Kinetics and mechanism of hydrolysis of aryl N-methoxycarbamates and their derivatives

1983 ◽  
Vol 48 (3) ◽  
pp. 900-905 ◽  
Author(s):  
Jaromír Mindl ◽  
Vojeslav Štěrba
Keyword(s):  
Rate Constants ◽  
Dissociation Constants ◽  
Ion Concentration ◽  
Ph Dependency ◽  
Hydroxyl Ion ◽  
Mechanism Of Hydrolysis ◽  
Elimination Mechanism ◽  
Methyl Derivatives ◽  
Ph Range ◽  
Hydrolysis Of

Hydrolysis kinetics have been studied of 3- and 4-substituted phenyl N-methoxycarbamates and their N-methyl derivatives in aqueous buffers at 60 °C. The N-methyl derivatives show linear dependence of the rate constants on concentration of hydroxyl ion in the pH range measured. Hydrolysis of aryl N-methoxycarbamates is independent of hydroxyl ion concentration at higher pH values. Logarithms of the rate constants have been correlated with the substituent constants σ. The calculated values 0.9 for N-methyl derivatives, 4.5 and 3.3 for aryl N-methoxy-carbamates in the region of linear pH-dependency and pH-independency, respectively, suggest that the hydrolysis follows the BAC2 and ElcB mechanisms in the case of the N-methyl derivatives and aryl N-methoxycarbamates, respectively. Difference between the two ρ constants for the hydrolysis of aryl N-methoxycarbamates agrees with the found value ρ = 1.2 for dissociation constants of these compounds. The elimination mechanism has been confirmed by reaction of the isocyanate formed with added aniline to give the respective urea.

scholarly journals Hydrolysis of p-NN′-phenylenebismaleimide and its adducts with cysteine. Implications for cross-linking of proteins

1979 ◽  
Vol 179 (1) ◽  
pp. 191-197 ◽  
Author(s):  
P Knight
Keyword(s):  
Second Order ◽  
Ion Concentration ◽  
Cross Linking ◽  
Imide Ring ◽  
Hydroxyl Ion ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Competing Reactions

To understand the extent of the cross-linking of proteins by the bifunctional reagent p-NN′-phenylenebismaleimide, a quantitative study of competing reactions has been undertaken. The two reactive maleimide rings of the bismaleimide are hydrolysed in mildly alkaline aqueous solutions much more rapidly than is the single maleimide ring of the monofunctional analogue N-ethylmaleimide. The kinetics of hydrolysis are second-order, depending on both imide and hydroxyl ion concentration in the pH range 8-10. The hydrolysis of the first imide ring of the bismaleimide is more rapid than the second, with second-order rate constants of 1600 M-1 . s-1 and 500 M-1 . s-1 respectively, at 25 degrees C. The half-times for hydrolysis of the first and second imide rings at pH 9.0 are therefore only 43s and 140s. Because it renders the maleimide ring unreactive towards cysteine, this rapid hydrolysis can limit the extent of cross-linking of proteins by the bismaleimide.

Micellar catalysis of organic reactions. VIII. Kinetic studies of the hydrolysis of 2-acetyloxybenzoic acid (aspirin) in the presence of micelles

1982 ◽  
Vol 35 (7) ◽  
pp. 1357 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Aqueous Solution ◽  
Cetyltrimethylammonium Bromide ◽  
Cetylpyridinium Chloride ◽  
Kinetic Studies ◽  
Base Catalysis ◽  
Plateau Region ◽  
General Base ◽  
Mechanism Of Hydrolysis ◽  
Ph Range ◽  
Hydrolysis Of

The hydrolysis of 2-acetyloxybenzoic acid in the pH range 6-12 has been studied in the presence of micelles of cetyltrimethylammonium bromide (ctab) and cetylpyridinium chloride (cpc). In the plateau region (pH 6-8) the hydrolysis is inhibited by the presence of micelles, while in the region where the normal BAC2 hydrolysis (pH > 9) occurs the reaction is catalysed by micelles of ctab and cpc. The mechanism of hydrolysis in the plateau region is shown to involve general base catalysis by the adjacent ionized carboxy group both in the presence and absence of micelles. This reaction is inhibited in the presence of micelles because the substrate molecules are solubilized into the micelle and water is less available in this environment than in normal aqueous solution.

