Environ. Sci. Technol. 1993, 27, 2612-2613
CORRESPONDENCE Comment On “Reaction of Suwannee River Fulvic Acld with Chloramine: Characterization of Products via 15N NMR”
Table I. Chlorine Incorporation During Chloramination of Fulvic Acids
incorporation of NHzCl chlorine (%) 56
SIR: In their recent publication, Ginwalla and Mikita (1) showed that reaction of an aquatic fulvic acid with monochloramine at pH 10.5 results in the incorporation of nitrogen. Further, they argued that the true reactive species for N addition may be ammonia, since chloramination and reaction with ammonia produced similar 15N NMR spectra. This work is the first to demonstrate nitrogen incorporation from the chloramination of humics. However, the authors neglected to mention that many investigators have shown that monochloramine donates N in reaction with individual organic compounds. For example, N incorporation has been observed in the reaction of monochloramine with aldehydes (2-5), ketones (5-7), ketenes (B), and amines (9-12). At high pH, monochloramine donates N to phenol to form indophenol (13). This is the basis of the phenate method for ammonia measurement (14) and can be used for the quantification of monochloramine itself (15). Since the electronegativities of N and C1 are similar, (16) both the nitrogen and chlorine in monochloramine can react as electrophiles, nucleophiles, or radicals (17). Based on these observations, it is not unreasonable that monochloramine may donate N in its reactions with aquatic humics. In fact, the possibility of N incorporation by reaction of monochloramine with aldehydic or ketonic moieties in humics under basic conditions was forwarded by Jensen and co-workers (18) in 1985. Ginwalla and Mikita provided good evidence for N incorporation upon chloramination of humics. However, their conclusion that N incorporation resulted from the reaction of ammonia is suspect for two reasons. First, the conclusion is not supported by the experimental data. Using their data, one can calculate that chloramination resulted in 6 % incorporation of NHZC1-N in the aquatic fulvic acid [range = 2-10% based on measured errors (113. In reaction with ammonia under identical conditions, little incorporation of ammonia N was observed (range = -7 to 1%of added “3-N incorporated). If N incorporation during chloramination resulted from the reaction with ammonia, then one would have expected at least as much N incorporation from the reaction with ammonia alone. Second, the conclusion that N incorporation stems from ammonia addition is inconsistent with reasonable mechanistic interpretations. The reaction of ammonia with carbonyl carbons is thought to be a nucleophilic attack (19). The monochloramine nitrogen is expected to be more nucleophilic than the ammonia nitrogen because of the electron-withdrawing ability of chlorine. Thus, both the data and suspected mechanisms do not support the con2612
Envlron. Scl. Technol., Vol. 27, No. 12, 1993
product chlorine-to-carbon ratio (mg/mg) 0.074
5-10
0.016-0.018
0.3-2
0.01-0.04
0.3-2
0.01-0.06
chloramination conditions aquatic fulvic pH 10.5 120-h reaction aquatic fulvic PH 7 24-h reaction aquatic, peat FA PH 7 100-h reaction aquativ fulvic pH6.9-9.2 30-min reaction
ref 1 20
21
24
