The hydration of mesitylketene in aqueous solution: detection of acid catalysis for an aromatic ketene

1995 ◽  
Vol 73 (4) ◽  
pp. 539-543 ◽  
Author(s):  
J. Andraos ◽  
A.J. Kresge ◽  
N.P. Schepp
Keyword(s):  
Aqueous Solution ◽  
Carbon Atom ◽  
Perchloric Acid ◽  
Reaction Rate ◽  
Acid Catalysis ◽  
Sodium Perchlorate ◽  
Nucleophilic Attack ◽  
Acid Solutions ◽  
Uncatalyzed Reaction ◽  
Acid Catalyzed

Mesitylketene was generated flash photolytically in aqueous solution by the photo-Wolff reaction of 2,4,6-trimethyldiazoacetophenone and also by rearrangement of mesitylynol obtained through photodecarbonylation of mesitylhydroxycyclopropenone, and rates of hydration of this ketene were measured in dilute perchloric acid, sodium perchlorate, and sodium hydroxide solutions as well as in concentrated sodium perchlorate and perchloric acid solutions. In dilute solution only an uncatalyzed reaction and a sodium-hydroxide-catalyzed process were observed, both of which could be attributed to nucleophilic attack, by water and by hydroxide ion, respectively, at the ketene carbonyl carbon atom. In concentrated sodium perchlorate solutions, a mild decrease in reaction rate with increasing salt concentration was observed, as expected on the basis of decreasing water activity and a consequent slowing of the uncatalyzed reaction. A similar mild decrease was found in perchloric acid solutions up to [Formula: see text] but this then gave way to a rate increase that became dominant above [Formula: see text] This appearance of acid catalysis indicates a change in reaction mechanism from nucleophilic attack of water to an electrophilic process involving rate-determining protonation on the β-carbon atom of the ketene group. Analysis of the acid-catalyzed reaction rate by the Cox–Yates method gives the catalytic coefficient [Formula: see text] This, when compared with [Formula: see text] for ketene itself, shows that the mesityl group retards acid-catalyzed hydration by a factor of 2200, and consequently the acid-catalyzed reaction of this, and other aromatic ketenes as well, becomes apparent only under strongly acidic conditions. Keywords: mesitylketene, ketene hydration, acid catalysis, Cox–Yates excess acidity correlation.

Kinetics of the Decomposition of Sulphur Dicyanide in Aqueous Solution

1962 ◽  
Vol 15 (2) ◽  
pp. 211 ◽  
Author(s):  
W Kitching ◽  
RH Smith ◽  
IR Wilson
Keyword(s):  
Aqueous Solution ◽  
Aqueous Solutions ◽  
Nucleophilic Substitution ◽  
Perchloric Acid ◽  
Reaction Path ◽  
Acid Solutions ◽  
Kinetics Of

The kinetics and stoicheiometry of the decomposition of aqueous solutions of sulphur dicyanide have been studied at temperatures between 0-70 �C and in media ranging from dilute perchloric acid to pH 7. The predominant reaction is nucleophilic substitution at carbon, but in perchloric acid solutions an alternative reaction path has been revealed.

Kinetics and Mechanism of Oxidation of Selenium(IV) by Permanganate Ion in Aqueous Perchlorate Solutions

1993 ◽  
Vol 58 (3) ◽  
pp. 538-546 ◽  
Author(s):  
Refat M. Hassan ◽  
Sahr A. El-Gaiar ◽  
Abd El-Hady M. El-Summan
Keyword(s):  
Reaction Mechanism ◽  
Reaction Rate ◽  
Oxidation Process ◽  
Selenium Dioxide ◽  
Order Reaction ◽  
Acid Solutions ◽  
First Order ◽  
Acid Catalyzed ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

The kinetics of permanganate oxidation of selenium dioxide in perchloric acid solutions at a constant ionic strength of 2.0 mol dm-3 has been investigated spectrophotometrically. A first-order reaction in [MnO4-] and fractional order with respect to selenium(IV) were observed. The reaction rate was found to be pH-independent at lower acid concentrations ([H+] < 0.5 mol dm-3) and was acid-catalyzed beyond this range. Addition of Mn2+ and F- ions leads to the prediction that MnO4- is the sole reactive species in the oxidation process. A tentative reaction mechanism consistent with the reaction kinetics has been proposed.