Stability of the Nerve Gas Antidote BIS (4-Hydroxyiminomethyl-1-Pyridinomethyl) Ether Dichloride (Toxogonin®)

1968 ◽  
Vol 2 (9) ◽  
pp. 234-243 ◽  
Author(s):  
Inga Christenson
Keyword(s):  
Aqueous Solution ◽  
Hydrochloric Acid ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Kinetics Of Hydrolysis ◽  
Dilute Aqueous Solution ◽  
Nerve Gas ◽  
Ph Range ◽  
Kinetics Of ◽  
Hydrolysis Of

The products and kinetics of hydrolysis of the nerve gas antidote bis(4-hydroxyiminomethyl - 1 - pyridinemethyl) ether dichloride (Toxogonin ®) have been investigated. A survey of these studies is given: The hydrolytic reactions were studied in the pH range 1 M hydrochloric acid to 1 M sodium hydroxide at 25, 45, 75 and 85° C. Rate constants were determined in dilute aqueous solution, generally with an initial Toxogonin concentration of 0.01 mg per ml. In addition, a report is given concerning two-year storage of 25 percent (w/v) Toxogonin solutions at pH 2.5, 3.0 and 3.5. The solutions were stored in glass or polypropylene ampuls at 5, 15, 25 and 45°C. At 5 and 15C° decomposition was negligible, at 25 and 45 °C average decomposition was 1.5 percent and 3.3 percent, respectively.

An anomalous effect of methyl group on acidity of acylthioureas

1987 ◽  
Vol 52 (8) ◽  
pp. 1992-1998 ◽  
Author(s):  
Jaromír Kaválek ◽  
Josef Jirman ◽  
Vladimír Macháček ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Acetyl Derivative ◽  
Methyl Groups ◽  
Anomalous Effect ◽  
Methyl Group ◽  
Methyl Derivatives

Dissociation constants and methanolysis rate constants have been measured of 1-acetyl- and 1-benzoylthioureas and their N-methyl derivatives. Replacement of hydrogen atom at N(1) (next to the acyl group) by methyl group increases the acidity of the benzoyl derivative by one order, that of the acetyl derivative by as much as two orders of magnitude. Replacement of both hydrogens at N(3) by methyl groups lowers the methanolysis rate constant by more than two orders, whereas the replacement of hydrogen atom at N(1) by methyl group increases the methanolysis rate by the factor of 30.

Role of trinuclear Zn(II) complexes in promoting the hydrolysis of 4-nitrophenyl acetate

2004 ◽  
Vol 82 (3) ◽  
pp. 409-417 ◽  
Author(s):  
Qing-Chun Ge ◽  
Yan-He Guo ◽  
Hai Lin ◽  
Dong-Zhao Gao ◽  
Hua-Kuan Lin ◽  
...  
Keyword(s):  
Rate Constants ◽  
Volume Fraction ◽  
Bound Water ◽  
Catalytic Efficiency ◽  
Active Species ◽  
Nucleophilic Attack ◽  
Carboxyl Oxygen Atom ◽  
Ph Range ◽  
Hydrolysis Of

Potentiometric determination shows that trinuclear Zn(II) complexes of the four tripods 1,3,5-tri(2′,5′-diazahexyl)benzene (L1), 1,3,5-tri(2′,5′-diazaheptyl)benzene (L2), 1,3,5-tri(2′,5′-diazaoctyl)benzene (L3), and 1,3,5-tri(2′,5′-diazanonyl)benzene (L4) could be potential hydrolytic catalysts. CH3CN solutions containing [3Zn:L]T (0.5~2 × 10–3 mol·dm–3) with I = 0.10 mol·dm–3 of KNO3 and Good's buffer (10% volume fraction) were studied for the catalyzing hydrolysis of p-nitrophenyl acetate (NA, 0.5~2 × 10–3 mol·dm–3), at 298 K, in the 6.5–8.2 pH range. The observed rate constants, kobs, fit the equilibrium equation kobs = kcom [3Zn:L]T + kOH[OH–] + k0. The sigmoid pH~kcom profiles for NA hydrolysis suggest that either the Zn(II)-bound hydroxyl or the Zn(II)-bound water forms of the catalysts can be the active species. The observed second-order rate constants are 0.0082, 0.011, 0.0059, and 0.0019 mol–1·dm3·s–1 for the four Zn3L–H2O complexes (kA) and 0.342, 0.257, 0.382, and 0.091 mol–1·dm3·s–1 for the four Zn3L–OH- groups (kB), respectively. However, under the condition that [NA] = 0.5 × 10–3 mol·dm–3 and [3Zn:L1]T = 2~4 × 10–2 mol·dm–3 at pH 7.6, the observed rate constants, kobs, obey the equilibrium kobs = kcom[3Zn:L]T/(1/K′ + [3Zn:L]T). This indicates that the 3:1 complex (or its deprotonated hydroxide form) mediates NA hydrolysis by nucleophilic attack of the carboxyl center with the pre-formation of a coordination bond between the carboxyl oxygen atom and the Zn(II) ion. Comparison with other models was made, and the reasons for the high catalytic efficiency of the tripodal complexes were given.Key words: tripod, Zn(II), catalysis, NA hydrolysis, polynuclear.

