QUANTUM-CHEMICAL INVESTIGATION OF THE EFFECT OF SOLVENT POLARITY ON THE DIRECTION OF SULFONATION OF PYRROLE

Abstract

The relative stability of the isomeric  σ-complexes formed in the sulfonation of pyrrole at the  α- or β− position  (the  α-isomer is energetically more favorable) does not agree with the experimentally established positional selectivity of  substitution (the formation of  β-pyrrolesulfonic acid). However, quantum-chemical calculations of the energy  parameters for the reaction of pyrrole and SO3 with due regard to the solvation effect in the model solvent methylene chloride (ε = 8.93) lead to the conclusion that the calculated activation energy of the rearrangement to the more favorable β-pyrrolesulfonic acid for the less favorable  β-isomer of the  σ-complex is lower than on the path to the formation of the α-pyrrolesulfonic acid. It was shown that the significant increase in the polarity of the model medium in the transition to DMSO (ε = 46.7) does not lead to substantial change in the energy parameters of the reaction. The explanation for the positional selectivity during the sulfonation of pyrrole using Py⋅SO3, according to previous data, involves the participation of the pyridine in the transformation of the σ-complexes into the products. The calculations  were made by the B3LYP/6-31G(d) and HF/3-21+G methods using the model of overlapping spheres to take account of solvation.

How to Cite
Belen'kii, L. I.; Nesterov, I. D.; Chuvylkin, N. D..  Chem. Heterocycl. Compd. 2007, 43, 28. [Khim. Geterotsikl. Soedin. 2007, 34.]

For this article in the English edition see DOI 10.1007/s10593-007-0004-2