Solvated proton as the main reagent and a catalyst in the single-stage aromatic sulfonation and protodesulfonation of sulfonic acids

Abstract

This review is devoted to the critical analysis of the existing contradictory ideas about kinetic description and the mechanisms of electrophilic aromatic substitution (EAS), ie, reversible arene sulfonation and hydrolysis (protodesulfonation) of arenesulfonic acids. Contemporary scientific and educational literature contains prevailing, widespread points of view on the multistage nature processes of the EAS that proceed via πand σ-complexes and are accompanied by arenium ion formation. This interpretation does not account for determining influence of the medium, and the process accompanies the loss of aromaticity. The review presents an alternative point of view: These processes proceed via singlestage and the same transition state. To substantiate this position, we reviewed in detail the contemporary ideas on the solvated proton structure, the limits of applicability of acidity function Н о and excess acidity Х scales, and the experimental solubility data of arenesulfonic acid hydrates in sulfuric acid. This solubility depends on the medium acidity (h o ), which provides the formation of 3 conjugated types of hydrates: anionic (АrSO 3 − ·H 2 O), hydroxonium-arene sulfonated (АrSO 3 − ·H 3 O + ), and the hydroxonium complex with the H-form of АrSO 3 Н·H 3 O + acid. In sulfuric acid solutions with an excess of water, irreversible hydrolysis proceeds with the participation of ArSO 3 − ·H 3 O + . However, protodesulfonation becomes reversible and proceeds with the participation of ArSO 3 Н·H 3 O + in solutions with an excess of sulfuric acid. A conclusion has been made about determining the role of the hydrated proton environment by means the formation of a cyclic transition state. An alternative 2-stage mechanism of EAS is logically and energetically unsubstantiated and, therefore, should be rejected.

The key mechanism of conductivity in PEDOT:PSS thin films exposed by anomalous conduction behaviour upon solvent-doping and sulfuric acid post-treatment

“…22 Studies have already addressed the complex mechanism of aromatic polymer desulfonation by sulfuric acid. [23][24][25] Desulfonation is initiated when sulfuric acid dissociates into the hydronium ion and HSO 4 À . The sulfonic acid (-SO 3 H) and sulfonate ion (-SO 3 À ) groups are not conjugated with the benzene ring and the enhancement of the electron density at a meta-position of the benzene ring on the carbon atom from the C-S bond creates a strong, partially positive charge on the sulfur atom 26 (Fig.…”

Anthraquinone Flow Battery Reactants with Nonhydrolyzable Water-Solubilizing Chains Introduced via a Generic Cross-Coupling Method

“…6,7,16,17 It appears that redox cores bonded to watersolubilizing groups via C−heteroatom bonds are susceptible to nucleophilic substitution reactions, resulting in the detachment of water-solubilizing groups from redox cores. 10,18,19 Because 9 Redox centers and -SO 3 − , -CO 2 − , and -PO 3 2− water-solubilizing groups are considered electron-withdrawing because of their resonance and negative inductive effects. When there is only a single unsubstituted methylene group (-CH 2 -) between a redox center and a water-solubilizing group, the close proximity of the electron-withdrawing groups to the redox core may cause molecules to be vulnerable to nucleophilic attack.…”

Long-lifetime, potentially low-cost anthraquinone flow battery chemistry developed from study of effects of water-solubilizing group and connection to core

“…6,7,16,17 It appears that redox cores bonded to watersolubilizing groups via C−heteroatom bonds are susceptible to nucleophilic substitution reactions, resulting in the detachment of water-solubilizing groups from redox cores. 10,18,19 Because carbon-carbon bonds are more chemically resistant against nucleophilic attack than carbon-heteroatom bonds such as C−O (S, N), it is desirable to incorporate carbon-carbon bonds between redox centers and water-solubilizing ending groups. 9 Redox centers and −SO3 − , −CO2 − , −PO3 2− water-solubilizing groups are considered electronwithdrawing because of their resonance and negative inductive effects.…”