Kinetics and mechanism of acid-catalyzed hydrolysis of the diazo functional groups of 1-diazo-2-indanone and 2-diazo-1-indanone in aqueous solution

2005 ◽  
Vol 83 (9) ◽  
pp. 1202-1206 ◽  
Author(s):  
Yvonne Chiang ◽  
A Jerry Kresge ◽  
Oleg Sadovski ◽  
Xiaofeng Zeng ◽  
Yu Zhu
Keyword(s):  
Formic Acid ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Diazo Compound ◽  
Acid Buffer ◽  
Buffer Solutions ◽  
Hydronium Ion ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

Rates of hydrolysis of 1-diazo-2-indanone and 2-diazo-1-indanone were measured in dilute aqueous perchloric acid solutions using both H2O and D2O as the solvent, and rates of hydrolysis of the latter substrate were measured in dilute aqueous (H2O only) formic acid buffer solutions as well. The data for 1-diazo-2-indanone gave the hydronium ion catalytic coefficient kH+ = 5.7 × 10–3 (mol/L)–1 s–1 and the isotope effect kH+/kD+ = 2.9. The normal direction (kH/kD > 1) of this isotope effect was taken as evidence for a reaction mechanism involving rate-determining hydron transfer from the hydronium ion to the substrate's diazo carbon atom; followed by rapid displacement of diazo nitrogen by a water molecule, giving the observed 1-hydroxy-2-indanone product. The data for 2-diazo-1-indanone, on the other hand, gave a hydronium ion catalytic coefficient two orders of magnitude greater than the value for 1-diazo-2-indanone (kH+ = 5.9 × 10–1 (mol/L)–1 s–1), and an isotope effect near unity (kH+/kD+ = 1.2). It is argued that this isotope effect represents a situation in which diazo carbon hydronation and displacement of diazo nitrogen are each partly rate determining, a conclusion supported by incipient saturation of buffer catalysis in the formic acid buffer solutions. The 100-fold difference in hydronium ion catalytic coefficients for the two substrates is rationalized in terms of differing electron densities on the diazo carbon atoms.Key words: diazo compound hydrolysis, solution kinetics, acid catalysis, solvent isotope effects, buffer catalysis saturation.

Solvent isotope effects in the oxidation of dipeptides by aqueous chlorine

1999 ◽  
Vol 77 (5-6) ◽  
pp. 997-1004 ◽  
Author(s):  
X L Armesto ◽  
M Canle L. ◽  
V García ◽  
J A Santaballa
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Second Step ◽  
Solvent Isotope Effect ◽  
General Base ◽  
Peptide Oxidation ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

A kinetic study of the mechanism of oxidation of Ala-Gly and Pro-Gly by aqueous chlorine has been carried out. Among other experimental facts, the deuterium solvent isotope effects were used to clarify the mechanisms involved. In a first stage, N-chlorination takes place, and then the (N-Cl)-dipeptide decomposes through two possible mechanisms, depending on the acidity of the medium. The initial chlorination step shows a small isotope effect. In alkaline medium, two consecutive processes take place: first, the general base-catalyzed formation of an azomethine (β ca. 0.27), which has an inverse deuterium solvent isotope effect (kOH-/kOD- ~ 0.8). In a second step, the hydrolysis of the azomethine intermediate takes place, which is also general base-catalyzed, without deuterium solvent isotope effect, the corresponding uncatalyzed process having a normal deuterium solvent isotope effect (kH2O/kD2O ~ 2). In acid medium, the (N-Cl)-dipeptide undergoes disproportionation to a (N,N)-di-Cl-dipeptide, the very fast decomposition of the latter in deuterium oxide preventing a reliable estimation of the solvent isotope effect.Key words: chlorination, deuterium isotope effects, fractionation factors, peptide oxidation, water treatment.

