Production of polychlorinated phenoxyphenols (predioxins) by aqueous chlorination of organic compounds

C h e m o s p h e r e , Vol.19, Nos.l-6, P r i n t e d in Great B r i t a i n

PRODUCTION

pp 675-680,

OF P O L Y C H L O R I N A T E D AQUEOUS

CHLORINATION

1989

0 0 4 5 - 6 5 3 5 / 8 9 $3.00 P e r g a m o n Press plc

PHENOXYPHENOLS OF O R G A N I C

(PREDIOXINS)

+ .OO

BY

COMPOUNDS

S. ONODERA, M. OGAWA, C. YAMAWAKI, K. YAMAGISHI AND S. SUZUKI Faculty of Pharmaceutical Sciences, Tokyo University of Science, 12 Ichigaya-funagawara, Shinjuku-ku, Tokyo 162 Japan

ABSTRACT The reactions of phenolic substances with hypochlorite in water were investigated by means gas chromatography-mass spectrometry. Chlorinated and methylated phenols were shown produce polychlorinated phenoxyphenols (predioxins), having one to nine chlorine atoms, the by-products in c h l o r i n e - t r e a t e d water. The production of some of these compounds dependent on the number of equivalents of chlorine per mol of compound and on the reaction

of to as is pH.

KEYWORDS Chlorinated phenoxyphenol; predioxin; c h l o r i n e - d i s i n f e c t i o n ; chlorine-bleaching INTRODUCTION Polychlorinated aromatic compounds are environmental contaminants which may cause risks to human health. An important group for i n v e s t i g a t i n g is the chlorinated dimers, l i k e the dioxins (PCDDs) and furans (PCDFs), formed during the i n d u s t r i a l production of chlorophenolic compounds and the combusion of c h l o r i n e - c o n t a i n i n g materials. Although the discussion of the o r i g i n of PCDDs and PCDFs has been focused on the above two p o t e n t i a l s , we have demonstrated that teratment with hypochlorite of phenol and cresols in water produces compounds corresponding to the polychlorinated phenoxyphenols (PCPPs, Onodera et a l . , 1984 a; 1986 a). PCPPs are chlorinated phenolic dimers, some of which are well known as precursors of highly t o x i c PCDDs (Jensen and Renberg, 1972; Rappe and Nilsson, 1972). I t is, therefore, necessary to confirm whether formation of PCPPs takes place during the c h l o r i n a t i o n of waters contaminated with other phenolic compounds. EXPERIMENTAL Materials Phenolic substances were obtained from Tokyo Chemicals and have presented in Table I. A 5-chloro-2-(2,4-dichlorophenoxy)phenol (Irgasan DP 300) was commercially a v a i l a b l e ( p u r i t y , 99.3%). Standard solutions of these compounds were prepared by dissolving the compounds in methanol and subsequent d i l u t i o n s . Hypochlorite solution was prepared by d i l u t i n g a NaOCI solution (ca. 10% a v a i l a b l e CI, Nakarai Chemicals) in phosphate buffer solution. The NaOCI concentrations were determined by iodometric t i t r a t i o n . The organic solvents (chloroform, d i e t h y l ether, and methanol) used in t h i s work were of a n a l y t i c a l - r e a g e n t grade (pesticide residue analysis, Cika-Merck). Treatment of aqueous phenolic substances with hypochlorite and e x t r a c t i o n of reaction mixture Aqueous phenolic solutions (0.5 mmol/l) were treated with hypochlorite s t i r r i n g at various pH values and with various equivalents of chlorine 675

at 20°C for 1 h with per mol of c~npound.