Kinetics and mechanism of the reaction of dimethyl acetylphosphonate with water. Expulsion of a phosphonate ester from a carbonyl hydrate

1978 ◽  
Vol 56 (13) ◽  
pp. 1792-1795 ◽  
Author(s):  
Ronald Kluger ◽  
David C. Pire ◽  
Jik Chin
Keyword(s):  
Rate Constant ◽  
Electronic Effect ◽  
Order Rate Constant ◽  
Ion Concentration ◽  
First Order ◽  
Cleavage Reactions ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Hydrolysis Of ◽  
Mechanism Of The Reaction

Dimethyl acetylphosphonate (DAP) is rapidly cleaved in water to acetate and dimethylphosphonic acid. The half time for reaction at pH 7, 25 °C is estimated to be 3 s. The reaction is first order in hydroxide ion concentration and first order in DAP concentration. Rates of reaction were measured over the pH range 3.8 to 6.5 at 25 °C, 6.5 and 7.0 at 5 °C, 4.5 to 6.5 at 35 °C, and 4.5 to 6.0 at 45 °C. The average observed second-order rate constant at 25 °C is 2.4 × 106M−1 s−1. DAP is converted rapidly to a hydrated carbonyl adduct. The mechanism for the formation of the observed products is proposed to be analogous to cleavage reactions of other carbonyl hydrates, proceeding from a monoanion conjugate in this case. The estimated rate constant for the unimolecular cleavage of the carbonyl hydrate anion is 2 × 103 s−1. The rapid hydrolysis of DAP results from energetically favourable formation of a hydrate due to the electronic effect of the phosphonate diester. This effect also promoles ionization of the hydrate. The ionized hydrate readily expels the phosphonate diester to achieve the overall rapid hydrolysis.

The uncatalysed, and the imidazole and o-mercaptobenzoic acid catalysed, hydrolysis of p-nitrophenyl N-benzyloxycarbonylglycinate

1969 ◽  
Vol 22 (1) ◽  
pp. 109 ◽  
Author(s):  
RW Hay ◽  
RJ Trethewey
Keyword(s):  
Active Species ◽  
Ion Concentration ◽  
Nucleophilic Catalysis ◽  
First Order ◽  
Catalysed Reaction ◽  
Catalytically Active ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The uncatalysed hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate has been studied in 40% (v/v) ethanol-water over the pH range 7.6-8.5. The reaction shows a first-order dependence on the hydroxide ion concentration. The quite rapid hydrolysis (k = (4.4�0.4) x 104 1. mole-1 min-1 at 20�) may possibly indicate the formation of a 2-benzyloxyoxazoline-5-one intermediate. ��� Unlike the hydrolysis of the p-nitrophenyl esters of α-amino acids, the hydrolysis of the N-protected derivatives is not catalysed by carbon dioxide. The hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate is, however, catalysed by imidazole in 40% v/v ethanol-water. Unprotonated imidazole (Im) is the catalytically active species. N-Benzyloxycarbonylaminoacetylimidazole has been detected spectrophotometrically as an intermediate in the reaction, indicating nucleophilic catalysis by the base. o-Mercaptobenzoic acid was also found to catalyse the hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate. pH-rate profile studies indicate that the dianion of o-mercaptobenzoic acid is the catalytically active species, the substrate presumably hydrolysing via the thioester intermediate Z- NHCH2COSC6H4COO-, although efforts to detect such an intermediate have been unsuccessful. Some evidence for a thioester intermediate in the L- cysteine-catalysed reaction has been obtained.

