Environ. Sci. Technol. 1984, 18, 932-935
Increased Chloroform Production from Model Components of Aquatic Humus and Mixtures of Chlorine Dioxide/Chlorine Sechoing Lin, Robert J. Liukkonen, Rebecca E. Thorn, John G. Bastian, Marta 1. Lukasewycz, and Robert M. Carlson"
Department of Chemistry, University of Minnesota, Duluth, Minnesota 55812 The addition of aqueous solutions of chlorine and chlorine dioxide mixtures to model aqueous humus components showed that increased levels of chloroform production can be observed from some systems (i.e., 2,4- and 3,5-dihydroxybenzoicacids, 2,4,6-trihydroxybenzoicacid, and 3,5-dimethoxybenzoic acid). A detailed study of the reaction pathway for 2,4-dihydroxybenzoic acid was performed after it was observed that, under the identical reaction conditions, resorcinol gave the same product distribution. This observation suggested that the chloroform enhancement was due to a chlorine dioxide mediated decarboxylation and subsequent degradation pathway involving a hydroxybenzoquinone that was common both to 2,4-dihydroxybenzoic acid and to resorcinol. On the basis of differing product distributions, there appeared to be no commonality in the pathways for increased chloroform production for the 2,4- and 3,5-dihydroxybenzoic acids. Introduction The well-established use of chlorine for water renovation has been the subject of extensive reinvestigation due primarily to the formation of hazardous organic byproducts, including the haloforms ( I ) . Oxidants such as chlorine dioxide or chloramine have been suggested as alternatives, to be used singly or, in combination, with chlorine. If such alternatives are used, the chemical pathways for degradation of the organic components present in the water (2-16) would also be expected to be altered. Trihalomethanes (THM) represent a well-studied fraction from chlorine-induced chemical degradation, and several hydroxybenzoic and cinnamic acids, as commonly used model components of aquatic humus, were examined for possible changes in THM production accompanying a variation in oxidant. Experimental Section Equipment and Apparatus. (1) Chloroform Production. The gas chromatograph (GC) (Perkin-Elmer Model F-42) was fitted with a 20% SP-2100/0.1% Carbowax 1500 on 100/120 Supelcoport column (6 ft., SS) and an electron capture detector. Argon-methane (95/5) was the carrier gas. A Hewlett-Packard Model 3390A integrator and a Graphics Control pH meter (Model PHM 7900) equipped with a Fisher Microprobe combination electrode were used. Reactions were carried out in a Haake NB22 proportional constant temperature water bath. (2) Product Isolation and Structure Determination. The Hewlett-Packard 5995C GC-MS was equipped with a split/splitless interface and a cross-linked methylsilicone fused silica column (Hewlett-Packard, 15 m X 0.2 mm i.d.1. Some fractions were screened prior to GC-MS analysis using a Tracor 550 capillary gas chromatograph fitted with a J & W DB-5 narrow bore column and a flame ionization detector (FID). GC temperature programs were from 40 (or 70 "C) to 290 OC. The HPLC instrumentation consisted of a Beckman llOA pump and a Rheodyne 7126 injector, a C-18 column (Perkin-Elmer 25 cm X 4.6 mm i.d., Sil-X) or a resin column (Hamilton 18 cm X 4.6 mm i.d., PRP-l), a Schoeffel SF 770 variable wavelength de932 Environ. Sci. Technol., Vol. 18, No. 12, 1984
