Glyoxal is an organic compound with the chemical formula OCHCHO. It is the smallestdialdehyde. It is a crystalline solid, white at low temperatures and yellow near the melting point. The liquid is yellow, and the vapor is green. Pure glyoxal is not commonly encountered because it forms hydrates, which oligomerize. For many purposes, these hydrated oligomers behave equivalently to glyoxal. It is produced industrially as a precursor to many products.
Production
Glyoxal was first prepared and named by the German-British chemist Heinrich Debus by reacting ethanol with nitric acid. Commercial glyoxal is prepared either by the gas-phase oxidation of ethylene glycol in the presence of a silver or coppercatalyst or by the liquid-phase oxidation of acetaldehyde with nitric acid. 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.
Laboratory methods
Glyoxal may be synthesized in the laboratory by oxidation of acetaldehyde with selenious acid. Anhydrous glyoxal is prepared by heating solid glyoxal hydrate with phosphorus pentoxide and condensing the vapors in a cold trap. The experimentally determined Henry's law constant of glyoxal is:
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 derivative dimethylol ethylene urea, which is used for wrinkle-resistant chemical treatments of clothing, i.e. permanent press. Glyoxal 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. A convenient form of the reagent for use in the laboratory is its bis 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. Glyoxal and its derivatives are also used in the chemical probing of RNA structure, as they react with free guanines in RNAs.
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, some of which remain of uncertain structure. For most applications, the exact nature of the species in solution is inconsequential. At least one hydrate of glyoxal is sold commercially, glyoxal trimer dihydrate: 32. Other glyoxal equivalents are available, such as the ethylene glycol hemiacetal 1,4-dioxane-trans-2,3-diol, It is estimated that, at concentrations less than 1 M, glyoxal exists predominantly as the monomer or hydrates thereof, i.e., OCHCHO, OCHCH2, or 2CHCH2. At concentrations above 1 M, dimers predominate. These dimers are probably dioxolanes, with the formula 2O2CHCHO. Dimer and trimers precipitate as solids from cold solutions.
