Chemoselective Schmidt Reaction Mediated by Triflic Acid: Selective Synthesis of Nitriles from Aldehydes
Balaji V. Rokade and Kandikere Ramaiah Prabhu*
*Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, Karnataka, India, Email: prabhuorgchem.iisc.ernet.in
B. V. Rokade, J. R. Prabhu, J. Org. Chem., 2012, 77, 5364-5370.
The Schmidt reaction of aldehydes with NaN3 furnishes the corresponding nitriles in near quantitative yields in the presence of TfOH and tolerates various electron-withdrawing and electron-donating substituents. Formanilides, common side products, are not observed. The reaction is easily scalable, high yielding, and nearly instantaneous.
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Caution! Hydrazoic acid (HN3) is toxic if inhaled, and can be explosive if concentrated. Hydrazoic acid at concentration above 20% (w/w) can be explosive, although an ignition source (e.g. spark) is required for detonation of its vapours. Hydrazoic acid solutions with concentration under 10% (w/w) are safe to store and handle. Therefore, to minimize its potential hazards, reactions should be performed on low scale (0.5 - 1.5 mmol) and at low concentration of NaN3 / hydrazoic acid in closed systems inside the fume hood. (see also: Copper-Catalyzed Azide-Alkyne Cycloaddition of Hydrazoic Acid Formed In Situ).
The workup process described here involves the removal of the solvent under reduced pressure, where HN3, with a boiling point of 37 °C, is initially removed and possibly initially condensed in dangerously high concentrations.