Dissociation constants in dimethyl sulfoxide (DMSO) of various uncharged acids, monovalent cation acids, and some sulfonephthaleins have been determined. For uncharged acids, the anions of which have a localized charge, the difference between pKdSA in acetonitrile (AN) and DMSO is 9.7 to 10. For acids, the undissociated forms of which have intramolecular hydrogen bonding in AN, the difference is of the order of 11.5. This larger difference is attributed to breaking of these bonds by the strongly protophylic aprotic solvent DMSO. For ammonium and aliphatic amine cations, 3* + in AN and DMSO varies between 6 and 10, whereas ^ + in

No abstract

No abstract

No abstract

The protonation in acetonitrile (AN) of the bases (B) water, alcohols, and diethyl ether has been studied by determining spectrophotometrically with Hammett indicators and dibromothymolbenzein their interaction with the solvated proton. Water forms the species BH+, B2H+, B3H+, and B4H+; methanol and «-butyl alcohol yield

The dissociation constant of 2,6-dinitro-4-chlorophenol in , -dimethylformamide (DMF) has been determined conductometrically and spectrophotometrically, while that of 2,6-dinitrophenol was found spectrophotometrically. Dissociation constants of the corresponding tetraethylammonium salts were found of the order of 0.05. The glass electrode was calibrated in mixtures

Evidence is presented that in the three dipolar aprotic solvents, AN, DMF, and MegSO, the p value in the Hammett equation is mainly determined by the rate of the proton exchange in the hydrogen bonded primary reaction product between an un-ionized acid and uncharged base, • • • , to form ionized BH+A". The p value for pifd(HA) of non-ortho-substituted benzoic acids in the solvent AN, which is an extremely weak base, is equal to 2.4, while in the reaction of tetramethylguanidine with these acids in AN, in which salt formation is quantitative, the p value for the formation of BH+A" is 2.1. In conjugation reactions between an uncharged acid and an anion under conditions in which no proton transfer occurs, p values of the hydrogen bonding reaction were found to be much smaller than 2. For Kf(HR-A-), HR being 4-bromophenol and Aan non-ortho-substituted benzoate, p is only -0.6 and -1.2g for phenolates. Exactly the same ratio of 2.1 is found for p values for pKd(HA) in water for phenols (p = 2.1) and benzoic acids (p = 1). Resolution, R, of acid strength of non-ortho-substituted phenols between water and the three dipolar aprotic solvents, AN, DMF, and Me2SO, is equal to 2.0 as compared to 2.4 for non-ortho-substituted benzoic acids and 1.92 for non-hydroxyacetic acids. This similarity in R is attributed mainly to a similar extent of solvation of phenolate, benzoate, and acetate ions in water.

To demonstrate the applicability of cyclic derivative voltammetry to the measurement of rate constants for rapid coupled chemical reactions, the: oxidation of ascorbic acid followed by a rapid hydration reaction was studied. This system has been studied at a variety of pH's (13). The conditions chosen for study here were a pH of 7.2 in phosphate buffer at ambient room temperature. The rate constant for the succeeding chemical reaction was obtained from the measured ratio of the derivative anodic and cathodic peaks obtained at a scan (13) S. P. Perone and W. J. Kretlow, Anal. Chem., 38, 1760. rate of 413 volts/second. The value measured for this rate constant was 1.3 X 103 second-1. This is in good agree ment with values obtained previously with conventional readout (13).