Kinetics of reactions of 1,2,4-triazole-3-diazonium ions with phenol and with hydroxyl ion

1985 ◽  
Vol 50 (3) ◽  
pp. 658-674
Author(s):  
Vladimír Macháček ◽  
Josef Kořínek ◽  
Daniela Kreuzigová ◽  
Vojeslav Štěrba
Keyword(s):  
Main Reaction ◽  
Basic Medium ◽  
Phenyl Derivative ◽  
Rate Limiting Step ◽  
Diffusion Controlled ◽  
Hydroxyl Ion ◽  
Diazonium Ions ◽  
Diazonium Ion ◽  
Hydroxy Compounds ◽  
Intramolecular Hydrogen

5-Methyl- and 5-phenyl-l,2,4-triazole-3-diazonium ions (IIIa, IIIb) react with undissociated phenol in diluted hydrochloric acid. At pH > 1 the reactions with phenolate ions become kinetically significant, their bimolecular rate constants approaching those of the diffusion-controlled reactions. At the same time, the diazonium ions are dissociated into the dipolar ions IIIb and IVb. At pH > 4 (for the phenyl derivative) and pH > 5 (for the methyl derivative), the reaction of the dipolar ions with phenolate ion becomes the main reaction path. The rate constant of the reaction of the dipolar ion IIIb with hydroxyl ion (3 . 103 l mol-1 s-1) is comparable with that of the analogous reaction of benzenediazonium ion, but the reverse reaction of the dipolar ion IIIb is slower by about 5 orders of magnitude, and the pKA value of the diazo hydroxide formed is higher by about 4 units than that of benzenediazo hydroxide. The high stability of the heterocyclic diazo hydroxide and its low acidity are explained by formation of a strong intramolecular hydrogen bond. In sodium hydroxide solutions, the (Z)-diazotate IIId initially formed is transformed into the (E)-isomer (the corresponding half-life being about 10 h) which, in contrast to the (Z)-isorner, does not practically react with aromatic hydroxy compounds in basic medium. The transformation of the (E)-isomer to the diazonium ion is general acid-catalyzed reaction. Transformation of nitrosamine into diazo hydroxide is suggested to be the rate-limiting step of this reaction in solutions of pH < 5.

scholarly journals INFLUENCE OF CHEMICAL STRUCTURE ON THE RATE OF AZO COUPLING AND ITS SIGNIFICANCE IN HISTOCHEMICAL METHODOLOGY

1959 ◽  
Vol 7 (1) ◽  
pp. 50-65 ◽  
Author(s):  
MARVIN M. NACHLAS ◽  
THEODORE P. GOLDSTEIN ◽  
DAVID H. ROSENBLATT ◽  
MARVIN KIRSCH ◽  
ARNOLD M. SELIGMAN
Keyword(s):  
Aromatic Amines ◽  
Diazonium Salt ◽  
Tissue Sections ◽  
Coupling Techniques ◽  
Diazonium Ions ◽  
Coupling Rate ◽  
Diazonium Ion ◽  
Hydroxy Compounds ◽  
Positive Groups ◽  
Electro Negativity

Reliability of enzymatic localization in tissue sections by the simultaneous coupling techniques is dependent to a great extent upon the speed of coupling. Therefore, the influence on coupling rate of the structure of the diazonium ion and of the coupling component was studied. Electro-negative groups in the diazonium ion increase the rate of coupling, while the same groups in the coupling component decrease the rate. Electro-positive groups in the coupling component accelerate coupling, but slow it when present in the diazonium ion. The relation of coupling rate and electro-negativity of the substituents in the diazonium ion follows Hammett's equation (8). Although the relations is linear on coupling with aromatic hydroxy compounds, it is not so with aromatic amines. The most active diazonium ions showed no increase in coupling rate with aromatic amines. This suggests that for those enzymes hydrolyzing an ester link, increase of coupling rate might be accomplished by modifying the structure of either the coupling component used in the substrate or the diazonium salt. However, for enzymes splitting amide linkages, the only possibility of improving the localization is by modifying the structure of the coupling component.

scholarly journals New Diazo Coupling Reactions for Visible Spectrophotometric Determination of Alfuzosin in Pharmaceutical Preparations

