Factors controlling regioselectivity in the reduction of polynitroaromatics in aqueous solution

Susan E. Barrows, Chris Cramer, Donald G Truhlar, Michael S. Elovitz, Eric J. Weber

Research output: Contribution to journalArticlepeer-review

65 Scopus citations

Abstract

Regioselectivities in the bisulfide reduction of 10 polynitroaromatics (PNAs) to monoamine products have been determined; four of these compounds have also been reduced by anoxic sediments in heterogeneous aqueous solution, and the same regioselectivities are observed. Analyses of Austin Model 1- Solvation Model 2 electrostatic potential surfaces for the radical anions of these polynitroaromatic compounds provides a reliable method of predicting the regioselectivity of their reduction. In particular, at their minimum- energy geometries in aqueous solution, it is the more negative nitro group that is selectively reduced. This is consistent with a mechanism where regioselection occurs upon kinetic protonation at the site of maximum negative charge in the radical anion formed after the first electron transfer to the neutral PNA. Inclusion of solvation effects is critical in order to confidently predict the electrostatic preference for the reduction of one nitro group over the others. Sterically uncongested nitroaromatic radical anions have gas-phase geometries in which the nitro group is coplanar with the aromatic ring. However, ortho substituents and solvation effects both oppose this tendency and can lead to nitro groups that are rotated out of the ring plane and pyramidalized.

Original languageEnglish (US)
Pages (from-to)3028-3038
Number of pages11
JournalEnvironmental Science and Technology
Volume30
Issue number10
DOIs
StatePublished - Oct 15 1996

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