Can O=NOOH undergo homolysis?

被引:106
作者
Koppenol, WH [1 ]
Kissner, R [1 ]
机构
[1] ETH Zurich, Anorgan Chem Lab, CH-8092 Zurich, Switzerland
关键词
D O I
10.1021/tx970200x
中图分类号
R914 [药物化学];
学科分类号
100701 ;
摘要
Recent thermodynamic calculations of Merenyi and Lind [(1997) Chem. Res. Toxicol. 10, 1216-1220] suggest that O=NOOH can undergo homolysis to form the hydroxyl radical and nitrogen dioxide. This result is based in part on our statement that the enthalpy of ionization of O=NOOH is close to zero [Koppenol et al. (1992) Chem. Res. Toxicol. 5, 834-842]. As the ionization of O=NOOH is sensitive to the milieu and the rate of isomerization (to nitrate) to the total concentration of O=NOOH and O=NOO- [Kissner et al. (1997) Chem. Res. Toxicol. 10, 1285-1292], we reinvestigated the temperature dependence of the ionization constant and determined a Delta H degrees of 4 +/- 2 kcal mol(-1) This results in a standard Gibbs energy of homolysis of 16 kcal mol(-1) and a rate of homolysis of 1 x 10(-2) s(-1). Given the uncertainty in the Gibbs energy of homolysis, upper and lower rates are 1 x 10(-4) and 0.6 s(-1), slower than the rate of isomerization, 1.2 s(-1) at 25 degrees C. The recombination of the homolysis products NO2 . and HO . is known to lead to mainly peroxynitrous acid. If one assumes that a few percent of the recombinations lead to nitrate instead, then the rate of homolysis must be much higher than the rate of isomerization. We conclude therefore that homolysis is unlikely.
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页码:87 / 90
页数:4
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