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CORRESPONDENCE Comment on “Homogeneous Hydrolysis Rate Constants for Selected Chlorinated Methanes, Ethanes, Ethenes, and Propanes” SIR: The comprehensive study of the reactions of C1-Cs chloroaliphatic compounds with OH-and H 2 0 by Jeffers, Ward, Woytowitch, and Wolfe (1)represents a substantial contribution to our understanding of the rates and pathways by which these compounds undergo dechlorination in aqueous solution. However, we are writing to clarify an apparent discrepancy (1)between some of the data from the Jeffers et al. study and data from our own work (2). In discussing their results, Jeffers et al. (1) compare their kinetic data on the dehalogenation of 1,2-dichloroethane (1,2-DCA) in water at neutral pH with ours ( 2 ) . In their paper, Jeffers et al. (1) state, “For the neutral reaction, Barbash and Reinhard found ... [a] 37-year half-life at 25 “C [which]is about half our 72-year calculated value”. The estimated half-life obtained by Jeffers et al. for 1,2-DCA at 25 “C was based on experiments conducted in dilute HCl(3). The data that they quote from our work, however, include the effect of 0.05 M phosphate buffer (0.025 M Na2HP0, + 0.025 M KH?P04)on the reaction rate. When
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we extrapolated our rate constants to zero buffer concentration, we obtained an estimated half-life for 1,ZDCA at 25 “C of 64 years (2),in close agreement with the 72-year estimate calculated by Jeffers et al. (1) and the 72-year value computed (2) from the data of Ehrenberg et al. (4). The foregoing example illustrates the importance of accounting for the potential influence of phosphate buffers on the rates of dehalogenation of haloaliphatic compounds in aqueous solution. Registry No. 1,2-DCA, 107-06-2; chloromethane, 74-87-3; chloroethene, 75-01-4; chloropropane, 26446-76-4.
Literature Cited (1) Jeffers, P. M.; Ward, L. M.; Woytowitch, L. M.; Wolfe, N. L. Enuiron. Sci. Technol. 1989, 23, 965-969. (2) Barbash, J. E.; Reinhard, M. Enuiron. Sei. Technol. 1989, 23, 1349-1358. (3) Jeffers, P. M., personal communication (9/18/89). (4) Ehrenberg, L.; Osterman-Golkar, S.; Singh, D.; Lundqvist, U. Radiat. Bot. 1974, 15, 185-194.
Jack E. Barbash,” Martin Reinhard Department of Civil Engineering Stanford University Stanford, California 94305
0013-936X/90/0924-0268$02.50/0
0 1990 American Chemical Society
