Glyoxal
Glyoxal is an organic compound with the chemical formula OCHCHO, making it the smallest dialdehyde (a compound with two aldehyde groups)[1]. It appears as a crystalline solid, white at low temperatures and yellow near its melting point (15 °C), with a yellow liquid and green vapor[1]. Pure glyoxal is not commonly encountered, as it is usually handled as a 40% aqueous solution (density near 1.24 g/mL), which forms a series of hydrates, including oligomers[1]. These hydrated oligomers behave equivalently to glyoxal for many purposes.
Glyoxal was first prepared and named by the German-British chemist Heinrich Debus (1824–1915) by reacting ethanol with nitric acid[1]. Commercially, 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]. The first commercial glyoxal source was in Lamotte, France, started in 1960, and the single largest commercial source is BASF in Ludwigshafen, Germany, at around 60,000 tons per year[1]. Other production sites exist also in the US and China.
Glyoxal has various applications, including as a crosslinker for starch-based formulations in coated paper and textile finishes[1]. It condenses with urea to afford 4,5-dihydroxy-2-imidazolidinone, which further reacts with formaldehyde to give the bis(hydroxymethyl) derivative dimethylol ethylene urea, used for wrinkle-resistant chemical treatments of clothing, i.e., permanent press[1]. Glyoxal is also used as a solubilizer and cross-linking agent in polymer chemistry[1]. Additionally, it is a valuable building block in organic synthesis, especially in the synthesis of heterocycles such as imidazoles[1]. Glyoxal solutions can also be used as a fixative for histology, a method of preserving cells for examining them under a microscope[1].
In the context of immunostaining, glyoxal has been shown to be a successful alternative fixative to formaldehyde, offering stronger and more accurate fixation, and being less toxic than formaldehyde[2]. It has been tested in tissue preparations, enabling accurate immunostainings in both Drosophila and mouse samples[2].
Glyoxal is also used as an antimicrobial preservative in cosmetic products, working by forming formaldehyde[5]. However, it has raised concerns due to its potential to cause formaldehyde allergy or allergy to the ingredient itself, and its use is restricted in cosmetics due to its toxicity and irritation potential[5].
Citations:
[1] https://en.wikipedia.org/wiki/Glyoxal
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5753035/
[3] https://www.univarsolutions.com/glyoxal-40-3405300
[4] https://www.bostick-sullivan.com/product/glyoxal-40-sol-100ml/
[5] https://www.ewg.org/skindeep/ingredients/702723-GLYOXAL/