Pyrazine

Structural formula
General
Surname	Pyrazine
other names	1,4-diazabenzene 1,4-diazine
Molecular formula	C 4 H 4 N 2
Brief description	colorless crystals or waxy liquid
External identifiers / databases
CAS number 290-37-9 EC number 206-027-6 ECHA InfoCard 100.005.480 PubChem 9261 ChemSpider 8904 Wikidata Q424284
properties
Molar mass	80.09 g mol −1
Physical state	firmly
density	1.03 g cm −3
Melting point	53 ° C
boiling point	115-116 ° C
solubility	soluble in water, ethanol and diethyl ether
Refractive index	1.4953 (61 ° C)
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 228-315-319-335 P: 210-261-305 + 351 + 338
Thermodynamic properties
ΔH f 0	139.8 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Pyrazine ( 1,4-diazine ) is a chemical compound and namesake for the group of substances called pyrazines . It is a heteroaromatic , more precisely a diazine or diazabenzene.

history

The synthesis of pyrazine was first reported by Auguste Laurent in 1844 , and in 1897 by LH Snape and A. Brooke it was confirmed that it was 2,3,5,6-tetraphenylpyrazine . Laurent called this connection "Amarone".

From this point on, various derivatives of pyrazine were made. In 1882, however , Severin Segelcke Wleügel was the first to suggest that pyrazine should consist of a six-membered ring analogous to pyridine . In 1887 Arthur T. Mason and Ludwig Wolff separately suggested that the word "pyrazine" could be used for the above-mentioned compound. They made it clear that a six-membered ring compound consisting of four carbon and two nitrogen atoms is classified as a diazine. The parent compound pyrazine was produced in traces by Ludwig Wolff in 1888 by heating aminoacetaldehyde diethyl acetal with oxalic acid. During this time chemists debated the possible bonding structure of pyrazine. Either a Kekulé-type or a Dewar-type arrangement was under discussion. The Kekulé type refers to the conjugated double bond within the pyrazine molecule, while the Dewar type refers to the long para bond that binds the two nitrogen atoms. After analyzing the molecular refraction of various pyrazine derivatives, Julius Wilhelm Brühl finally confirmed that the pyrazine exists in the Kekulé configuration.

Proposed structures for pyrazine (left Kekulé type, right Dewar type)

Occurrence

Pyrazine is found in roasted peanuts and other heated foods.

Extraction and presentation

Pyrazine can be conveniently produced from the oxidation of dihydropyrazine , which is the condensation product of glyoxal with 1,2-diaminoethane . Copper (II) oxide and manganese oxide are commonly used as oxidizing agents for dihydropyrazine.

Yozo Ohtsuka, et al. reported in 1979 on an alternative route to the synthesis by cyclization of 2,3-bis (arylidenamino) -3-cyanoarylamides to form the pyrazine precursor 1,2-dihydropyrazine.

It is also possible to prepare by reacting diamine with diols in the presence of a metal catalyst (for example by reacting ethylene diamine with ethylene glycol at 400 ° C. over zinc oxide catalysts) or by reacting diamine with dicarbonylene .

Also the synthesis by catalytic dehydrogenation of monoethanolamine in the presence of copper , copper and zinc oxide, zinc oxide and sodium carbonate at 250-300 ° C or by deaminocyclization of ethylenediamine followed by dehydrogenation over copper chromite or by condensation of glyoxal and ethylenediamine at high temperatures with a copper -Chrome oxide catalyst is possible.

properties

Pyrazine is a colorless, highly flammable solid that is soluble in water, ethanol and diethyl ether . It has an orthorhombic crystal structure with the space group Pmnn (space group no. 58, position 3) and two molecules per unit cell. The molecule is planar. Since pyrazine is an aromatic compound, it can be represented as a resonant hybrid of a number of canonical structures. Due to the symmetrical nature of the molecule, the dipole moment of pyrazine is zero.

