To a 250 mL round bottom flask was added 3-(methylthio)propionic acid (14.29 g, 118.9 mmol) followed by 57 mL of acetic anhydride and 57 mL of acetic acid. The reaction mixture was cooled in an ice bath and stirred continuously for 30 min. Then, 36 mL of 30% aqueous hydrogen peroxide solution was added dropwise at 15-minute intervals (50 mL total) using a syringe in 5 mL amounts at a time. The progress of the reaction was monitored by nuclear magnetic resonance (NMR), and after confirming the completion of the reaction, a small amount of manganese dioxide (MnO2) was added to quench the excess hydrogen peroxide, and stirring was continued for 2 hours. The reaction mixture was filtered through a diatomaceous earth pad and the filtrate was used to remove the organic solvent using a rotary evaporator. The residue was placed in a vacuum oven for 24 h to give 3-(methylsulfonyl)propionic acid (18.05 g, 99% yield) as a white solid. Melting point: 100-102 °C. 1H NMR (DMSO-d6, 400 MHz) δ: 12.59 (br s, 1H), 3.33 (t, J = 7.2 Hz, 2H), 2.99 (s, 3H), 2.68 (t, J = 7.2 Hz, 2H).13C NMR (DMSO-d6, 100 MHz) δ: 172.72, 50.35, 41.15, 28.03. High resolution mass spectrometry (HRMS-ESI) m/z: [M + Na]+ Calculated value 175.0036, measured value 175.0035.
