Solvent Anions in Supercritical Carbon Dioxide:  Formation of Complexes with Polar Solutes

Abstract

It is shown that high-mobility multimer (CO 2 ) n •-anions in supercritical (sc)-CO 2 form stable complexes with water, aliphatic alcohols, alkyl halides, and alkyl nitriles. The complexation rate is 10-50% of the diffusion controlled rate or faster. The complexes are formed both with the monomer and with the dimer polar solutes. The equilibrium constants of the monomer complexation range from 10 to 350 M -1 ; the reaction heat is -(15-21) kJ/mol, and the reaction entropy is negative. The stability of the complex increases with the dipole moment of the polar group and decreases with the substitution at the R-carbon. None of these polar solutes directly reacts with quasifree electrons in sc-CO 2 .

Multimer Radical Ions and Electron/Hole Localization in Polyatomic Molecular Liquids: A Critical Review

“…0.15 eV due to the electrostatic binding to a monomer or dimer molecule with a dipole moment of (2-4) Debye is sufficient to halt the charge hopping completely [29]. The same effect of polar solutes on the hopping rate of high-mobility solvent radical cations (with fairly similar thermochemistry) was observed in neat cis-and trans-decalin (section V Carbon disulfide is isovalent to carbon dioxide and it also has a bent monomer anion.…”

“…For ρ r > 0.85, the scavenging radii of these diffusion-controlled reactions systematically decrease with the solvent density, ρ r [18]. Interestingly, in addition to the electron transfer reactions, solvent anions in sc CO 2 form 1:1 and 1:2 complexes with polar molecules that have large dipole moments, such as water, aliphatic alcohols, alkyl halides, and alkyl nitriles [29]. None of these polar low-EA g solutes directly reacts with quasifree electrons in sc CO 2 .…”

On the structure of anionic clusters in liquid CO2 and photodisintegration of (CO2) n − clusters

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The physicochemical properties of ëé 2 solutions in the supercritical state (sc-ëé 2 ) have been extensively studied in the past decade [1][2][3][4]. This interest stems from the fact that sc-ëé 2 is an environmentally safe solvent that substitutes for toxic nonpolar solvents, such as acetone, methanol, and toluene, in industry.

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“…In addition, sc-ëé 2 is a candidate for a coolant for nuclear reactors. A specific feature of sc-CO 2 is the formation of clusters of anions with the number of particles n = 2, 3, 4, 7, 13, or more [3]. The quasi-free electron is localized in the potential well arising from the interaction of the electron with the surrounding atoms of ëé 2 molecules.…”

“…Shkrob and Sauer [3] suggested that the nucleus of the atomic clusters with n ≤ 6 and n ≥ 14 is the dimer, whereas, in the clusters with 6 < n < 14, the nucleus is the ion, which interacts with surrounding molecules with a binding energy of 0.22 eV per molecule. Any informational, mathematical, physical, crystal, and biological structures are based on polyhedra; therefore, it is reasonable to assume the formation of more or less regular structures in sc-ëé 2 .…”