5740-42-1Relevant academic research and scientific papers
A comprehensive picture of the one-electron oxidation chemistry of enols, enolates and α-carbonyl radicals: oxidation potentials and characterization of radical intermediates
Schmittel, Michael,Lal, Mukul,Lal, Rupali,R?ck, Maik,Langels, Anja,Rappoport, Zvi,Basheer, Ahmad,Schlirf, Jens,Deiseroth, Hans-J?rg,Fl?rke, Ulrich,Gescheidt, Georg
experimental part, p. 10842 - 10855 (2010/02/28)
Oxidation potentials of 40 enols, enolates and some selected α-carbonyl radicals are presented along with their characterization by various techniques as applicable (X-ray, EPR, ENDOR, general TRIPLE, magnetic susceptibility measurements, UV-vis, fast sca
Sterically hindered enols of carboxylic acids and esters. the ketonisation reactions of 2,2-bis(2,4,6-trimethylphenyl)ethene-1,1-diol and 2,2-bis(pentamethylphenyl)ethene-1,1-diol
Allen, Barbara M.,Hegarty, Anthony F.,O'Neill, Pat
, p. 2733 - 2736 (2007/10/03)
The ketonisation of two enols of carboxylic acids, 2,2-bis(2,4,6-trimethylphenyl)ethene-1,1-diol 2a and 2,2-bis(pentamethylphenyl)ethene-1,1-diol 2b have been studied at 25°C in 1:1 acetonitrile-water. The stability of these compounds arises from the inhibition of the β-carbon site to protonation, and this effect is now quantified. A pKa of 8.18 is reported for ionisation of the first hydroxyl group Of(MeS)2C=C(OH)2 2a and 8.63 for (PMP)2C=C(OH)2 2b. A pH-rate profile has been determined over the full pH range for both species. General acid catalysis was detected, yielding Bronsted a values of 0.35 and 0.34 for 2a and 2b, respectively. Similarly, Bronsted a'′ values of 0.48 and 0.45 were calculated for general acid catalysis of both enolate mono-anions. Studies of the ketonisation of the enols of the corresponding methyl esters have permitted comparative studies on the reactivity of enols of carboxylic acids, esters and ketene acetals. The reactivity of MeS2C=C(OH)(OCH3) lies closer to the enediol, MeS2C=C(OH)2 2a than to the ketene acetal, suggesting that in this case, one hydroxy group is almost as efficient as two such groups in the stabilisation of the positive charge developing at Cβ as protonation occurs.
Hydration of Bis(pentamethylphenyl)- and Bismesityl-ketenes leading to Ene-1,1-diols (Enols of Carboxylic Acids)
Allen, Barbara M.,Hegarty, Anthony F.,O'Neill, Pat,Nguyen, Minh Tho
, p. 927 - 934 (2007/10/02)
The reaction of the sterically hindered diarylketenes (Ar = Me5C6 or 2,4,6-Me3C6H2) with water is pH independent over the range 1-9 and is not subject to strong buffer catalysis.The primary products formed are the corresponding ene-1,1-diols which result from addition across the C=O (rather than the C=C) of the ketene.These "enols of carboxylic acids" are relatively long lived owing to slow protonation of the β-carbon (because of steric hindrance caused by the o-Me groups) and evidence for their structures in solution is presented.On attempted isolation of theene-1,1-diols facile oxidation to a stable free radical, as well as ketonisation to the corresponding acids, occurs.Evidence is presented in terms of the large negative entropy of activation (ca. 200 J K-1 mol-1), solvent isotope effects and the absence of significant general-base catalysis, that (despite the sterically hindered nature of these ketenes) the characteristics of their hydration are typical of other ketenes and that this most likely involves an initial concerted reaction with a water oligomer.Updated ab initio calculations are also presented, which are consistent with this view.