tector, and a Hewlett-Packard Model 3390A integrator. Chromatographic conditions were varied to achieve adequate retention for the organic components under investigation. The mobile phase was 10% or 15% acetonitrile in lo-' M KH2P04brought to pH 2.5 with H3PO4. The flow was 1.0 mL/min. Chemicals. All organic substrates were obtained from Aldrich Chemical Co. with the following exceptions: p hydroxybenzoic acid and 2,4,6-trichlorophenol(Eastman), resorcinol (Merck), and chloroform (Fisher Scientific). 2-Hydroxy-p-benzoquinone and 2-chloroesorcinol were synthesized by using literature procedures (17,18). The inorganic reagents were obtained from Fisher Scientific Co. except for ammonium hydroxide (Du Pont). The Teflon-rubber septa and 20-mm standard seals were from Supelco. The isooctane was Baker "Resi-analyzed" or Fisher pesticide grade. The water was purified by passage through a Continental deionizer and a Milli-Q system (Millipore Corp.). Procedures. (1) Chloroform Production. The septum bottles were completely filled with 1.0 X M phosphate buffer of appropriate pH containing the organic substrate in known concentration M) and crimpsealed with Teflon/rubber septa. The measured amounts of oxidants were injected by syringe, an equal volume displaced, and the bottles shaken and placed inverted into a water bath (21 or 24 f 2 "C). The reactions were M sodium thiosulfate (3 quenched by injection of equiv) after 24 h and analyzed (extraction into isooctane/EC-GC) following a literature method (19). Chlorine dioxide and chlorine were introduced individually or as mixtures by injection. Where there were separate additions of chlorine dioxide and chlorine, there was a 15-min interval before the chlorine was introduced. (2) Product Isolation and Structure Determination. The sodium hypochlorite (5%; Fisher) and chlorine dioxide reagent solutions were prepared by dilution from concentrated stock solutions and were titrated (iodometric)prior to use. The concentrated chlorine dioxide was generated as described in the literature (20). The chlorine content of the chlorine dioxide was determined by a double titration (21). Chloramine solutions were prepared from the commercial concentrated ammonium hydroxide and mixed with hypochlorite immediately before addition to the organic substrate to achieve an ammonia to hypochlorite ratio of 3:l. Solutions of the substrate were prepared by stirring a carefully weighed amount of the organic (ca. 4 mg) into 4 L of phosphate-buffered water. Each reaction was initiated at 24 f 2 "C by addition, with stirring, of a predetermined volume of the oxidizing reagent to the bottle containing the organic solution. The pH and organic content (HPLC analysis) were monitored throughout the reaction period, and the reactions with chlorine were quenched with sodium thiosulfate (4 equiv). Samples were acidified (pH 2, H3PO4) and concentrated by liquid-liquid extraction (3X, ether). The ether was dried (Na2S04)and concentrated to 1-2 mL in vacuo, with additional concentration effected under a stream of nitrogen.
0013-936X/84/0918-0932$01.50/0
0 1984 American Chemical Society
Table I. Variation in Chloroform Production from 2,4,6-TrihydroxybenzoicAcid and Syringic Acid with Changes in Cl0,:Cl2 Ratios
[C102], [Cl,], mol % CHC13 produced X10" M X10-6 M from substrate 0 5 1.3 (h0.5)
[substrate] 1 x 10-5 M 2,4,6-trihydroxybenzoic acid
S
O
H
Y 1
> 0""0
CIO2
4 6
9.0 6.6
8
5
10
5
0
5
0.2 0.1 0.13 (k0.05)
M syringic
2
5 5 5 5 5
4 6 8 10
0
r AOH 1 L
,
0
3
.OH
2
1.4
acid
"'"2
o_R CIO-
0
QoH
5 5 5
2
1X
Scheme I
0.52 0.39 0.28
0.21 0.23
0
Scheme I1 pH7, 2 4 W C stepwka .ddlliM ol oxidants 24 hr reaction time 1 0 - I ~l i ~ k i g t n i . 0 3,5-dihydroxybnmlc aCld 0 2,4-dlhydr&ybenzo~c add 0 resarciool
1.4 0 0
1.2
0
0
4
FQ
0.6
9
8
fE
I
1
0
0
0
0
04 0
P
d
n 0 0
0.2
0
1 I
1
I
2
I
I
I
3
4
5
mole chlorine dioxidehnole substrate
Figure 1. Example of variation In chloroform production by the addition of chlorine dioxide and chlorine.
