Environ. Sci. Technol. 1984, 18, 985-986
Facile Incorporation of Bromine into Aromatic Systems under Conditions of Water Chlorination Secholng Lln, Marta 1.Lukasewycz, Robert J. Llukkonen, and Robert M. Carlson" Department of Chemistry, University of Minnesota, Duluth, Minnesota 55812
Experimental Section
(mol/mol) ammonium hydroxide (Du Pont)-sodium hypochlorite immediately before use (pH 11). Preparation of the stock chlorine dioxide solutions followed a common procedure (17). The oxidants were sealed, refrigerated, and titrated (iodometric) prior to use. Procedures. (1) Product Distribution/Reaction Rate. For each reaction, the appropriate buffer (100 mL, M; KH2P04+ NaOH, or NaC2H302)was split into two portions. To one portion was added a predetermined volume of stock organic substrate solution (approximately 1.5 X M). The other received an appropriate volume of stock NaOC1, C102, or NH2C1. Both solutions were diluted to 100 mL with water and combined to initiate the reaction. The final concentrations in the reaction mixture were the following organic substrate, (7-20 X lo-' M; oxidant 2.7 X lo4 M KBr, 1.26 X lo-' M. The reactions were kept at 24 f 2 "C in Teflon-sealed amber-glass bottles and were periodically monitored by HPLC (10-90% acetonitrile in water over 15 min, 1.5 mL/min). (2) Product Identification. Solutions of the substrates were prepared by stirring a carefully weighed amount (approximately 3 mg) of the compound into 2 L of buffer M phosphate or acetate). Each reaction was initiated by addition, with stirring, of a predetermined volume of the "disinfectant" to the bottle containing the solution. The reaction was periodically monitored by HPLC until substantial product formation was observed, at which time the solutions were acidified, extracted into ether (2 X 200 mL portions), dried over Na2S04,and evaporated to a final volume of 0.5-2 mL for GC-MS analyses. The reactions with chlorine were quenched with 4 equiv of Na2S203prior to acidification. HPLC data taken before and after product isolation were compared to assure that the product distribution did not change,
Equipment. Analytical high-pressure liquid gradient chromatography (HPLC) was employed by using a Perkin-Elmer Series 3 pumping system, a Rheodyne Model 7126 injector, a C-18 column (Perkin-Elmer Sil-X or Alltech), and a Waters 440 UV detector. Data were taken with a Hewlett-Packard 3390A integrator. A Graphic Controls PHM 7900 pH meter with either a Fisher or Corning combination electrode was used to measure pH. The gas chromatographic mass spectrometer (GC-MS) was a Hewlett-Packard 5995C fitted with a 12-m SE-54 fused-silica column. Chemicals. Naphthalene and biphenyl were obtained from Aldrich Chemical Co. and were purified by sublimation. Standard brominated compounds were obtained from Ultra Scientific with the exception of 4-bromobiphenyl (Eastman). The 2-bromo-1,4-naphthoquinone (mp 132-133 "C, lit. mp 131-132 "C) (16) was prepared from l-naphthol. Sodium thiosulfate, sodium hydroxide, phosphoric acid, sodium phosphate (monobasic), and sodium hypochlorite were purchased from Fisher Chemicals, the potassium bromide was from Merck, and the sodium acetate was from Mallinckrodt. The monochloramine was prepared by mixing 3:l
Results and Discussion The results (Tables I and 11) indicate that the presence of bromide during chlorination (HOC1, OC-) leads to substantial bromine incorporation into biphenyl and naphthalene. Moreover, the formation of bromine (HOBr, OBr-) results in reactivity (e.g., loss of organic substrate) typically greater than that of chlorine itself at pH 4.5. Chloramine is unreactive at pH 7.5, but when brought to a pH of 4.5 in the presence of bromide, there is a significant loss of naphthalene (34%) with the formation of 1,4naphthoquinone, l-bromonaphthalene, 2-bromo-1,4naphthoquinone, and traces of other compounds (Tables I and 11). These results reflect the probable involvement of other species (e.g., dichloramine, hypochlorous acid, etc.) due to the known instability of monochloramine at low pH. On the other hand, the use of dilute freshly prepared chlorine dioxide solutions singly or, in combination with, bromide-containing solutions of the organics caused losses of less than 5% for either biphenyl or naphthalene. The results are consistent with the ability of chlorine to oxidize the bromide to bromine (hypobromite) (18),while chloramine and chlorine dioxide are not able to effect these conversions.
The reaction of aqueous solutions of biphenyl and naphthalene with chlorine in the presence of potassium bromide resulted in the loss of organic substrate and the formation of a series of chlorinated and brominated products. The extent of the reaction in the presence of bromide was typically greater than with chlorine alone. Chloramine (pH >6.0) and chlorine dioxide (pH 4.5-7.5) in the presence or in the absence of bromide resulted in no substantial loss of biphenyl or naphthalene.
Introduction The isolation of haloforms containing bromine from the chlorination of drinking water suggests that the efficiency of bromine incorporation (relative to the chlorinating capacity of the medium) is quite high (1-3). The question remains as to the possible bromination of substrates that do not result in the formation of trihalomethanes in the presence of bromide when the oxidant chlorine, chlorine dioxide, or chloramine is used (4-12). Naphthalene and biphenyl were chosen for study because of their significance as industrial products, their presence in environmental settings, the interest in their halogenated derivatives, their differing reactivity to electrophilic aromatic substitution (e.g., naphthalene > biphenyl), and the availability of halogenated product standards. In addition, earlier studies had examined in detail the reactions of aqueous solutions of naphthalene with chlorine dioxide (13)and biphenyl and naphthalene (14, 15) with chlorine in the absence of bromide.
0013-936X/84/0918-0985$01.50/0
0 1984 American Chemical Society
Environ. Sci. Technol., Vol. 18, No. 12, 1984
985
Table I. Summary of Halogenated Products Observed from the Aqueous Chlorination of Naphthalene and Biphenyl in the Presence and in the Absence of Potassium Brbmide disinfectant/ time, h / % loss of substrate
substrate
PH
naphthalene
7.5 7.5
NaOC1/24/ 6.0) and chlorine dioxide (pH 4.5-7.5) in the Dresence or in the absence of bromide resulted in no substantial loss of bbhenvl or naphthalene (Le.,
