Investigation of intermolecular proton exchange of 3,6-di-tert-butyl-2-oxyphenoxyl withN-phenylanthranilic acid by ESR spectroscopy method

Abstract

Investigation of intermolecular proton exchange of 3,6-di-tert-butyl-2-oxyphenoxyl with N-phenylanthranilic acid by ESR spectroscopy method In this work we studied the intermolecular proton exchange (IPE) reaction between the spin probe of 3,6-ditert-butyl-2-hydroxyphenoxyl (I) and the aromatic amino acid N-phenylanthranilic acid (N-PhAA). The experimental spectra of the 3,6-di-tert-butyl-2-hydroxyphenoxyl-N-phenylanthranilic acid system were recorded using dynamic EPR spectroscopy. The studies were carried out in a non-aqueous indifferent solvent toluene in a wide temperature range. The theoretical EPR spectra of the radical IN -PhAA system corresponding to various process rates were successfully simulated using the ESR-EXHANGE program. This program is written in the modern version of the algorithmic language Fortran 90. The general line-form equation for the four-jump model have been derived from the modified Bloch equations. The second-order rate constants for the intermolecular proton exchange process between radical I and N-PhAA were determined by comparison of the experimental and simulated EPR spectra. The iterative least squares procedure was used for computer analysis of the kinetic data of intermolecular proton exchange and for obtaining activation parameters of the reaction. From kinetic data it follows that N-phenylanthranilic acid has the lowest value of protolytic ability in comparison with aminobenzoic acids.

ESR-Study of the Proton Exchange with Aliphatic Amino Acids in Toluene

“…The Arrhenius plot showed a good linear relationship between lgkexch and 1/T (Fig. 2 Table 1 shows similar parameters of hexanoic, hexanedioic, 2-anilinobenzoic acids and dodecan-1amine for comparison [17,18]. Analysis of available data suggests that despite their amphoteric nature 2and 6-aminohexanoic acids in toluene react with the spin probe at a rate comparable to the rate of the proton exchange reaction with aliphatic monocarboxylic acids (hexanoic acid is given for an example).…”

“…Along with the above reaction (A↔C, B↔D), it includes tautomeric transformations of a semiquinone radical, i.e., intramolecular migration of the hydrogen atom of the hydroxyl group between oxygen atoms (A↔B, C↔D) [17].…”

“…It should be noted that the proton exchange process presumably has a "cooperative" mechanism, that is, a cyclic hydrogen-bonded complex is formed during the reaction. The lifetime of this complex directly affects the rate of the whole process [17].…”

DFT Study of Complexation Reactions Involving Dicarboxylic Acids: Hydrogen Bonds, Influence of Solvent Nature

“…Previously obtained ESR spectroscopy data suggest the ability of carboxylic acids to form dimer associates in nonpolar solvents. The authors of [3][4][5][6][7] showed that the proton exchange between the semiquinone radical and formic acid in toluene occurs predominantly with the dimeric form of the acid. Dicarboxylic acids containing two carboxyl groups are of greater interest compared to monosubstituted analogues since they have more pronounced electron acceptor properties [8].…”

“…In addition, it is assumed that intermolecular proton exchange is facilitated by the formation of a complex transition intermediate of the reaction due to the coordination of both carbonyl groups. Furthermore, the presence of different functional groups affects the coordination of the four-center cyclic complex due to steric hindrances when approaching the reaction centers [3][4][5][6][7][8]. However, modern physical methods that make it possible to determine the kinetic parameters of reactions, such as the rate constant or the activation energy of the process, are not suitable for detecting the formation of intermediate particles in the composition of hydrogenbonded complexes.…”