The Simplest, Isolable, Alkynyl Isocyanate HC≡CNCO: Synthesis and Characterization

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Alkynyl isocyanates are theoretically highly reactive intermediates.
• Previous studies suggested very short lifetimes for these compounds at room temperature.

Purpose of the Study:

• To isolate and characterize the parent alkynyl isocyanate, HC≡CNCO.
• To determine the stability and properties of HC≡CNCO.

Main Methods:

• Isolation of HC≡CNCO.
• Gas-phase lifetime studies at 2 mbar and 300 K.
• Spectroscopic characterization including IR (gas, solid, matrix), 1H and 13C NMR, and UV/Vis spectroscopy.
• Determination of melting point and enthalpy of vaporization (ΔHvap).

Main Results:

• HC≡CNCO was successfully isolated for the first time.
• The gas-phase lifetime of HC≡CNCO was determined to be 55 hours at 300 K, significantly longer than previously expected.
• Physical properties such as melting point (-79.5°C) and ΔHvap (23.1 kJ mol⁻¹) were measured.
• Photoisomerization to acylnitrene HC≡CC(O)N and cyanoketene NCC(H)CO was observed.

Conclusions:

• The parent alkynyl isocyanate (HC≡CNCO) is a stable, isolable compound with a surprisingly long gas-phase lifetime.
• This finding challenges previous assumptions about the reactivity and stability of alkynyl isocyanates.
• The characterized properties and observed photoisomerization provide new insights into the chemistry of these intermediates.