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Updated: Oct 3, 2026

Efficient Synthesis of Polyfunctionalized Benzenes in Water via Persulfate-promoted Benzannulation of α,β-Unsaturated Compounds and Alkynes
Published on: December 16, 2019
Molecular Modeling Studies on Aromatic Sulfonation. 1. Intermediates Formed in the Sulfonation of Toluene
John O. Morley1, D. W. Roberts
1Department of Chemistry, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP, and Unilever Research Port Sunlight Laboratory, Quarry Road East, Bebington, Wirral L63 3JW.
Abstract:
Molecular modeling studies suggest that the mechanism of the sulfonation of toluene with sulfur trioxide proceeds via the formation of a pi-complex (4b) which rearranges to form a Wheland intermediate (5). This structure is unable to form toluenesulfonic acid (8) directly and prefers to react with a further molecule of sulfur trioxide to form a pyrosulfonate intermediate (6a) which undergoes a facile prototropic rearrangement involving the transfer of the ring hydrogen at the sp(3) carbon of 6a to the sulfonate oxygen atom to form the corresponding acid (7). The formation of toluenesulfonic acid (8) appears to arise from an exothermic reaction of between the pyrosulfonic acid (7) and toluene. The overall calculated thermodynamic change in moving from the reaction of one molecule of sulfur trioxide with toluene to the sulfonic acid (8b) is fully consistent with an estimated experimental value of -33.5 kcal mol(-1) for the same reaction using simple alkylbenzenes.
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