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ACS Symposium Series 82; American Chemical Society: Washington, DC, 1979; p p 278-91. (26) Conyers, B.; Scully, F. E., Jr. Environ. Sci. Technol., following paper in this issue. Received for review May 21,1992. Revised manuscript received
October 1,1992. Accepted October 5,1992. This research is based on work supported by the National Science Foundation, Grant BCS-9002442, Dr. Edward Bryan, project manager. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the National Science Foundation.
N-Chloroaldimines. 3. Chlorination of Phenylalanine in Model Solutions and in a Wastewater Barbara Conyers and Frank E. Scully, Jr.*
Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia 23529-0126 The chlorination reactions of phenylalanine in water and wastewater were studied. At the lower Cl/N molar ratios N-chlorophenylalanine and phenylacetaldehyde were identified as the main products while phenylacetonitrile and N-chlorophenylacetaldiminewere the major products at Cl/N ratios of 2.0 and beyond. The concentration of phenylalanine in a primary municipal wastewater effluent was determined, and the chlorination products were found to be the same as those in model solutions. N-Chlorophenylacetaldimine decomposes slowly ( t l I z= 35 h) in water (pH 7.0 and 8.0) and in wastewater (pH 7.0, estimated t l / 2 of 58 h). The distribution of chlorination products in the wastewater supports the theory that monochlorinated organic amino nitrogen compounds may represent a disproportionately high fraction of the chlorine-containing oxidants present in marginally chlorinated primary effluent.
Introduction With the recognition over the past 15 years that chlorinated municipal wastewaters can have adverse effects on various life stages of fish and other aquatic life, there has been considerable interest in the identification of chlorination byproducts responsible for these effects and concern about the environmental impact of the discharge of chlorinated wastewater into otherwise clean receiving waters. Chloramines, a group of chlorination byproducts formed in wastewater, have been particularly associated with toxic effects in fish (1-3). Organic N-chloramines, known byproducts of wastewater chlorination (4, 5 ) , pose an additional problem. Although they are not bactericidal, they respond to conventional methods of disinfection analysis as if they were. For this reason,. there is concern that the disinfectant concentration in a chlorinated wastewater may be overestimated (6-12). Recent studies of the reactions of aqueous chlorine with wastewater amino acids demonstrated that a new class of N-chlorinated organic nitrogen byproducts, N-chloroaldimines, are among the products formed when sufficient chlorine is added (13, 14). The present study of the chlorination of phenylalanine is an extension of this work. The UV-absorbing properties of phenylalanine’s chlorination products have enabled us to probe more carefully the mechanisms of formation of these compounds. Furthermore, the chlorination of this amino acid in a wastewater provided new insights into the potential disinfection interference of amino acids and into the the apparent reaction of some of phenylalanine’s chlorination products with other wastewater organic components. 0013-936X/93/0927-0261$04.00/0
Experimental Section General Information. All chemicals were reagent grade or better. Phenylalanine was obtained from Sigma Chemical Co. Phenylacetonitrile (98%) and phenylacetaldehyde were purchased from Aldrich Chemical Co. The Amersham Corp. was the source of ~-[2,3,4,5,6-~H]phenylalanine obtained in an aqueous solution containing 2% ethanol (130 Ci/mmol, lot no. TRK.648, batch 57). Reagents and methods used for the analysis of residual chlorine and for the concentration, derivatization, and HPLC analysis of amino acids in wastewaters have been described elsewhere (13-17). The IR, NMR, GC, and GC/MS instrumentation and methods used in these studies have been described elsewhere (14). High-performance liquid chromatography (HPLC) was performed using a Waters Associates liquid