Kinetic Solvent Isotope Effect for the Spontaneous Solvolysis Acetic and Propionic Anhydrides

1971 ◽  
Vol 49 (22) ◽  
pp. 3665-3670 ◽  
Author(s):  
R. E. Robertson ◽  
B. Rossall ◽  
W. A. Redmond
Keyword(s):  
Acetic Anhydride ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Temperature Dependency ◽  
Solvent Isotope Effect ◽  
Propionic Anhydride ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The large kinetic solvent isotope effects for the neutral hydrolysis of acetic and propionic anhydride show unusual temperature dependency; the former passing through a maximum at about 15°, the latter showing a minimum at 30°. This unusual temperature dependency is the consequence of widely different values of the apparent ΔCp≠ in H2O and D2O: the value for acetic anhydride in H2O being −74 ± 2 cal deg−1 mol−1 but −32 ± 4 in D2O. The corresponding values for propionic anhydride being −31 ± 2 in H2O but −94 ± 10 in D2O. The implications of these differences are discussed.

Studies in Solvolysis. Part IV. Substituent and Solvent Isotope Effects in the Solvolysis of a Series of Benzyl Trifluoroacetates

1972 ◽  
Vol 50 (12) ◽  
pp. 1886-1890 ◽  
Author(s):  
June G. Winter ◽  
J. M. W. Scott
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
The Other ◽  
Solvent Isotope Effect ◽  
Other Hand ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The rates of neutral hydrolysis of a series of 4-substituted benzyl trifluoroacetates 4-X-C6H4CH2OCOCF3, X = NO2, Cl, H, CH3, and OCH3 have been studied in water and deuterium oxide, both solvents containing 0.012 mol fraction of acetone. The alteration of the rates with the nature of the 4-substituent and the kinetic solvent isotope effect (k(H2O)/k(D2O)) are consistent with the proposal that the esters with X = NO2, Cl, H, and CH3 all react by an acyl–oxygen BAc2 mechanism. On the other hand, the same mechanistic criteria indicate that the 4-methoxybenzyl ester reacts by both the BAc2 and the SN1 alkyl–oxygen fission paths in equal amounts.

?-Secondary deuterium isotope effect and solvent isotope effects in catalysis by subtilisin BPN?

1990 ◽  
Vol 3 (4) ◽  
pp. 260-265 ◽  
Author(s):  
Ildiko M. Kovach ◽  
Son Do ◽  
Richard L. Schowen
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Phosphato complexes of cobalt(III). IV. Hydrolysis in basic solution

1968 ◽  
Vol 21 (7) ◽  
pp. 1733 ◽  
Author(s):  
SF Lincoln ◽  
DR Stranks
Keyword(s):  
Isotope Effects ◽  
Base Hydrolysis ◽  
Basic Solution ◽  
Tracer Technique ◽  
Hydroxide Ion ◽  
Solvent Water ◽  
Coordination Spheres ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The rates of hydrolysis of phosphato complexes of cobalt(111) in sodium hydroxide concentrations ranging from 0.02M to 0.37M, and at several ionic strengths, have been measured with a tracer technique. Bidentate phosphato complexes exhibit the same rates of hydrolysis as the corresponding monodentate complexes, due to a rapid conversion of the bidentate into the monodentate form. The general rate law for base hydrolysis of all the phosphato complexes is: d[PO34]/dt = {kH2O + kOH[OH-]}[complex] At 60� and at unit ionic strength, the rate constants for the complexes cis-[Co(NH3)4OH.PO4]-, cis-[Co en2OH.PO4]-, and [Co(NH3)5PO4] respectively are: 103kH2O (min-l) 85.0, 2.0, <1; and 103kOH (1. mole-1 min-l) 42.7, 12.0, 69.5. Mechanistic conclusions have been based on the measured enthalpies and entropies of activation and deuterium solvent isotope effects. For all complexes, kH2O is identified with an aquation mechanism involving synchronous interchange of the phosphate and solvent water between the first and second coordination spheres of the complexes. In the case of the tetrammine and bis(ethylenediamine) complexes, kOH is identified with a process involving synchronous interchange of phosphate and hydroxide ion between the first and second coordination spheres of the complexes. In the case of the pentammine complex, an SN2CB mechanism is considered to be more probable. A comparison with the base hydrolysis of halogen complexes of cobalt(111) is presented.

