Kinetics and mechanism of acid catalyzed decomposition of substituted 1,3-diphenyltriazenes

1987 ◽  
Vol 52 (9) ◽  
pp. 2217-2224 ◽  
Author(s):  
Petr Svoboda ◽  
Oldřich Pytela ◽  
Miroslav Večeřa
Keyword(s):  
Diazonium Salt ◽  
Bond Formation ◽  
Reaction Constant ◽  
The Media ◽  
Acid Catalyzed ◽  
Reaction Constants ◽  
Kinetics Of ◽  
Better Than ◽  
Nitrogen Bond ◽  
Bond Splitting

The kinetics of acid catalyzed decomposition of 3-substituted and 1,3-disubstituted 1,3-diphenyl-3-methyltriazenes have been studied in 40% aqueous ethanolic buffers at 25 °C. The reaction constant for substitution of the phenyl ring at the 3 position of the triazene chain has been determined and the reaction constants of the protonation and bond splitting between the nitrogen atoms 2 and 3 have been estimated. By the covariance analysis it has been found that the standard constants of the Hammett relation are better than the constants determined in the media of organic solvents. Also estimated were the values of the slope β1g of the linear relation between the rate constants and the equilibrium between the diazonium salt and diazotate. The A-SE2 mechanism is suggested as probable, the bond between nitrogen atoms of triazene chain being more than half split in the transition state and the nitrogen-proton bond formation being more advanced than the nitrogen-nitrogen bond splitting.

The Formation of Cu3Si from Cu/a-Si Multilayers

1997 ◽  
Vol 481 ◽  
Author(s):  
R. R. Chromik ◽  
W. K. Neils ◽  
E. J. Cotts
Keyword(s):  
Diffusion Couples ◽  
X Ray Diffraction ◽  
Limited Growth ◽  
Scanning Calorimetry ◽  
Individual Layer ◽  
Diffusion Limited ◽  
Reaction Constant ◽  
Multilayered Composites ◽  
Reaction Constants ◽  
Kinetics Of

ABSTRACTThe kinetics of the formation of Cu3Si in Cu/a-Si diffusion couples have been investigated by means of differential scanning calorimetry and x-ray diffraction. Multilayered composites of average stoichiometry Cu3Si were prepared by sputter deposition with individual layer thicknesses varying in different samples between 2 and 100 nm. We observed diffusion limited growth of Cu3 Si upon annealing these diffusion couples below 500 K. Reaction constants were measured for a temperature range of 455 to 495 K for thicknesses of growing Cu3Si between 2.6 and 80 nm. The temperature dependence of the reaction constant, k2, was characterized as k2 = k0 exp(− Ea/kbT) with activation energy, Ea = 1.0 eV/atom and pre-factor, k0 = 1.9×10−3 cm2/s.

Kinetics of acid catalyzed decomposition of substituted 1,3-diphenyl-3-methyltriazenes

1986 ◽  
Vol 51 (3) ◽  
pp. 553-563 ◽  
Author(s):  
Petr Svoboda ◽  
Oldřich Pytela ◽  
Miroslav Večeřa
Keyword(s):  
Experimental Data ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Kinetics Of

Kinetics of the acid catalyzed decomposition of fifteen 1-substituted-1,3-diphenyl-3-methyltriazenes have been studied in 40% aqueous ethanolic buffers at 25 °C. The slope found for the dependence log kobsvs pH of the buffer is not equal to unity, and a method of treating such experimental data is suggested. The reaction constant found (ρ = -3.70) indicates that substituents have similar effects on both protonation and decomposition of the triazene chain.

Dissociation of substituted benzenesulphonamides in water, methanol and ethanol

1984 ◽  
Vol 49 (5) ◽  
pp. 1182-1192 ◽  
Author(s):  
Miroslav Ludwig ◽  
Oldřich Pytela ◽  
Karel Kalfus ◽  
Miroslav Večeřa
Keyword(s):  
Linear Regression ◽  
Multiple Linear Regression ◽  
Potentiometric Titration ◽  
Principal Components ◽  
Dissociation Constants ◽  
Benzoic Acids ◽  
Reaction Constant ◽  
The Media ◽  
Reaction Constants

Thirteen monosubstituted arylsulphonamides (XC6H4SO2NH2) and two 3,4-disubstituted arylsulphonamides (X2C6H3SO2NH2) have been synthetized and their dissociation constants have been measured by potentiometric titration in water, methanol, and ethanol. The Hammett substitution dependences have been calculated for all the media, and changes in the reaction constants due to transition from water to alcohols are discussed in confrontation with analogous dependences of benzoic acids. The reaction constant ρ found in methanol is lower than that in water. The dissociation constants have been treated mathematically by the method of the principal components and by multiple linear regression.

