Glyoxal

Glyoxal is an organic compound with the chemical formula OCHCHO. It is a yellow-colored liquid that evaporates to give a green-colored gas. Glyoxal is the smallest dialdehyde (two aldehyde groups). Its structure is more complicated than typically represented because the molecule hydrates and oligomerizes. It is produced industrially as a precursor to many products.^[1]

Production

Commercial glyoxal is prepared either by the gas-phase oxidation of ethylene glycol in the presence of a silver or copper catalyst (the Laporte process) or by the liquid-phase oxidation of acetaldehyde with nitric acid.^[1] Global nameplate capacity is around 220,000 tons, with production rates less, due to overcapacity mostly in Asia. Most production is done via the gas-phase oxidation route.

The first commercial glyoxal source was in Lamotte, France, started in 1960. The single largest commercial source is BASF in Ludwigshafen, Germany, at around 60,000 tons per year. Other production sites exist also in the US and China. Commercial bulk glyoxal is made and reported as a 40%-strength solution in water.

Glyoxal may be synthesized in the laboratory by oxidation of acetaldehyde with selenious acid.^[2] The preparation of anhydrous glyoxal entails heating solid glyoxal hydrate(s) with phosphorus pentoxide and condensing the vapors in a cold trap.^[3] The experimentally determined Henry's law constant of glyoxal is:

K_H = 4.19 × 10⁵ × exp[62.2 × 10³/R × (1/T − 1/298)].^[4]

Applications

Coated paper and textile finishes use large amounts of glyoxal as a crosslinker for starch-based formulations. It condenses with urea to afford 4,5-dihydroxy-2-imidazolidinone, which further reacts with formaldehyde to give the bis(hydroxymethyl) derivative used for wrinkle-resistant chemical treatments. It is used as a solubilizer and cross-linking agent in polymer chemistry:

Glyoxal is a valuable building block in organic synthesis, especially in the synthesis of heterocycles such as imidazoles.^[5] A convenient form of the reagent for use in the laboratory is its bis(hemiacetal) with ethylene glycol, 1,4-dioxane-2,3-diol. This compound is commercially available.

Glyoxal solutions can also be used as a fixative for histology, that is, a method of preserving cells for examining them under a microscope.

Speciation in solution

Glyoxal is supplied typically as a 40% aqueous solution. Like other small aldehydes, glyoxal forms hydrates. Furthermore, the hydrates condense to give a series of oligomers, the structures of which remain uncertain. For most applications, the exact nature of the species in solution is inconsequential. At least two hydrates of glyoxal are sold commercially:

glyoxal dimer dihydrate: [(CHO)₂]₂[H₂O]₂, 1,4-dioxane-trans-2,3-diol (CAS 4845-50-5, m.p. 91–95 °C),
glyoxal trimer dihydrate: [(CHO)₂]₃(H₂O)₂ (CAS 4405-13-4).

It is estimated that, at concentrations less than 1 M, glyoxal exists predominantly as the monomer or hydrates thereof, i.e., OCHCHO, OCHCH(OH)₂, or (HO)₂CHCH(OH)₂. At concentrations above 1 M, dimers predominate. These dimers are probably dioxolanes, with the formula [(HO)CH]₂O₂CHCHO.^[6] Dimer and trimer can precipitate, due to lower solubility, from solution at below 4 °C (40 °F).

Other occurrences

Glyoxal is an inflammatory compound formed when cooking oils and fats are heated to high temperatures.

Glyoxal has been observed as a trace gas in the atmosphere, e.g. as an oxidation product of hydrocarbons.^[7] Tropospheric concentrations of 0–200 ppt by volume have been reported, in polluted regions up to 1 ppb by volume.^[8]

References

1 2 Mattioda, Georges; Blanc, Alain (2005), "Glyoxal", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH
↑ Ronzio, A. R.; Waugh, T. D. (1944). "Glyoxal Bisulfite". Org. Synth. 24: 61. ; Coll. Vol. 3, p. 438
↑ Harries, C.; Temme, F. (1907). "Über monomolekulares und trimolekulares Glyoxal" [On monomoleular and trimoecular glyoxal]. Berichte 40 (1): 165–172. doi:10.1002/cber.19070400124. Man erhitzt nun das Glyoxal-Phosphorpentoxyd-Gemisch mit freier Flamme und beobachtet bald, dass sich unter Schwarzfärbung des Kolbeninhalte ein flüchtiges grünes Gas bildet, welches sich in der gekühlten Vorlage zu schönen Krystallen von gelber Farbe kondensiert. [One heats the mixture of (crude) glyoxal and P₄O₁₀ with an open flame and soon observes, upon blackening of the contents, a mobile green gas which condenses in the cooled flask as beautiful yellow crystals.]
↑ Ip, H. S.; Huang, X. H.; Yu, J. Z. (2009). "Effective Henry's law constants of glyoxal, glyoxylic acid, and glycolic acid". Geophys. Res. Lett. 36 (1): L01802. Bibcode:2009GeoRL..36.1802I. doi:10.1029/2008GL036212.
↑ Snyder, H. R.; Handrick, R. G.; Brooks, L. A. (1942). "Imidazole". Org. Synth. 22: 65. ; Coll. Vol. 3, p. 471
↑ Whipple, E. B. (1970). "Structure of Glyoxal in Water". J. Am. Chem. Soc. 92 (24): 7183–7186. doi:10.1021/ja00727a027.
↑ Vrekoussis, M.; Wittrock, F.; Richter, A.; Burrows, J. P. (2009). "Temporal and spatial variability of glyoxal as observed from space". Atmos. Chem. Phys 9: 4485–4504. doi:10.5194/acp-9-4485-2009.
↑ Volkamer, Rainer; et al. (2007). "A missing sink for gas‐phase glyoxal in Mexico City: Formation of secondary organic aerosol". Geophys. Res. Lett. 34: 19.

External links

"Glyoxal Industrial Applications". BASF.

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