scholarly journals OXIDATION OF BENZALDEHYDE BY QUINOXALINIUM DICHROMATE

2016 ◽  
Vol 12 (9) ◽  
pp. 4396-4403 ◽  
Author(s):  
K Anbarasu ◽  
N. GEETHA
Keyword(s):  
Acetic Acid ◽  
Perchloric Acid ◽  
Reaction Rate ◽  
Sodium Perchlorate ◽  
Activation Parameters ◽  
Probable Mechanism ◽  
Water Medium ◽  
First Order ◽  
Rate Of Reaction ◽  
Acetic Acid Water

The kinetics and mechanism of oxidation of benzaldehyde by quinoxalinium dichromate has been studied in the presence of perchloric acid in 70 % acetic acid - water medium. The reaction follows first order with respect to benzaldehyde, quinoxalinium dichromate and fractional order with respect to perchloric acid. There is no effect on the reaction rate with increase in ionic strength of the medium by adding sodium perchlorate. The rate of reaction increases with increase in the percentage of acetic acid. The reaction does not induce the polymerization with acrylonitrile. The rate of reaction decreases with increase in the concentration of manganoussulphate. The thermodynamic and activation parameters have been calculated and a probable mechanism has been proposed.

PRESSURE EFFECT AND MECHANISM IN ACID CATALYSIS: VIII. HYDROLYSIS OF ACETAMIDE AND BENZAMIDE

1961 ◽  
Vol 39 (5) ◽  
pp. 1101-1108 ◽  
Author(s):  
A. R. Osborn ◽  
T. C-W. Mak ◽  
E. Whalley
Keyword(s):  
Water Molecule ◽  
Transition State ◽  
Perchloric Acid ◽  
Acid Catalysis ◽  
Pressure Effect ◽  
Protonated Form ◽  
Dilute Acid ◽  
Additional Information ◽  
Acid Catalyzed ◽  
Hydrolysis Of

The effect of pressures up to 3 kbar on the rate of the acid-catalyzed hydrolysis of acetamide and benzamide in both dilute and concentrated perchloric acid has been measured. The volumes of activation in dilute acid are consistent with a transition state that is not highly polar. It follows from this that if the attacking water molecule adds to the amidium ion then the reactive amidium ion is the O-protonated form, and if the attacking water molecule substitutes then the reactive amidium ion is the N-protonated form.The volume of activation for acetamide in concentrated acid provides no additional information about the mechanism. That for benzamide in concentrated acid is tentatively interpreted as favoring the O-protonated benzamidium ion as the reactive ion.

Kinetics of acid-catalyzed hydration in aqueous solution of 1-methoxy- and 1-methylthio-2-phenylethyne and some related acetylenes

1987 ◽  
Vol 65 (2) ◽  
pp. 441-444 ◽  
Author(s):  
N. Banait ◽  
M. Hojatti ◽  
P. Findlay ◽  
A. J. Kresge
Keyword(s):  
Aqueous Solution ◽  
Proton Transfer ◽  
Isotope Effect ◽  
Rate Constants ◽  
Acid Catalysis ◽  
The Other ◽  
Buffer Solutions ◽  
Hydronium Ion ◽  
Acid Catalyzed ◽  
Kinetics Of

The rates of conversion of C6H5C≡COCH3 to C6H5CH2CO2CH3 were measured in dilute HClO4/H2O, DCIO4/D2O, and H3PO4–H2PO2−/H2O buffer solutions, and the rates of conversion of C6H5C≡CSCH3 to C6H5CH2COSCH3, C6H5C≡CH to C6H5COCH3, 2,4,6-(CH3)3C6H2C≡CH to 2,4,6-(CH3)3C6H2COCH3, and p-CH3OC6H4C≡CCH3 to p-CH3OC6H4COCH2CH3 were measured in concentrated HClO4/H2O solutions, all at 25 °C. The reaction of C6H5C≡COCH3 showed general acid catalysis and gave the isotope effect [Formula: see text], which indicates that it proceeds through rate-determining proton transfer from catalyst to substrate. The hydronium ion catalytic coefficient for this reaction is [Formula: see text], and those for the other four, in the order given above, are [Formula: see text], and 8.5 × 10−6 M−1 s−1. Relative reactivities based on these rate constants are discussed.

