Preparation of the Reagent o-Nitrobenzenesulfonylhydrazide

o-Nitrobenzenesulfonylhydrazide (NBSH) has been shown to be a valuable reagent for the synthesis of allenes from propargylic alcohols, for the reductive transposition of allylic alcohols, and, most recently, for the deoxygenation of unhindered alcohols. Each of these transformations proceeds by Mitsunobu displacement of an alcohol with NBSH followed by in situ elimination of o-nitrobenzenesulfinic acid to form a monoalkyl diazene intermediate. The mild reaction conditions (neutral pH, reaction temperatures ≤23 °C) are especially attractive for substrates containing sensitive functional groups. The success of this methodology relies critically upon the purity of the NBSH reagent employed in the reaction. A simple and practical procedure for the preparation of NBSH of high purity and guidelines for the handling and storage of the reagent are provided in this note.