2007 ◽  
Vol 4 (4) ◽  
pp. 496-501 ◽  
Author(s):  
M. Vamsi Krishna ◽  
D. Gowri Sankar
Keyword(s):  
Pharmaceutical Preparations ◽  
Pharmaceutical Formulations ◽  
Molar Absorptivity ◽  
Basic Medium ◽  
Coupling Reactions ◽  
Acetyl Acetone ◽  
Diazo Coupling ◽  
Optimum Reaction ◽  
Diazonium Ion

Simple, rapid and sensitive spectrophotometric procedures were developed for the analysis of Alfuzosin hydrochloride (AFZ) in pure form as well as in pharmaceutical formulations. The methods are based on the reaction of AFZ with nitrite in acid medium to form diazonium ion, which is coupled with ethoxyethylenemaleic ester (Method A) or ethylcyanoacetate (Method B) or acetyl acetone (method C) in basic medium to form azo dyes, showing absorption maxima at 440, 465 and 490 nm respectively. Beer’s law is obeyed in the concentration of 4-20 μg/mL of AFZ for methods A, B and 3-15 μg/mL of AFZ for method C. The molar absorptivity and sandell’s sensitivity of AFZ- ethoxyethylenemaleic ester, AFZ- ethylcyanoacetate and AFZ-acetyl acetone are1.90 × 104, 0.022; 1.93 × 104, 0.021 and 2.67 × 104L mole-1cm-1, 0.015 μg cm-2respectively. The optimum reaction conditions and other analytical parameters were evaluated. The methods were successfully applied to the determination of AFZ in pharmaceutical formulations.

True symmetry or pseudosymmetry: 5-amino-1-(4-methylphenylsulfonyl)-4-pyrazolin-3-one and a comparison with its 1-phenylsulfonyl analogue

2012 ◽  
Vol 69 (1) ◽  
pp. 90-92 ◽  
Author(s):  
Galal H. Elgemeie ◽  
Shahinaz H. Sayed ◽  
Peter G. Jones
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Intramolecular Hydrogen Bond ◽  
Title Compound ◽  
Acta Cryst ◽  
Interplanar Angle ◽  
Phenyl Derivative ◽  
Compound C ◽  
Independent Molecules ◽  
Intramolecular Hydrogen

The title compound, C10H11N3O3S, (I), crystallizes as the NH tautomer. The two rings subtend an interplanar angle of 72.54 (4)°. An intramolecular hydrogen bond is formed from the NH2group to a sulfonyl O atom. The molecular packing involves layers of molecules parallel to thebcplane atx≃ 0, 1etc., with two classical linear hydrogen bonds (amino–sulfonyl and pyrazoline–carbonyl N—H...O) and a further interaction (amino–sulfonyl N—H...O) completing a three-centre system with the intramolecular contact. The analogous phenyl derivative, (II) [Elgemeie, Hanfy, Hopf & Jones (1998).Acta Cryst.C54, 136–138], crystallizes with essentially the same unit cell and packing pattern, but with two independent molecules that differ significantly in the orientation of the phenyl groups. The space group isP21/cfor (I) butP21for (II), which is thus a pseudosymmetric counterpart of (I).

Study of cyclization of 2-acetyl-3-methylamino-N-benzoyl-2-butenethioamide

1981 ◽  
Vol 46 (1) ◽  
pp. 256-261 ◽  
Author(s):  
Vladimír Macháček ◽  
Said El Bahaie ◽  
Vojeslav Štěrba
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Hydroxyl Ion ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Cyclic Intermediate

Kinetics has been studied of cyclization of 2-acetyl-3-methylamino-N-benzoyl-2-betenethioamide (Ia) and 2-acetyl-3-amino-N-benzoyl-2-butenethioamide (Ib) giving 5-acetyl-2-phenyl-1,6-dimethyl-4-(1H)pyrimidinethione (IIa) and 5-acetyl-2-phenyl-6-methyl-4-(3H)-pyrimidinethione (IIb), respectively, in aqueous buffers within pH 2 to 9. Formation of the cyclic intermediate is rate-limiting in the cyclization of Ib within the whole range. In the case of Ia the rate-limiting step consists in acid-catalyzed splitting off of water from the cyclic intermediate above pH 5 and in base-catalyzed splitting off of hydroxyl ion above pH 7.

