Fluorinated Alkoxides. Part IX. The Resolution Of Perfluoro(2,3-diphenylbutane-2,3-diol) and its use in preparing Optically Active Complexes Of Ni2+ and Cu2+

Perfluoro(2,3-diphenylbutane-2,3-diol), CF3(C6F5)C(OH)C(OH)(C6F5)CF3, prepared by the reductive dimerization of C6F5COCF3, has been separated into meso- and DL-isomers and the latter resolved via its cinchonidine salt into optical enantiomers. The doubly ionized diol, PDBD2−, acts as a dinegative, chelating, ligand, and neutral complexes of the form (PDBD)-ML2 may be isolated, where L is a neutral nitrogen- or phosphorus-containing ligand and M = Ni2+ or Cu2+. Use of the resolved diol enables optically active metal complexes to be prepared, and from their o.r.d./c.d. spectra we assign an absolute configuration to the diol. The partially fluorinated diols CF3(C6H5)C(OH)C(OH)(C6H5)CF3 and CH3(C6F5)C(OH)C(OH)(C6F5)CH3 have also been prepared from the appropriate ketones. The former, which appears to be exclusively the meso-isomer, has more limited chelating ability than the fully fluorinated analog, while the latter shows no ligand properties; these differences are ascribed to the reduced acidity resulting from the lower degree of fluorination.Nuclear magnetic resonance studies suggest hindered rotation of the C6F5 groups through steric interaction with CF3 groups in perfluoro(2,3-diphenylbutane-2,3-diol); an alternate explanation involving hydrogen bonding from the hydroxylic proton to aromatic fluorine atoms is considered less likely.

Mechanism of Oxidative Decarboxylation of α-Hydroxy Acids by Bromine Water. Part I. Oxidation in Neutral and Alkaline Medium

A kinetic study of the oxidative decarboxylation of α-hydroxy acids by bromine water shows that above pH 6 Br2 is a much more significant oxidant for these compounds than is HOBr, and that OBr− is virtually inert. The rate law – d[oxidant]/dt = k[oxidant][substrate] is observed and the oxidation pattern differs from that of alcohols in that the α-hydrogen is not involved in the reaction.All the compounds studied (benzilic, mandelic, and 2-hydroxy-2-methylpropanoic acids) exhibit bell-shaped pH-rate profiles with maxima at about pH 8. A mechanism is proposed involving the attack of Br2 (or HOBr) at the carboxylate site concurrently with base-catalyzed loss of the hydroxylic proton. A steady state treatment based on this mechanism yields calculated rates in good agreement with the observed values. Furthermore, the same parameters predict the rates observed at lower pH in the presence of added excess bromide. The Br2 oxidation rate is greater than the HOBr rate by a factor of 60 for benzilic acid, 37 for 2-hydroxy-2-methylpropanoic acid, and 10 for mandelic acid.