The Hydrolysis of Disubstituted Alkyl Phosphorochloridates and N,N,N′,N′-Tetra-stibstituted Phosphorodiamidic Chlorides in Water and Deuterium Oxide: Heat Capacity of Activation and Kinetic Solvent Isotope Effects

1973 ◽  
Vol 51 (4) ◽  
pp. 597-603 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Heat Capacity ◽  
Thermodynamic Parameters ◽  
Alkyl Group ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Potential Relationship ◽  
Mechanism Of Reaction ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The pseudo-thermodynamic parameters, ΔH≠, ΔS≠, and ΔCp≠ and the kinetic solvent isotope effects have been determined for the three alkyl-phosphorochloridates, where the alkyl group is ethylisopropyl and n-propyl; for tetra-methyl and tetra-ethyl phosphorodiamidic chlorides; the di-n-propyl and di-isopropyl analog, the di(isopropylmethylcarbinyl)phosphorochloridate and the tetra-ethylthiophosphorodiamidic chloride. These compounds have a potential relationship to compounds used as insecticides and as polymers. The mechanism of reaction is discussed on the basis of these data.

Generation of 6-methylene-2,4-cyclohexadienylidene ketene by flash photolysis of benzocyclobutenone in aqueous solution and study of the reactions of this ketene in that medium

2003 ◽  
Vol 81 (6) ◽  
pp. 607-611 ◽  
Author(s):  
Y Chiang ◽  
A J Kresge ◽  
H -Q Zhan
Keyword(s):  
Aqueous Solution ◽  
Ring Opening ◽  
Flash Photolysis ◽  
Isotope Effects ◽  
Buffer Solutions ◽  
Product Identification ◽  
Rate Profile ◽  
Solvent Isotope ◽  
Rates Of Decay ◽  
Solvent Isotope Effects

Flash photolysis of benzocyclobutenone in aqueous solution produced a transient species with a microsecond lifetime whose rates of decay were measured in perchloric acid, sodium hydroxide, and buffer solutions over the acidity range [H+] 1 × 10–13 – 100 M. This produced a rate profile, isotope effects, and buffer behaviour typical of ketene reactions, and that, together with product identification, served to identify this transient as 6-methylene-2,4-cyclohexadienylidene ketene, formed by electrocyclic opening of the four-membered ring of benzocyclobutenone. Comparison of rates of reaction of this ketene with those of its saturated analog, pentamethyleneketene, produced some expected as well as some unexpected results. Key words: cyclobutenone chemistry, electrocyclic ring opening, ketene hydration, rate profile, solvent isotope effects.

Vinyl ether hydrolysis. XXIV. 1-Methoxycyclooctene and the question of reversibility of the carbon protonation step

1991 ◽  
Vol 69 (1) ◽  
pp. 84-87 ◽  
Author(s):  
A. J. Kresge ◽  
Y. Yin
Keyword(s):  
Reaction Mechanism ◽  
Proton Transfer ◽  
Vinyl Ether ◽  
Isotope Effects ◽  
Hydrolysis Rate ◽  
Hydronium Ion ◽  
Mineral Acids ◽  
Dilute Aqueous Solutions ◽  
Solvent Isotope ◽  
Hydrolysis Of

An argument is presented which suggests that hydrolysis of the vinyl ether group of 1-methoxycyclooctene may occur by reversible proton transfer from a catalyzing acid to the β-carbon atom of the substrate, instead of by the conventional reaction mechanism in which this proton transfer is rate determining and not reversible. Hydrolysis of this substrate is then examined by measuring rates of reaction in dilute aqueous solutions of strong mineral acids (perchloric and hydrochloric) as well as in buffer solutions of seven carboxylic acids, biphosphate ion, and 1,1,1,3,3,3-hexafluoro-2-propanol. General acid catalysis is observed and a Brønsted relation with the exponent α = 0.73 is constructed. That, plus the isotope effects kH/kD = 2.9 and 6.0 for catalysis by hydronium ion and acetic acid respectively, as well as the lack of deuterium incorporation into the substrate when the reaction is carried out in D2O with D2PO4−/DPO42− buffer at pD = 8, show that carbon protonation of the substrate is not reversible and that the conventional reaction mechanism is operative. Key words: 1-methoxycyclooctene, vinyl ether hydrolysis, rate-determining proton transfer, Brønsted relation, solvent isotope effect.

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