Glyoxal is an organic compound with the formula OCHCHO. This yellow colored liquid is the smallestdialdehyde (two aldehyde groups). Its tautomer acetylenediol is unstable.
Production
Commercial glyoxal is prepared either by the gas phase oxidation of ethylene glycol in the presence of a silver or copper catalyst or by the liquid phase oxidation of acetaldehyde with nitric acid. Global nameplate capacity is ~220,000 tons, with production rates less, due to over-capacity 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 and currently owned by Clariant. The single largest commercial source is BASF in Ludwigshafen, Germany at ~60,000 tons/annum. Until recently only 2 production sites (Geismer, LA and Charlotte, NC) existed in the Americas, however the 45kMT Charlotte facility is closed. Significant capacity has been added recently in China. Commercial bulk glyoxal is made and reported as a 40%-strength solution.
Glyoxal may be synthesized in the laboratory by oxidation of acetaldehyde with selenious acid. The preparation of anhydrous glyoxal entails heating solid glyoxal hydrate(s) with phosphorus pentoxide and condensing the vapors in a cold trap. The experimentally determined Henry’s law constants of glyoxal is: KH = 4.19 × 105 × exp[(62.2 × 103/R) × (1/T − 1/298)]
Applications
Coated paper and in the textile finishes use large amounts of glyoxal as a crosslinker for starch-based formulations and as a starting material with ureas for wrinkle-resistant chemical treatments. It is used as a solubilizer and cross-linking agent in polymer chemistry:
- proteins (leather tanning process)
- collagen
- cellulose derivatives (textiles)
- hydrocolloids
- starch (paper coatings)
It is a valuable building block in organic synthesis, especially in the synthesis of heterocycles such as imidazoles. 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.
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 >1 M, dimers predominate. These dimers are probably dioxolanes, with the formula [(HO)CH]2O2CHCHO. Dimer and trimer can precipitate, due to lower solubility, from solution at <40 F.
Other occurrences
Glyoxal is an inflammatory compound formed when cooking oils and fats are heated to high temperatures.