chromatography system described previously (13). In all experiments involving phenylalanine or [3H]phenylalanine, the chlorination products were separated with a 15-cm Whatman 5-pm Partisil ODS-3 column. Radiochromatograms were generated as previously reported (14). The average recovery from the column was 91 f 5% of the radioactivity applied. Model Solutions of Phenylalanine. Model solutions M) in 0.025 M NaH2P04(pH of phenylalanine (1.43 X 7.0) were prepared. Aliquots (15 mL) were chlorinated to Cl/N molar ratios of 0.4,0.8, 1.2, 1.6, 2.0, 2.4, and 2.8. Sufficient chlorine-demand-free (CDF) water was added to produce a total volume of 18.5 mL. Each solution was incubated at room temperature in the dark for 30 min before a 250-pL volume of each reaction mixture was analyzed by HPLC (UV detector). The solvent system and gradient employed were the same as those described previously (13). All eluting peaks were tested for oxidizing chlorine as described previously (14). The experiment was repeated with model solutions containing [3H]phenylalanine (0.70pCi/mL) in a manner similar to that described previously for other tritiated amino acids (13, 14). Determination of Volatile Chlorination Products. Aliquots (15 mL) of the model phenylalanine solution at pH 6.0, 7.0, and 8.0 were reacted with chlorine, and the active chlorine was reduced with sodium thiosulfate solution as reported previously (14). Internal standard (1.0 mL of 4.6 X M anisole in water) and sufficient CDF water were added to bring the final volume to 18.5 mL. Each reaction mixture was extracted with 3 mL of freshly distilled ether, and l-pL volumes of the extract were analyzed (three replicates) by GC (14) (N2, flow rate 1.25 mL/min). Thirty seconds after a splitless injection, a 601 split was applied. After an initial column temperature of
0 1993 American Chemical Society
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60 "C was maintained for 10 min, the temperature was increased at a rate of 10 "C/min to a final temperature of 130 "C. The experiment was also carried out on solutions chlorinated to Cl/N molar ratios of 0.8,1.6, and 2.4 at pH 7.0 which were not reduced with thiosulfate prior to analysis. Internal standard was added and the volume adjusted as above before extraction and analysis. The response of the GC detector to phenylacetaldehyde and phenylacetonitrile was standardized using anisole as an internal standard. The standard curve for phenylacetaldehyde had a slope of 2.31 f 0.07, an intercept of -0.03 f 0.02, and a correlation coefficient of 0.998. The curve for phenylacetonitrile had a slope of 9.63 f 0.07 and an intercept of -0.23 f 0.02. The correlation coefficient was 0.999, Synthesis and Characterization of N-Chlorophenylacetaldimine. N-Chlorophenylacetaldiminewas synthesized in a manner similar to that described previously for N-chloroisobutyraldimine (14). A dried chloroform extract of the reaction mixture gave the following IR spectrum (between NaCl plates) after spectral subtraction of the CHC1,: 3090 (w), 3070 (w), 3030 (m), 2280 (C=N, w), 1620 (w), 1500 (m), 1450 (m), 1410 (w), 1220 (m) cm-l (w, weak; m, medium; s, strong). The proton NMR spectrum (CDCl,, Figure 3) showed the following: 8.24 (t,0.7 H, HC=N, J = 6.4 Hz), 8.06 (t, 0.3 H, HC=N, J = 4.6 Hz), 7.31 (8, 5 H, Cdr,), 3.87 (d, 0.6 H, CH,C=N, J = 4.6 Hz), 3.72 ppm (d, 1.4 H, H2CC=N, J = 6.4 Hz). The noise-decoupled 13C spectrum (CDC1,) of the dried extract produced a series of singlets with the following chemical shifts: 175 (C=NCl), 173 (C=NCl), 133-126 (aromatic C),42 (CH,), 40 ppm (CH,). Chromatographic conditions for GC/MS analysis were the same as those described above for analysis of volatile products. The detector filament was activated 270 s after injection. Ether extracts were used to obtain methane CI mass spectra: MS m / z (relative intensity) 156 (2), 154 (12) (MH+), 119 (6), 118 (63) (MH - HCl)+, 117 (14), 92 (15), 91 (100). Description, Handling, and Analyses of Wastewater. The wastewater used in this study was primary effluent obtained on January 8, 1991, from a typical secondary treatment plant described