Proton transfer equilibria, temperature and substituent effects on hydrogen bonded complexes between chloranilic acid and anilines

Abstract

The proton transfer equilibrium constants (KPT) for 1 : 1 complex formation between Chloranilic Acid (CA) and a series ofp- andm‒substituted anilines have been measured in 1,4-dioxane spectrophotometrically. The results supported the concept of amine-solvent hydrogen bond formation (short range solvation effect). Beside, this effect, theKPTvalues were apparently affected by the electron donation power of the aniline ring substituent, which was transmitted to the interaction center via resonance and inductive effects. Linear relationships betweenKPTand σ-Hammett substituent constants, or pKvalues formandpanilines,were obtained verifying the above conclusions. The solute-solvent hydrogen bond formation might increase the reactivity of the aniline nitrogen than would the inductive effect of the alkyl group, in case of CA-N-alkyl aniline complexes. The thermodynamic parameters for the proton transfer complex formation were estimated and it was indicated that the solvent–aniline hydrogen bond formation was preferred in the case ofp-substituted aniline complexes more than in the case of the correspondingm‒isomer. It has been found that the proton transfer process was enthalpy and entropy controlled.

FTIR spectroscopic studies and AM1 semi‒empirical calculations of some hydrogen‒bonded complexes of 2,5‒dihydroxy‒3,6‒dichlorobenzoquinone and anilines

“…This could be explained by the fact of a complete proton transfer complex formation. It is worth noting that the proton transfer equilibrium constant between CA and p-anisidine in 1,4-dioxane has a higher value, which is in agreement with the obtained vibration spectral results [5]. In addition, the shift of the carbonyl frequency to a relatively lower one (1614 cm −1 ) could be rationalized in terms of appreciable conjugation including the hydroxyl, and carbonyl groups of CA.…”

“…Intra-and intermolecular proton transfer reactions are among the most common and fundamental chemical processes [1][2][3][4][5][6]. They play a significant role in both inorganic and organic/biochemical reaction mechanisms.…”

Experimental and Computational Evaluation of Chloranilic Acid as an Universal Chromogenic Reagent for the Development of a Novel 96-Microwell Spectrophotometric Assay for Tyrosine Kinase Inhibitors

“…It is well known that CLA has three different ionic forms depending on the pH value. The first form that occurs at low pH is the neutral yellow–orange form (H 2 A), while the second form is the purple form (HA − ), which is stable at pH = 3, and lastly the third form is the pale violet form (A 2– ), which is stable at high pH [ 53 ]. It was observed that the resulting products of all the investigated TKIs with CLA were purple; accordingly, the form HA − was the concluded form of CLA that is involved in the current reaction.…”

Vibrational spectroscopic studies of hydrogen‒bonded complexes between 2,5‐dihydroxy‐P‐benzoquinone and amines

“…There is a massive amount of available data which prove that by varying the donor-acceptor capability of the interaction components in hydrogen bonded complexes, an inversion (critical) region can be reached, intermediate between the non-polar species (HB) and the polar species (PT). In solution, this region is characterized by a proton transfer equilibrium [20] AH · · · B K PT A − · · · HB + (AB) (PT)…”