Nitrous Acid In Aqueous Solution Research Articles

Enhancement of antiradical properties of dihydroquercetin by nitrosation

Dihydroquercetin was converted to nitroso derivative by treatment with nascent nitrous acid in aqueous solution. The chemical structure of the synthesized compound was determined by quantitative 1H and 13C NMR spectroscopy. As shown by the NMR spectra, the nitroso group is incorporated at the catechol ring of the flavonoid. The antiradical properties of nitrosated dihydroquercetin were evaluated by inhibition of the pyrocondensate formed in ethylene and propylene production, which readily polymerizes upon heat treatment. Nitrosated dihydroquercetin is 10–15% more active than the initial compound. The probable mechanisms of the radical-scavenging action of nitrosated dihydroquercetin are considered.

Reactions of p‐Substituted Phenols with Nitrous Acid in Aqueous Solution

ABSTRACTThe reaction of phenols with nitrite (nitrous acid HONO, or its conjugated base, NO2−) is of importance in stomach fluids (low pH) and in atmospheric hydrometeors (mild acid and basic pH). The initial reaction associated with the oxidation/nitration of 4‐substitued phenols promoted by HONO/NO2 depends on the pH of the solution. At low pH, the initial step involves the reaction between HONO and phenol, whereas at basic conditions this involves an electron transfer from the phenoxy anion to nitrogen dioxide (NO2) producing the nitrite anion. The rate of both processes is determined by the donor capacity of the substituent at the 4‐position of the phenol, and the data obtained at pH 2.3 follow a linear Hammett‐type correlation with a slope equal to –1.23. The partition of the gaseous intermediates (NO and NO2) makes the rate of HONO‐mediated oxidation dependent on their gas–liquid distribution. At low pH, the main process is phenol oxidation, even in oxygen‐free conditions, and the presence of any 4‐substituted phenol decreases the rate of HONO auto‐oxidation.

Accurate Rate Constants for Decomposition of Aqueous Nitrous Acid

Decomposition of nitrous acid in aqueous solution has been studied by stopped flow spectrophotometry to resolve discrepancies in literature values for the rate constants of the decomposition reactions. Under the conditions employed, the rate-limiting reaction step comprises the hydrolysis of NO(2). A simplified rate law based on the known elementary reaction mechanism provides an excellent fit to the experimental data. The rate constant, 1.34 × 10(-6) M(-1) s(-1), is thought to be of higher accuracy than those in the literature as it does not depend on the rate of parallel reaction pathways or on the rate of interphase mass transfer of gaseous reaction products. The activation energy for the simplified rate law was established to be 107 kJ mol(-1). Quantum chemistry calculations indicate that the majority of the large activation energy results from the endothermic nature of the equilibrium 2HNO(2) ⇆ NO + NO(2) + H(2)O. The rate constant for the reaction between nitrate ions and nitrous acid, which inhibits HNO(2) decomposition, was also determined.

Spectroscopic and Optimization Modeling Study of Nitrous Acid in Aqueous Solution

Nitrous acid (HONO) and the nitrite ion represent a particularly important conjugate pair of trace species with regard to heterogeneous behavior within the bulk, and on the surface, of aqueous atmospheric dispersions: this role results from their chemical reactivity, photolysis pathways, solubility, and ambient concentration levels. The actual ratio of NO(2)(-): HONO in solution is determined by the pH and the nitrous acid dissociation constant (pK(a)) which is generally quoted in the literature as 3.27 at 298 K. However there is much disagreement in published works as to the exact value, which should be used in model calculations relevant to the atmosphere. Furthermore even though the nitrite ion is known to absorb solar radiation in the 300-400 nm region and represents a dominant source of *OH radicals in surface seawater, large variations in the measured molar decadic absorption coefficients, epsilon, for nitrite ions (and aqueous HONO) are evident in the literature. In the current study, using a UV-vis spectrometric approach with careful baseline subtraction, the relevant epsilon values for the nitrite ion were determined to be 8.16 +/- 0.08 M(-1) cm(-1) for the npi transitions at 290 nm and 22.1 +/- 0.22 M(-1) cm(-1) at 354 nm. For HONO, the wavelength maximum for the strongest vibronic band in solution was found at 372 nm with an epsilon value of 60.52 +/- 0.6 M(-1) cm(-1). Using the Henderson-Hasselbalch equation and the above data, a value of 2.8 +/- 0.1 is therefore reported here for the pK(a) of nitrous acid. A Newton-Gauss method was then employed to solve a set of nonlinear equations defining the chemical speciation model for HONO in solution using an algorithm written in FORTRAN 90. A model based on a simple one-step protonation worked well for intermediate pHs (6-3) but departed from the experimental observations in highly acidic media. A two-step equilibrium model involving the nitroacidium ion, H(2)ONO(+), gave a much closer fit in the very acidic region, while having little or no effect on the pH 6-3 section of the profile.

