ELECTROPHILIC DISPLACEMENT REACTIONS: XV. KINETICS AND MECHANISM OF THE BASE-CATALYZED PROTODEBORONATION OF ARENEBORONIC ACIDS

1963 ◽  
Vol 41 (12) ◽  
pp. 3081-3090 ◽  
Author(s):  
Henry G. Kuivila ◽  
Joseph F. Reuwer Jr. ◽  
John A. Mangravite
Keyword(s):  
Acid Catalysis ◽  
Low Ph ◽  
Ion Concentration ◽  
Buffer Concentration ◽  
Hammett Equation ◽  
Hydroxide Ion ◽  
Displacement Reactions ◽  
Acid Catalyzed ◽  
Ph Range ◽  
Kinetics Of

An investigation of the kinetics of the protodeboronation of benzeneboronic acid in water in the pH range 2.0 to 6.7 is described. In addition to the acid-catalyzed reaction studied earlier a reaction whose rate is independent of pH and one whose rate increases linearly with hydroxide ion concentration have been observed. The effect of malonate buffer concentration at low pH confirms the earlier observations of general acid catalysis. Changes in buffer concentration at pH 6.70 have no effect on rate indicating specific hydroxide ion catalysis. Effect of substituents in the ortho, meta, and para position of the benzene ring on the rate of protodeboronation have been examined. Ortho–para ratios for this reaction are high; possible reasons for this are discussed. The Hammett equation using σ correlates the rates for meta and para substituents.

Kinetics and Mechanisms for the Isomerization of Internucleosidic 3'-O-P-CH2-5' and 3'-O-P-CH(OH)-5' Linkages to Their 2',5'-Counterparts

2006 ◽  
Vol 71 (6) ◽  
pp. 859-870 ◽  
Author(s):  
Tuomas Lönnberg ◽  
Šárka Králíková ◽  
Ivan Rosenberg ◽  
Harri Lönnberg
Keyword(s):  
Hydrogen Bond ◽  
Hydroxy Group ◽  
Phosphorus Atom ◽  
Hydrolytic Stability ◽  
Model Compounds ◽  
Hydroxide Ion ◽  
Wide Ph Range ◽  
Acid Catalyzed ◽  
Ph Range

Isomerization of internucleosidic 3'-O-P-CH2-5' and 3'-O-P-CH(OH)-5' phosphonate linkages to their 2',5'-counterparts has been studied over a wide pH-range. The model compounds employed are phosphonate analogs of adenylyl-(3',5')-adenosine and adenylyl-(2',5')-adenosine having either adenosine ((R,S)-1, (R,S)-2) or 5'-deoxyadenosine (3, 4) bonded to the phosphorus atom through the C5'-atom. For comparative purposes, the hydrolytic stability of C5'-hydroxyphosphonate analogs derived from 2'-deoxyadenosine ((R,S)-5) has also been studied. In addition to the expected acid-catalyzed (pH < 3) and pH-independent reactions (pH 3-9), the diastereomeric C5'-hydroxyphosphonate analogs ((R,S)-1, (R,S)-2), but not their deoxy counterparts (3, 4), have been observed to undergo a hydroxide-ion-catalyzed isomerization around pH 11 (90 °C). Evidently a hydrogen bond between the dianionic phosphorane and the C5'-hydroxy group stabilize the phosphorane to such an extent that isomerization via kinetically invisible protonation to monoanion becomes possible. The mechanisms of the isomerization reactions taking place under various conditions are discussed.

Reaction kinetics of 1,2-diaminobenzene with ethyl 2-oxopropanoate and 2,3-butanedione

1988 ◽  
Vol 53 (12) ◽  
pp. 3154-3163 ◽  
Author(s):  
Jiří Klicnar ◽  
Jaromír Mindl ◽  
Ivana Obořilová ◽  
Jaroslav Petříček ◽  
Vojeslav Štěrba
Keyword(s):  
Reaction Kinetics ◽  
Acid Catalysis ◽  
Reaction Pathway ◽  
Hydroxide Ion ◽  
Tetrahedral Intermediate ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
General Acid ◽  
Rate Limiting ◽  
Kinetics Of

The reaction of 1,2-diaminobenzene with 2,3-butanedione is subject to general acid catalysis in acetate and phosphate buffers (pH 4-7). The rate-limiting step of formation of 2,3-dimethylquinoxaline consists in the protonation of dipolar tetrahedral intermediate. In the case of the reaction of 1,2-diaminobenzene with ethyl 2-oxopropanoate, the dehydration of carbinolamine gradually becomes rate-limiting with increasing pH in acetate buffers, whereas in phosphate buffers a new reaction pathway makes itself felt, viz. the formation of amide catalyzed by the basic buffer component and by hydroxide ion.