in previous work as plant 2 (18). Handling and analyses have been described previously (13,18). The method for determining (a) the 30min chlorine demand curve (breakpoint curve) of the wastewater (13) and (b) the concentrations of the amino acid phenylalanine in the wastewater (14) have been described elsewhere. The standard concentration curve for phenylalanine had a slope of 7.21 (f0.04) X lo4, an intercept of 1.21 (f1.40) X lo3,and a correlation coefficient of 0.999. Due to coelution problems, an acceptable internal standard was not found. The average (n = 5) recovery efficiency from the cation exchange column used to preconcentrate the phenylalanine from wastewater was 45 (f12%). The average (n = 4) phenylalanine concentration in grab samples of wastewater collected over a 2-month period was 1.3 (f0.3) X lo-' M. Analysis of Phenylalanine Chlorination Products in Wastewater, Wastewater was buffered, inoculated with [,H]phenylalanine (0.70 pCi/mL), and chlorinated in a manner identical to that described previously for the study of valine chlorination products (14) in wastewater. The reaction mixture was chromatographed by HPLC using the same chromatographic conditions described above in the analysis of model solutions. Fractions of column effluent were analyzed by liquid scintillation counting (14). 262
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I
1201 -0-
%Nitrile
1
80
/ v-
0.0 [O]
04 (401
08 12 16 20 [80] [I201 (1601 [ZOO] Chlorine Nitrogen Mole Ratio [Chlorine Applied (mgiL)]
24 [2401
28 [2801
Figure 1. Yields of volatile products formed followlng a 30-mln chlorination in the dark at pH 7 of 1.43 X M phenylalanine and dechlorlnation with thiosulfate.
N-Chlorophenylacetaldimine Decomposition. NChlorophenylacetaldiminewas synthesized by chlorinating at room temperature a solution of phenylalanine (1.43 X lo-, M) in phosphate buffer (0.025 M) to a Cl/N molar ratio of 2.0 at pH 7.0 and at pH 8.0. The solutions were analyzed by HPLC 2 min after chlorination and seven times over the subsequent 24 h. The loss in area of the N-chlorophenylacetaldiminepeak was noted in addition to the appearance of other peaks. In a third study, the solution was chlorinated as in the first study at pH 7.0 and analyzed after 2 min. The pH was then increased to 10.0, and the solution was analyzed over the next 24 h. A similar study was performed using a 15-mL aliquot of phosphate-buffered (0.025 M, pH 7.0) wastewater inoculated with 1mL of [3H]phenylalanine (0.70 pCi/mL). The wastewater was chlorinated to 200 ppm, incubated at room temperature in the dark for 30 min before a 250-pL volume was analyzed by HPLC. Fractions (1 mL) of column effluent were collected and assayed by liquid scintillation counting. The reaction mixture was stored in the dark and analyzed again after 24 h.
Results Volatile Chlorination Products. GC and GC/MS analysis of ether extracts of chlorinated phenylalanine reaction mixtures, dechlorinated prior to analysis, revealed the formation of phenylacetaldehyde and phenylacetonitrile. The percent conversion of the phenylalanine to these products at pH 7 at each Cl/N ratio is plotted in Figure 1. Error analysis of these data showed standard deviations not greater than 4% at any given point. Reactions were also carried out at pH 6.0 and 8.0. At lower chlorination levels, aldehyde was the major product at each pH. At the higher Cl/N ratios, the percent of phenylalanine converted to nitrile increased significantly at the expense of aldehyde formation. At a pH of 6 and a Cl/N molar ratio of 2.8,50% of the phenylalanine was converted to phenylacetonitrile. As the pH increased the percent yield of phenylacetonitrile increased (72% at pH 8). In one set of experiments the reaction mixtures were not dechlorinated with thiosulfate. The chromatograms of these mixtures (Cl/N ratios 0.8, 1.6, 2.4; pH 7) displayed a third peak, identified below as N-chlorophenylacetal-
NCI
H
n
10
20
30
40
Retention Time (minutes)
Flgure 2. High-performance llquid chromatogram with UV detection 30 min after chiorination of a model phenylalanine solution (pH 7) to a CI/N molar ratio of 1.2.
