2}}</ref>

:500px|Gutknecht pyrazine synthesis

The '''Gastaldi synthesis''' (1921) is another variation:<ref>G. Gastaldi, Gazz. Chim. Ital. 51, ('''1921''') 233</ref><ref>''Amines: Synthesis, Properties and Applications'' Stephen A. Lawrence 2004 Cambridge University Press {{ISBN|0-521-78284-8}}</ref>

:400px|Gastaldi synthesis

== 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 == {{reflist}}

== External links == * [http://www.inchem.org/documents/jecfa/jecmono/v48je12.htm Safety evaluation of food additives – pyrazine derivatives]

Category:Pyrazines Category:Simple aromatic rings