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The room temperature photoinduced reactivity of liquid ethanol has been studied as a function of pressure up to 1.5 GPa by means of a diamond anvil cell. Exploiting the dissociative character of the lowest electronic excited states, reached through two-photon absorption of near-UV photons (350 nm), irreversible reactive processes have been triggered in the pure system. The active species are radicals forming along two main dissociation channels involving the split of C−O and O−H bonds. The characterization of the reaction products has been performed by in situ FTIR and Raman spectroscopy. At pressures of a few megapascals, molecular hydrogen is the main reaction product, an important issue in the framework of environmentally friendly synthesis of this energetic vector. In the gigapascal range, the main products are ethane, 2-butanol, 2,3-butanediol, 1,1-diethoxyethane, and some carbonylic compounds. The relative amount of these species changes with pressure reflecting the nature of the radicals formed in the photodissociation process. As the pressure increases, the processes requiring a greater molecularity are favored, whereas those requiring internal rearrangements are inhibited. Disproportion products like CH4, H2O, and CO2increase when the amount of ethanol decreases due to the reaction, becoming the main products only when ethanol is exhausted. [ABSTRACT FROM AUTHOR]

The ambient temperature photoinduced reactivity of mixtures containing water and some of the simplest model hydrocarbons has been studied in a diamond anvil cell below 1 GPa. The near-UV 350 nm emission of an Ar ion laser has been employed to photodissociate water molecules through two-photon absorption processes. The hydroxyl radicals generated through this process are able to trigger a chemical reaction in the mixtures containing ethane and acetylene, which are otherwise stable under the same P−T−hν conditions, whereas the contribution of water has no effect or is very limited in the case of the ethylene and propene mixtures, respectively. The reaction evolution and the reaction products were characterized by using FTIR spectroscopy. The formation of fluorescent products limits or prevents, as in the case of acetylene, the characterization by Raman spectroscopy. Particularly relevant is the in situ efficient sequestration of the CO2formed during the reaction, through the formation of a clathrate hydrate, in the mixtures where water is largely in excess. [ABSTRACT FROM AUTHOR]

The pressure induced reactivity of carbon monoxide was investigated in a wide temperature range (100−400 K) completely avoiding any irradiation of the sample with visible or higher frequency light. FTIR spectroscopy was employed to monitor the reaction and infrared sensors for measuring the pressure. With this approach we have been able to separate the effects of the three variables (P, T and hν) that establish the conditions for the occurrence of the chemical reaction. A new instability boundary, not affected by the photoactivation of the reaction, is provided. The reaction has been studied in three different crystal phases (ϵ, δ, and β), but the small differences in the reaction products are ascribable to the temperature changes rather than to the crystalline arrangement. For T< 300 K the analysis of the IR spectra reveals the formation of an extended amorphous material formed, according to the vibrational assignment and to the kinetic data, by polycarbonyl linear chains containing a large amount of anhydride groups. For T≥ 300 K the formation of carbon dioxide and epoxy rings, and the simultaneous decrease of carbonyl species, let suppose a decarboxylation of the extended solid product. Once exposed to the atmosphere, the reaction product readily and irreversibly reacts with water giving rise to carboxylic groups. [ABSTRACT FROM AUTHOR]

The high-pressure reactivity of isoprene has been studied at room temperature up to 2.6 GPa by using the diamond anvil cell technique in combination with Fourier transform infrared spectroscopy. Both dimerization and polymerization reactions take place above 1.1 GPa. At this pressure, the two processes are well separated in time, the dimerization being the only one occurring in the first 150 h. Both processes simultaneously occur as the pressure increases. The reaction product is composed of a volatile fraction, identified as sylvestrene, and a transparent rubberlike solid formed by cis-1,4- and 3,4-polyisoprene. The activation volume of the dimerization reaction has been obtained from the kinetic data. The photoinduced reaction, studied at room temperature for two different pressures, takes place through a two-photon absorption process, and the threshold pressure is lowered to 0.5 GPa. At this pressure, both the dimerization and polymerization processes occur, but the dimerization is not as selective as in the purely pressure-induced reaction. 4-Ethenyl-2,4-dimethylcyclohexene is obtained in addition to sylvestrene. By increasing the pressure, the photoinduced reaction becomes more selective, and the monomer is quantitatively transformed into the same polymer obtained in the purely pressure-induced reaction. [ABSTRACT FROM AUTHOR]