676

Aft e r the desired time the unreacted chlorine was removed by adding a Na2S203 solution. The reaction mixture was then a c i d i f i e d to pH 2 with 1M HCl before e x t r a c t i o n with d i e t h y l ether (30 mm x 2), The solvents were dried over anhydrous Na2SO4 and concentrated under vacuum at 40°C to a s u i t a b l e volume for subsequent experiments. Fractionation of extracts by t h i n - l a y e r chromatography (TLC) and product r e s o l u t i o n The d i e t h y l ether extracts were fractionated i n t o several f r a c t ions by TLC on polyamide I I F254 plates (20 x 20 cm, thickness, 0.15 mm, Merck) using chloroform as developing solvent. TEe detection of the spots on the plate was performed by U V- ir r a d ia t io n . The separated zones were scraped o f f from the plate by using special recovery tubes (Wako Pure Chemicals) and the adsorbed substances were eluted with d i e t h y l ether. The d ie h t y l ether eluates were then analyzed by means of gas chromatography-mass spectrometry (GC-MS). A Shimadzu GC-6A gas chromatograph equipped with flame i o n i z a t i o n detector and 2 m x 3 mm I.D. glass column packed with 2% OV-I on Uniport HP (60-80 mesh) was programmed from 80 to 260°C at a rate of 5°C/min. The c a r r i e r gas (nitrogen) f l o w - r a t e was 50 ml/min. A Shimadzu Chromatopac-IA data system was used to determine the retention times and peak areas of the chromatograms. A Hitachi M-80 mass spectrometer-gas chromatograph equipped with a Hitachi M-O03 data processing system was used f o r the q u a l i t i t a t i v e analyses of samples under the f ollow ing conditions; The ion source was operated at 260°C with a trap current of 70 #A and an electron energy of 70 eV. A glass column (2 m x 3 mm I . D . ) packed with 2% OV-I on Uniport HP (60-80 mesh) was programmed from I00 to 250°C at a rate of 5°C/min. The products were i d e n t i f i e d by comparing t h e i r r e t e n t i o n times and mass spectra with those of authentic compounds. RESULTS AND DISCUSSION Production of PCPPs durin 9 reactions of phenolic substances with hypochlorite in water The condensation products of chlorinated phenolic substances (PCPPs) have b e e n shownto be formed not only in the reactions of phenol with hypochlorite in water (Onodera et a l . , 1984 a; 1986 a) but also during the treatment with ozone or H202/peroxidase of water containing chlorophenols (Duquet et a l . , 1986). However, e a r l i e r workers demonstrated the presence of the corresponding chlorinated dimers (ethers and PCDDs) in the mass spectra of chlorinated phenols and concluded that these dimers are formed by pyrolysis of the chlorinated compounds (Sanderman et a l . , 1957; Rappe and Nilsson, 1972). Diethyl ether extracts of c h l o r i n e - t r e a t e d phenolic solutions were, therefore, fractionated into several f r a c t ions by polyamide TLC before GC and GC-MS analyses. Phenol

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Fractionation of d i e t h y l ether extracts of c h l o r i n e - t r e a t e d phenolic solutions by TLC on polyamide plates with chloroform. Closed spots indicate the unknown compound zones (probably PCPP f r a c t i o n s ) . The asterisk indicates each s t a r t i n g material . a = TCA;b : phenol; c = 2,4,6-TCP; d = Irgasan DP 300 and e = PCDDs.

Fig. 1 shows t y p i c a l t h i n - l a y e r chromatograms of diet hy l ether extracts from chlorophenol and methylphenol solutions a f t e r treatment with hypochlorite at three equivalents of chlorine per mol of compound for 1 h. Several compounds including o r i g i n a l materials, c h l o r i n e - s u b s t i t u t e d products and unknown compounds were observed in these extracts. These unknown compounds occurring in the extracts of c h l o r i n e - t r e a t e d chlorophenol solutions gave Rf values s i m i l a r

677

to t h a t of Irgasan DP 300 on polyamide TLC p l a t e . However, d i f f e r e n t TLC behavior of the unknown compounds occurring in the e x t r a c t s from the methylphenol s o l u t i o n s was observed, as compared with t h a t of Irgasan DP 300. 200

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A t y p i c a l mass chromatogram of the unknown compounds occurring in the polyamide TLC f r a c t i o n of a d i e t h y l ether e x t r a c t from a c h l o r i n e - t r e a t e d 2,6-dichlorophenol (2,6-DCP) s o l u t i o n is shown in Fig. 2. The mass spectra of the compounds corresponding to the peaks of scan 236 and 283 gave a molecular ion at m/z 288 (three C1 atoms) and at m/z 322 ( f o u r C1 atoms), r e s p e c t i v e l y . C h a r a c t e r i s t i c fragment peaks at m/z 146 (two C1 atoms f o r the former compound) and at m/z 180 (three C1 atoms f o r the l a t t e r compound) are i n d i c a t i v e of a 2-PPs, since the hydrogen t r a n s f e r rearrangement from the OH group to the nearest aromatic ring is t y p i c a l of the fragmentation of an orthohydroxy ether ( B a l l a n t i n e and P i l l i n g e r , 1968). The compound corresponding to the l a r g e s t peak of scan 356 gave a molecular ion at m/z 356 ( f i v e Cl atoms) and very small fragment peaks at m/z 146 and 180, suggesting the compound to be p e n t a c h l o r i n ated 4-PP. These MS f i n d i n g s , t h e r e f o r e , i n i d c a t e t h a t t r i and t e t r a c h l o r i n a t e d 2-PPs ( p r e d i o x i n s ) and pentachlorinated 4-PP ( i s o - p r e d i o x i n ) are present in the TLC-separated f r a c t i o n of the 2,6-DCP reaction products. Other unknown compounds occurring in polyamide TLC-separated f r a c t i o n s of diethy! ether e x t r a c t s from the c h l o r i n e - t r e a t e d methylphenol s o l u t i o n s were also determined from the mass spectrum of each compound in the same manner as described f o r the 2,6-DCP products. These GC-MS studies demonstrated t h a t PCPPs including predioxins and i s o - p r e d i o x i n s with d i f f e r e n t numbers of c h l o r i n e atoms were present in each TLC-separated f r a c t i o n . A summary of GC determinations of t o t a l PCPPs remained in c h l o r i n e - t r e a t e d phenolic s o l u t i o n s is presented in Table I. On the basis of TLC, GC, and GC-MS studies, i t is concluded t h a t the production of a v a r i e t y of PCPPs occurs during the reactions of phenolic substances with h y p o c h l o r i t e in water. However, no production of PCPPs could be observed in c h l o r i n e - t r e a t e d waters contaminated with d i - and t r i h y d r i c phenols, amino- and nitrophenols, hydroxybenzoic acids and t h e i r a l k y l esters, g a l l i c acid and the. r e l a t e d compounds.

