Вінілгваякол

4-Vinylguaiacol (CAS 7786-61-0) is a phenolic compound formed by the decarboxylation of ferulic acid. It is guaiacol with a vinyl group attached to the fourth carbon. Eugenol, the most abundant molecule in the essential oil of cloves, differs from it only by one added carbon in the residue attached to the fourth carbon of the phenol ring. It is a colourless or pale straw oily liquid.

It is one of the compounds responsible for the natural aroma of buckwheat. It has also been reported in Angelica gigas and Humulus lupulus, and it is an odorant in green tea. During coffee roasting, decarboxylation of ferulic acid yields 4-vinylguaiacol, guaiacol and phenol. Pyrolysis of sugarcane bagasse lignins yields compounds including guaiacol, 4-methylguaiacol and 4-vinylguaiacol. In soft pretzels, it can be generated from hemicelluloses such as arabinoxylans that contain bound ferulic acid, which is liberated during the alkaline treatment of the dough and thermally decarboxylated during baking. 4-Vinylguaiacol is one of the top three odour-active phenols in food, together with vanillin and guaiacol.

Ferulic acid, the precursor of 4-vinylguaiacol, is found in the bran of wheat and barley. Dimers of ferulic acid crosslink the polysaccharides of plant cell walls, and the acid is present in cereal brans and sugar beet pulp. In the mechanism proposed for ferulic acid decarboxylases, the phenolic hydroxyl group is deprotonated and turned into a quinoid intermediate, and the carboxylic group then leaves the molecule as carbon dioxide.

The yeast enzyme involved, cinnamate decarboxylase, is produced by strains with an active form of the POF gene, which include wheat beer yeast strains, most wine strains and many wild yeasts. Most wild strains of Saccharomyces are POF+. Other microbes, including Torulaspora delbrueckii and Pseudomonas fluorescens, can also convert ferulic acid into 4-vinylguaiacol. By varying mashing conditions to release more or less ferulic acid, brewers can somewhat control the amount of spicy, clove flavour in beer. It has been suggested that the clove-like aroma of fresh specialty beers, such as wheat beers and top-fermented Belgian-style ales, may shift toward sweeter, more vanilla-like impressions as they age.

It is applied in the pharmaceutical, cosmetic and food industries. Its commercial price is forty times greater than that of ferulic acid. Some insects, such as the red palm weevil Rhynchophorus ferrugineus, use it for chemical signalling.

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