The reaction mechanism for this reaction is not clear and several potential pathways exist. The N-hydroxybenzenesulfonamide 1 or its deprotonated form 2 is a nucleophile in reaction with the aldehyde3 to intermediate 4. After intramolecular proton exchange to 5 a sulfinic acid anion is split off and hydroxamic acid 8 results through nitrone6 and intermediate 7. Alternatively aziridine intermediate 9 directly forms the end=product. The formation of the nitrene intermediate 10 is ruled out given the lack of reactivity of the chemical mixture towards simple alkenes.
^Gattermann, Ludwig, The Practical Methods of Organic Chemistry, 1937Link (4.5 MB)
^Reaction of aldehydes with N-hydroxybenzenesulfonamide. Acetal formation catalyzed by nucleophilesAlfred Hassner, E. Wiederkehr, and A. J. Kascheres J. Org. Chem.; 1970; 35(6) pp 1962 - 1964; (doi:10.1021/jo00831a052)
^Angeli-Rimini's Reaction on Solid Support: A New Approach to Hydroxamic Acids Andrea Porcheddu and Giampaolo Giacomelli J. Org. Chem.; 2006; 71(18) pp 7057 - 7059; (Note) (doi:10.1021/jo061018g)