The hydrolysis of some N-benzoylamino acids in dilute mineral acid

1967 ◽  
Vol 45 (17) ◽  
pp. 1921-1924 ◽  
Author(s):  
J. B. Capindale ◽  
H. S. Fan
Keyword(s):  
Carboxylic Acid ◽  
Hydrochloric Acid ◽  
Glutamic Acid ◽  
Rate Constants ◽  
Mineral Acid ◽  
Dilute Solution ◽  
Acid Catalyzed ◽  
Ph Range ◽  
Hydrolysis Of ◽  
Derivatives Of

The behavior of N-benzoylaspartic acid and N-benzoylglutamic acid has been investigated at 100° in dilute solution in water and aqueous hydrochloric acid within the pH range 3.1–0.5. Some data are presented concerning the hydrolysis of the N-benzoyl derivatives of alanine, β-alanine, leucine, glycine, serine, and β-ethanolamine in water, 0.1 N hydrochloric acid, and 2 N hydrochloric acid. Benzoylglutamic acid undergoes a pH-independent conversion into pyrrolid-2-one-5-carboxylic acid, which then hydrolyses in mineral acid to glutamic acid; however, N-benzoylaspartic acid, under similar conditions, hydrolyses much more rapidly by a route which does not involve the corresponding lactam as an intermediate. In anhydrous alcohols the solvolysis of N-benzoylaspartic acid gives mixtures of aspartic acid and the β ester.First-order rate constants have been obtained for the acid-catalyzed hydrolysis of pyrrolid-2-one-5-carboxylic acid (I) and azetidin-2-one-4-carboxylic acid (II) in water over this pH range.

N-Chlorination of secondary amides. I. Kinetics of N-chlorination of N-methyl acetamide

1969 ◽  
Vol 47 (14) ◽  
pp. 2561-2567 ◽  
Author(s):  
M. Wayman ◽  
E. W. C. W. Thomm
Keyword(s):  
Rate Constants ◽  
Reaction Rate ◽  
Hypochlorous Acid ◽  
Chloride Ion ◽  
Active Species ◽  
Ion Concentration ◽  
Kcal Mole ◽  
Ph Range ◽  
Kinetics Of ◽  
Secondary Amides

The rate of N-chlorination of N-methyl acetamide has been studied in acetate buffered hypochlorous acid solutions. The reaction rate is dependent upon pH, chloride ion concentration, and acetic acid concentration. The results fit the following rate expression[Formula: see text]The observed rate constant, kobs, has three components[Formula: see text]The results suggest that the active chlorinating species in the pH range 3.0–6.0 are HOCl, Cl2, and CH3COOCl, in order of increasing reactivity. The values of the corresponding rate constants at 25 °C are [Formula: see text], and [Formula: see text] l mole−1 min−1, the last two rate constants being related to k2 and k3 through the respective equilibrium constants.At temperatures near room temperature, the N-chlorination reaction has an apparent activation energy of 14 kcal/mole when Cl2 is the active species, and 5 kcal/mole when CH3COOCl is the chlorinating agent.

THE HYDROLYSIS OF THE CONDENSED PHOSPHATES: II (A). THE ROLE OF THE HYDROGEN ION IN THE HYDROLYSIS OF SODIUM PYROPHOSPHATE: II (B). THE DISSOCIATION CONSTANTS OF PYROPHOSPHORIC ACID

1954 ◽  
Vol 32 (2) ◽  
pp. 174-185 ◽  
Author(s):  
J. D. McGilvery ◽  
Joan Pedley Crowther
Keyword(s):  
Dissociation Constants ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Rate Equations ◽  
Hydrogen Ion Concentration ◽  
Pyrophosphoric Acid ◽  
Condensed Phosphates ◽  
Anionic Species ◽  
Hydrolysis Of

The general rate equations for the hydrolysis of pyrophosphate anion proposed by Muus have been proved to be inapplicable over the pH range 2.0 to 11.0. A general rate equation is proposed which is based on the assumption that each anionic species of pyrophosphoric acid hydrolyzes at a rate which depends on its concentration, and that the only role of the hydrogen ion concentration is to determine the proportion of each species present in the solution. A mechanism for the hydrolysis of pyrophosphate anion is suggested.The dissociation constants of pyrophosphoric acid have been determined at 65.5 °C. for the concentration range 0.08 to 0.18 molar.

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