Guaiacol

Guaiacol (2-methoxyphenol, o-methoxyphenol, methylcatechol, o-hydroxyanisole) is the monomethyl ether of catechol. At room temperature it is a colorless to pale yellow oily liquid or low-melting solid with a smoky, spicy and herbal note — a phenol-ether fine chemical combining preservative, antibacterial and fragrance-fixing functions. Slightly soluble in water, readily soluble in ethanol, ether, chloroform and sodium hydroxide solution; melting point 26-29 °C, boiling point 204-206 °C; meets both food-grade and pharmaceutical-grade standards.

It can be produced by methylating catechol with dimethyl sulfate under alkaline conditions, or via diazotization and hydrolysis of o-anisidine, and also occurs naturally in wood tar and guaiac resin. The phenolic hydroxyl is weakly acidic and can be salted, etherified and esterified; the methoxy group is an ortho/para director that facilitates building multi-substituted benzene derivatives. The product oxidizes and discolors readily in air and must be stored sealed and protected from light.