Photodecomposition of Nitrite and Undissociated Nitrous Acid in Aqueous Solution

Quantum yields of phenol and nitrate, produced by photodecomposition in aqueous solutions of NO2- and HNO2 in the presence of benzene as scavenger for OH radicals, have been determined as a function of wavelength between 280 and 390 nm. The production of phenol was used to calculate primary OH quantum yields. For NO2- photolysis at pH 6 Φ1(OH) was found to decrease with increasing wavelength from 0.069 ± 0.008 at 280 nm to 0.022 ± 0.004 at 390 nm, in agreement with previous data. The OH quantum yield Φ2(OH) for the photolysis of HNO2 at pH 2 was essentially constant over the entire wavelength range with Φ2 = 0.35 ± 0.02 (2σ). Quantum yields for NO3- are comparable in magnitude to those of phenol, indicating that NO as primary product is largely oxidized to nitrate. The most likely conversion processes are reactions of NO with O2- (pH 6), the latter resulting from the oxidation of benzene, to form peroxynitrous acid, which undergoes thermal decomposition, and of NO2 with HO2 (pH 2) to form peroxynitric aci...

Kinetic studies on the oxidation of uranium(IV) in nitric acid solution

Abstract The kinetics of oxidation of U(IV) in nitric acid solution by nitrous acid and air oxygen have been studied. The effects of concentrations of U(IV), nitric acid, hydrogen ion and nitrous acid in aqueous solution or oxygen in gas on the oxidation rate have been examined. The oxidation rate increases with increasing temperature and the activation energies are 47 kJ mol–1 for nitrous acid and 91 kJ mol–1 for oxygen. The mechanisms for both oxidation reactions are discussed.

Consumption rate of nitrous acid in aqueous solution.

気相が共存しない状態で, 均一水溶液中の亜硝酸の消失速度を, 288～313Kで測定して, 速度解析を行った.水溶液中での亜硝酸の自己分解は, 既往の気液系で行われた研究で導かれている素過程にしたがって起こるが, 気相が存在しない場合には, 溶解度の小さい生成物である一酸化窒素の放出が抑制され, 気液系では無視できる逆反応の影響が大きくなる.また, 亜硝酸は自己分解で消失するだけではなく, 溶存酸素による液相酸化によっても消失する.この反応系においては, 亜硝酸の自己分解における迅速な第1素過程で生成する一酸化窒素の溶存酸素による液相酸化が律速過程である.以上の考察に基づいて, 溶存酸素が存在する水溶液中における亜硝酸の総括消失速度を, 一酸化窒素の液相酸化速度を考慮して導いた.また, 総括反応速度定数および総括反応平衡定数の温度依存性を明らかにした.

The oxidation rate of iodide ion by nitrous acid in aqueous solution.