678

Table I.

P r o d u c t i o n o f PCPPs in t h e r e a c t i o n s w i t h h y p o c h l o r i t e in w a t e r

Compound tested

Amount* (mmol/mol)

Phenol** 2 - C h l o r o p h e n o l (2-CP) 3-CP 4-CP 2,3-DCP 2,4-DCP 2,5-DCP 2,6-DCP 3,4-DCP 3,5-DCP 2,4,5-TCP 2,4,6-TCP 2,3,4,6-TeCP PCP 2-Methylphenol (2-MP)** 4-C-2-MP 6-C-2-MP

No. o f C1 atoms in PCPPs

4 4 1 1 1 1 1 40 1 1 2 l l 2 25 25 25

3 3 5 5 3 3 3 3 3 5 5 6 l l l

, , 5 , 5 -

5 5 6 6 6

o f p h e n o l i c substances

Compound tested

Amount (mmol/mol)

4,6-DC-2-MP 3-MP 4-C-3-MP 6-C-3-MP 4-MP** 2,6-DC-4-MP 2,3-DMP 2,4-DMP 2,5-DMP 2,6-DMP 3,4-DMP 3,5-DMP 2,3,5-TMP 2,3,6-TMP 2,4,5-TMP 2,4,6-TMP 2,3,5,6-TeMP

6 5 6 6 6 7 9 4 4 4

No. o f C1 atoms in PCPPs

25 5 5 5 40 40 15 I0 15 1 25 trace trace trace l 0 trace

1 - 4 5 5 5 1 - 4 1 - 4 1 - 3 1 , 2 1 - 3 N.D*** l - 3 N.D N.D N.D N.D N.D

* The y i e l d s were d e r i v e d from GC peak areas, r e l a t i v e t o t h e area o f I r g a s a n DP 300. * * See References o f Onodera e t a l . (1984 a and 1986 a ) . * * * Not d e t e r m i n e d . Effect

of chlorine

dose and s o l u t i o n

pH on t h e p r o d u c t i o n o f PCPP in c h l o r i n a t e d

water

GC a n a l y s e s o f t h e d i e t h y l e t h e r e x t r a c t s i n d i c a t e d t h a t a marked r e d u c t i o n in t h e o r i g i n a l amount o f p h e n o l i c substances in w a t e r o c c u r w i t h i n c r e a s e d molar r a t i o s o f HOCI t o t h e compound. F i g , 3 shows t h e r e s u l t s o f GC d e t e r m i n a t i o n s o f PCPPs in s e v e r a l c h l o r o p h e n o l and m e t h y l p h e n o l s o l u t i o n s a f t e r t r e a t m e n t w i t h h y p o c h l o r i t e a t v a r i o u s m o l a r r a t i o s o f HOCI to the compound f o r 1 h. The PCPPs were found t o be p r e s e n t a t high c o n c e n t r a t i o n s in w a t e r a t t h r e e e q u i v a l e n t s o f HOCl t o t h e compound, w i t h t h e e x c e p t i o n found in t h e 2 , 4 - d i m e t h y l p h e n o l (2,4-DMP) s o l u t i o n . At molar r a t i o s o f HOCl t o t h e compound o f > I 0 a small amount o f these

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R e s i d u a l amounts o f PCPPs in n e u t r a l p h e n o l i c s o l u t i o n s (I mM) after treatment with hypochlorite a t v a r i o u s molar r a t i o s o f c h l o r i n e t o t h e compound and at 20°C f o r 1 h. The y i e l d s were d e r i v e d from GC peak a r e a s , r e l a t i v e t o t h e area o f I r g a s a n .

