Premium
Solvated proton as the main reagent and a catalyst in the single‐stage aromatic sulfonation and protodesulfonation of sulfonic acids
Author(s) -
Kozlov Vladimir A.,
Ivanov Sergey N.,
Koifman Oskar I.
Publication year - 2017
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3715
Subject(s) - chemistry , sulfuric acid , solubility , acid catalysis , reagent , proton , protonation , electrophile , catalysis , computational chemistry , organic chemistry , ion , physics , quantum mechanics
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 π‐ and 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 single‐stage 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.