In 1957, Peter Jaffrey Wheatley determined the structure of pyrazine using X-ray structure analysis , with the lengths of the CC, CN and CH bonds being 1.378  Å , 1.334 Å and 1.050 Å, respectively. In 1977, studies using gas-phase electron diffraction showed that the C — C bond of pyrazine is somewhat larger than that of benzene , but similar to that of pyridine . In contrast, the CN bond of pyrazine and pyridine was the same within the error limit. It is noteworthy that the C [BOND] H bond of pyrazine is longer compared to that of benzene and pyridine. In these investigations, the values ​​were determined to be: r (CC) = 1.339 ± 0.002 Å. r (CN) = 1.403 ± 0.004 Å, r (CH) = 1.115 ± 0.004 Å. CCN = 115.6 ± 0.4 °, and CCH = 123.9 ± 0.6 °.

use

Pyrazine can be used as an intermediate in the manufacture of other chemical compounds. Thus, the complete hydrogenation of the pyrazine leads to piperazine . The N -alkylation of pyrazine gives pyrazinium salts , which can serve as ionic liquids . Pyrazine is suitable as a ligand for metal complexes, for the production of coordination polymers and for the construction of supramolecular structures.

Individual evidence

1. ↑ ^{a b c d e} entry on pyrazine. In: Römpp Online . Georg Thieme Verlag, accessed on September 29, 2014.
2. ↑ ^{a b c} data sheet pyrazine at AlfaAesar, accessed on June 1, 2010 ( PDF )(JavaScript required) .
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-448.
4. ↑ ^{a b} Pyrazine data sheet from Sigma-Aldrich , accessed on April 22, 2011 ( PDF ).
5. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-25.
6. ↑ ^{a b c d e f} KOK TONG ONG, ZHI-QIANG LIU, MENG GUAN TAY: Review on the Synthesis of Pyrazine and Its Derivatives. In: Borneo Journal of Resource Science and Technology. 7, 2017, p. 60, doi : 10.33736 / bjrst.591.2017 .
7. ^ ^{A b c} Gordon Bruce Barlin: The Pyrazines . John Wiley & Sons, 2009, ISBN 0-470-18869-3 , pp. 3 ( limited preview in Google Book Search).
8. ↑ Science of Synthesis: Houben-Weyl Methods of Molecular Transformations Vol. 16 Six-Membered Hetarenes with Two Identical Heteroatoms . Georg Thieme Verlag, 2014, ISBN 3-13-171881-1 , p. 751 ( limited preview in Google Book search).
9. ↑ JW Brühl, journal for physical chemistry , stoichiometry and kinship theory, 22, 373 (1897) (spectrochemical behavior of imino ethers)
10. ↑ Hans-Dieter Belitz, Werner Grosch: Textbook of food chemistry . Springer-Verlag, 2013, ISBN 978-3-662-08304-8 , pp. 328 ( limited preview in Google Book search).
11. ↑ Yozo Ohtsuka, Eiko Tohma et al. a .: Chemistry of diaminomaleonitrile. 5. Dihydropyrazine synthesis. In: The Journal of Organic Chemistry. 44, 1979, p. 4871, doi : 10.1021 / jo00394a027 .
12. ↑ ^{a b} Vishnu Ji Ram, Arun Sethi, Mahendra Nath, Ramendra Pratap: The Chemistry of Heterocycles Chemistry of Six to Eight Membered N, O, S, P and Se Heterocycles . Elsevier, 2019, ISBN 978-0-12-819211-5 , pp. 147 ( limited preview in Google Book search).
13. ^ ^{A b} P. J. Wheatley: The crystal and molecular structure of pyrazine. In: Acta Crystallographica. 10, p. 182, doi : 10.1107 / S0365110X57000596 .
14. ↑ BJM Bormans, G. De With, FC Mijlhoff: The molecular structure of pyrazine as determined from gas-phase electron diffraction data. In: Journal of Molecular Structure. 42, 1977, p. 121, doi : 10.1016 / 0022-2860 (77) 87035-X .