Protonation acidity constants for benzotoluidides in sulfuric acid solutions

Abstract

Abstract:The protonation of o-, m-and p-benzotoluidide in sulfuric acid solutions is studied by UV spectroscopy in the 190-350 nm region. Principal component analysis is applied to estimate the contributions of the effect of protonation and the medium effect. For the substances studied in this work, the first principal component (PC) captures about 98 % of the variance and the second PC ∼100 % of the cumulative percentage variance in the 210-350 nm region. The same spectral region is used for calculation of the ionization ratio from the coefficients of the first PC and mole fractions of the base and its conjugate acid. Using these data and Hammett's equation (pK BH+ = H X + log I), the pK BH+ values for the protonation reaction are obtained. The dissociation constants as well as the solvent parameters m* (∼0.43) and φ (∼0.60) are calculated using the Excess Acidity Method (-pK BH+ = 2.28-2.30) and the BunnettOlsen Method (-pK BH+ = 2.24-2.28). The probable sites of protonation are discussed.

Determination of protonation constants and structural correlations for some tertiary formamides and acetamides in sulfuric acid with UV spectroscopy

“…In this study, the CVA applied for medium effect removing has not given the expected results, as it was successfully done in substituted benzamides [10] and toluidides [11]. The reason for this is that the absorption bands of BH + for the spectra recorded in sulfuric acid at concentrations higher than 6 mol dm -3 are present under 190 nm.…”

“…While, in the case of DiPAA ionization ratios, these were calculated by molar fractions on unprotonated and protonated form (Fig. 5), method that was previously applied with success for toluidides [11]. Similarly, in our previous investigation for indoles, the same approach was used, with the exception that the calculations are based on the absorbances used at four selected wavelengths [33].…”

Analysis of acid-base properties of some p-substituted aromatic hydrazones in aqueous perchloric acid by spectrophotometric and semiempirical methods

“…The influence of the solvent can be eliminated by employing various methods such as principal component analysis (PCA) [19], the target-testing method of factor analysis [20] and characteristic vector analysis (CVA) [21]. One of the most commonly used is CVA, which has been tested and proven to be applicable in the analysis of spectroscopic data, to investigate problems dealing with protonation [22].…”

Crystal Structure of the 5-Chloro Salicylamides: Three Different Types of the H-bonding Influenced Linear Chain Formation in the Solid State

“…The ability of an amide to act as a proton acceptor (C=O group is the site of protonation in amides) can be illustrated by the protonation acidity constants for structurally similar N-benzylbenzamide (pK a (BH + ) = −1.83 in water [44]) and for related N-(4-methylphenyl)benzamide (pK a (BH + ) = −2.28 in water [45]). From the negligible difference in these two values it is clear that the acceptor ability of the amide carbonyl group towards protons is almost the same.…”