Results and Discussion The production of chloroform from model aqueous humic components [2,4- and 3,5-dihydroxybenzoic acids, p-hydroxybenzoic acid, 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid), p-hydroxycinnamic acid, 3,4,5- and 2,4,6-trihydroxybenzoic acids, and 4-hydroxy-3-methoxybenzoic acid] in the presence of chloramine and chlorine dioxide was found to be below the limits of quantitation (3 pg/L) of the analytical method (19). Moreover, the chloroform generated from the addition of chlorine closely matched those values reported earlier (9, 11). Further study was initiated when significantly increased levels of chloroform were produced when mixtures of chlorine dioxide and chlorine were reacted with 2,4- and 3,5-dihydroxybenzoic acids, 2,4,6-trihydroxybenzoic acid, and syringic acid and not with p-hydroxybenzoic and phydroxycinnamic acid or 3,4,5-thihydroxybenzoic acid. The increased chloroform production exhibited clearly recognized maxima (Figure 1and Table I). A detailed study of the products from 2,4-dihydroxybenzoic acid (1) and resorcinol (2) was performed after the same product
(J! HO H
5
NaBH4
OH
-H:i
@OH
CHZN2 CI
HO H
O_R AC20
OH
distribution (based on identical HPLC chromatograms) was observed for these two substrates. The results of this study led to the development of a proposed reaction pathway (Scheme I), Documentation for the suggested pathway includes the following: (1)First there was the independent synthesis of the hydroxy-p-benzoquinone (3) from 1,2,4-trihydroxybenzene and silver oxide (17). Hydroxyquinone (3) not only gave the same HPLC retention time but also generated the same products upon chlorine-chlorine dioxide oxidation. Moreover, GC-MS analysis of both samples of 3 gave no evidence of the parent system, but both gave trace of 1,3-~yclopentenedione[via loss of CO; m/z 96 (loo), 68 (52), 54 (57)]. (2) The treatment of 1,2,4-trihydroxybenzene with chlorine dioxide gave a different set of the reaction products, thereby suggesting the absence of this compound as the initial common oxidation product of 1 and 2. (3) The analogous oxidative decarboxylation of p hydroxybenzoic acid and 4-hydrox~-3,5-dimethoxybenzoic acid in the presence of chlorine dioxide gave p-benzoquinone and 2,6-dimethoxybenzoquinone[mlz 168 (21), 138 (8), 125 (9)) 112 (4), 97 (9), 80 (20), 69 (loo), 53 (26)]. (4) The IR spectrum of a sample of 5 indicated substantial hydrogen-bonded hydroxyl (e.g., gem-OH) and a conjugated carbonyl (1620 cm-I). The mass spectrum showed only peaks corresponding to 6, presumably resulting from thermal decarbonylation in the heated inlet of the GC-MS. (5) Additional chlorine dioxide results in the conversion of 5 to 6 (based on HPLC retention times), and if aqueous chlorine is added at this stage, no further degradation of 6 is observed. (6) The reduction of 5 with sodium borohydride and subsequent treatment with diazomethane or acetic anhydride gave a series of mono-, di-, and trimethylated or -acylated derivatives of a chloro-1,2,4-trihydroxybenzene (Scheme 11). (7) There was the close correlation of the maximum observed in chloroform production, with the maximum in the formation of 5 (Table 11). (8) There was the isolation of 2,2-dichloro-1,3-cyclopentenedione (6) and the generation of IR and NMR spectra which showed a strong carbonyl band (1780 cm-l), Environ. Sci. Technol., Vol. 18, No. 12, 1984
933
Table 11. Relationship of Quinone (5) Production from 2,l-Dihydroxybenzoic Acid (DHBA) to Chloroform Formation
Scheme I11
mol of CIOz/mol of DHBA, [Cl,] M) in second peak height pg of CHC& (*2)/ addition = 5 X [DHBA] 240 pg of DHBA (5), mm 59 67 65 44 25