dimine. The peak area increased with increasing Cl/N molar ratio. There was also a significant decrease in the phenylacetaldehyde peak at the higher Cl/N molar ratios. HPLC Analysis of Product Mixtures of Model Solutions. Model solutions of phenylalanine were chlorinated and analyzed by HPLC with UV detection. Figure 2 is a chromatogram of a solution of phenylalanine chlorinated to a Cl/N molar ratio of 1.2. Standard compounds chromatographed under identical conditions were used to identify phenylalanine (retention time 6-7 rnin), phenylacetaldehyde (broad peak at 16 min), and phenylacetonitrile (23 min). As chlorine was added to phenylalanine a peak appeared in the chromatogram with a retention time of 10 min. Since it oxidized iodide in the presence of Nfl-diethyl-p-phenylenediamine(DPD) and phosphate buffer, it was believed to be N-chlorophenylalanine. This assignment was supported by the fact that the peak area increased as the chlorination level approached the Cl/N molar ratio of 1.0 and decreased at higher chlorination levels. The final peak to elute had a retention time of 33 min and also oxidized iodide. The peak appeared in the chromatogram at chlorination levels greater than 1 and increased as the chlorination level approached a Cl/N ratio of 2.0. For reasons discussed below, this peak was believed to be N-chlorophenylacetaldimine. Spectral Identification of N-Chlorophenylacetaldimine. The synthesis of N-chlorophenylacetaldimine produced a compound that, upon standing in nonaqueous solvents, decomposed to a brown solid. The IR spectrum and proton and I3C NMR spectra were obtained immediately after extracting and drying the product. Unlike that of N-chloroisobutyraldimine (14), the IR spectrum of N-chlorophenylacetaldimineshowed no strong evidence for a C=N stretching band. The presence of weak absorbance at 2280 cm-' revealed contamination by phenylacetonitrile. The proton spectrum (Figure 3) is consistent with a mixture of stereoisomers of N-chlorophenylacetaldimine. The aldiminic proton is split into a triplet by the adjacent methylene hydrogens. The splitting pattern between 6 7.95 and 8.35 is a pair of triplets. The larger of the two (0.7 H) is assigned to the more thermodynamically stable anti isomer and suggests the mixture contains 70% of the anti isomer and 30% of the syn isomer. The triplet due to the aldiminic proton of the anti isomer is farther downfield due to the deshielding effect of the proximate chlorine atom. The methylene hydrogens are split into doublets by the aldiminic proton. Two distinct doublets are ob-
9
6
7
6
5
4
3
2
1
0
6
Figure 3. Proton NMR spectrum of the CDCI, extract of an aqueous solution containing 20 mmol of chlorine (0.025 M NaH,PO,, pH 7) mixed with 10 mmol of phenylalanine.
served. The smaller is assigned to the less thermodynamically stable syn isomer whose methylene hydrogens (0.6 H) are deshielded by the proximate chlorine atom. Part of the aromatic singlet and the half of the doublet of the anti isomer which is oversized are due to contamination by phenylacetonitrile, another chlorination product. The I3C spectrum indicates that both isomeric forms of N-chlorophenylacetaldimineare present. The aldiminic carbons with chemical shifts of 175 and 173 ppm are upfield from the corresponding carbon of phenylacetaldehyde. The larger peak (175 ppm) is assigned to the less sterically hindered anti isomer. For the same reason, the larger of the two methylene carbon peaks (42 ppm) is also assigned to the anti isomer. The ether extract of a chlorinated phenylalanine solution (Cl/N = 2.8) was analyzed by GC/MS. Two peaks were observed in the chromatogram. Phenylacetonitrile had a retention time and spectrum identical to the earlier peak. Attempts to obtain distinctive mass spectral data of the second peak by electron impact ionization yielded spectra similar to that of phenylacetonitrile. The methane-induced chemical ionization (CI) mass spectrum of the second chromatographic peak contained a one-chlorine isotope cluster at m/z 154 (5%) and 156 (2%) corresponding to the molecular weight of a protonated N-chlorophenylacetaldimine. The loss of HC1 produces an m/z 118 ion (67%), the protonated parent ion of phenylacetonitrile. Subsequent loss of HCN leaves the characteristic tropylium ion ( m / z 91, 100%). Only two compounds were present in both the HPLC and the GC/MS chromatograms of phenylalanine solutions reacted with 2.8 equiv of chlorine. Phenylacetonitrile was identified as one of the components of each Chromatogram. Since the mass spectrum of the remaining peak in the total ion chromatogram was consistent