Hydrolysis of 4-Nitro-2-(trifluoroacetylamino)benzoic acid: Buffer catalysis, micellar catalysis and intramolecular general acid catalysis

1984 ◽  
Vol 37 (5) ◽  
pp. 977
Author(s):  
TJ Broxton
Keyword(s):  
Benzoic Acid ◽  
Acid Catalysis ◽  
Acidic Solution ◽  
Micellar Catalysis ◽  
Bond Breaking ◽  
Solution Rate ◽  
Solution Ph ◽  
General Acid ◽  
Ph Range ◽  
Hydrolysis Of

The hydrolysis of 4-nitro-2-(trifluoroacetylamino)benzoic acid was studied over the pH range 0-13. In strongly acidic solution (pH 0-3), intramolecular general acid catalysis was observed. In alkaline solution, rate determining protonation of the nitrogen atom of the intermediate complex formed by attack of hydroxide ion on the substrate, was observed. The alkaline hydrolysis was subject to significant micellar catalysis and this was accompanied by a change of mechanism to solvent assisted C-N bond breaking. At intermediate pH (4-8), the reaction was subject to significant buffer catalysis, and deprotonation of the intermediate formed by the attack of water on the substrate was proposed.

Intramolecular catalysis of organic reactions. III. Hydrolysis of 5-Nitro-2-(trifluoroacetylamino)benzoic acid

1983 ◽  
Vol 36 (9) ◽  
pp. 1885
Author(s):  
TJ Broxton
Keyword(s):  
Water Molecule ◽  
Benzoic Acid ◽  
Carboxy Group ◽  
Acid Catalysis ◽  
Buffer Concentration ◽  
Solution Ph ◽  
Tetrahedral Intermediate ◽  
Ph Range ◽  
Rate Limiting ◽  
Hydrolysis Of

The hydrolysis of 5-nitro-2-(trifluoroacetylamino)benzoic acid (2) has been studied over the pH range 0-12. In acidic solution (pH 0-3.5), the hydrolysis occurs with intramolecular general acid catalysis by the adjacent CO2H group. Between pH 3.5 and 8, a plateau is observed in the pH-rate profile, and this is interpreted as acid catalysis by a water molecule of the breakdown of the tetrahedral intermediate formed between (2) and another water molecule. In alkaline solution (pH > 8), hydrolysis occurs with general acid-catalysed C-N bond breaking. Catalysis by phosphate and borate buffers was observed in the pH range 6-10. Phthalate buffers did not catalyse the reaction. For phosphate and borate buffers, plots of buffer concentration against rate showed a saturation phenomenon which was interpreted as indicating a change from rate-limiting decomposition of the tetrahedral intermediate to rate-limiting formation of the tetrahedral intermediate as the buffer concentration was increased. The pKa of the acid group was found to be about 2.5 as expected, but the pKa of the NH group is 10.4, higher than expected. The reduced acidity of the NH group is attributed to electrostatic effects of the adjacent ionized carboxy group. Unlike for aspirin, intramolecular catalysis by the ionized carboxy group was not observed, a result, perhaps, of intramolecular hydrogen bonding between the carboxylate ion and the adjacent NH group. Such an interaction would be geometrically unfavourable for either intramolecular general base or nucleophilic participation by the carboxylate ion.

General acid catalysis in the hydrolysis of benzo[a]pyrene 7,8-diol 9,10-epoxides

1979 ◽  
Vol 101 (17) ◽  
pp. 5086-5088 ◽  
Author(s):  
Dale L. Whalen ◽  
Angela M. Ross ◽  
Jean A. Montemarano ◽  
Dhiren R. Thakker ◽  
Harukiko Yagi ◽  
...  
Keyword(s):  
Acid Catalysis ◽  
General Acid ◽  
Hydrolysis Of

Kinetics of the hydrolysis of the dichromate ion. V. General acid catalysis

1969 ◽  
Vol 73 (12) ◽  
pp. 4391-4394 ◽  
Author(s):  
R. Baharad ◽  
Berta Perlmutter-Hayman ◽  
Michael A. Wolff
Keyword(s):  
Acid Catalysis ◽  
General Acid ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics and mechanism of the oxidation of mercaptoethanol by riboflavin

1977 ◽  
Vol 30 (6) ◽  
pp. 1387 ◽  
Author(s):  
JW Holden ◽  
L Main
Keyword(s):  
Kinetic Study ◽  
Acid Catalysis ◽  
Kinetics And Mechanism ◽  
Alternative Mechanism ◽  
Semiquinone Radical ◽  
Radical Intermediate ◽  
General Acid ◽  
Elimination Mechanism ◽  
Ph Range ◽  
Kinetic Form

Kinetic study of the oxidation of mercaptoethanol (RSH) by riboflavin (FlH) over the pH range 8.5-10.5 establishes that the rate is given by the term 0.036[FlH][RSH][RS-]]2 mol-2 s-1, there being no buffer catalysis. Any reactivity of the N 3-ionized riboflavin species (Fl-) is sufficiently low to be kinetically undetected. The kinetic form and lack of general acid catalysis are consistent with a nucleophilic (thiolate) 4a-addition-elimination mechanism previously proposed, but a possible alternative mechanism involving a flavin semiquinone (radical) intermediate is suggested.

scholarly journals pH-dependence and structure–activity relationships in the papain-catalysed hydrolysis of anilides

1971 ◽  
Vol 124 (1) ◽  
pp. 117-122 ◽  
Author(s):  
G. Lowe ◽  
Y. Yuthavong
Keyword(s):  
Acid Catalysis ◽  
Ph Dependence ◽  
Base Catalysis ◽  
General Base ◽  
Structure Activity ◽  
Equilibrium Binding ◽  
General Acid ◽  
Leaving Group ◽  
Hydrolysis Of ◽  
Equilibrium Binding Constant

The pH-dependence of the Michaelis–Menten parameters for the papain-catalysed hydrolysis of N-acetyl-l-phenylalanylglycine p-nitroanilide was determined. The equilibrium binding constant, Ks, is independent of pH between 3.7 and 9.3, whereas the acylation constant, k+2, shows bell-shaped pH-dependence with apparent pKa values of 4.2 and 8.2. The effect of substituents in the leaving group on the acylation constant of the papain-catalysed hydrolysis of hippuryl anilides and N-acetyl-l-phenylalanylglycine anilides gives rise in both series to a Hammett ρ value of -1.04. This indicates that the enzyme provides electrophilic, probably general-acid, catalysis, as well as the nucleophilic or general-base catalysis previously found. A mechanism involving a tetrahedral intermediate whose formation is general-base-catalysed and whose breakdown is general-acid-catalysed seems most likely. The similarity of the Hammett ρ values appears to exclude facilitated proton transfer as a means through which the specificity of papain is expressed.

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