Greener Production of Vanillin
Almost the entire fraction of the global and increasing vanillin demand (~20,000 tonnes in 2018) is met by synthetic vanillin produced at five plants (three in China, one in France and one in the U.S.) from petroleum-derived phenol (converted into guaiacol) and glyoxylic acid. The latter acid and guaiacol react in a two-step process starting with condensation promoted by base, followed by oxidative decarboxylation of vanillylmandelic acid to vanillin catalyzed by copper(II) in an aqueous alkaline medium at a temperature of 80-130 °C. Crude vanillin is then purified via vacuum distillation and recrystallization to obtain vanillin of commercial grade (1).
The resulting synthetic vanillin is sold at about 10$/kg to food (especially chocolate), flavor and fragrance, and pharmaceutical companies.
Contrary to what happened with citric acid originally sourced from lemon juice, (2) however, the industrial synthesis did not entirely displace the natural extraction route, with Vanilla planifolia being increasingly harvested in several warm countries, including Madagascar, Indonesia, Mexico, Uganda, ...