| Abstract
| - Organically complexed iron species can play a significantrole in many subsurface redox processes, including reactions that contribute to the transformation and degradationof soil and aquatic contaminants. Experimental results demonstrate that complexation of FeII by catechol- and thiol-containing organic ligands leads to formation of highly reactivespecies that reduce RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and related N-heterocyclic nitramine explosivecompounds to formaldehyde and inorganic nitrogen byproducts. Under comparable conditions, relative reactionrates follow HMX << RDX << MNX < DNX < TNX. Observed rates of RDX reduction are heavily dependent on theidentity of the FeII-complexing ligands and the prevailingsolution conditions (e.g., pH, FeII and ligand concentrations).In general, reaction rates increase with increasing pH andorganic ligand concentration when the concentration ofFeII is fixed. In solutions containing FeII and tiron, a model catechol, observed pseudo-first-order rate constants (kobs) forRDX reduction are linearly correlated with the concentrationof the 1:2 FeII−tiron complex (FeL26-), and kinetic trends arewell described by −d[RDX]/dt = kFeL26−[FeL26-][RDX], wherekFeL26− = 7.31(±2.52) × 102 M-1 s-1. The reaction productsand net stoichiometry (1 mol of RDX reduced for every 2 molof FeII oxidized) support a mechanism where RDX ringcleavage and decomposition is initiated by sequential1-electron transfers from two FeII-organic complexes.
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