Aminolysis of naphthyl acetates catalyzed by cyclodextrins

1999 ◽  
Vol 77 (5-6) ◽  
pp. 950-959 ◽  
Author(s):  
Oswald S Tee ◽  
Michael J Boyd
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Rate Constants ◽  
Nucleophilic Attack ◽  
Reactivity Ratios ◽  
Aryl Group ◽  
First Order ◽  
Free Amine ◽  
Transition State Stabilization ◽  
Pseudo First Order

The effects of cyclodextrins (CDs) on the rate of nucleophilic attack on 1- and 2-naphthyl acetates (1-NA and 2-NA) in aqueous solution have been investigated. Analysis of the variation of the pseudo-first-order rate constants with [nucleophile] and [CD] affords rate constants for reaction of the nucleophiles with free ester (kN) and with ester bound to the CD (kcN). The reaction of 1-NA and 2-NA with the trifluoroethoxide anion is slowed down by β-CD as the ratios kcN/kN are 0.11 and 0.30, respectively. For reaction with the anion of 2-mercaptoethanol in the presence of α-CD, β-CD, "hydroxypropyl-β-CD" (hp-β-CD) and γ-CD, the reactivity ratios kcN/kN vary between 0.04 and 2.4, ranging from strong retardation to modest catalysis; the retardations arise with β-CD and hp-β-CD, which bind the esters strongly. By contrast, the attack of primary alkylamines is generally accelerated, and in many cases substantially so. For the aminolysis of 1-NA in the presence of β-CD, values of kcN/kN range from 7 to 460, assuming that free amine reacts with CD-bound ester. Alternatively, if the CD-catalyzed reaction involves free ester reacting with CD-bound amine, with rate constant kNc, the ratios kNc/kN vary from 43 to 140. Either way, there is appreciable catalysis of the aminolysis of 1-NA by β-CD. For the aminolysis of 2-NA, the effects are less dramatic: the ratios kcN/kN range from 0.19 to 17, and values of kNc/kN vary from 17 to 110. The reaction of 1-NA with n-hexylamine is also catalyzed by γ-CD. The variations of kinetic parameters with alkylamine chain length suggest that the CD-catalyzed aminolysis basically takes place by the attack of CD-bound amine on the free ester. However, there must be some stabilizing interactions between the aryl group of the ester and the CD during the reaction, since the transition state stabilization is different for 1-NA and 2-NA, as well for other esters.Key words: aminolysis, catalysis, cyclodextrin, ester cleavage, kinetics.

scholarly journals Efficient degradation of naproxen by persulfate activated with zero-valent iron: performance, kinetic and degradation pathways

2020 ◽  
Vol 81 (10) ◽  
pp. 2078-2091
Author(s):  
Shuyu Dong ◽  
Xiaoxue Zhai ◽  
Ruobing Pi ◽  
Jinbao Wei ◽  
Yunpeng Wang ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Hydroxyl Radical ◽  
Rate Constants ◽  
Zero Valent Iron ◽  
Degradation Pathways ◽  
First Order ◽  
First Order Kinetics ◽  
Degradation Rates ◽  
Initial Ph ◽  
Pseudo First Order

Abstract Degradation of naproxen (NAP) by persulfate (PS) activated with zero-valent iron (ZVI) was investigated in our study. The NAP in aqueous solution was degraded effectively by the ZVI/PS system and the degradation exhibited a pseudo-first-order kinetics pattern. Both sulfate radical (SO4•−) and hydroxyl radical (HO•) participate in the NAP degradation. The second-order rate constants for NAP reacting with SO4•− and HO• were (5.64 ± 0.73) × 109 M−1 s−1 and (9.05 ± 0.51) × 109 M−1 s−1, respectively. Influence of key parameters (initial pH, PS dosage, ZVI dosage, and NAP dosage) on NAP degradation were evaluated systematically. Based on the detected intermediates, the pathways of NAP degradation in ZVI/PS system was proposed. It was found that the presence of ammonia accelerated the corrosion of ZVI and thus promoted the release of Fe2+, which induced the increased generation of sulfate radicals from PS and promoted the degradation of NAP. Compared to its counterpart without ammonia, the degradation rates of NAP by ZVI/PS were increased to 3.6–17.5 folds and 1.2–2.2 folds under pH 7 and pH 9, respectively.

Kinetics and mechanism of the decarboxylation of pyrimidine-2-carboxylic acid in aqueous solution

1977 ◽  
Vol 55 (13) ◽  
pp. 2478-2481 ◽  
Author(s):  
Gerald E. Dunn ◽  
Edward A. Lawler ◽  
A. Brian Yamashita
Keyword(s):  
Carbon Dioxide ◽  
Aqueous Solution ◽  
Carboxylic Acid ◽  
Rate Constants ◽  
Kinetics And Mechanism ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Positively Charged

Pseudo-first-order rate constants for the decarboxylation of pyrimidine-2-carboxylic acid have been determined at 65 °C in aqueous solution over the acidity range pH = 2 to H0 = −9.5. Rate constants increase rapidly from pH = 2 to H0 = −3, then remain constant. This behaviour can be accounted for by a Hammick-type mechanism in which monoprotonated pyrimidine-2-carboxylic acid loses carbon dioxide to form an ylide (stabilized by the adjacent positively charged nitrogens) which rapidly converts to pyrimidine.