Untersuchungen über die Kinetik der Spaltung von Di- und Tripeptiden

1964 ◽  
Vol 19 (12) ◽  
pp. 1095-1100 ◽  
Author(s):  
Hermann Hartmann ◽  
Joachim Heidberg
Keyword(s):  
Aqueous Solution ◽  
Hydrochloric Acid ◽  
Freeze Drying ◽  
Proteolytic Enzymes ◽  
Pure Water ◽  
Peptide Bond ◽  
Nucleophilic Attack ◽  
Acid Solutions ◽  
Hydrochloric Acid Solutions ◽  
Hydrolysis Of

The kinetic data of the hydrolysis of some serine peptides in diluted hydrochloric acid and in pure water and of the rearrangement of O-glycyl-DL-serine to glycyl-DL-serine were determined.The hydrolysis of glycyl-DL-serine and DL-alanyl-DL-serine proceeds surprisingly rapidly in pure water as compared with the hydrolysis of those peptides in 0.5 N hydrochloric acid as well as the hydrolysis of glycyl-DL-alanine in purely aqueous solution. The O → N migration of the glycyl residue in O-glycyl-DL-serine which probably is an intermediate in the cleavage of glycyl-DL-serine in purely aqueous solution represents a three center reaction in which the nucleophilic attack on the O-peptide and peptide bond, respectively, involves a free basic amino group. The analogy between the serine peptide interconversion and the hydrolysis catalyzed by certain proteolytic enzymes is referred to.Under the conditions of freeze drying are formed in hydrochloric acid solutions of DL-alanyl-DL-serine O-peptide and depsipeptide.

scholarly journals Kinetics of the base-catalyzed bromination of ethyl cyclopentanone 2 -carboxylate

1948 ◽  
Vol 192 (1031) ◽  
pp. 479-489 ◽  
Keyword(s):  
Aqueous Solution ◽  
Acid Catalysis ◽  
Bromine Atom ◽  
Acid Solutions ◽  
Buffer Solutions ◽  
Hydrochloric Acid Solutions ◽  
Carboxylate Anions ◽  
Basic Catalysts ◽  
Bromine Concentration ◽  
Kinetics Of

The kinetics of the bromination of ethyl cyclopentanone 2-carboxylate in the presence o f a number of basic catalysts have been investigated in aqueous solution at 25° C. Under the conditions chosen the bromination proceeds to completion and its rate is independent o f the bromine concentration, being determined by the rate of transfer of a proton to the catalyzing species. Since only one bromine atom is introduced, the kinetics are free from com plications due to successive stages. N o detectable acid catalysis occurs. Values o f the catalytic constants o f seven basic species have been determined from measurements in buffer solutions and in hydrochloric acid solutions. The relation between the catalytic constants o f the four carboxylate anions studied is accurately expressed by an equation of the form due to Bronsted. The ion H 2 P0 4 does not obey this equation. In its general kinetic behaviour the bromination of ethylcyclopentanone 2-carboxylate is found to conform to the regularities previously shown in the ionization of related substrates.

Acid-catalyzed enolization of acetophenone: catalysis by bisulfate ion in sulfuric acid solutions

1986 ◽  
Vol 64 (6) ◽  
pp. 1224-1227 ◽  
Author(s):  
J. R. Keeffe ◽  
A. J. Kresge ◽  
J. Toullec
Keyword(s):  
Aqueous Solution ◽  
Sulfuric Acid ◽  
Acidity Constant ◽  
Acidity Function ◽  
Acid Solutions ◽  
Dilute Aqueous Solution ◽  
Acid Catalyzed ◽  
The Difference ◽  
Carbon Acid ◽  
Sulfuric Acid Solutions

