TY - JOUR
T1 - Reactivity of substituted benzotrichlorides toward granular iron, Cr(II), and an iron(II) porphyrin
T2 - A correlation analysis
AU - Kohn, Tamar
AU - Arnold, William A.
AU - Roberts, A. Lynn
PY - 2006/7/1
Y1 - 2006/7/1
N2 - Cross-correlations of rate constants between a system of interest and a better-defined one have become popular as a tool in studying transformations of organic pollutants. A slope of unity (if the correlation is conducted on a log-log basis) in such plots has been invoked as evidence of a common mechanism. To explore this notion, benzotrichloride and several of its substituted analogues were reacted with Cr(H2Ol62+, an iron(II) porphyrin (iron mesotetra(4-carboxyphenyl)porphine chloride, Fe(II)TCP), and granular iron. The first two reductants react with organohalides by dissociative inner sphere single-electron transfer, while mechanism(s) for organohalide reduction by granular iron are still debated. Apart from sterically hindered compounds, good correlations were obtained in comparing any two systems, although slopes (on a log-log basis) deviated from unity. We argue that a slope of unity is neither necessary norsufficient evidence of a common mechanism. Overall rate constants may be composite entities, consisting in part of rate or equilibrium constants for adsorption onto surfaces or for precursor formation in solution; these components may differ between systems in their susceptibility to substituent effects. Cross-correlations may prove useful in predicting reactivity in the absence of steric effects, butadditional evidence is required in deducing reaction mechanisms.
AB - Cross-correlations of rate constants between a system of interest and a better-defined one have become popular as a tool in studying transformations of organic pollutants. A slope of unity (if the correlation is conducted on a log-log basis) in such plots has been invoked as evidence of a common mechanism. To explore this notion, benzotrichloride and several of its substituted analogues were reacted with Cr(H2Ol62+, an iron(II) porphyrin (iron mesotetra(4-carboxyphenyl)porphine chloride, Fe(II)TCP), and granular iron. The first two reductants react with organohalides by dissociative inner sphere single-electron transfer, while mechanism(s) for organohalide reduction by granular iron are still debated. Apart from sterically hindered compounds, good correlations were obtained in comparing any two systems, although slopes (on a log-log basis) deviated from unity. We argue that a slope of unity is neither necessary norsufficient evidence of a common mechanism. Overall rate constants may be composite entities, consisting in part of rate or equilibrium constants for adsorption onto surfaces or for precursor formation in solution; these components may differ between systems in their susceptibility to substituent effects. Cross-correlations may prove useful in predicting reactivity in the absence of steric effects, butadditional evidence is required in deducing reaction mechanisms.
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U2 - 10.1021/es051737x
DO - 10.1021/es051737x
M3 - Article
C2 - 16856743
AN - SCOPUS:33746687895
SN - 0013-936X
VL - 40
SP - 4253
EP - 4260
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 13
ER -