Substitution of acyclic sugar acetals. Perchloric acid catalyzed acetolysis of poly-O-acetyl acyclic oxygen and sulfur acetals and epimerization of monothioacetals

1967 ◽  
Vol 45 (13) ◽  
pp. 1467-1473 ◽  
Author(s):  
Norman H. Kurihara ◽  
Edgar Page Painter
Keyword(s):  
Acetic Acid ◽  
Perchloric Acid ◽  
Rate Constants ◽  
First Order ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Sugar Derivatives

The rate constants are reported for the substitution of acyclic sugar poly-O-acetyl diethyl dithioacetals, poly-O-acetyl diethyl acetals, and poly-O-acetyl dimethyl acetals and for the epimerization of poly-O-acetyl S-ethyl monothioacetals when catalyzed by perchloric acid in acetic acid. All the reactions are pseudo first order. Monothioacetals substitute faster than oxygen acetals, and oxygen acetals substitute faster than sulfur acetals. A group bonded to C1 of these acyclic sugar derivatives is substituted faster than when the group is bonded to C1 of poly-O-acetyl pyranose derivatives.

SUBSTITUTION OF ACYCLIC SUGAR ACETALS: RATE OF PERCHLORIC ACID CATALYZED ACETOLYSIS OF 2,3,4,5,6-PENTA-O-ACETYL-D-GLUCOSE DIETHYL DITHIOACETAL AND 1,2,3,4,5,6-HEXA-O-ACETYL-D-GLUCOSE S-ETHYL MONOTHIOACETAL

1966 ◽  
Vol 44 (15) ◽  
pp. 1773-1782 ◽  
Author(s):  
Norman H. Kurihara ◽  
Edgar Page Painter
Keyword(s):  
Acetic Acid ◽  
Acetic Anhydride ◽  
Perchloric Acid ◽  
Rate Constants ◽  
Acetoxy Group ◽  
Rate Determining Step ◽  
Conjugate Acid ◽  
Acid Catalyzed ◽  
Sugar Derivatives

The rate constants for the perchloric acid catalyzed substitution of one ethylthio group of 2,3,4,5,6-penta-O-acetyl-D-glucose diethyl dithioacetal (Va) and the acetoxy group bonded to C1 of 1,2,3,4,5,6-hexa-O-acetyl-D-glucose S-ethyl monothioacetal (VIa) have been measured when the substrates were dissolved in solutions of acetic acid and acetic anhydride. The rate-determining step is interpreted to be the dissociation of the substrate conjugate acid to give a carbonium–sulfonium cation. The rate constants indicate that acyclic sugar derivatives are substituted faster than cyclic (pyranose) derivatives, and that an acetoxy group is substituted faster than an ethylthio group.

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 Kinetics and Mechanism of the Change of the 4-Nitrobenzylthio-System into 4,4′-Diformylazoxybenzene in Alkaline Dioxane-Water Media

1985 ◽  
Vol 40 (11) ◽  
pp. 1128-1132
Author(s):  
Y. Riad ◽  
Adel N. Asaad ◽  
G.-A. S. Gohar ◽  
A. A. Abdallah
Keyword(s):  
Acetic Acid ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Main Product ◽  
Reaction Medium ◽  
Aqueous Dioxane ◽  
Proton Abstraction ◽  
First Order ◽  
Water Media ◽  
Different Temperatures

Sodium hydroxide reacts with α -(4-nitrobenzylthio)-acetic acid in aqueous-dioxane media to give 4,4'-diformylazoxybenzene as the main product besides 4,4'-dicarboxyazoxybenzene and a nitrone acid. This reaction was kinetically studied in presence of excess of alkali in different dioxane-water media at different temperatures. It started by a fast reversible a-proton abstraction step followed by two consecutive irreversible first-order steps forming two intermediates (α -hydroxy, 4-nitrosobenzylthio)-acetic acid and 4-nitrosobenzaldehyde. The latter underwent a Cannizzaro's reaction, the products of which changed in the reaction medium into 4,4'-diformylazoxybenzene and 4,4'-dicarboxyazoxybenzene. The rate constants and the thermodynamic parameters of the two consecutive steps were calculated and discussed. A mechanism was put forward for the formation of the nitrone acid.Other six 4-nitrobenzyl, aryl sulphides were qualitatively studied and they gave mainly 4,4'-diformylazoxybenzene beside 4,4'-dicarboxyazoxybenzene or its corresponding azo acid.

Acid-catalyzed Solvolysis of Isonitriles. I

1971 ◽  
Vol 49 (14) ◽  
pp. 2455-2459 ◽  
Author(s):  
Y. Y. Lim ◽  
A. R. Stein
Keyword(s):  
Formic Acid ◽  
Acid Catalysis ◽  
Hydrolysis Product ◽  
Rate Dependence ◽  
Linear Rate ◽  
First Order ◽  
Methyl Amine ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of methyl isonitrile has been examined. The initial hydrolysis product is N-methylformamide which is further hydrolyzed to methyl amine and formic acid at a much slower rate. The hydrolysis to N-methylformamide is pseudo-first order in methyl isonitrile and shows a linear rate dependence on concentration of general (buffer) acid at fixed pH. The significance of general acid-catalysis in terms of the mechanism of the hydrolysis is considered and taken as evidence for carbon protonation rather than nitrogen protonation as the initiating step.

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.

scholarly journals Kinetic Evidence of a Common Mechanism in the Oxidation by Chromium(vi) Complexes: Oxidation of Benzyl Alcohol

2000 ◽  
Vol 2000 (3) ◽  
pp. 114-115 ◽  
Author(s):  
Chockalingam Karunakaran ◽  
Sadasivam Suresh
Keyword(s):  
Acetic Acid ◽  
Benzyl Alcohol ◽  
Perchloric Acid ◽  
Mineral Acid ◽  
Common Mechanism ◽  
Aqueous Acetic Acid ◽  
First Order ◽  
Chromium Vi ◽  
Oxidation Of Benzyl Alcohol

The oxidation of benzyl alcohol by dichromate and seven chromium(VI) complexes in aqueous acetic acid in the presence of perchloric acid is first order each in the oxidants, the alcohol and the mineral acid. The oxidation conforms to the isokinetic and Exner relationships and follows a common mechanism.

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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