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(The) effect of added anions on the aqueous oxidation of nitrous acid by hydrogen peroxide

(The) effect of added anions on the aqueous oxidation of nitrous acid by hydrogen peroxide
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교육대학원 과학교육전공화학교육분야
anionsaqueous oxidationnitrous acidhydrogen peroxide
이화여자대학교 교육대학원
산성 수용액에서 H_(2)O_(2)에 의한 HNO_(2)의 산화 반응 (1)은 산 침적(acid deposition) 현상의 주 요인 중 하나인 HNO_(3)를 생성한다는 측면에서 중요한 반응이며, nitrosation반응의 메카니즘을 따르는 일종의 O-nitrosation반응이다. N-nitrosation과 S-nitrosation 반응에 특정 음이온이 첨가되면 촉매효과가 나타나 반응속도가 빨라짐이 보고되었으므로 반응(1)에 여러가지 음이온 (X-: CIO^(-)_(4), NO^(-)_(3), Cl^(-), Br^(-) SCN^(-))을 첨가하여 반응속도에 미치는 음이온들의 효과를 관찰하였다. 반응(1)에 ClO^(-)_(4),NO^(-)_(3)를 첨가했을 때는 이들 음이온에 의한 촉매 효과가 나타나지 않았으며, '반응 (1)의 속도식은 -d[HNO_(2)]/dt = ka_(H)[HNO_(2)] (H_(2)O_(2))임을 확인하였고, pH 2-4, 이온 세기 0.5M, 0℃에서 측정된 k값은 (1.12 ± 0.11) × 10^(3) M^(-2) s^(-1) 으로 선행 연구 결과들과 잘 일치하였다. 그러나. 반응(1)에 Cl^(-), Br^(-), SCN^(-)을 첨가했을 때는 촉매 효과를 보였고 그 크기는 SCN^(-) > Br^(-) > Cl^(-)의 순으로 관찰되었다. 이러한 효과는 음이온(X^(-))과 HNO_(2)로 부터 생성된 NOX도 nitrosating agent로 작용하는데 기인하는 것이며 NOX의 평형 농도를 고려하면 NOX의 반응성의 크기는 NOCI > NOBr > NOSCN의 순이 되며, 이결과는 N-nitrosation이나 S-nitrosation반응의 경우와 일치하였다.;The aqueous-phase oxidation of nitrous acid by hydrogen peroxide(1) has been regarded as an O-nitrosation reaction and has been considered to be important in the view of forming nitric acid that contributes much of the acid deposition phenomena. Since some anions such as C1^(-), Br^(-), and SCN^(-) have been suggested to show nucleophilic catalysis in the N-nitosation and S-nitrosation reactions, the effect of some added anions on the reaction (1), an O-nitrosation reaction has been studied at pH 2.08, 3.09,'and 3.80. No catalytic effect was found for ClO_(4)^(-) and NO_(3)^(-). The rate equation has been confirmed to be -d[HNO_(2)] / dt =ka_(H)^(+)[HNO_(2)][H_(2)O_(2)] and k determined is ( 1.12±0.11) × 10^(3) M^(-1) s^(-1) at 0℃ and ionic strength 0.5M which turns out to be consistent with those of earlier studies. The catalytic effect was found for C1^(-), Br^(-) and SCN^(-) with the order of the effect SCN^(-) > Br^(-) > C1^(-). This effect is due to the role of NOX as a nitrosating agent, which was formed in the presence of these anions from the reaction of an anion(X^(-)) with the nitrous acid. With regards to the equilibrium concentration of NOX formed, the reactivity of NOX is found to be in the order of NOCl > NOBr > NOSCN which is consistent with the results of other nitrosation reactions.
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