scholarly journals Electrocatalytic activity of Chemisorbed Hydroxyl ion towards Oxidation of Hydrogen peroxide anion in Alkaline media

2017 ◽  
Vol 41 (1) ◽  
pp. 29-36
Author(s):  
Md Rezwan Miah ◽  
Tarannuma Ferdous Manny ◽  
Debashis Sen ◽  
Md Azizur Rahman ◽  
Md Saiful Alam ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Electrocatalytic Activity ◽  
Chloride Ion ◽  
Alkaline Media ◽  
Linear Calibration ◽  
Diffusion Controlled ◽  
Hydroxyl Ion ◽  
Oxidation Of Hydrogen ◽  
Polycrystalline Gold ◽  
Academy Of Sciences

In situ chemisorbed hydroxyl ion (OH-) onto clean polycrystalline gold (Au (poly)) electrode showed an extraordinary enhanced electrocatalytic activity towards oxidation of hydrogen peroxide anion (HO2-) in alkaline media. The oxidation of HO2- at the fabricated electrode was found to be a diffusion controlled process. The anodic transfer coefficient of the oxidation reaction was estimated as 0.47. Chloride ion (Cl-) replaced the chemisorbed OH- from the surface of the modified Au (poly) (OH-)Au (poly)) electrode leading to diminishing the observed electrocatalytic activity. The optimized concentration of KOH solution for the highest catalytic activity was found to be ca. 0.1 M. A linear calibration curve for various concentrations of HO2-? in the range of 0.5 to 5 mM was obtained having sensitivity equal to 1.028 A cm-2 M-1.Journal of Bangladesh Academy of Sciences, Vol. 41, No. 1, 29-36, 2017

Reactions of 4-Amino-3-penten-2-one and Its NSubstituted Derivatives with Diazonium Ions

1995 ◽  
Vol 60 (8) ◽  
pp. 1367-1379 ◽  
Author(s):  
Vladimír Macháček ◽  
Alexandr Čegan ◽  
Aleš Halama ◽  
Olga Rožňavská ◽  
Vojeslav Štěrba
Keyword(s):  
Coupling Reaction ◽  
Butyl Alcohol ◽  
Azo Compounds ◽  
Coupling Reactions ◽  
Azo Coupling ◽  
Alcohol Water ◽  
Diazonium Ions ◽  
Coupling Rate ◽  
Reaction Orders ◽  
Intramolecular Hydrogen

Azo coupling reactions of benzenediazonium salts with substituted 4-amino-3-penten-2-ones take place at the C-3 atom. 1H and 13C NMR spectroscopy has been used to study the structure of both the starting enaminones and coupling products. In CDCl3, 3-(4-chlorophenylhydrazono)-2-(4-methylphenylimino)-4-pentanone exists in hydrazo form whereas 4-amino-3-(4-chlorophenylazo)-3-penten-2-one is present as a mixture of two azo compounds differing probably in the arrangement of the intramolecular hydrogen bond. The azo coupling reaction kinetics have been studied in acetate buffers and methanol-water or tert-butyl alcohol-water mixtures. The coupling rate has been found independent of pH and buffer concentration. The reaction orders with respect to the starting compounds have been determined and the reaction mechanism is suggested. Linear dependence has been found between log kobs and substituent constants according to the Hammett or Yukawa-Tsuno equations.

Devitrification kinetics and mechanism of Pyrex borosilicate glass

2001 ◽  
Vol 16 (6) ◽  
pp. 1752-1758 ◽  
Author(s):  
Jau-Ho Jean ◽  
Yu-Ching Fang
Keyword(s):  
Borosilicate Glass ◽  
Linear Growth ◽  
Energy Analysis ◽  
Three Dimensional ◽  
Rate Limiting Step ◽  
Dimensional Diffusion ◽  
Limiting Step ◽  
Diffusion Controlled ◽  
Rate Limiting ◽  
Kinetics Of

Cristobalite is formed when initially amorphous Pyrex borosilicate glass (Corning 7740) is fired at temperatures ranging from 700 to 1000 °C. The sigmoidal devitrification kinetics of cristobalite obeys Avrami-like three-dimensional diffusion-controlled kinetics. Activation energy analysis indicates that the diffusion of Na+ in the glass is the rate-limiting step during phase transformation. The above conclusion is further confirmed by calculated and measured results of linear growth rates.

