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Five ketenes, phenyl(ethyl)ketene, phenyl(methylthio)ketene, diphenylketene, pentafluorophenylketene, and 1-naphthylketene, were generated flash photolytically and solvent isotope effects (H2O vs. D2O) on their hydroxide-ion-catalyzed hydration in aqueous solution were determined. The values obtained are all weakly inverse and closely similar (kHO/kDO = 0.76-0.97), as expected for these fast, hydroxide-ion-consuming reactions, known to proceed by nucleophilic attack of hydroxide on the ketene carbonyl group. The characteristic magnitude of these isotope effects should prove useful in identifying new examples of this reaction.Key words: ketenes, flash photolysis, photo-Wolff reaction, solvent isotope effects on hydroxide ion consumption.

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Ketonization of the unusually acidic elongated enol generated by flash photolytic decarboxylation of p-formylphenylacetic acid in aqueous solution

Canadian Journal of Chemistry ◽

10.1139/v07-095 ◽

2008 ◽

Vol 86 (2) ◽

pp. 101-104 ◽

Cited By ~ 2

Author(s):

Yvonne Chiang ◽

Kirill Kolmakov ◽

A Jerry Kresge

Keyword(s):

Aqueous Solution ◽

Acetic Acid ◽

Sodium Hydroxide ◽

Perchloric Acid ◽

Flash Photolysis ◽

Isotope Effects ◽

Solvent Isotope ◽

Solvent Isotope Effects

Rates of photolysis of p-formylphenylacetic acid were measured flash photoytically in perchloric acid and sodium hydroxide solutions, and also in acetic acid, biphosphate ion, and tris-(hydroxymethyl)methaneammonium ion buffers, using H2O and D2O as solvents. The results provide rate profiles and solvent isotope effects, which indicate that photolysis occurs through an elongated enol intermediate. This enol is unusually strongly acidic, by some two to three pQa units, when compared with simple non-elongated enols.Key words: flash photolysis, elongated enols, rate profiles, solvent isotope effects.

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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

Canadian Journal of Chemistry ◽

10.1139/v03-038 ◽

2003 ◽

Vol 81 (6) ◽

pp. 607-611 ◽

Cited By ~ 1

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 × 1013 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.

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Correlation of rates of uncatalyzed and hydroxide-ion catalyzed ketene hydration. A mechanistic application and solvent isotope effects on the uncatalyzed reaction

Canadian Journal of Chemistry ◽

10.1139/v00-032 ◽

2000 ◽

Vol 78 (4) ◽

pp. 508-515

Author(s):

John Andraos ◽

A Jerry Kresge

Keyword(s):

Carbon Atom ◽

Rate Constants ◽

Isotope Effects ◽

Nucleophilic Attack ◽

Carbonyl Carbon Atom ◽

Basic Solution ◽

Carbonyl Carbon ◽

Hydroxide Ion ◽

Solvent Isotope ◽

Solvent Isotope Effects

Rates of hydration of a number of ketenes were measured in neutral and basic solution using flash photolytic techniques, and rate constants for their uncatalyzed, kuc, and hydroxide-ion catalyzed, kHO, reactions were determined. These results, plus additional data from the literature, were found to provide the remarkably good correlation log kuc = -3.21 + 1.14 log kHO, which spans 10 orders of magnitude in reactivity and includes 31 ketenes. This good correlation implies that uncatalyzed and hydroxide-ion catalyzed ketene hydraton occur by similar reaction mechanisms, which for the hydroxide-ion catalyzed process is known to involve nucleophilic attack on the carbonyl carbon atom of the ketene. Rate constants for phenylhydroxyketene, on the other hand, do not fit this correlation, which suggests that the mechanistic assignment upon which these rate constants are based may not be correct. Solvent isotope effects on these uncatalyzed ketene hydrations are weak; most are less than kH/kD = 2. It is argued that these isotope effects are largely, if not entirely, secondary in nature and that they are consistent with both a reaction mechanism in which nucleophlic attack of a single water molecule on the ketene carbonyl carbon atom produces a zwitterionic intermediate and also a mechanism that avoids this intermediate by passing through a cyclic transition state involving several water molecules.Key words: ketene hydration, rate correlation, nucleophilic attack, solvent isotope effects, phenylhydroxyketene.

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

Australian Journal of Chemistry ◽

10.1071/ch9681733 ◽

1968 ◽

Vol 21 (7) ◽

pp. 1733 ◽

Cited By ~ 5

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.

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