Kinetics and mechanisms of the reaction of chromium(III) and 2,4-hexanedione in aqueous solution

1989 ◽  
Vol 67 (8) ◽  
pp. 1305-1307 ◽  
Author(s):  
Carlos Blanco ◽  
José M. Hernando ◽  
Manuel Mateo
Keyword(s):  
Aqueous Solution ◽  
Concentration Dependence ◽  
Rate Constants ◽  
Metal Ion ◽  
Reversible Reaction ◽  
First Order ◽  
Pseudo First Order ◽  
Enol Tautomer ◽  
Metallic Species ◽  
Mechanism Of The Reaction

The kinetics and mechanism of the reaction between Cr(III) and 2,4-hexanedione in aqueous solution have been studied. Complexation occurs by coordination of both oxygen atoms of the ligand to the chromium(III) center, with concomitant loss of a proton yielding 1:1 complex of the type [Cr(CH3COCHCOC2H5)(H2O)4]2+. When the metal ion is in pseudo first-order excess the concentration dependence of the observed rate constants agrees with a mechanism involving reversible reaction between the enol tautomer of 2,4-hexanedione and the metallic species Cr(H2O)63+ and Cr(H2O)5OH2+, with rate constants of 8.0 × 10−4 and 3.5 × 10−2 dm3 mol−1 s−1, respectively. Keywords: chromium(III), β-diketones, β-diketonates, kinetics, complexation.

Effect of β-cyclodextrin on the reaction of α-amino acid anions with p-nitrophenyl acetate and p-nitrophenyl hexanoate

1997 ◽  
Vol 75 (1) ◽  
pp. 83-91 ◽  
Author(s):  
Oswald S. Tee ◽  
Timothy A. Gadosy ◽  
Javier B. Giorgi
Keyword(s):  
Aqueous Solution ◽  
Amino Acids ◽  
Data Analysis ◽  
Amino Acid ◽  
Rate Constants ◽  
First Order ◽  
Yield Rate ◽  
Pseudo First Order ◽  
Rate Ratios ◽  
Kinetics Of

The effects of β-cyclodextrin (β-CD) on the kinetics of the reaction of α-amino acid anions with p-nitrophenyl acetate (pNPA) and p-nitrophenyl hexanoate (pNPH) have been investigated. Pseudo-first-order rate constants obtained with various concentrations of nucleophile and β-CD, in aqueous solution at pH 9.88, were analyzed to yield rate constants for reaction of the nucleophiles with free ester (kN) and with ester bound to β-CD (kcN). For pNPA reacting with amino acids that bind weakly to β-CD, if at all, the ratio kcN/kN is very close to one, but for amino acids that bind appreciably to β-CD this ratio is greater than one (up to 3.5). Generally similar behaviour is observed for reactions with pNPH, but the rate ratios are smaller and all less than one. These findings are comparable to those obtained in this laboratory for the CD-mediated reactions of p-nitrophenyl alkanoate esters with other nucleophiles, including simple alkylamines that bind quite strongly to CDs, but they differ from those reported in an earlier study of the reaction of pNPA with amino acid anions (Can. J. Chem. 69, 1124 (1991)) where the data analysis suggested more substantial catalysis by cyclodextrins. Key words: amino acids, cyclodextrin, ester cleavage, kinetics, catalysis.

A kinetic standard for precise calibration of spectrophotometer cell temperature.

1981 ◽  
Vol 27 (5) ◽  
pp. 753-755 ◽  
Author(s):  
P A Adams ◽  
M C Berman
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Cell Temperature ◽  
First Order ◽  
Order Rate ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

Abstract We describe a simple, highly reproducible kinetic technique for precisely measuring temperature in spectrophotometric systems having reaction cells that are inaccessible to conventional temperature probes. The method is based on the temperature dependence of pseudo-first-order rate constants for the acid-catalyzed hydrolysis of N-o-tolyl-D-glucosylamine. Temperatures of reaction cuvette contents are measured with a precision of +/- 0.05 degrees C (1 SD).

scholarly journals Photocatalytic degradation of sulfamethazine in aqueous solution using ZnO with different morphologies

2018 ◽  
Vol 5 (4) ◽  
pp. 171457 ◽  
Author(s):  
Zhigang Yi ◽  
Juan Wang ◽  
Tao Jiang ◽  
Qiong Tang ◽  
Ying Cheng
Keyword(s):  
Aqueous Solution ◽  
Photocatalytic Degradation ◽  
Reaction System ◽  
Degradation Pathway ◽  
Order Reaction ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Different Shapes ◽  
Pseudo First Order ◽  
Release Ratio