scholarly journals Redox Chemistry in Laccase-Catalyzed Oxidation of N-Hydroxy Compounds

2000 ◽  
Vol 66 (5) ◽  
pp. 2052-2056 ◽  
Author(s):  
Feng Xu ◽  
Juozas J. Kulys ◽  
Kyle Duke ◽  
Kaichang Li ◽  
Kastis Krikstopaitis ◽  
...  
Keyword(s):  
Redox Potential ◽  
Oxidation Rate ◽  
Outer Sphere ◽  
Enzymatic Oxidation ◽  
Proton Release ◽  
Rate Limiting Step ◽  
Redox Active ◽  
Hydroxy Compounds ◽  
Rate Limiting ◽  
Catalyzed Oxidation

ABSTRACT 1-Hydroxybenzotriazole, violuric acid, andN-hydroxyacetanilide are three N-OH compounds capable of mediating a range of laccase-catalyzed biotransformations, such as paper pulp delignification and degradation of polycyclic hydrocarbons. The mechanism of their enzymatic oxidation was studied with seven fungal laccases. The oxidation had a bell-shaped pH-activity profile with an optimal pH ranging from 4 to 7. The oxidation rate was found to be dependent on the redox potential difference between the N-OH substrate and laccase. A laccase with a higher redox potential or an N-OH compound with a lower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other redox-active compounds, an “outer-sphere” type of single-electron transfer from the substrate to laccase and proton release are speculated to be involved in the rate-limiting step for N-OH oxidation.

scholarly journals Study of the Microstructural and First Hydrogenation Properties of TiFe Alloy with Zr, Mn and V as Additives

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1217
Author(s):  
Abhishek Kumar Patel ◽  
Alexandre Duguay ◽  
Bernard Tougas ◽  
Bettina Neumann ◽  
Chris Schade ◽  
...  
Keyword(s):  
High Capacity ◽  
Interface Velocity ◽  
Secondary Phase ◽  
Secondary Phases ◽  
Fast Reaction ◽  
Hydrogen Storage Properties ◽  
Rate Limiting Step ◽  
Diffusion Controlled ◽  
Rate Limiting ◽  
Storage Properties

In this paper, we report the effect of adding Zr + V or Zr + V + Mn to TiFe alloy on microstructure and hydrogen storage properties. The addition of only V was not enough to produce a minimum amount of secondary phase and, therefore, the first hydrogenation at room temperature under a hydrogen pressure of 20 bars was impossible. When 2 wt.% Zr + 2 wt.% V or 2 wt.% Zr + 2 wt.% V + 2 wt.% Mn is added to TiFe, the alloy shows a finely distributed Ti2Fe-like secondary phase. These alloys presented a fast first hydrogenation and a high capacity. The rate-limiting step was found to be 3D growth, diffusion controlled with decreasing interface velocity. This is consistent with the hypothesis that the fast reaction is likely to be the presence of Ti2Fe-like secondary phases that act as a gateway for hydrogen.

Einfluß der Enolisierung auf die Reduktion von β Ketocarbonsäure-Derivaten mit Zinkborhydrid / Influence of the Enol Formation on the Reduction of β-Keto Carboxylic Acid Derivatives by Zinc Borohydride

1991 ◽  
Vol 46 (12) ◽  
pp. 1713-1719 ◽  
Author(s):  
Herbert Meier ◽  
Volker Krause
Keyword(s):  
Hydrogen Bonding ◽  
Carboxylic Acid ◽  
Structure Determination ◽  
Intramolecular Hydrogen Bonding ◽  
Steric Effects ◽  
Group A ◽  
Hydroxy Compounds ◽  
Intramolecular Hydrogen ◽  
Enol Formation

Depending on the keto-enol equilibrium 1 ⇄ 2 reduction of the esters and the amides 1/2 a—g with Zn(BH4)2/ZnCl2 attacks either at the CO or at the CO2R group. A high diastereoselectivity (98:2 or more) is observed for the formation of the β-hydroxy compounds 3a,b,c,e,f in favour of the erythro forms. As to the structure determination of 3, different steric effects and different intramolecular hydrogen bonding have to be considered, leading to different rotameric populations.

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