High pressure reactivity of solid furan probed by infrared and Raman spectroscopy

The behavior of crystalline furan has been investigated, at room temperature, along the 0-47-0 GPa pressure cycle by using IR and Raman spectroscopy. These data, joint to high pressure low temperature IR data, allow the identification of two solid phases in the 1.2-12 GPa pressure range: the low-pressure orientationally disordered phase IV and the high-pressure ordered phase III. Above 10-12 GPa solid furan starts to chemically transform. The threshold pressure for the transformation is much lower than in benzene, as expected according to the minor stability of the heteroaromatic ring. The reaction proceeds continuously along the compression path, but it becomes complete only with releasing pressure, and a yellow-brownish sample is recovered. This compound was identified as an amorphous hydrogenated carbon (a-C:H) containing alkylpolyether type segments, alcoholic functions, and C=O bonds. The presence of these new chemical species attests to the opening of the original furan rings and to the transfer of hydrogen atoms. The reaction seems to be very similar to that induced in crystalline benzene. This comparison indicates a general behavior for the reactivity under ultrahigh pressures of the whole class of aromatic compounds. (C) 2003 American Institute of Physics.