We recently published details of a new diazo transfer reagent (benzotriazole-1-sulfonyl azide) (CAS Registry No. 1246367-30-5). We reported in our publication (J. Org. Chem., DOI: 10.1021/jo101296s) that differential scanning colorimetry of this compound shows that it is stable below 95 °C (melting point, 88 °C). Melting and resolidifying over two cycles of heating to 95 °C and cooling to −100 °C resulted in negligible material loss according to the heats of fusion and freezing.
Over more than a year we prepared this reagent on dozens of occasions and used it to convert amines into azides and a smaller number of active methylene compounds into diazo derivatives.
Until recently, we encountered no difficulty or untoward behavior in handling this compound. However, we recently found that when the experimental procedure was altered by mistake and an acidic workup (6N HCI) performed—followed by an attempt to remove the last traces of the solid using a metal spatula from a round-bottom flask—an explosion occurred, shattering the flask.
We still believe this compound can be used as an extremely effective diazo transfer reagent, but it requires very careful handling. In particular, the following safety measures are strongly recommended: All the safety precautions cited in the Journal of Organic Chemistry published work, particularly reference 7 (Bräse, S., and K. Banert. “Organic Azides, Syntheses and Applications,” 1st ed. West Sussex: John Wiley & Sons, 2009, 3–27), should be examined carefully for adequate protection, and the experimental procedure described in our JOC article for the synthesis of benzotriazole-1-sulfonyl azide should be strictly followed.
In particular, acidic workup should be avoided because of the possibility that trace amounts of residual sodium azide could be converted to highly explosive hydrazoic acid. It is possible that this was responsible for the explosion that occurred in this case.
By Alan R. Katritzky, Director Mirna El Khatib Florida Center for Heterocyclic Compounds
University of Florida Gainesville