Protolysis of Nitrous Acid in Aqueous Sodium Nitrate and Sodium Nitrite Solutions at Different Temperatures.

Tummavuori, Jouni; Lumme, Paavo; Karvonen, Pertti; Virtanen, Artturi I.; Paasiv́irta, Jaakko

doi:10.3891/acta.chem.scand.22-2003

Cited by 46 publications

(29 citation statements)

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“…The absorbance at 325 nm decreased as shown in Table 1, as the total stoichiometric concentration of nitrous acid increased. At this pH the ionisation of nitrous acid is partial, so, in a quantitative analysis this must be taken into account (pK a = 3.15 10 ).…”

Section: Results (A) Nitrosation Of 4-mercaptopyridinementioning

confidence: 99%

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Kinetics and mechanism of the formation and reactions of S-nitroso derivatives of some heterocyclic thiones

Amado

Blakelock

Holmes

et al. 2001

J. Chem. Soc., Perkin Trans. 2

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Rate and equilibrium measurements have been obtained for the nitrosation (using nitrous acid in dilute acid aqueous solution) of the following thione-thiol nitrogen heterocyclic species and for the decomposition reactions of the formed S-NO ϩ ions: 4-mercaptopyridine (1), 2-mercaptopyridine 1-oxide (2), 2-mercaptopyrimidine (3) and 2-mercapto-1H-imidazole (4). The nitrosation reactions were all rapid and rate constants were obtained by stoppedflow spectrophotometry. In all cases kinetic analysis showed that the halide ion-catalysed and the uncatalysed reactions occurred at or close to the diffusion-controlled limit and the reactive form of the substrate is its thione form. In some cases at high [nitrous acid] reaction occurred via N 2 O 3 where the rate-limiting step is that of N 2 O 3 formation. Similarly reaction of 1 and 3 in the presence of thiocyanate showed that reaction takes place via ratelimiting formation of ONSCN. All of the nitrosation reactions were somewhat reversible, with large equilibrium constants of 2.0 × 10 7 , ~4 × 10 5 , 1.7 × 10 3 and 1.5 × 10 5 dm 6 mol Ϫ2 respectively for 1, 2, 3, and 4. All of the S-NO ϩ ions decomposed rapidly in solution generating the disulfides and nitric oxide. This reaction was monitored only for the S-NO ϩ derived from 1 and 2 because of stability problems. The deprotonated form of the S-nitroso product from 1 was identified from measurements at pH 7.4 and the pK a value of the protonated form estimated as 4.5. It decomposed fairly rapidly to give the thione. We report some results where thiones show considerable catalytic activity in nitrosation reactions of N-methylaniline and ascorbic acid.

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Section: Results (A) Nitrosation Of 4-mercaptopyridinementioning

confidence: 99%

“…We obtained values for these second-order rate constants [k XNO defined by eqn. (10)] of (3.2 ± 0.1) × 10 9 and (5.4 ± 0.1) × 10 9…”

Section: Results (A) Nitrosation Of 4-mercaptopyridinementioning

confidence: 99%

Kinetics and mechanism of the formation and reactions of S-nitroso derivatives of some heterocyclic thiones

Amado

Blakelock

Holmes

et al. 2001

J. Chem. Soc., Perkin Trans. 2

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“…On the other hand, the keto–enol tautomerization is an equilibrium process, K E , in the ClPD system, but a slower reaction than nitrosation in the EPD system. (No reference to the acid–base equilibrium of nitrous acid is required, since, under the acidity conditions of this work, the stoichiometric [nitrite] is in the form of HNO 2 , pK a = 3.1) 27.…”

Section: Discussionmentioning

confidence: 99%

Substituent effects on enol nitrosation of 1,3‐diketones

Iglesias

2012

Int J of Chemical Kinetics

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The keto-enol tautomerism of 3-chloro-pentane-2,4-dione (ClPD) was studied in aqueous micellar solutions of cationic, anionic, and nonionic surfactants. The enol of ClPD tautomerizes rapidly in water to the equilibrium proportions of the keto form, K E = 0.55; whereas the keto-enol conversion of 3-ethyl-pentane-2,4-dione (EPD) is a much slower reaction than the enol nitrosation. Kinetics of enol -nitrosation of both ClPD and EPD in aqueous acid medium using nitrous acid shows first-order dependence upon [ketone] and linear or curve relationships of the observed rate constant, k o , as a function of [nitrite] or [H + ]; the observed behavior depends on the molecular structure of diketone and varies with the experimental conditions. The reaction is strongly catalyzed by Cl − , Br − , or SCN − , and the observed rate constant shows a curve dependence on [Br − ] or [SCN − ], which is more pronounced at high acidity. The results are consistent with a reaction mechanism in which the nitrosation occurs initially on the enol-oxygen and releasing a proton to form a chelate-nitrosyl complex intermediate in steady state. Fine differences on the mechanistic spectrum of enols nitrosation are considered on the basis of the molecular structure of the diketone. C

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“…Since Eq. (3) allows one to obtain k 2H 2 O by extrapolating to [phthalate] 0 and taking into account the dissociation of nitrous acid (pK a 3.148 [28]) it is possible to express k 2corr as a function of k 2 : The reaction mechanism can be explained in terms of aromatic electrophilic substitution by nitrosonium or nitrous acidium ions (Scheme 1), a mechanism previously suggested in other studies [29,30] and handled by us earlier [26,27]. Since the slow step is a proton transfer (see Scheme 1) and since, under the working conditions, nitrite NO À 2 HNO 2 , the rate equation is readily achieved:…”

Section: Resultsmentioning

confidence: 99%

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González‐Mancebo¹,

Lacadena²,

García-Alonso

et al. 2002

Monatshefte fuer Chemie

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Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water=acetonitrile were studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO =NO 2 H 2 followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron donating substituents, and a good Hammett correlation was observed with À6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH % 3, decreasing strongly for higher pH values. The study in water=acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant.

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Protolysis of Nitrous Acid in Aqueous Sodium Nitrate and Sodium Nitrite Solutions at Different Temperatures.

Cited by 46 publications

References 0 publications

Kinetics and mechanism of the formation and reactions of S-nitroso derivatives of some heterocyclic thiones

Kinetics and mechanism of the formation and reactions of S-nitroso derivatives of some heterocyclic thiones

Substituent effects on enol nitrosation of 1,3‐diketones

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