with the other spectral data for the identification of N-chlorophenylacetaldimine, it was concluded that the 33-min peak in the HPLC chromatogram was due to N-chlorophenylacetaldimine. N-ChlorophenylacetaldimineDecomposition Rate. Within 2 h after chlorination of model solutions of phenylalanine (Cl/N = 2.0, pH 7.0 or 8.0) N-chlorophenylacetaldimine was observed to decompose while phenylacetaldehyde and a second unidentified compound with a retention time of 9.7 min were detected. The area of these two peaks increased over 24 h. There was virtually no change in the peak area of phenylacetonitrile as the N-chloroaldimine decomposed (33% in 24 h). A log plot Envlron. Sci. Technol., Vol. 27, No. 2, 1993 263
of the fraction of N-chlorophenylacetaldimine remaining vergus time suggested a first-order half-life of 36 h at pH 7.0 and 34 1: at pH 8.0. When the pH of a chlorinated phenylalanine solution was increased to 10.0 2 min after chlorination, the N-chloroaldimine decomposed at a much faster rate ( t I j z= 12 h). Several new unidentified produch appeared to form in addition to those observed at the lower pH values. A similar experiment was conducted using wastewater inoculated with tritiated phenylalanine and chlorinated at pH 7.0 to the breakpoint. A comparison of the radiochromatograms 30 min and 24 h after chlorination showed a 25% loss (dpm) of the N-chloroaldimine over 24 h (calculated tl,z = 58 h). Any changes in the amounts of the other phenylalanine chlorination products over the 24 h were too small to measure with any significance.
Discussion Volatile Chlorination Products. Analysis of the dechlorinated (thiosulfate) phenylalanine reaction mixtures detected only two products, phenylacetaldehyde and phenylacetonitrile, at different Cl/N molar ratios. Product distributions at pH 7 are similar to those obtained in studies of the chlorination products of valine (14) and isoleucine (13). When phenylalanine was reacted at pH 7 with 2.4 equiv of aqueous chlorine and the reaction mixture was analyzed prior to dechlorination, only phenylacetonitrile and Nchlorophenylacetaldiminewere formed. It is believed that the phenylacetaldehyde present in the GC studies at the lower Cl/N ratios was the result of the decomposition of N-chlorophenylalanine. At the higher Cl/N ratios, reduction of the N-chloroaldimine by thiosulfate and the subsequent hydrolysis of the imine leads to formation of the aldehyde. While previously considered unstable intermediates, the N-chloroaldimines identified in this and in a related study were stable enough to be analyzed by GC/MS. It was observed, however, that the N-chloroaldimines studied here and previously (13, 14) are very sensitive to temperature and excessive injector temperatures contribute to their decomposition. At the higher Cl/N molar ratios, the percentage of phenylalanine converted to phenylacetonitrile increased with increasing pH at the expense of N-chloroaldimine (and hence aldehyde) formation. It is likely that the increase in the concentration of hydroxide ion or other base readily facilitates dehydrohalogenation of NJV-dichlorophenylalanine by a pathway competing with formation of N-chloroaldimine. The subsequent loss of C1- and COz then produces phenylacetonitrile. This proposal is supported by studies of the decomposition of the N-chloroaldimine discussed below. Decomposition of N-Chlorophenylacetaldimine. The results of this study suggested that dilute aqueous solutions of N-chlorophenylacetaldimineare remarkably stable both in the model solutions at pH 7 and pH 8 and in the wastewater (pH 7), where approximately 75% of the byproduct remained intact 24 h after chlorination. Model studies indicated that the decomposition produced two byproducts, one of which was phenylacetaldehyde. The formation of the aldehyde is likely to be the result of hydrolysis of the N-chloroaldimine and subsequent loss of "$1. The N-chloroaldimine was significantly less stable at pH 10. Although phenylacetaldehyde appears to be a byproduct, the formation of several unidentified peaks not observed at pH 7 or pH 8 suggests other pathways may exist at higher pH values. Previously it was believed that N-chloroaldimines were precursors of nitriles (13). Stanbro and Lenkevich (19) 264
Environ. Scl. Technol., Vol. 27, No. 2, 1993
Chlorine Nitrogen Mole Ration [Chiorlne Applied (mg/L)]
Flgure 4. Percent yields of products and unreacted phenylalanlne remaining 30 rnin after phenylalanine model solutlons (1.43 X lo3 M) containing 0.025 M phosphate buffer (pH 7) and inoculated with [3H]phenylalanine were chlorinated to increasing CVN molar ratios.
