Difluoroacetyl azide: Synthesis, characterization, and decomposition

- The synthesis, characterization, and conformation of difluoroacetyl azide and its Curtius-rearrangement product difluoromethyl isocyanate are studied.
- The photo-induced Curtius-rearrangement of difluoroacetyl azide is explored in solid Ne matrix.
- The unexpected formation of novel carbonyl isocyanide from the flash vacuum pyrolysis of difluoroacetyl azide is observed.
- The mechanism for the concerted and stepwise decomposition of difluoroacetyl azide is analyzed with the aid of quantum chemical calculations.

Difluoroacetyl azide, CHF2C(O)N3, has been synthesized and characterized. The azide decomposes slowly at room temperature (300 K) 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 193 nm laser photolysis of the azide in solid Ne matrix at 2.8 K. Unexpectedly, flash vacuum pyrolysis (FVP) of CHF2C(O)N3 at 500 K yields a novel carbonyl isocyanide FC(O)NC with N2, HF, FCN, CO, and traces of CHF2NCO. Subsequent irradiation (193 nm) 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 1000 K due to a formidable activation barrier.

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