In this study, photocatalytic experiments of 20 mg l −1 sulfamethazine (SMN) in aqueous solution containing ZnO with different morphologies, tetra-needle-like ZnO (T-ZnO), flower-like ZnO (F-ZnO) and nanoparticles ZnO (P-ZnO), were performed. The results indicated that photocatalytic degradation of SMN was effective and followed the pseudo-first-order reaction, but the degree of SMN mineralization showed obvious differences using ZnO with different shapes. After 12 h irradiation, 86%, 71% and 50% of the initial total organic carbon was eliminated in SMN suspension containing T-ZnO, F-ZnO and P-ZnO, respectively. The release ratio of sulfur was close to 100% in the presence of T-ZnO, but reached to 86% and 67% in the presence of F-ZnO and P-ZnO, respectively. The release ratio of nitrogen was about 76%, 63% and 40% using T-ZnO, F-ZnO and P-ZnO as photocatalyst, respectively. The morphology of ZnO played an important role in determining its catalytic activity. Seven intermediates were observed and identified in the UV/T-ZnO reaction system by LC-MS/MS analysis, and a possible degradation pathway was proposed.

On the Chemical Reactivity of the Phytochrome Chromophore in the Pr and Pfr Form

1985 ◽  
Vol 40 (3-4) ◽  
pp. 215-218 ◽  
Author(s):  
Fritz Thümmler ◽  
Peter Eilfeld ◽  
Wolfhart Rüdiger ◽  
Doo-Khil Moon ◽  
Pill-Soon Song
Keyword(s):  
Reaction Kinetics ◽  
Rate Constants ◽  
Chemical Reactivity ◽  
Order Reaction ◽  
First Order Reaction ◽  
Limiting Factor ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo First Order ◽  
The Difference

The reactivity of the phytochrome chromophore and related tetrapyrroles towards ozone and tetranitromethane was investigated. Both oxidizing reagents cause bleaching of the main absorp­tion band of the pigment. The rate constants for this bleaching were determined under conditions of pseudo first order reaction kinetics. The rate constants for the reaction with ozone are similar for native phytochrome and for freely accessible tetrapyrroles (biliverdin, small chromopeptides from phytochrome) indicating that accessibility is not the limiting factor for the reaction with ozone. Under a variety of conditions, the Pfr chromophore reacts by about 10% faster than the Pr chromophore. This may reflect the true difference in reactivity. The rate constants for the reaction with tetranitromethane are much larger for biliverdin, bilirubin and small chromopeptides from phytochrome than for native phytochrome. The limiting factor for this reaction in native phytochrome therefore is the accessibility of the chromophore by the reagent. Previous conclusions on the difference in exposure of the tetrapyrrole chromophore in Pr and Pfr are confirmed.

The mercury(II)-induced aquation of trans-Chloroamminebis(dimethylglyoximato)cobalt(III) complex

1975 ◽  
Vol 28 (5) ◽  
pp. 1133 ◽  
Author(s):  
S Chan ◽  
S Tan
Keyword(s):  
Rate Constants ◽  
Aqueous Ethanol ◽  
Association Constants ◽  
First Order ◽  
Order Rate ◽  
Leaving Group ◽  
Pseudo First Order ◽  
Activated Complex

The pseudo first-order rate constants for the mercury(II)-induced aquation of trans-[Co(Hdmg)2(NH3)Cl] (Hdmg = dimethylglyoximate ion) have been measured in aqueous and aqueous ethanol solutions (ethanol- water mole ratio 1 : 5.1) containing various excess amounts of mercury(II)ion at 273.2 K. Association constants of the complex formed with mercury(II) ion and rate constants for dissociation of the activated complex in both solutions have been calculated. The kinetic results are discussed in terms of formation of an activated complex Co-C1-Hg, followed by a simple rate-determining aquation in which HgCl+ acts as the leaving group.

Kinetics of the Ozonation of Tetrabromobisphenol-A in Wastewater

2011 ◽  
Vol 383-390 ◽  
pp. 2945-2950 ◽  
Author(s):  
Jie Zhang ◽  
Shi Long He ◽  
Mei Feng Hou ◽  
Li Ping Wang ◽  
Li Jiang Tian
Keyword(s):  
Rate Constants ◽  
Apparent Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Kinetic Studies ◽  
Tetrabromobisphenol A ◽  
First Order ◽  
Reaction Rate Constants ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of TBBPA degradation by ozonation in semi-batch reactor was studied. The reaction rate constants of TBBPA with O3 and •OH were measured by means of direct ozone attack and competition kinetics, and the values of which were 6.10 l/(mol•s), 4.8×109 l/(mol•s), respectively. Results of kinetic studies showed that TBBPA degradation by ozonation under the different conditions tested followed the pseudo-first-order. The values of apparent rate constant of TBBPA degradation increased with the increase of ozone dosage and pH, but decreased with the increase of initial TBBPA concentration.

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