Studies on Horseradish Peroxidase. XII. A Kinetic Study of the Oxidation of Sulfite and Nitrite by Compounds I and II

1973 ◽  
Vol 51 (4) ◽  
pp. 588-596 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Ground State ◽  
Ph Dependence ◽  
Intermediate Formation ◽  
Ion Concentration ◽  
Compound I ◽  
Hydrogen Ion Concentration ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of sulfite and nitrite by horseradish peroxidase compounds I and II have been studied as a function of pH at 25° and ionic strength 0.11. The pH dependence of the rate of the reaction between compound I and sulfite over the pH range 2–7 is interpreted in terms of two ground state enzyme dissociations with pka values of 5.1 and 3.3, and that for the compound II reaction with sulfite in terms of a single ground state enzyme dissociation with a pKa value of 3.9. Whereas the reaction between compound I and sulfite produces the native enzyme without the intermediate formation of compound II, the reaction of compound I with nitrite yields compound II. The second-order rate constants for the reactions of compounds I and II with nitrite increase linearly with increasing hydrogen ion concentration over the pH range 6–8.

The oxidation of secondary alcohols by potassium tetraoxoferrate(VI)

1997 ◽  
Vol 75 (2) ◽  
pp. 129-139 ◽  
Author(s):  
Bruce E. Norcross ◽  
William C. Lewis ◽  
Huifa Gai ◽  
Nazih A. Noureldin ◽  
Donald G. Lee
Keyword(s):  
Acid Catalysis ◽  
Isotope Effects ◽  
Low Ph ◽  
Base Catalysis ◽  
Secondary Alcohols ◽  
Acid And Base ◽  
Deuterium Isotope Effects ◽  
Reactive Oxidant ◽  
Kinetics Of ◽  
Large Primary

The kinetics of the oxidation of 2-propanol, 1,1,1-trifluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 1-phenyl-2,2,2-trifluoroethanol, 1-(4-methylphenyl)-2,2,2-trifluoroethanol, 1-(3-bromophenyl)-2,2,2-trifluoroethanol, and 1-(3-nitrophenyl)-2,2,2-trifluoroethanol by potassium tetraoxoferrate(VI) have been studied under basic conditions. The products are ketones, formed in almost quantitative yields, iron(III) hydroxide, and dioxygen. The reactions are characterized by substantial enthalpies of activation (40–60 kJ/mol), very unfavorable entropies of activation, large primary deuterium isotope effects, and a positive Hammett ρ value. Both acid and base catalysis are observed. Acid catalysis is attributed to formation of a more reactive oxidant, HFeO4−, at low pH. Base catalysis is attributed partly to the conversion of the reductants to alkoxide ions at high pH, and partly to the reaction of hydroxide ion with tetraoxoferrate(VI) to give a five-coordinated species, HOFeO43−, that reacts rapidly with nucleophiles. A reaction mechanism involving formation of an intermediate ferrate ester is proposed. Keywords: oxidation, alcohols, potassium tetraoxoferrate(VI), ferrate esters, base catalysis, acid catalysis.

Kinetics and mechanism of hydrolysis of 3-diazobenzofuran-2-one and its hydrolysis product (3-hydroxybenzofuran-2-one)

2002 ◽  
Vol 80 (1) ◽  
pp. 82-88
Author(s):  
Y Chiang ◽  
A J Kresge ◽  
Q Meng
Keyword(s):  
Acid Catalysis ◽  
Hydrolysis Product ◽  
Diazo Compound ◽  
Acidity Function ◽  
Hydroxide Ion ◽  
Mechanism Of Hydrolysis ◽  
Acid Catalyzed ◽  
Catalyzed Reactions ◽  
Rate Profile ◽  
Hydrolysis Of

Rates of acid-catalyzed hydrolysis of 3-diazobenzofuran-2-one, measured in concentrated aqueous perchloric acid and hydrochloric acid solutions, were found to correlate well with the Cox–Yates Xo excess acidity function, giving kH+ = 1.66 × 10–4 M–1 s–1, m‡ = 0.86 and kH+ /kD+ = 2.04. The normal direction (kH/kD > 1) of this isotope effect indicates that hydrolysis occurs by rate-determining protonation of the substrate on its diazo-carbon atom. It was found previously that the next higher homolog of the present substrate, 4-diazoisochroman-3-one, also undergoes hydrolysis by this reaction mechanism but with a rate constant 15 times greater than that for the present substrate; this difference in reactivity can be understood in terms of the various resonance forms that contribute to the structures of these substrates. The product of the present hydrolysis reaction is 3-hydroxybenzofuran-2-one, which itself quickly undergoes subsequent acid-catalyzed hydrolysis to 2-hydroxymandelic acid. The acidity dependence of this subsequent hydrolysis is much shallower than that of the diazo compound precursor, and rates of reaction correlate as well with [H+] as with Xo. This is due in part to incursion of a nonproductive protonation on the hydroxy group of 3-hydroxy benzo furan-2-one that impedes hydrolysis and produces saturation of acid catalysis. Rates of hydrolysis of the hydroxy compound were also measured in dilute HClO4 and NaOH solutions as well as in CH3CO2H, H2PO4–, (CH2OH)3CNH3+, and NH4+ buffers, and the rate profile constructed from these data showed the presence of uncatalyzed and hydroxide ion-catalyzed reactions. This hydroxide-ion catalysis became saturated at [NaOH] [Formula: see text] 0.05 M, implying occurrence of yet another nonproductive substrate ionization. Key words: diazo compound hydrolysis, lactone hydrolysis, Cox–Yates excess acidity, acid catalysis, alcohol protonation.

