Heteroaromatic thiols may be oxidized to the sulfonyl chloride at low temperature (-25 degrees C) by using 3.3 equiv of aqueous sodium hypochlorite. The reaction is rapid, avoids the use of chlorine gas, and succeeds with substrates that have previously been found to afford little or none of the sulfonamide product with other procedures. The method allows the preparation of the sulfonyl fluorides, which are stable enough to be purified and stored, making them potentially useful monomers in parallel chemistry efforts.