QUANTUM-CHEMICAL INVESTIGATION OF THE MECHANISM OF THE SULFONATION OF PYRROLE

Abstract

A detailed quantum-chemical study of the sulfonation of pyrrole with regard to the effect of the solvent (the model of overlapping spheres) on the energy characteristics of the formation of the σ-complexes produced during attack on the  α- and  β-positions of the heterocycle and their possible transformation paths was made by density functional theory [the B3LYP/6-31G(d) method]. The possibility of mutual transformations between the isomeric σ-complexes by  α/β-migration of the SO3 is examined. The formation of pyrrolesulfonic acids was studied for the case of the intramolecular rearrangement of the complexes. Comparison of the activation energies shows that in contrast to the gas-phase reaction the formation of the β-sulfonic acid is preferred in methylene chloride: the solvation energy of the α-isomer of the σ-complex is higher than the energy for the transition state of its rearrangement and its product, α-pyrrolesulfonic acid, leading to an increase in the kinetic barrier and to a decrease of the energy gain on the path to the formation of the latter. The opposite variation of the energy characteristics on the path to the  β-isomer with regard to solvation leads to  agreement between the calculated data and the experimentally observed preferred formation of the β-pyrrolesulfonic acid.

How to Cite
Belen'kii, L. I.; Nesterov, I. D.; Chuvylkin, N. D.  Chem. Heterocycl. Compd. 2006, 42, 1414. [Khim. Geterotsikl. Soedin. 2006, 1647.]

For this article in the English edition see DOI 10.1007/s10593-006-0257-1