Rates of acid-catalyzed enolization of acetophenone in dilute aqueous solution, measured under conditions where the solvated proton is the only acidic species present, give a hydrogen ion catalytic coefficient, [Formula: see text], that is 35% smaller than the value obtained by X acidity function extrapolation of measurements made in moderately concentrated sulfuric acid solutions. The difference may be attributed to catalysis by bisulfate ion in the sulfuric acid solutions; this is supported by direct measurement of the bisulfate ion catalytic coefficient in dilute sulfuric acid. This revised value of [Formula: see text] leads to new, but only slightly different, values of the keto–enol equilibrium constant for acetophenone in aqueous solution, pKE = 7.96 ± 0.04, the acidity constant for acetophenone ionizing as a carbon acid, [Formula: see text] and the encounter-controlled rate constant for the reaction of acetophenone enol with molecular bromine, k = (3.2 ± 0.4) × 109 M−1 s−1.

Distribution of dibenzyl sulfoxide between the aqueous and organic phases

1979 ◽  
Vol 44 (6) ◽  
pp. 1918-1924 ◽  
Author(s):  
František Vláčil ◽  
Huynh Dang Khanh
Keyword(s):  
Aqueous Solution ◽  
Nitric Acid ◽  
Perchloric Acid ◽  
Distribution Ratio ◽  
Protonation Constant ◽  
Metal Salts ◽  
Acid Solutions ◽  
Lower Solubility ◽  
Extraction Constants ◽  
Distribution Constants

The distribution of dibenzyl sulfoxide (DBSO) between toluene or tetrachloromethane and aqueous solution of nitric, hydrochloric, or perchloric acid was investigated for different acid concentrations. The solubility of DBSO in the two solvents was established (0.0555 mol l-1 in toluene, 0.0121 mol l-1 in tetrachloromethane at 20 °C) and its distribution constants KD were determined for the systems toluene-water and CCl4-water (133.7 and 27.4, respectively, at 20 °C). Employing the dependence of the distribution ratio of DBSO on the Hammett function for nitric and perchloric acids solutions (1-6M) and taking into account the extraction of the solvates of these acids as described previously, the value of the DBSO protonation constant was calculated to be KH1 (B + H+ ##e BH+) = 1.00 . 10-2, and more accurate values of the extraction constants of the nitric acid solvates were obtained, Kex1 (HNO3 . B) 1.1 . 10-3 and Kex2 ((HNO3)2 . B) 4.3 . 10-5. Owing to the lower solubility of DBSO in water as well as in acid solutions as compared with aliphatic or cyclic sulfoxides and also with tri-n-butylphosphate, solution of DBSO in toluene suits better as the stationary phase for extraction chromatography of metal salts.

Substituent effects in the intramolecular photoredox reactions of benzophenones in aqueous solution

2007 ◽  
Vol 85 (9) ◽  
pp. 561-571 ◽  
Author(s):  
Nikola Basarić ◽  
Devin Mitchell ◽  
Peter Wan
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Acid Catalysis ◽  
Secondary Alcohol ◽  
Substituent Effects ◽  
Phenyl Substituent ◽  
Aqueous Acid ◽  
Single Compound ◽  
Acid Catalyzed

A number of α-hydroxy-3-benzylbenzophenones 7–11 have been synthesized for the purpose of studying the effect of a phenyl substituent on the intramolecular photoredox reaction of 3-(hydroxymethyl)benzophenone (5) discovered in our laboratory. This latter compound was found to undergo a unimolecular (formal) intramolecular redox reaction upon photolysis in aqueous acid that results in clean reduction of the benzophenone ketone (to secondary alcohol) and oxidation of the alcohol to aldehyde. Three of the phenyl-substituted compounds with simple phenyl (7), p-methylphenyl (8), and p-methoxyphenyl (9) were found to undergo the acid-catalyzed intramolecular photoredox reaction with the observation that 9 also undergoes a residual photoredox reaction that is not acid-mediated and may involve initial photoinduced electron transfer, which is supported by LFP data. The m-methoxyphenyl (10) compound did not undergo the reaction. The trend in observed relative reactivity may be partially rationalized by examining changes in molecular orbital coefficients observed in the calculated HOMOs and LUMOs. The photoredox reaction has also been applied twice in succession in a single compound 11, demonstrating that the photoredox reaction may be useful for sequential photoredox reactions in a multifunctional compound.Key words: intramolecular photoredox, acid catalysis, meta effect, benzophenone photochemistry.

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