The mechanism of redox scavenging of a highly active cyclic seleninate was modeled by using density functional theory and solvent-assisted proton exchange (SAPE), a method of microsolvation intended to mimic the role of the solvent in proton-transfer reactions. Models of the proposed mechanism suggest that a pathway to a selenenyl sulfide, a possible dead-end intermediate, is favored over regeneration of the seleninate catalyst. Alternate pathways through selenurane intermediates and a cyclic selenenate also appear to lead to the selenenyl sulfide. Based upon the DFT-SAPE results, we suggest that the high level of catalysis shown by the cyclic seleninate may be attributed to experimental reaction conditions, in which the excess oxidant ensures that the catalytic cycle bypasses the selenenyl sulfide. Catalysis under less oxidizing conditions are proposed to occur through oxidation of the selenenyl sulfide to the seleninyl sulfide.