Aqueous trifluoroacetic acid as a medium for organic reactions. I. Acidity functions and the identity of the manganese(VII) species found in powerfully acidic media

Abstract

. Can. J. Chem. 54,440 (1976). The HR acidity function has been determined for the trifluoroacetic acid -water system, and extended beyond 100% acid by the addition of trifluoroacetic anhydride, to 99.5 wt.7, anhydride. The existing Ho acidity function is corrected and extended to 1007, trifluoroacetic acid, confirming Eaborn's observation that Ho attains a minimum value at approximately 977, acid.Comparison of the acidity functions shows that although trifluoroacetic acid is only weakly protonating, it is a strongly protonating-dehydrating medium. Changes in the uv-visible spectrum of potassium permanganate produced by changing acid concentration are used to calculate the degree of further ionization of the permanganate ion; the correlation of this with the HR acidity function further suggests the presence of the permanganyl cation, MnO3+, or its trifluoroacetate complex or ester, MnO3.02CCF3, in these solutions. A cryoscopic investigation into the mode of ionization of permanganate in trifluoroacetic acid reveals that extensive ion-pair formation occurs in this solvent. Although this effect prevents an unequivocal determination of the number of solute particles being made the results are consistent with the presence of a permanganyl species in solution.

Aqueous trifluoroacetic acid as a medium for organic reactions. II. The oxidation of hydrocarbons by manganese(VII)

“…The chemical changes that occur as the TFA content of an aqueous TFA solution of potassium permanganate is increased were the subject of a previous paper (7). There we showed that the green species that appears in solutions containing more than 82 Can.…”

Site of Protonation of Carboxylic and Non-Carboxylic Amides in the Gas Phase and in Water

“…Thus, N-protonation is borne out [39] but the data may be compatible with some intervention of Oprotonation. Kricheldorf [62] interpreted Dd( 15 N) À 4.6 as Nprotonation, but the acid used (CF 3 COOH, H 0 À 2.7 [63] ) is far too weak to protonate MeSO 2 NH 2 (H 0`À 9 is required). [39] Nitrosamides: The most basic site of Me 2 NNO is predicted to be the oxygen atom in both gas and aqueous phases, by ca.…”

Solid-phase synthesis of oligodeoxynucleotides using nucleobase N-unprotected oxazaphospholidine derivatives bearing a long alkyl chain

“…The amount of a loaded nucleoside on solid-support was estimated by the calculation of released 4,4′-dimethoxytrityl cation by a solution of 0.1 M TsOH/CH 3 CN using a molar absorption constant at 498 nm ( ε = 76 000 L mol −1 cm −1 ). 33…”