scholarly journals Evidence for Polarity- and Viscosity-Controlled Domains in the Termination Reaction in the Radical Polymerization of Acrylonitrile

2021 ◽  
Author(s):  
Xiaopei Lin ◽  
Tasuku Ogihara ◽  
Tatsuhisa Kato ◽  
Yasuyuki Nakamura ◽  
Shigeru Yamago
Keyword(s):  
Radical Polymerization ◽  
Bond Formation ◽  
Carbon Formation ◽  
Molding Process ◽  
Processing Step ◽  
The Media ◽  
Small Model ◽  
First Time ◽  
Polymerization Conditions ◽  
Nitrogen Bond

The termination mechanism in the radical polymerization of acrylonitrile (AN) was determined by the reaction of structurally well-defined polyacryronitrile (PAN) chain-end radical <b>1a</b> and PAN-end mimetic small model radical <b>1b</b>. The contributions of three mechanisms, i.e., the disproportionation (<i>Disp</i>), the combination by carbon-carbon formation (<i>CC-Comb</i>), and the combination by carbon-nitrogen bond formation (<i>CN-Comb</i>), were unambiguously determined. The <i>CN-Comb</i> pathway was experimentally proved for the first time. The selectivity between <i>Disp </i>and<i> CC-Comb</i> showed a good correlation with the viscosity and temperature, and the <i>Disp</i> selectivity increased as the viscosity increased, as previously reported for the termination of other monomers. In contrast, <i>CN-Comb</i> is insensitive to viscosity but sensitive to polarity; the selectivity decreases as the polarity of the media increases. The results strongly suggest the presence of two domains in the termination reaction, namely, the polarity- and viscosity-controlled domains. <i>CN-Comb</i> product<b> 5</b> was stable under the polymerization conditions but decomposed to <i>Disp</i> and <i>CC-Comb</i> products at high temperatures. Therefore, care must be taken in the processing step, such as the molding process, because the physical properties could be altered due to changes in the <i>Disp</i> and <i>CC-Comb</i> compositions.

Substituent effects on azo coupling of indoles

1993 ◽  
Vol 71 (12) ◽  
pp. 2144-2149 ◽  
Author(s):  
Hassan A. Albar ◽  
Ahmad S. Shawali ◽  
Magda A. Abdaliah
Keyword(s):  
Diazonium Salt ◽  
Substituent Effects ◽  
General Mechanism ◽  
Coupling Reactions ◽  
Azo Coupling ◽  
Straight Line ◽  
Reaction Constant ◽  
Methyl Derivatives ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of the azo coupling of eight para-substituted benzenediazonium tetrafluoroborates 2a–h with indole and its 1-, 2-,and 3-methyl derivatives 1a–d, respectively, were studied in acetonitrile at 25 °C under pseudo-first-order conditions. The relation k1(obs) = k2[diazonium salt] was found applicable in all cases. The logarithms of the rate constants k2 for each reaction series were correlated by the Hammett equation. A plot of the values of the reaction constant, ρ, obtained against the acidity constants pKa of 1a–d gave a straight line: ρ = 2.97 – 0.15 pKa. These results indicate that the azo-coupling reactions of indoles 1a–d follow one general mechanism involving rate-limiting initial electrophilic attack at the 3-position for all four compounds, contrary to the previous conclusion of Jackson and Lynch that the final deprotonation step is rate limiting.

Synthesis, kinetics and mechanism of cyclization of 1-(2-aryloxycarbonylphenyl)-3-phenyltriazenes

1990 ◽  
Vol 55 (11) ◽  
pp. 2692-2700 ◽  
Author(s):  
Oldřich Pytela ◽  
Zdeněk Bahník
Keyword(s):  
Kinetic Isotope Effect ◽  
Intramolecular Proton Transfer ◽  
Steric Effects ◽  
Aqueous Methanol ◽  
Kinetic Isotope ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Substituted 1

Twelve substituted 1-(2-aryloxycarbonylphenyl)-3-phenyltriazenes have been synthetized and kinetics of their reactions have been measured in 52.1% (by mass) aqueous methanol at pH 3 to 11. Plots of kobs vs pH show three regions: noncatalyzed cyclization (pH 4 to 7), acid-catalyzed splitting of the triazene chain, and base-catalyzed cyclization. The non-catalyzed cyclization exhibits a kinetic isotope effect, the reaction constant ρ = 2.69 (σ-p), and β1g = 1.02, which indicates a mechanism of E1cB type with intramolecular proton transfer and a transient formation of a ketene intermediate. The base-catalyzed cyclization, on the other hand, exhibits the reaction constant ρ = 1.05 (σ-p), β1g = 0.4, and distinct steric effects, which indicates a cyclization by BAc2 mechanism with rate-limiting formation of the tetrahedral intermediate.