clusion that ammonia is the N donor during chloramination. Finally, the data of Ginwalla and Mikita are not representative of other fulvic acid chloramination results in two ways. First, the percentage of monochloramine incoporated as organic halide and the resulting chlorineto-carbon ratio in the product are much larger than observed by other investigators (Table I). Second, Ginwalla and Mikita found that the percentage of the monochloramine C1was incorporated into products (56 % ) was higher than the percentage of free chlorine C1 incorporated (22 %) in parallel experiments. This contradicts the observations that monochloramine produces smaller quantities of chlorinated byproducts (i.e., total organic halide) than free chlorine (20, 21). [The higher chlorine incorporation with monochloramine may be due to the high pH employed in their work. For example, it is known that monochloramine is a better disinfectant that OC1- at high pH (22,23).] The high degree of chlorine incorporation may limit the applicability of their work to other systems. In summary, Ginwalla and Mikita have made a strong contribution to the field of fulvic acid oxidation by showing that N incorporation occurs during chloramination at high pH. Their work is in agreement with numerous other investigators who have shown that monochloramine donates nitrogen upon reaction with various functional groups. However, their conclusion that N incorporation may be due to ammonia based on l5N NMR is not in line with either their data or mechanistic expectations. In addition, the high degree of chlorine incorporation brings into question the applicability of their data to water treatment. Literature Cited (1) Ginwalla, A. S.; Mikita, M. A. Enuiron. Sci. Technol. 1992, 26, 1148-1150. (2) Hauser, C. R.; Gillaspie, A. G.; LeMaistre, J. W. J . Am. Chem. SOC.1935,57,567-70. (3) Cross, C. F.; Bevan, E. J.; Bacon, W. J. Chem. SOC.1910, 2404-2406. 0013-936X/93/0927-2612$04.00/0
0 1993 Amerlcan Chemical Soclety
(4) Drago, R. S. J. Chem. Educ. 1910,34,541-545. (5) Crochet, R. A.; Kovacic, P. J. Chem.SOC.Chem. Commun. 1973,716-717. (6) Hauser, C. R.; Hauser, M. L.J.Am. Chem. SOC.1930,52, 2050-2054. (7) Theilacker, W.; Wegner, E. In Newer Methods of Preparative Organic Chemistry; Foerst, W., Ed.; Academic Press, Inc.: New York, 1964;Vol. 111,pp 303-317. (8) Coleman, G. H.; Peterson, R. L.;Goheen, G. E. J. Am. Chem. SOC.1936,58,1875-1876. (9)Omietanski, G. M.;Kelmaers, A. D.;Shellman, R. W.; Sisler, H. H. J. Am. Chem. SOC.1956, 78,3874-3877. (10)Omietanski, G. M.; Sisler, H. H. J. Am. Chem. SOC.1956, 78,1211-1213. (11)Forester, M. 0.J. Chem. SOC.1915,107, 260-267. (12)Hoegerle, K.; Erlenmeyer, H. Helv. Chim. Acta 1956,39, 1203-1207. (13)Patton, C. J.; Crouch, S. R. Anal. Chem. 1977,49,464-469. (14) Standard Methods for the Examination of Water and Wastewater; APHA, AWWA, WPCF: Washington, DC, 1989;pp 4-120-4-121. (15)Hempel, C. E.; Jensen, J. N. Proceedings of the Water Quality Technology Conference;AWWA Denver, CO, 1990;pp 1033-1037. (16) Pauling, L.C. The Nature of the Chemical Bond and the Structure of Molecules and Crystals, 3rd ed.; Cornel1 University Press: Ithaca, NY, 1960;pp 85-90.
Kovacic, P.; Lowery, M. K.; Field, K. W. Chem.Rev. 1970, 70,639-665. Jensen, J. N.; Johnson, J. D.; St. Aubin, J.; Christman, R. F. Org. Geochem. 1985,8,71-76. March, J. Advanced Organic Chemistry, 3rd ed.; John Wiley and Sons: New York, 1985;p 796. Jensen, J. N.; St. Aubin, J. J.; Christman, R.C.; Johnson, J. D. In Water Chlorination: Chemistry,Environmental Impact andHealthEffects;Jolley,R. L.,et al.,Eds.;Lewis Publishers, Inc.: Chelsea, MI, 1985;Vol. 5, pp 939-949. Fleischacker, S. J.; Randtke, S. J. J. Am. Water Works ASSOC. 1983,75, 132-138. Weber, G. R.; Levine, M. Am. J. Public Health 1944,34, 719-728. Norman, T. S.; Harms, L. L.; Looyenga, R. W. J.Am. Water Works Assoc. 1980, 72,176-180. Sander, R. Dr.-Ing. Dissertation, Universitat Fridericiana Karlsruhe, Karlsruhe, Germany, 1981.
James N. Jensen Department of Civil Engineering 212 Ketter Hall State University of New York, Buffalo Buffalo, New York 14260
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