Oxalyl chloride → 2-Trifluoromethylbenzylsulfonyl chloride

To a suspension of (2-trifluoromethylphenyl)methanesulfonic acid (20.3 g, 84 mmol) in THF (1.9 L) and DMF (5.0 mL) at −20° C. was added oxalyl chloride (44.7 mL, 0.5 mol) slowly dropwise over 1 hr. The bath temperature was maintained below 0° C. for 4 h, at which point the reaction was evaporated to a volume of ˜250 mL and diluted with 500 mL of ethyl acetate. This solution was washed with brine in a separatory funnel and dried over magnesium sulfate. The solution was then evaporated to a brown oil. This oil was taken up in 500 mL of pet ether (30-50°) and heated with a heat gun until the oil went into solution. The solution was then placed into a dry-ice acetone bath to cool resulting in formation of a white crystalline material. This material was collected via filtration and dried to afford 19 g (85%) of (2-trifluoromethylphenyl)methanesulfonyl chloride as a white solid.