PNNL

Abstract

The reaction of the ?-hydroxyalkyl radical of 2-propanol (1-hydroxy-1-methylethyl radical) with nitrite ions was characterized. A product of the reaction was assigned as the adduct nitro radical anion, [HO-C(CH3)2NO2]•?. This radical was identified using time-resolved electron spin resonance (TRESR). The radical’s magnetic parameters, the nitrogen hyperfine coupling constant aN of 26.39 G and its g-factor of 2.0052, are the same as those of the nitro radical anion previously discovered in •OH spin-trapping experiments with the aci-anion of (CH3)2CHNO2. The rate constant for the decay of the ESR kinetic trace of (CH3)2C•-OH is of the same order of magnitude as the rate constant for the growth of the ESR kinetic trace of [HO-C(CH3)2NO2]•?, further confirming the nature of the reaction. The bimolecular rate constant for the reaction at pH 7 is ~1.7 ´ 106 M?1 s?1 measured by following ESR kinetic traces of (CH3)2C•-OH and 2.4 ´ 106 M?1 s?1 following the growth of [HO-C(CH3)2NO2]•?. The lack of better match in these two measurements is discussed. The yield of [HO-C(CH3)2NO2]•? was measured to be ~27% of the reaction of (CH3)2C•-OH with nitrite. Pulse radiolysis-conductivity experiments at lower pH (4.7) also show that electron transfer or the equivalent formation of [HO-C(CH3)2ONO]•? followed by rapid loss of •NO represent only part of the reaction. These reactions are discussed with guidance by computations using density functional theory. Acknowledgment. PF and DMC gratefully acknowledge support by the U.S. Department of Energy (DOE) Office of Biological and Environmental Research Environmental Management Science Program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute. The Notre Dame Radiation Laboratory is supported by Basic Energy Sciences of DOE. This is Document No. NDRL-4491 from the Notre Dame Radiation Laboratory. The authors thank Professor D. Meisel for critical comments. Professor Kenneth Ruud (University of Tromsoe, Norway) is thanked for a program.