0
40
80
120 160 200 Chiorine Applied (mgiL)
240
280
Flgure 5. Percent yields of products and unreacted phenylalanine remalning 30 min after alquots of primary wastewater containing 0.025 M phosphate buffer (pH 7) and Inoculated wlth [3H]phenylalaninewere chlorinated to increasing levels.
have proposed the intermediacy of an a-N-haloimino acid in the formation of nitriles. Results presented here suggest that the nitrile and the N-chloroaldimine are formed by the decomposition of the NJV-dichloroamino acid by competitive pathways (see Figure 6). Chlorination Products in Solution. Implications for Wastewater Disinfection. Throughout this study model solutions of phenylalanine were prepared with a concentration that would produce a breakpoint curve that would mimic that of the wastewater studied. Phenylalanine exhibited a chlorine demand curve similar to those of isoleucine (13) and valine (14) (total residual chlorine in Figure 4). The primary effluent used in this work had an ammonia concentration of 20.3 mg/L and a total Kjeldahl nitrogen (TKN) concentration of 23.7 mg/L. The breakpoint curve (total residual chlorine in Figure 5) appeared typical for a wastewater containing a high ammonia concentration. The concentration of phenylalanine in the wastewater was 1.8 X M (29 ppb). A comparison of the radiochromatograms generated by the HPLC studies of tritiated model phenylalanine solutions and the tritiated wastewater showed all major peaks observed in the chlorinated model solutions were also present in the chlorinated wastewater. Figures 4 and 5 show the yields of products and unreacted phenylalanine chlorinated at the seven Cl/N ratios in the model solutions and wastewater, respectively. Data points represent the average of two determinations. The distribution of products appears to
I-;- co*
QCHC ,N .
(0)
CH2\
c=o
H'
Figure 8. Proposed scheme for the reactlons of aqueous chlorine and phenylalanine and the decomposition of the chlorinated products to form phenylacetaldehde, phenylacetonltrlle, and N-chlorophenylacetaldlmine.
