Solvent isotope effect on the hydroxide-ioncatalyzed hydration of ketenes in aqueous solution

Abstract

Five ketenes, phenyl(ethyl)ketene, phenyl(methylthio)ketene, diphenylketene, pentafluorophenylketene, and 1-naphthylketene, were generated flash photolytically and solvent isotope effects (H 2 O vs. D 2 O) on their hydroxide-ioncatalyzed hydration in aqueous solution were determined. The values obtained are all weakly inverse and closely similar (k HO /k DO = 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.Résumé : Faisant appel à la photolyse éclair, on a généré cinq cétènes (phényl(éthyl)cétène, phényl(méthylthio)cétène, diphénylcétène, pentafluorophénylcétène et 1-naphtylcétène) et on a déterminé les effets isotopiques de solvant (H 2 O vs. D 2 O) sur leur hydratation catalysée par l'ion hydroxyde, en solution aqueuse. Les valeurs obtenues sont toutes semblables, faibles et inverses (k HO /k DO = 0,76-0,97) comme on peut s'y attendre pour ces réactions rapides utilisant l'ion hydroxyde qui se produisent par une attaque nucléophile de l'hydroxyde sur le groupe carbonyle du cétène. L'amplitude caractéristique de ces effets isotopiques devrait s'avérer utile dans l'identification de nouveaux exemples de cette réaction.Mots clés : cétènes, photolyse éclair, réaction de photo-Wolff, effets isotopique du solvant sur la consommation de l'ion hydroxyde.[Traduit par la Rédaction] Andraos 462 These ketenes were generated by photo-Wolff reactions, eq. [2], of the corresponding diazo compounds, α-diazobutyrophenone, 6, S-methyl phenyldiazothioacetate, 7, azibenzil, 8, penta-Can.

100 Years of the Wolff Rearrangement

“…Two successively formed intermediates were assigned as ketene 193 and enol 194 by means of their pHrate profiles (Scheme 29). [173] The conversion of 193 into 194 [174] and of 194 into 195 [175] was explored in some detail. Although the carbenes 191 were trapped by protic solvents with formation of 192 (9Ϫ15%, see Section 3.4.1.…”

“…For a comprehensive list, including data from other sources, see ref. [223] effects of bulky groups (Table 4), small solvent isotope effects, [221,222] and molecular orbital theory. [224] Enols of carboxylic acids 252 were found to intervene on the reaction path from ketenes 2 to carboxylic acids (Scheme 36).…”

“…The cyclopentadiene moiety stabilizes enols strongly. Therefore, 253 was the first carboxylic acid enol to be characterized in aqueous solution, [225] followed by the benzo analogues 254 [173] and 255 [226] which were generated from diazoquinones. While 256 was rapidly formed (k H 2 O ϭ 2.2·10 5 s Ϫ1 ) and readily monitored, [227] the acyclic analogue 257 (k H 2 O ϭ 1.3·10 2 s Ϫ1 ) could not be detected.…”

Gold Catalysis: Hydrolysis of Di(alkoxy)carbenium Ion Intermediates as a Sensor for the Electronic Properties of Gold(I) Complexes

“…Nevertheless, this result demonstrates that the rate-determining step is not largely dominated by the degree of solvation of the nucleophile or by a proton/deuteron transfer step. 28 In the di(alkoxy)carbenium systems investigated, the ancillary ligand can influence the chemical properties of a reactive center located more than 600 pm away from the coordinating atom of the ligand. The pronounced dependence of LUMO energies and the orbital coefficients at the reactive center of the heterocyclic system clearly point to a transfer capability of electronic properties through the Au(I) bridge, resulting in different kinetics of the hydrolysis.…”

Effects of solvent, excitation wavelength, and concentration on the photobehavior of some diazonaphthoquinones

“…In the presence of substantial amounts of water (EtOH/H 2 0, 2:1) the ketene was completely undetectable, due to increased rate of the acid forming process by interaction of ketene with excess water. 29 In acetonitrile, the reaction was slowed down due to the scant water amount, present in the commercial solvent as a trace, and the ketene was still recognizable from the maximum at 293 nm. The thermal evolution of the spectra observed on warming solutions irradiated in a matrix at 80 K ( Figure 4, spectrum 2) evidences the characteristics of ketene.…”