Glyoxal
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| Glyoxal | |
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| Chemical name | ethane-1,2-dione |
| Other names | ethandial |
| Chemical formula | C2H2O2 |
| Molecular mass | 58.04 g mol-1 |
| Melting point | 15 °C |
| Boiling point | 51 °C |
| Density | 1.27 g cm-3 |
| CAS number | 107-22-2 |
| SMILES | O=CC=O |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Glyoxal is an organic compound with the formula OCHCHO. This yellow-coloured liquid is the smallest dialdehyde. It is used as a solubilizer and cross-linking agent in polymer chemistry. It is a valuable building block in organic synthesis, especially in the synthesis of heterocycles such as imidazoles.[1] Glyoxal is prepared by oxidation of acetaldehyde with selenious acid.[2]
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[edit] Speciation of glyoxal 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)4 (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 >1 M, dimers predominate. These dimers are probably dioxalanes, with the formula [(HO)CH]2O2CHCHO.[3]
[edit] Anhydrous glyoxal
The preparation of anhydrous glyoxal entails heating solid glyoxal hydrate(s) with phosphorus pentoxide.[4] A quote from this paper is instructive of the chemistry of that era “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 that upon blackening of the contents, a mobile green gas which condenses in the cooled flask as beautiful yellow crystals).
[edit] Other occurrences
Glyoxal is an inflammatory compound formed when cooking oils and fats at high temperatures.
[edit] References
- ^ Snyder, H. R.; Handrick, R. G.; Brooks, L. A. Imidazole Organic Syntheses, Collected Volume 3, p.471 (1955).
- ^ Ronzio, A. R.; Waugh, T. D. Glyoxal Bisulfite Organic Syntheses, Collected Volume 3, p. 438 (1955).
- ^ Whipple, E. B. “Structure of Glyoxal in Water” Journal of the American Chemical Society, 1970, volume 90, pages 7183-7186. DOI:10.1021/ja00727a027
- ^ Harries, C.; Temme, F. “Über monomolekulares und trimolekulares Glyoxal” Berichte der deutschen chemischen Gesellschaft, 1904, volume 40, page 165-172. DOI:10.1002/cber.19070400124
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