CHEMICAL AND PHYSICAL TRANSFORMATIONS OF CYANOGEN AND CARBON-MONOXIDE AT HIGH PRESSURE (SOLID-STATE, SPECTROSCOPY)

Unsaturated molecules are not stable under extreme compressions; however, the reactions and mechanisms which convert these molecules to saturated species are not known. C(,2)N(,2) and CO, the simplest unsaturated nitrile and carbonyl, are logical candidates for exploring these reactions. In addition to instabilities of these unsaturated molecules, some of the unique chemistry of highly compressed matter and effects of pressure on solid-state reactions are reported.;The kinetics of the conversion of p-DISN to paracyanogen have been determined by monitoring Fourier-transform infrared spectra at pressures between 10 and 12 GPa and temperature between 290 and 350 K. The reaction kinetics can be described by an Avrami equation with exponent 0.5 and specific rate constant 0.40 hr('-1(VBAR)(VBAR)2) at 10 GPa and 297 K. The activation enthalpy and volume are 28 KJ(VBAR)(VBAR)mol and -3.3 cm('3)(VBAR)(VBAR)mol, respectively. A two-step mechanism is suggested that involves diffusion of the p-DISN chains into an arrangement in which 4+2 cycloadditions occur between adjacent p-DISN chains.;At 297 K, CO is not stable photochemically at 4.2 GPa nor thermochemically at 5.0 GPa. At these and higher pressures, CO disproportionates into CO(,2) and lactone polymers which can be recovered at room pressure. A multimer of CO, probably (CO)(,5), is isolated in a matrix of N(,2) at 5.0 GPa. A possible mechanism of the disproportionated polymerization of CO may include the formation of multimer (CO)(,5), its fragmentation into CO, CO(,2) and C(,3)O(,2), and polymerization of these fragments.;Chemical and phase transformations of C(,2)N(,2) at room temperature and pressure as high as 12 GPa were studied by Raman and Fourier-transform infrared absorption spectroscopy. Three phase transitions of the monomer were identified; solidification to C(,2)N(,2) I at 0.3 GPa and two solid-solid transformations, C(,2)H(,2) I-to-C(,2)N(,2) II at 0.5 GPa and C(,2)N(,2) II- to-C(,2)N(,2) III at 2 GPa. At 3.5 GPa, C(,2)N(,2) reversibly polymerizes to a linear chain, (-(C(,2)N(,2))(,2)-)(,m). Above 10 GPa, further irreversible reactions convert these chains to a material that is very chemically and thermally stable and can be recovered at atmospheric pressure. Vibrational spectra and chemical arguments indicate that the linear chain polymer is poly-(2,3-diiminosuccinonitrile), p-DISN, and the stable product is paracyanogen, a ladder of fused pyrazine rings that may be highly cross-linked.