気相が共存しない状態での酸性水溶液中における亜硝酸によるヨウ素イオンの酸化挙動を分光吸光度スペクトルの繰り返し測定およびストップドフロー高速反応解析装置による吸光度の経時変化の追跡により観測した.この酸化反応の総括量論式は2I-+2HNO2+2H+→I2+2NO+2H2Oで示され, [I-] 0 [HNO2] 0の条件では [I2] ∞は (1/2) [HNO2] 0以上にまで酸化が進行する.これは, HNO2によるI-の酸化が密閉容器中で進行すると, 副生するNOが系内に存在する溶存酸素によって酸化されてNO2を経て, HNO2を再生する反応サイクルを構成するためと考えられる.本研究では, [I-] 0< [HNO2] 0の条件下での微分法による初速度解析からHNO2によるI-酸化速度を定式化した.さらに, 積分法解析によって, 微分法で得られた速度式および速度パラメータの妥当性について確認した.

Solubility and decomposition kinetics of nitrous acid in aqueous solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolubility and decomposition kinetics of nitrous acid in aqueous solutionJong Yoon Park and Yin Nan LeeCite this: J. Phys. Chem. 1988, 92, 22, 6294–6302Publication Date (Print):November 1, 1988Publication History Published online1 May 2002Published inissue 1 November 1988https://doi.org/10.1021/j100333a025RIGHTS & PERMISSIONSArticle Views1817Altmetric-Citations212LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Comparison of the reactivity of nine nitrous acid scavengers

Rate constants have been measured for the reaction of nitrous acid in aqueous solution at 25 °C with urea, 2,4-dinitroaniline, hydroxylamine, sulphanilic acid, hydrazoic acid, sulphanilamide, hydrazine, sulphamic acid, and 4-nitroaniline, as a function of acidity up to ca. 1.5M. The acid–rate profiles, which are all consistent with mechanisms involving electrophilic nitrosation and various protonation equilibria, give the order of reactivity at each acidity of these potential nitrous acid scavengers. The order of reactivity varies with the acidity because of the different acidity dependences, e.g. the ‘best’ scavenger at 0.05M-acid is 4-nitroaniline followed by sulphamic acid, whilst at 1.3M-acid the most reactive is the hydrazinium ion followed by hydrazoic acid. The effect of added halide ion, thiocyanate ion, and thiourea was also examined. Nitrosation of urea, 2,4-dinitroaniline, hydrazinium ion, and sulphamic acid was not catalysed by any added nucleophile, probably because of the importance, for these substrates containing electron-withdrawing groups, of the reversibility of the initial nitrosation. For the remaining five substrates normal nucleophilic catalysis was observed; analysis of the kinetic data enables the second-order rate constant for attack by the nitrosyl halide, etc. to be evaluated. The reactivity sequence NOCl > NOBr > NOSCN > NO[graphic omitted]C(NH2)2 was found in each case.

Spectroscopic, electrochemical and photochemical properties of brown ring compounds

Brown ring compounds have been produced by the reaction of ferrous ion with nitric oxide and with nitrous acid in aqueous solution. Spectroscopic results have showed that the brown color is due to charge-transfer bands associated with the FeNO bond. The cyclic voltammetric experiments indicated that the oxidation of this compound was completely irreversible. The influence of light was to stimulate the charge-transfer process in which the electrons were transferred from the donor orbital into the acceptor orbital, and finally led to the formation of the ion-pair Fe(I)NO + which was assumed to be more electroactive.

ChemInform Abstract: ELECTROPHILIC NITROSATION AT SULPHUR AND NITROGEN IN THIOUREA

AbstractMechanismus und Kinetik der Nitrosierung von Thioharnstoff mit salpetriger Säure in wäßriger Lösung wird untersucht und diskutiert.

Electrophilic nitrosation at sulphur and nitrogen in thiourea

Thiourea reacts rapidly with nitrous acid in aqueous solution to form an equilibrium concentration of a coloured S-nitroso-compound. The equilibrium constant has been measured, together with a preliminary value of the rate constant for the nitrosation. The kinetics of the much slower reaction to form nitrogen and thiocyanic acid have been investigated. The mechanism proposed is a rate-determining sulphur-to-nitrogen migration of the nitroso-group in the conjugate base of the S-nitroso-compound.

CCXLVIII.—The decomposition of nitrous acid in aqueous solution

CCXLVIII.—The decomposition of nitrous acid in aqueous solution