 The N-hydroxybenzenesulfonamide 1 or its deprotonated form 2 is a nucleophile in reaction with the aldehyde 3 to intermediate 4.After intramolecular proton exchange to 5 a sulfinic acid anion is split off and hydroxamic acid 8 results through nitrone 6 and intermediate 7.Alternatively aziridine intermediate 9 directly forms the end=product.