Changes in charge charactistics of soils after treatment with 0.5M calcium chloride at pH 1.5

Soil Research ◽  
1967 ◽  
Vol 5 (2) ◽  
pp. 247 ◽  
Author(s):  
CK Tweneboah ◽  
DJ Greenland ◽  
JM Oades
Keyword(s):  
Clay Minerals ◽  
Calcium Chloride ◽  
Negative Charge ◽  
Positive Charge ◽  
Low Ph ◽  
Rapid Rate ◽  
Constant Rate ◽  
Ph Range ◽  
Kinetics Of

The kinetics of the removal of iron, aluminium, and silicon from soils and clays in the pH range 0-3 have been studied using a number of oxides, clay minerals, and soils. At pH 1.5, aluminium is removed but little iron or silicon. An initial rapid rate of aluminium extraction is followed by a slower constant rate. The rapidly released aluminium is extracted in approximately 12 hr using 0.5M CaCl2 at pH 1.5.reatment of a range of soils and clays by this method reduced the positive charge developed at low pH very substantially but had little effect on the negative charge. It is suggested that the positive charges in the soils studied are mostly due to the 'active' aluminium oxides.

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.

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.

Vinyl ether hydrolysis. XVIII. The two-stage reaction of 2,3-dimethoxy-1,3-butadiene

1987 ◽  
Vol 65 (8) ◽  
pp. 1753-1756 ◽  
Author(s):  
A. Jerry Kresge ◽  
Ya Yin
Keyword(s):  
Vinyl Ether ◽  
Acid Catalysis ◽  
Inductive Effect ◽  
Isotope Effects ◽  
Resonance Effect ◽  
Stage I ◽  
Initial Substrate ◽  
Acid Catalyzed ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of acid-catalyzed hydrolysis of 2,3-dimethoxy-1,3-butadiene (1) to 3-methoxy-3-buten-2-one (2) and the subsequent 104 times slower conversion of the latter to biacetyl (3):[Formula: see text]were studied in aqueous solution at 25 °C. Both stages of this process give substantial hydrogen ion isotope effects, [Formula: see text] for Stage I and [Formula: see text] for Stage II, and Stage I shows general acid catalysis in formic and acetic acid buffers; both stages are therefore assigned the conventional mechanism for vinyl ether hydrolysis involving rate-determining proton transfer from catalyzing acid to substrate. The second vinyl ether group of the initial substrate (1) is found to have only a slight (3-fold) accelerative effect on the reactivity of the first group, but the acetyl substituent present in the intermediate 2 decreases its reactivity by a factor of 104; the latter appears to be due largely to the electron-withdrawing inductive effect of acetyl, with little or no influence from a countervailing electron-supplying resonance effect.

Enolization of the benzocyclohexadienone formed during the bromination of 1-naphthol in aqueous solution

1987 ◽  
Vol 65 (8) ◽  
pp. 1714-1718 ◽  
Author(s):  
Oswald S. Tee ◽  
N. Rani Iyengar
Keyword(s):  
Aqueous Solution ◽  
Carboxylic Acid ◽  
Hydroxide Ion ◽  
A Value ◽  
Ph Range ◽  
Effective Molarity ◽  
Kinetics Of

Benzo-4-bromo-2,5-cyclohexadienone (5) has been observed in the aqueous bromination of 1-naphthol and the kinetics of its enolization to 4-bromo-1-naphthol have been studied in the pH range 0–7. This process is catalyzed by the proton, hydroxide ion, water, buffer acids, and by buffer bases. For catalysis by general bases the Brønsted β = 0.59 whereas catalysis by general acids has a value of α ~ 0. These findings are very similar to those obtained previously for the 4-bromo-2,5-cyclohexadienone 2b, formed during the aqueous bromination of 2,6-dimethylphenol. The mechanistic implications of the results are discussed. The enolization of the related dienone 8, formed from bromine and 1-naphthol-2-carboxylic acid, was also studied. At acidic pHs the dienone 8 is much more reactive than 5, with the 2-COOH behaving as an internal catalyst having an "effective molarity" of about 110 M. The enolization of 8 is also catalyzed by buffer bases.

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