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The general procedure for the synthesis of 2-chloro-5-methoxybenzothiazole using 2-mercapto-5-methoxybenzothiazole as starting material was as follows: sulfuryl chloride (1.64 mL) was slowly added dropwise to a solution of tetrahydrofuran (THF, 20 mL) containing 5-methoxy-2-mercapto benzothiazole at room temperature. The reaction mixture was stirred overnight at room temperature. Upon completion of the reaction, the reaction was quenched by careful addition of ice water. After returning the mixture to room temperature, it was diluted with ethyl acetate (EtOAc, 100 mL). The organic phase was washed sequentially with water (50 mL) and saturated saline (50 mL), dried over anhydrous sodium sulfate (Na2SO4), filtered, and concentrated under reduced pressure to remove the solvent. The crude product was purified by silica gel column chromatography using a solvent mixture of hexane and ethyl acetate as eluent (gradient elution, volume fraction of ethyl acetate was increased from 0% to 3%) to obtain the target compound 2-chloro-5-methoxybenzothiazole (0.407 g, 20% yield) as a white solid. The product was analyzed by liquid chromatography-mass spectrometry (LC-MS) with a retention time (RT) of 9.05 min and a molecular ion peak [M+H]+ m/z = 200.0. Thin layer chromatography (TLC) analysis showed an Rf value of 0.38 (unfolding agent 10% ethyl acetate/hexane).

[1] Patent: WO2007/146066, 2007, A2. Location in patent: Page/Page column 89
[2] Journal of Organic Chemistry, 2009, vol. 74, # 8, p. 3229 - 3231
[3] Patent: US2011/263562, 2011, A1. Location in patent: Page/Page column 61