differ between the two samples. Statistically (99% confidence interval) there was a significantly greater amount of N-chlorophenylalanine formed at the 40 mg/L chlorination level than at the corresponding point (0.4 Cl/N molar ratio) on the breakpoint curve of the model solution (t-test t = 11.0; pooled sample variance sp2= 1.3). There was also correspondingly less phenylalanine remaining in the wastewater than in the model solutions at these levels, although the data were only significant within a 90% confidence interval (t = 4.0, sp2 = 53.4). The distribution of organic and inorganic chloramines is governed by relative reaction rates and the concentrations of the reactants. Kinetic studies (20-22)indicate aqueous chlorine reacts faster with organic amines and amino acids than with ammonia. Relative to ammonia, leucine reacts 14 times faster, glycine reacts 13times faster, and alanine reacts 16 times faster (21).This suggests that at low concentration levels the preferential chlorination of organic amino nitrogen compounds may result in the formation of a disproportionate amount of organic Nchloramines. The results of the current study of phenylalanine in wastewater support the theory that a disproportionate amount of N-chloramino acids may be formed in primary wastewater effluent marginally chlorinated. Because N-chlorinated organic amino nitrogen compounds are nonbactericidal (6-12)and because organic N-chloramino nitrogen compounds interfere with conventional methods of determining the concentration of NHzCl [the active bactericide in chlorinated wastewaters (6-12, 23-26)],the disinfection level of wastewater effluents may be overestimated. There were also major differences in the product distribution at the breakpoint of the model solutions and the wastewater. In the wastewater the percent of phenylalanine converted to phenylacetonitrile and N-chlorophenylacetaldimine was half of that observed in the model solutions. Preliminary interpretation of the chromatograms of chlorinated wastewater also suggested that, between the chlorination points of 80 and 200 mg/L, the amount of unchlorinated phenylalanine increased. However, phenylalanine elutes in the void volume along with all other ionized and very polar compounds. It is more likely that a phenylalanine chlorination product formed at higher dosages, such as N,N-dichlorophenylalanineor N-chlorophenylacetaldimine, reacts with other wastewater components to form very polar products which elute in the void volume. We have observed that some reversed-phase chromatography columns are not suitable for analysis of
N-chloroaldimines since the chloroaldimines appear to bind irreversibly to the organic packing material. The binding of chlorinated derivatives of phenylalanine to wastewater organics may be a similar phenomenon. Proposed Mechanism. Based on the work presented a reaction scheme is here and on previous work (13,14), proposed in Figure 6. At Cl/N molar ratios up to 1.0, N-chlorophenylalanine is formed. Decarboxylation and dechlorination produces an unstable imine which rapidly hydrolyses to form phenylacetaldehyde. At Cl/N molar ratios greater than 1.0, N,N-dichlorophenylalanine forms but rapidly undergoes decarboxylation and dechlorination to produce N-chlorophenylacetaldimine. A competitive pathway involving the initial dehydrohalogenation of the N,N-dichloroamino acid followed by decarboxylation and dechlorination is believed to produce the nitrile. Acknowledgments We are grateful to the Hampton Roads Sanitation District Commission for their cooperation in collecting samples and providing total Kjeldahl nitrogen and ammonia analyses on wastewater samples. Literature Cited (1) Brungs, W. A. J.-Water Pollut. Control Fed. 1973, 45, 2180-2193. ( 2 ) Brungs, W. A. Effects of Wastewater and Cooling Water Chlorination on Aquatic Life; Ecological Research Series; EPA-600/3-76-078; 1976. ( 3 ) Comparative Toxicity of Sewage-Effluent Disinfection to Fresh Water Aquatic Life; EPA-60013-75-012; United States Environmental Protection Agency, 1975. (4) Chosen, E.; Johnson, J. D.; Scully, F. E., Jr.; Jersey, J. A.; Jensen, J. N.; Jewell, J. T. In Water Chlorination: Environmental Impact and Health Effects; Jolley, R. L., et al., Eds.; Lewis: Chelsea, MI, 1990; Vol. 6, pp 751-761. (5) Jersey, J. A.; Chosen, E.; Jensen, J. N.; Johnson, J. D. Enuiron. Sci. Technol. 1990,24, 1536-1541. (6) Johnson, J. D. In Water Chlorination: Environmental Impact and Health Effects;Jolley, R. L., Ed.; Ann Arbor Science: Ann Arbor, MI, 1978; Vol. 1, pp 37-63. (7) Wolfe, R. L.; Ward, N. R.; Olson, B. H. J.-Am. Water Works Assoc. 1984, 76 (3,74-88. (8) Wolfe, R. L.; Olson, B. H. In Water Chlorination: Chemistry, Environmental Impact and Health Effects; Jolley, R. L., et al., Eds.; Lewis Publishers: Chelsea, MI, 1985; Vol. 5, pp 555-573. (9) Wolfe, R. L.; Ward, N. R.; Olson, B. H. Environ. Sci. Technol. 1985, 19, 1192-1195. Envlron. Sci. Technol., Vol. 27, No. 2, 1993
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McCormick, E. F.; Conyers, B.; Scully, F. E., Jr. Environ. Sci. Technol., preceding paper in this issue. Franson, M. A., Ed. Standard Methods For the Examination of Water and Wastewater,14th ed.;American Public Health Assoc., American Water Works Assoc., Water Pollution Control Federation: Washington DC, 1975. Jones, B. N.; Paabo, S.; Stein, S. J . Liquid Chromatogr. 1981, 4, 565-586.
