2-Mercaptobenzooxazole-6-carboxylic acid methyl ester

140-89-6

63435-16-5

72752-81-9

The general procedure for the synthesis of methyl 2-mercaptobenzo[D]oxazole-6-carboxylate from potassium ethylxanthate and methyl 4-amino-3-hydroxybenzoate was as follows: a suspension of methyl 4-amino-3-hydroxybenzoate (393 g, 2.35 mol) and potassium ethylxanthate (393 g, 2.45 mol) in pyridine (3 L) was heated and refluxed for 12 hours. Completion of the reaction was confirmed by monitoring the progress of the reaction by thin layer chromatography (TLC, unfolding agent ratio ethyl acetate/petroleum ether = 1:2). The reaction mixture was cooled to room temperature and slowly poured into four 5L flasks containing 1600mL of concentrated hydrochloric acid and 10L of ice water, respectively. After vigorous stirring for 5 minutes, the solid product was collected by filtration. The solid was washed with 1 L of water and dried in air for 30 min. The dried solid was dissolved in 10 L of ethyl acetate and the organic phase was washed sequentially with 2 L of 1N hydrochloric acid and 1 L of saturated saline. The organic phase was dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target product methyl 2-mercaptobenzo[D]oxazole-6-carboxylate (390 g, 79.3% yield) as a pink solid.