Difluoroacetyl azide: Synthesis, characterization, and decomposition

Abstract

Difluoroacetyl azide, CHF2C(O)N3, has been synthesized and characterized. The azide decomposes slowly at room temperature (300K) into N2 and difluoromethyl isocyanate CHF2NCO, which has also been isolated as neat substance and fully characterized. The elusive nitrene intermediate CHF2C(O)N in the stepwise Curtius-rearrangement of the azide is tentatively identified by IR spectroscopy during the 193nm laser photolysis of the azide in solid Ne matrix at 2.8K. Unexpectedly, flash vacuum pyrolysis (FVP) of CHF2C(O)N3 at 500K yields a novel carbonyl isocyanide FC(O)NC with N2, HF, FCN, CO, and traces of CHF2NCO. Subsequent irradiation (193nm) of the pyrolysis products results in the rearrangement of FC(O)NC to FC(O)CN. According to the quantum chemical calculations (B3LYP and CCSD(T)), the azide CHF2C(O)N3 prefers concerted Curtius rearrangement with minor contribution of the stepwise decomposition. The thermally generated CHF2NCO eliminates HF and forms FC(O)NC solely under the pyrolysis conditions, whereas, no HF-elimination occurs to isolated CHF2NCO even at 1000K due to a formidable activation barrier.