Reactions of dichloride anion radicals with pyrimidine and its derivatives.
Rate constants for the reactions of dichloride anion radicals with pyrimidine and its derivatives were determined by a conventional flash photolysis. Kinetic treatment was carried out by assuming that second-order self decay of the anion radicals and the reaction with a substrate proceed simultaneously. Values of the rate constants were found within 1.1 × 107 to 4.1 × 109 M-1 s-1; the lowest reactivity was observed for pyrimidine and the highest for 2, 4, 6triaminopyrimidine. Comparison of the rate constants with those for hydroxyl radicals suggests that the dichloride anion radicals undergo a different reaction with pyrimidine bases from that of the hydroxyl radicals. A transient absorption due to an intermediate produced in the reaction with the anion radicals was observed for 5-aminouracil. This is only a case where relatively long-lived absorption was observed. The absorption was used to determine the rate constants for the reactions with the anion radicals.
Energetics of reactions of O−aq and of O−-transfer reactions between radicals
Abstract Free energies of formation of various free radicals such as O−aq, CO-3aq, CO−2aq, and X−2aq (X  Cl, Br and I) have been derived and used to calculate standard potentials of radicals and free energies of their reactions. O−aq is an oxidizing radical with a potential E 0 ( O − aq +H 2 O 2OH - aq )= 1.9V , i.e. electron pick-up is accompanied by simultaneous breakage of a water molecule in the hydration shell. Water is also decomposed in the reaction between two O−aq radicals, HO2− + OH− being much more probable products than O+2OH−. O−aq is almost as strong a hydrogen atom abstracting radical as the hydroxyl radical. CO−3aq can denote O− to various radicals. These reactions may occur directly or via a complex that hydrolyses. O− -transfer occurs in competition with electron transfer from the substrate radical to CO−3aq. Transfer of O− from CO−2aq or HCO3aq radicals to form carbon monoxide is strongly exoergic. The formation of CO in the radiolysis of acid solutions of formate is explained by O−-transfer between the intermediate radicals. O−-transfer from a radical to an electrode is also considered.
Identification of Dihydroxy Aromatic Compounds in a Low-Temperature Pyrolysis Coal Tar by Gas Chromatography−Mass Spectrometry (GC−MS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)
Dihydroxy aromatics in coal tar undergo rapid coupling reactions with each other and with some coal-derived species during coal pyrolysis and liquefaction. However, only limited information on the structure of dihydroxy aromatics is known. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography−mass spectrometry (GC−MS) were used to characterize the dihydroxy aromatics in a low-temperature pyrolyzed coal tar and its distillate and residue fractions. Negative-ion electrospray ionization (ESI) FT-ICR MS spectra of coal-tar-derived samples had low molecular masses and narrow mass ranges. Negative-ion ESI is extremely selective for the dihydroxy aromatics present in coal tar. The O2 class species had the highest ion intensity among the species in the negative-ion FT-ICR mass spectrum for each sample. Dihydroxy compounds with an aromatic core structure of benzene, indan, biphenyl (and/or acenaphthene), and naphthalene were identified in the distillate fract...