2-Fluorobenzaldehyde (12.4 g, 0.1 mol, 1 eq.) and methanesulfonic acid (11.2 g, 0.11 mol, 1.1 eq.) were dissolved in DMSO (75 ml) and heated to 100 °C for 16 hours. After completion of the reaction, the mixture was cooled to room temperature and poured into crushed ice (100 g). The resulting 2-(methylsulfonyl)benzaldehyde was collected by filtration and dried under vacuum at 45 °C for 16 h to give a yellow solid product (9.2 g, 50% yield). The product was characterized as follows: 1H NMR (300 MHz, CDCl3) δ 10.77 (1H, s, CHO), 8.18-8.16 (1H, m, ArH), 8.10-8.08 (1H, m, ArH), 7.83-7.80 (2H, m, ArH), 3.28 (3H, s, SO2CH3); LCMS (6 min) Rt = 1.93 min, (M++1) = 185.1.
