Commentary on Kinetic Constants for Oxidation by Permanganate
PGT
When I was a postdoc with Jurg Hoigne at EAWAG (1989-1991), I was impressed that his work on chemistry of drinking water treatment was a major source of high-quality, standard-reference kinetic data for oxidation reactions in aqueous media. For environmentally relevant species, Hoigne’s data still is prominent in the (definitive) NDRL-NIST database of rate constants for solution phase oxidation reactions (http://kinetics.nist.gov/solution/).
Hoigne's approach and high standards inspired my 2002 SERDP project (ER-1289) to measure and compile kinetic data relevant to in situ chemical oxidation (ISCO). One outcome of this was the IscoKin database (now at http://cgr.ieh.ohsu.edu/iscokin/), which includes some rate constants mined from the NDRL-NIST database, but consists mainly of data we compiled from primary sources on contaminants (e.g., chlorinated ethenes) and oxidants (e.g., permanganate) of particular interest in ISCO.
With all of this data in hand, we became interested in meta-analysis of the dataset, which has many benefits. These benefits range from checking data quality (e.g., identifying outliers) to identifying broad trends in reactivity vs. structure (e.g. for estimating values of missing data). Our meta-analysis of kinetic data for oxidation of groundwater contaminants by permanganate was published in 2006 (http://dx.doi.org/10.1021/es051330s).
This background explains my motivation for publishing a comment on the recent paper by Mahmoodlu et al. titled "Evaluation of the kinetic oxidation of aqueous volatile organic compounds by permanganate” (2004 Sci. Total Environ. 485–486: 755-763, 10.1016/j.scitotenv.2013.11.066). Their paper reports several new rate constants for permanganate oxidation of groundwater contaminants obtained by fitting a second-order kinetic model.
In my commentary, I added some “meta-analysis” of their new rate constants vs. those that we had summarized previously. I also tried to add some perspective on the differences between second-order and pseudo-first-order methods for fitting kinetic data. The discussion is a nice window into both fundamental and applied aspects of applying chemical kinetics to environmental engineering problems.
My comment, and the original authors’ reply to my comment are as follows:
Tratnyek, P. G. 2015. Comment on “Evaluation of the kinetic oxidation of aqueous volatile organic compounds by permanganate” by M. G. Mahmoodlu, S. M. Hassanizadeh, and N. Hartog, in Science of the Total Environment (2014) 485–486: 755–763. Sci Total Environ 502: 722-723. [http://dx.doi.org/10.1016/j.scitotenv.2014.08.065]
Hartog, N., M. M. G, and S. M. Hassanizadeh. 2015. Bias by the inappropriate use of the pseudo-first order approach to estimate second-order reaction rate constants: Reply to the commentary by Tratnyek (this issue). Sci Total Environ 502: 724-725. [http://dx.doi.org/10.1016/j.scitotenv.2014.09.061]