“…On the contrary, this supposition cannot be applied to the results obtained in water−dioxane mixtures; as we can see from the data in Table (entries 5 and 6), values of k 0 obtained in the presence of Br - are higher than those obtained in the presence of Cl - or in the absence of X - , and the difference increases with the dioxane percentage, i.e., as the polarity of the medium decreases. When the polarity of the medium is decreased, the BrNO concentration increases (more stable in less polar media) whereas the NO + concentration decreases (more stable in more polar media). , 7 (A) Influence of SDS concentration on the pseudo-first-order rate constant of the nitrosation of BZA in an acid medium at [nitrite] = 1.67 × 10 -3 mol dm -3 and [H + ] = 0.032 mol dm -3 by using (·) HClO 4 , (▴) HCl, and (◆) HBr. (B) Linearization of the data according to eq 12 and corresponding to (▵) HCl and (◇) HBr and at (▿) [HClO 4 ] = 0.021 mol dm -3 and [SCN - ] = 1.04 × 10 -3 mol dm -3 .…”
The nitrosation reaction of benzoylacetone (1-phenyl-1,3-butadione) by nitrous acid in an aqueous acid
medium is studied in the presence of anionic and cationic micelles. The reaction involves enolization of
the ketone, followed by electrophilic nitrosation of the enol. The presence of micelles strongly modifies
the keto−enol equilibrium of β-dicarbonyl compounds, like benzoylacetone, in such a way that the enol
percentage increases with the surfactant concentration. The increasing enol amount with surfactant
concentration is quantitatively evaluated by studying the effect of surfactant addition on the UV−vis
spectra of benzoylacetone; the results are used to explain the kinetic data. The addition of hydrogen
dodecyl sulfate (HDS) to the reaction mixture increases the nitrosation reaction rate continuously until
levels off at high HDS concentrations. In the presence of sodium dodecyl sulfate (SDS), the observed rate
constant increases at low surfactant concentrations, passes through a maximum, and decreases at still
higher SDS concentrations. The observed kinetic effects in the presence of the cationic surfactants
tetradecyltrimethylammonium salts of Cl-, Br-, NO3
-, and SCN- anions, in general TTAX (with X being
Cl-, Br-, NO3
-, or SCN-), depend on the nature of the micellar counterion; for example, the addition of
TTANO3 decreases the reaction rate for the entire concentration range investigated, while the presence
of TTASCN calatyzes the reaction. The varying micellar effects are quantitatively interpreted on the basis
of reaction mechanisms, with consideration given to the possible nitrosating agent in every case.
“…On the contrary, this supposition cannot be applied to the results obtained in water−dioxane mixtures; as we can see from the data in Table (entries 5 and 6), values of k 0 obtained in the presence of Br - are higher than those obtained in the presence of Cl - or in the absence of X - , and the difference increases with the dioxane percentage, i.e., as the polarity of the medium decreases. When the polarity of the medium is decreased, the BrNO concentration increases (more stable in less polar media) whereas the NO + concentration decreases (more stable in more polar media). , 7 (A) Influence of SDS concentration on the pseudo-first-order rate constant of the nitrosation of BZA in an acid medium at [nitrite] = 1.67 × 10 -3 mol dm -3 and [H + ] = 0.032 mol dm -3 by using (·) HClO 4 , (▴) HCl, and (◆) HBr. (B) Linearization of the data according to eq 12 and corresponding to (▵) HCl and (◇) HBr and at (▿) [HClO 4 ] = 0.021 mol dm -3 and [SCN - ] = 1.04 × 10 -3 mol dm -3 .…”
The nitrosation reaction of benzoylacetone (1-phenyl-1,3-butadione) by nitrous acid in an aqueous acid
medium is studied in the presence of anionic and cationic micelles. The reaction involves enolization of
the ketone, followed by electrophilic nitrosation of the enol. The presence of micelles strongly modifies
the keto−enol equilibrium of β-dicarbonyl compounds, like benzoylacetone, in such a way that the enol
percentage increases with the surfactant concentration. The increasing enol amount with surfactant
concentration is quantitatively evaluated by studying the effect of surfactant addition on the UV−vis
spectra of benzoylacetone; the results are used to explain the kinetic data. The addition of hydrogen
dodecyl sulfate (HDS) to the reaction mixture increases the nitrosation reaction rate continuously until
levels off at high HDS concentrations. In the presence of sodium dodecyl sulfate (SDS), the observed rate
constant increases at low surfactant concentrations, passes through a maximum, and decreases at still
higher SDS concentrations. The observed kinetic effects in the presence of the cationic surfactants
tetradecyltrimethylammonium salts of Cl-, Br-, NO3
-, and SCN- anions, in general TTAX (with X being
Cl-, Br-, NO3
-, or SCN-), depend on the nature of the micellar counterion; for example, the addition of
TTANO3 decreases the reaction rate for the entire concentration range investigated, while the presence
of TTASCN calatyzes the reaction. The varying micellar effects are quantitatively interpreted on the basis
of reaction mechanisms, with consideration given to the possible nitrosating agent in every case.
“…HR is the acidity function for the protonation/dehydration equilibrium of triarylcarbinols (see [ 161). There is some evidence, however, for the reversibility of aromatic diazotisation in MeOH [19].…”
The rate of diazotisation of 2-aminothiazole was measured in 65 to 75% (w/w) aqueous H,SO,. The kinetic solvent isotope effect of the diazotisation in 72% D2S04/D20 was determined (k,/k, = 5.8 i 0.2). These data are consistent with a mechanism in which the 2-aminothiazole, protonated at the ring N-atom, but not at the NH, group, is attacked by the NO+ ion. The reaction does not go to completion, but to an equilibrium. The equilibrium concentration of the diazonium ion was determined in 30, 50, 70, and 90% ( w / w ) H,SO, at three initial concentrations of reagents (0.001,0.01, and 0.1~). The final concentrations of the reagents and the diazonium ion are consistent with a reversible process. This is the first diazotisation for which quantitative evidence for equilibration has been found. In the very large range of acidities used (Ifo = -1.73 to -9.01), it was not possible to calculate meaningful equilibrium constants that are independent of the acidity.Introduction. -Diazotisation of five-and six-membered heteroaromatic amines has been investigated for many years, according to Butler's 1975 review [l]
The diazotization of various substituted naphthylamines has been found to be catalysed by the nucleophiles Cl−, Br−, SCN− and thiourea due to the formation of the corresponding nitrosyl salts. The rate controlling steps depend on the concentration of catalyst, with respect to which the order of the reaction varies between 1 and 0. The theoretical rate constants deduced from the proposed reaction mechanism are discussed in terms of the basicity of the amines and the nucleophilicity of the catalysts. The reaction rate's dependence on ionic strength and acidity in the absence of catalysts is also reported and discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
