On the NH and CH acidities of toluidine isomers: theoretical description and practical consequences for the synthesis of certain aniline dyes

Abstract

For the toluidine isomers, amino group acidity represents a characteristic feature of these compounds in their electric neutral state. As demonstrated by theoretical calculations based on the quantum chemistry composite G4 method and density functional theory, the CH acidity of the methyl group is hidden under NH acidity. The transformation of toluidines into their mono‐ and bi‐oxidised states significantly increases the acidity of the methyl group. This study indicates that the presence or absence of these deprotonated species in reaction mixtures will determine the CN or CC coupling toluidine products. In agreement with published synthetic approaches for aniline dyes, such as mauveine and fuchsine, the results obtained explain the alternative reaction pathways occurring during the oxidation of toluidine isomers.

Analysis of certain samples of phenazine dyes from the Historical Dyestuff Collection of the Technical University Dresden by liquid chromatography–mass spectrometry

“…However, it can be assumed that during the synthesis of Chrysaniline by starting with certain aniline/toluidine mixtures, similar reactions proceed to those during the synthesis of Fuchsine with the only difference, that instead of para -toluidine the isomeric ortho -toluidine plays an important role. 24 Their behaviour during the Chrysaniline formation will be discussed subsequently more in detail.…”

Substitution effect of phenol derivatives on electrochemical oxidation potentials: Correlation of theoretical reaction Gibbs free energies

“…The use of implicit solvent approximation assumes that solvent molecules can be replaced by a homogeneously polarisable and thermally averaged isotropic medium (Mennucci et al, 2002). Many theoretical physicochemical properties calculated for flavonols (Michalík et al, 2019b), phenols (Michalík et al, 2017), alcohols (Michalík and Lukeš, 2016), model amines (Rimarčík et al, 2010), and toluidine isomers (Lukeš and Hartmann, 2021) solvated in different polar solvents are reasonably well estimated using implicit solvent models combined with DFT. Satisfactory predictions were also obtained for hydroxyl groups attached to non-aromatic rings (Žemlička et al, 2014) and alkyl chains (Štellerová and Lukeš, 2021).…”

Impact of molecular chain length on polarizabilities of model acenes and oligomers

“…Smaller oligomers are of particular interest due to their relatively well-defined structure directly affecting their electronic structure (Lukeš et al, 2003) and simplifying manipulation, e.g., solubility, purification, film preparation of thiophene derivatives (Lukeš et al, 2002). Nevertheless, a large number of electrochemical (Prasad et al, 1991) and chemical coupling (Schuetz et al, 1971;Lukeš et al, 2021) reactions are employed for the preparation of the above-mentioned compounds. An alternative to oligo mers is linear acenes (dos Santos, 2006).…”