Guayacol

A colorless aromatic oily substance, originally isolated from the medicinal guaiac ( Guaiacum officinale L. ), a tree found in India and South America. It was used as an expectorant, it has disinfectant effects. From guaiacol is derived guaifenesin ((RS)-3-(2-methoxyphenoxy)-1,2-propanediol), which is still used as an expectorant and mild sedative.

Guaiacol is used as a substrate for peroxidase reactions to detect hydrogen peroxide. This reaction is routinely used, for example, in the guaiac test for occult bleeding. Oxidation of guaiacol produces a blue-green colored mixture of products with an absorption maximum around 470 nm; the most represented in it is 3,3'-dimethoxy-4,4'-biphenylquinone.

Reference
DOERGE, Daniel R., Rao L. DIVI a Mona I. CHURCHWELL. Identification of the colored guaiacol oxidation product produced by peroxidases. Analytical Biochemistry. 1997, roč. 250, s. 10-17, ISSN 0003-2697. (http://dx.doi.org/10.1006/abio.1997.2191)