Lehnig Manfred, Kirsch Michael, Korth Hans-Gert
Organische Chemie, Fachbereich Chemie, Universität Dortmund, D-44221 Dortmund, Germany.
Inorg Chem. 2003 Jul 14;42(14):4275-87. doi: 10.1021/ic020650z.
The reaction of nitrous acid with hydrogen peroxide leads to nitric acid as the only stable product. In the course of this reaction, peroxynitrous acid (ONOOH) and, in the presence of CO(2), a peroxynitrite-CO(2) adduct (ONOOCO(2)(-)) are intermediately formed. Both intermediates decompose to yield highly oxidizing radicals, which subsequently react with excess hydrogen peroxide to yield peroxynitric acid (O(2)NOOH) as a further intermediate. During these reactions, (15)N chemically induced dynamic nuclear polarization (CIDNP) effects are observed, the analysis of the pH dependency of which allows the elucidation of mechanistic details. The formation and decay of peroxynitric acid via free radicals NO(2)() and HOO() is demonstrated by the appearance of (15)N CIDNP leading to emission (E) in the (15)N NMR signal of O(2)NOOH during its formation and to enhanced absorption (A) during its decay reaction. Additionally, the (15)N NMR signal of the nitrate ion (NO(3)(-)) appears in emission at pH approximately 4.5. These observations are explained by proposing the intermediate formation of short-lived radical anions O(2)NOOH()(-) probably generated by electron transfer between peroxynitric acid and peroxynitrate anion, followed by decomposition of O(2)NOOH()(-) into NO(3)(-) and HO() and NO(2)(-) and HOO() radicals, respectively. The feasibility of such reactions is supported by quantum-chemical calculations at the CBS-Q level of theory including PCM solvation model corrections for aqueous solution. The release of free HO() radicals during decomposition of O(2)NOOH is supported by (13)C and (1)H NMR product studies of the reaction of preformed peroxynitric acid with [(13)C(2)]DMSO (to yield the typical "HO() products" methanesulfonic acid, methanol, and nitromethane) and by ESR spectroscopic detection of the HO() and CH(3)() radical adducts to the spin trap compound POBN in the absence and presence of isotopically labeled DMSO, respectively.
亚硝酸与过氧化氢反应生成硝酸，这是唯一的稳定产物。在该反应过程中，会中间形成过氧亚硝酸（ONOOH），并且在有二氧化碳存在时，会形成过氧亚硝酸根 - 二氧化碳加合物（ONOOCO₂⁻）。这两种中间体都会分解产生高氧化性自由基，这些自由基随后与过量的过氧化氢反应生成过氧硝酸（O₂NOOH）作为进一步的中间体。在这些反应过程中，观察到了¹⁵N化学诱导动态核极化（CIDNP）效应，对其pH依赖性的分析有助于阐明反应机理细节。通过¹⁵N CIDNP的出现证明了过氧硝酸通过自由基NO₂⁺和HOO⁺的形成和衰变，在其形成过程中导致O₂NOOH的¹⁵N NMR信号出现发射（E），在其衰变反应过程中导致吸收增强（A）。此外，硝酸根离子（NO₃⁻）的¹⁵N NMR信号在pH约为4.5时以发射形式出现。通过提出可能由过氧硝酸和过氧亚硝酸根阴离子之间的电子转移产生的短寿命自由基阴离子O₂NOOH⁻的中间形成来解释这些观察结果，随后O₂NOOH⁻分别分解为NO₃⁻和HO⁺以及NO₂⁻和HOO⁺自由基。在包括水溶液PCM溶剂化模型校正的CBS - Q理论水平上的量子化学计算支持了此类反应的可行性。通过预先形成的过氧硝酸与[(¹³C₂)]DMSO反应的¹³C和¹H NMR产物研究（产生典型的“HO⁺产物”甲磺酸、甲醇和硝基甲烷）以及通过分别在不存在和存在同位素标记的DMSO的情况下对自旋捕获化合物POBN的HO⁺和CH₃⁺自由基加合物的ESR光谱检测，支持了O₂NOOH分解过程中游离HO⁺自由基的释放。