scholarly journals Evidence for Polarity- and Viscosity-Controlled Domains in the Termination Reaction in the Radical Polymerization of Acrylonitrile

2021 ◽  
Author(s):  
Xiaopei Lin ◽  
Tasuku Ogihara ◽  
Tatsuhisa Kato ◽  
Yasuyuki Nakamura ◽  
Shigeru Yamago
Keyword(s):  
Radical Polymerization ◽  
Bond Formation ◽  
Carbon Formation ◽  
Molding Process ◽  
Processing Step ◽  
The Media ◽  
Small Model ◽  
First Time ◽  
Polymerization Conditions ◽  
Nitrogen Bond

The termination mechanism in the radical polymerization of acrylonitrile (AN) was determined by the reaction of structurally well-defined polyacryronitrile (PAN) chain-end radical <b>1a</b> and PAN-end mimetic small model radical <b>1b</b>. The contributions of three mechanisms, i.e., the disproportionation (<i>Disp</i>), the combination by carbon-carbon formation (<i>CC-Comb</i>), and the combination by carbon-nitrogen bond formation (<i>CN-Comb</i>), were unambiguously determined. The <i>CN-Comb</i> pathway was experimentally proved for the first time. The selectivity between <i>Disp </i>and<i> CC-Comb</i> showed a good correlation with the viscosity and temperature, and the <i>Disp</i> selectivity increased as the viscosity increased, as previously reported for the termination of other monomers. In contrast, <i>CN-Comb</i> is insensitive to viscosity but sensitive to polarity; the selectivity decreases as the polarity of the media increases. The results strongly suggest the presence of two domains in the termination reaction, namely, the polarity- and viscosity-controlled domains. <i>CN-Comb</i> product<b> 5</b> was stable under the polymerization conditions but decomposed to <i>Disp</i> and <i>CC-Comb</i> products at high temperatures. Therefore, care must be taken in the processing step, such as the molding process, because the physical properties could be altered due to changes in the <i>Disp</i> and <i>CC-Comb</i> compositions.

PENGEMBANGAN MEDIA BIG BOOK UNTUK MENINGKATKAN HASIL BELAJAR PECAHAN SENILAI SISWA SD

2018 ◽  
Vol 16 (1) ◽  
pp. 67-76
Author(s):  
Disyacitta Neolia Firdana ◽  
Trimurtini Trimurtini
Keyword(s):  
Learning Outcomes ◽  
Large Scale ◽  
Fourth Grade ◽  
Learning Activities ◽  
Equivalent Fractions ◽  
Fourth Grade Students ◽  
Teacher Needs ◽  
The Media ◽  
Test Result ◽  
Better Than

This research aimed to determine the properness and effectiveness of the big book media on learning equivalent fractions of fourth grade students. The method of research is Research and Development  (R&D). This study was conducted in fourth grade of SDN Karanganyar 02 Kota Semarang. Data sources from media validation, material validation, learning outcomes, and teacher and students responses on developed media. Pre-experimental research design with one group pretest-posttest design. Big book developed consist of equivalent fractions material, students learning activities sheets with rectangle and circle shape pictures, and questions about equivalent fractions. Big book was developed based on students and teacher needs. This big book fulfill the media validity of 3,75 with very good criteria and scored 3 by material experts with good criteria. In large-scale trial, the result of students posttest have learning outcomes completness 82,14%. The result of N-gain calculation with result 0,55 indicates the criterion “medium”. The t-test result 9,6320 > 2,0484 which means the average of posttest outcomes is better than the average of pretest outcomes. Based on that data, this study has produced big book media which proper and effective as a media of learning equivalent fractions of fourth grade elementary school.

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Influence of medium on alkaline hydrolysis of succinic acid monomethyl and monopropyl esters

1980 ◽  
Vol 45 (11) ◽  
pp. 2873-2882
Author(s):  
Vladislav Holba ◽  
Ján Benko
Keyword(s):  
Succinic Acid ◽  
Kinetic Parameters ◽  
Alkaline Hydrolysis ◽  
Specific Interactions ◽  
Nonaqueous Media ◽  
The Media ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of alkaline hydrolysis of succinic acid monomethyl and monopropyl esters were studied in mixed aqueous-nonaqueous media at various temperatures and ionic strengths. The results of measurements are discussed in terms of electrostatic and specific interactions between the reactants and other components of the reaction mixture. The kinetic parameters in the media under study are related to the influence of the cosolvent on the solvation sphere of the reactants.

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