Ja. Perlinger et al., IRON PORPHYRIN AND MERCAPTOJUGLONE MEDIATED REDUCTION OF POLYHALOGENATED METHANES AND ETHANES IN HOMOGENEOUS AQUEOUS-SOLUTION, Environmental science & technology, 32(16), 1998, pp. 2431-2437
Reduction rate constants of seventeen polyhalogenated methanes and eth
anes were measured in aqueous solutions containing bulk reductants and
the electron-transfer mediators iron porphyrin or juglone (5-hydroxy-
1,4-naphthoquinone). Rate constants Varied 4 orders of magnitude in th
e case of reaction with iron porphyrin and 7 orders of magnitude in th
e reaction with mercaptojuglone, an addition product of juglone and hy
drogen sulfide. For the iron porphyrin system the results support a re
action mechanism in which one electron is transferred in an outer-sphe
re process to the polyhalogenated alkane with bond breakage in the tra
nsition state. In the juglone system two competing reaction mechanisms
are proposed: an outer-sphere electron transfer to the polyhalogenate
d alkane and an S(N)2 reaction at the halogen. The kinetic results are
directly applicable to environmental systems containing common reduct
ants such as natural organic matter and reduced iron species, providin
g a ''fingerprint'' of reactivity for examination of reactive species
and rate-limiting steps in those systems.