Syringol

Syringol is the organic compound with the formula HO(CH3O)2C6H3. The molecule is a phenol, with methoxy groups in the flanking (2 and 6) positions. It is the symmetrically dimethylated derivative of pyrogallol. It is a colorless solid, although typical samples are brown owing to air-oxidized impurities. Together with guaiacol, syringol and its derivatives are produced by the pyrolysis of lignin. Specifically, syringol is derived from the thermal decomposition of the sinapyl alcohol component. As such, syringol is an important component of wood smoke.

Syringol[1]
Syringol
Names
Preferred IUPAC name
2,6-Dimethoxyphenol
Other names
Syringol
2-Hydroxy-1,3-dimethoxybenzene
Pyrogallol 1,3-dimethyl ether
Identifiers
3D model (JSmol)
1526871
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.001.856
EC Number
  • 202-041-1
UNII
  • InChI=1S/C8H10O3/c1-10-6-4-3-5-7(11-2)8(6)9/h3-5,9H,1-2H3 checkY
    Key: KLIDCXVFHGNTTM-UHFFFAOYSA-N checkY
  • InChI=1/C8H10O3/c1-10-6-4-3-5-7(11-2)8(6)9/h3-5,9H,1-2H3
    Key: KLIDCXVFHGNTTM-UHFFFAOYAG
  • O(c1cccc(OC)c1O)C
Properties
C8H10O3
Molar mass 154.16 g/mol
Appearance Gray to light brown solid
Density 1.15857 g/cm3 (60 °C) [2]
Melting point 50 to 57 °C (122 to 135 °F; 323 to 330 K)
Boiling point 262 °C (504 °F; 535 K)[2]
Slightly soluble
Vapor pressure 15.8 Pa (60 °C) [2]
Hazards[1]
Flash point 140 °C (284 °F; 413 K)
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

Syringyl/guaiacyl ratio

Lignin, comprising a major fraction of biomass, is sometimes classified according to the syringyl component. Pyrolysis of lignin derived from sinapyl alcohol affords syringol. The conversion involves replacement of the propenyl alcohol substituent of the sinapyl alcohol by hydrogen. A high syringyl (or S) content is indicative of lignin from angiosperms. In contrast, pyrolysis of lignin from gymnosperms gives more guaiacol, resulting from conversion of coniferyl alcohol. These lignins have a high guaiacyl (or G) content.[3]

Food preparation

In preparation of food by smoking, syringol is the main chemical responsible for the smoky aroma, while guaiacol contributes mainly to taste. Artificial liquid or solid smoke flavorings also contain these chemicals, on average composing 13.73% and 13.42% of those products by mass respectively.[4]

Chemical feedstock

Pyrolysis oil, a biofuel derived from woody biomass, can be optimized to yield syringol as a byproduct, potentially competing with petroleum-derived phenols.[5] Some studies indicate that syringol can substitute for phenol formaldehyde resin, a commonly used, water resistant adhesive for plywood.[6]

See also

References
  1. 2,6-Dimethoxyphenol at Sigma-Aldrich
  2. Baird, Zachariah Steven; Uusi-Kyyny, Petri; Pokki, Juha-Pekka; Pedegert, Emilie; Alopaeus, Ville (6 Nov 2019). "Vapor Pressures, Densities, and PC-SAFT Parameters for 11 Bio-compounds". International Journal of Thermophysics. 40 (11): 102. Bibcode:2019IJT....40..102B. doi:10.1007/s10765-019-2570-9.
  3. Li, Laigeng; Cheng, Xiao Fei; Leshkevich, Jacqueline; Umezawa, Toshiaki; Harding, Scott A.; Chiang, Vincent L. (2001). "The Last Step of Syringyl Monolignol Biosynthesis in Angiosperms is Regulated by a Novel Gene Encoding Sinapyl Alcohol Dehydrogenase". The Plant Cell. 13 (7): 1567–1586. doi:10.1105/tpc.010111. PMC 139549. PMID 11449052.
  4. Chichester, C. O.; Mrak, E. M.; Schweigert, B. S., eds. (1984). Advances in Food Research. Vol. 29. London: Academic Press. pp. 129–130. ISBN 978-0-08-056748-8.
  5. Dinesh Mohan; Charles U. Pittman Jr.; Philip H. Steele (2006). "Pyrolysis of Wood/Biomass for Bio-oil: A Critical Review". Energy & Fuels. 20 (3): 863. doi:10.1021/ef0502397.
  6. Bridgwater, A.V.; Effendi A; Gerhauser H (2008). "Production of Renewable Phenolic Resin by Thermochemical Conversion of Biomass: A Review". Renewable and Sustainable Energy Reviews. 12 (8): 2092–2116. doi:10.1016/j.rser.2007.04.008.
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