Tautomeric equilibrium of ethyl acetoacetate in compressed CO2 + ethanol and CO2 + methanol mixtures

Ultraviolet-visible study of tautomeric behavior of some carbonyl and thiocarbonyl pyrimidine derivatives: experimental evidence of enolization and thioketonization

Tautomeric behaviors of the protonated forms of recently synthesized 1-Amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-one (I), and 1-Amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-thione (II), were investigated with respect to pH and time in aqueous methanol (5%, v/v methanol) and in pure methanol by electronic absorption spectra to elucidate the nature of the tautomeric interconversions and the role of carbonyl oxygen in I and thiocarbonyl sulfur in II. At room conditions, the carbonyl group at position 2 in I was found to undergo a significant spontaneous enolization (66%) at pH 1.0 in aqueous methanol medium in 8 h. On the other hand, thioketonization for the protonated form of the thiocarbonyl group in II was comparably small (37%) in pure methanol at pH 10.0 over a 5-day period. The interconversion mechanism was identified for each compound using the UV-vis data. The equilibrium constant for each compound was estimated in an ionic strength of 0.10 M (LiCl) at room temperature, from the ratios of molar absorptivities of the pure tautomeric forms. For I, the spontaneous enolization equilibrium constant (pKenol) was 0.291 in aqueous methanol solution, while the thioketonization equilibrium constant (pKthiocarbonyl) for II was 0.234 in pure methanol.

Oxygen reduction activity of carbon-supported Pt-M (M = V, Ni, Cr, Co, and Fe) alloys prepared by nanocapsule method

Monodispersed Pt and Pt-M (M = V, Cr, Fe, Co, and Ni) alloy nanoparticles supported on carbon black (denoted as Pt/CB and Pt-M/CB) were prepared by the simultaneous reduction of platinum acetylacetonate and the second metal acetylacetonate within nanocapsules formed in diphenyl ether in the presence of carbon black. For the Pt/CBs, the average Pt diameters measured by scanning transmission electron microscopy (STEM) or X-ray diffraction (XRD) ranged from 2.0 to 2.5 nm, regardless of the catalyst-loading level from 10 to 55 wt % on CB. The alloy composition was found to be well-controlled to the projected value among the supported particles. The activities for the oxygen reduction reaction (ORR) at Nafion-coated catalysts in O2-saturated 0.1 M HClO4 solution were evaluated by using a channel flow electrode (CFE) cell at 30 degrees C. The area-specific ORR activities at Pt-M/CB were found to be 1.3 to 1.8 times higher than that at Pt/CB. The ORR activity increased in the order Pt/CB < Pt-Ni/CB < Pt-Fe/CB < Pt-Co/CB < Pt-V/CB < Pt-Cr/CB.