Synthesis
General procedure for the synthesis of 4-hydroxy-2-methylbenzoic acid from 4-methoxy-2-methylbenzoic acid: boron tribromide (20 mmol, 5 g, 10 eq.) was slowly added to a solution of 4-methoxy-2-methylbenzoic acid (2 mmol, 0.332 g) in dichloromethane (20 mL) under argon protection. The reaction mixture was stirred at room temperature until high performance liquid chromatography (HPLC) analysis showed complete consumption of the feedstock. Subsequently, 0.1 M hydrochloric acid (20 mL) was added to the reaction system to quench the reaction and the insoluble material was removed by filtration. The aqueous phase was concentrated under reduced pressure and the residue was dissolved in methanol and concentrated again under reduced pressure to remove the solvent. This dissolution-concentration process was repeated three times, resulting in purified 4-hydroxy-2-methylbenzoic acid as a yellow solid (0.24 g, 80% yield).
References
[1] European Journal of Organic Chemistry, 2008, # 5, p. 816 - 825
[2] Patent: WO2006/64286, 2006, A1. Location in patent: Page/Page column 93-94
[3] Patent: WO2007/144379, 2007, A1. Location in patent: Page/Page column 39
[4] Indian Journal of Chemistry, Section B: Organic Chemistry Including Medicinal Chemistry, 1987, vol. 26, p. 679 - 682
[5] Patent: WO2006/79099, 2006, A2. Location in patent: Page/Page column 68; 69