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Received for review May 21, 1992. Revised manuscript received October 1, 1992. Accepted October 5,1992. This research was presented in part at the 202nd National Meeting of the American Chemical Society, Washington, DC, and is based on work supported by the National Science Foundation,Grant BCS-9002442, Dr. Edward Bryan, project manager. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and to not necessarily reflect the views of the National Science Foundation.
Application of the Mobile Order Theory to the Prediction of Aqueous Solubility of Chlorinated Benzenes and Biphenyls Paul Ruelie," Michel Buchmann, H6 Nam-Tran, and Uirich W. Kesselrlng Institut d' Analyse Pharmaceutique, Ecole de Pharmacie, Universit6 de Lausanne, BEP, CH-10 15 Dorigny-Lausanne, Switzerland
Prediction of the aqueous solubility of solid and liquid polychlorinated biphenyls and benzenes is obtained by means of the mobile order theory. The solubility values are mainly determined by the magnitude of the hydrophobic effect. This effect does not result from the breaking of solvent H-bonded chains in order to separate the solvent molecules to provide a suitably sized cavity for the solute, but from a decrease of the mobile order entropy of each water molecule when the hydrogen-bonded molecules are brought in a large volume consecutively to the addition of the solute. The evolution of the solubility with the chlorine substitution is further explained. The predictive ability of the present model compared to other approaches adapted to predict aqueous solubility as well as its applicability to any given solvent makes this model a very attractive one.
Introduction Influence of the Mobile Order on the Entropy and the Hydrophobic Effect. Both the order introduced in the liquid by the formation of the hydrogen bonds and the perpetually moving character of these bonds constitute the basic foundations of the "mobile order" theory initiated by Huyskens and Siege1 (1-3). The mobile order theory starts from the statement that, in a liquid, the neighbors of a given molecular group of a molecule constantly change identity, distance, and direction. Nevertheless, for the groups like hydroxyl protons that form hydrogen bonds, this change of environment occurs only during a limited fraction of the time, y, during which the H bond is temporarily broken and the OH proton is free. During the 286
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complementary fraction (1- y) of the time, the considered proton is involved in H bonding and is confined in a small volume, Vo, of its domain, DomA, in the vicinity of one of the electron lone pairs of the oxygen atom of a neighboring molecule. (The domain, DomA, of an alcohol molecule in solution is the total volume of the solution, V, divided by the number, N,,, of alcohol molecules). If y would be entirely negligible, the effect on the molar entropy of the alcohol, brought about by the mobile order, would be equal to Asmobile order = '%ith mobile order - Swithout mobile order = R In (Vo/DomA) = R In ( V a a l c )- R In V As Vo is much smaller than DomA, the mobile order leads to a decrease of the entropy (ASmobileorderis negative) with respect to the situation where all the OH protons would be free, which is related to the ratio Vo/DomA (4-6). This ratio corresponds to the reduction of freedom of one alcohol molecule in the liquid consecutive to the mobile order. Furthermore, as the addition of an inert substance to an alcohol or to water leaves Va,, unchanged but increases the total volume of the liquid, V, it is clearly seen that the entropy of mobile order still becomes more negative. The chief reason for the hydrophobic effect, which is at the origin of the low solubility of inert substances in alcohols or in water (7), is thus that the dissolution of a foreign substance in perpetually moving molecular systems increases the domain of each alcohol or water molecule and thus extends the territory of the mobile order: the H bonds move in a larger domain, which decreases the entropy. The bigger the size of the solute, the larger the decrease.
0013-936X/93/0927-0266$04.00/0
0 1993 American Chemical Society