679

c h l o r i n a t e d i n t e r m e d i a t e s was found. In g e n e r a l , lower c h l o r i n a t e d PPs were detected in c h l o r i n e - t r e a t e d p h e n o l i c s o l u t i o n s a t molar r a t i o s of HOCl o f < 3 , w h i l e higher c h l o r i n a t e d PPs were observed at the molar r a t i o s o f >3. S i m i l a r d i s t r i b u t i o n p a t t e r n s were also observed f o r c h l o r i n e - s u b s t i t u t e d products formed in these c h l o r i n a t e d waters o f p h e n o l i c compounds.

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Residual amounts of PCPPs formed in aqueous p h e n o l i c s o l u t i o n s (I mM) a f t e r t r e a t m e n t w i t h t h r e e e q u i v a l e n t s of c h l o r i n e per mol of compound at v a r i o u s pH values and at 20:C f o r 1 h.

Fig. 4 shows the r e s u l t s o f GC d e t e r m i n a t i o n s of PCPPs in aqueous p h e n o l i c s o l u t i o n s a f t e r t r e a t m e n t w i t h h y p o c h l o r i t e (3 HOCl/compound) at v a r i o u s pH values f o r 1 h. The PCPPs formed in the r e a c t i o n s o f o r t h o - c h l o r i n a t e d phenols (2-CP and 2,6-DCP) w i t h h y p o c h l o r i t e were d e t e c t e d at high c o n c e n t r a t i o n s in a c i d i c s o l u t i o n s , although small amounts o f PCPPs were obtained in c h l o r i n e - t r e a t e d waters c o n t a i n i n g the p a r a - c h l o r i n a t e d phenols (4-CP and 2,4-DCP, Table I ) . I t i s noteworthy t h a t small amounts of PCPPs were detected in the r e a c t i o n s o f phenol w i t h h y p o c h l o r i t e even under a c i d i c c o n d i t i o n s . The reason f o r t h i s might be t h a t p a r a - c h l o r i n a t e d phenols are the main products in the p h e n o l - h y p o c h l o r i t e r e a c t i o n s at a c i d i c conditions. In c o n t r a s t t o the c h l o r o p h e n o l - h y p o c h l o r i t e r e a c t i o n s , the PCPPs formed in the r e a c t i o n s o f methylphenols w i t h h y p o c h l o r i t e were found t o be at high c o n c e n t r a t i o n s in water under n e u t r a l and weak a l k a l i n e c o n d i t i o n s .

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Reactions o f PCPPs w i t h an excess o f h y p o c h l o r i t e (20 equiv, of HOCl per mol o f compound in b u f f e r e d s o l u t i o n s of pH 5, 7, and 9 at 20°C f o r I , 2, and 5 h. . Open symbols : o r i g i n a l PCPPs. Closed symbols ; c h l o r o p h e n o l i c compounds formed.

680

Further reactions of PCPPs with hypochlorite in water In order to determine how the PCPPs are converted into other chlorinated substances,a mixture of I00 ml of hypochlorite solution and the PCPPs dissolved in 1 ml of methanol was shaken in a separatory funnel at 20°C. Two kinds of the PCPPs prepared by polyamide TLC f r a c t i o n a t i o n s of d i e t h y l ether extracts from c h l o r i n e - t r e a t e d 2,6-DCP and 4-methylphenol (4-MP) solutions (see Figs. 1 and 2 and Table I) were used for these experiments. Fig. 5 shows the results of GC determinations of d i e t h y l ether extracts from e a c h PCPPs s o l u t i o n a f t e r treatment with an excess of hypochlorite at various pH values for I, 2 and 5 h. A rapid decrease in the amounts of o r i g i n a l PCPPs and a formation of chlorinated phenolic monomers in water occurred with an increase of the pH values of the solutions and the time of contact with hypochlorite0 as can be seen in Fig. 5. Since the ultimate reaction products of phenol with hypochlorite in water have b e e n i d e n t i f i e d as t r i c h l o r o a c e t i c acid and chloromaleic acid (Onodera et a l . , 1986 b), the PCPPs-hypochlorite reactions may take place in a manner s i m i l a r to that of the phenol reactions. In the present work, PCDDs and PCDFs in c h l o r i n e - t r e a t e d PCPPs solutions were also tested by means of FID-GC° However, none of these compounds was detected. CONCLUSION Aqueous chlorine is widely used to d i s i n f e c t sewage water and raw water destined f or human consumption and to bleach wood pulp in paper industry. Phenolic substances have been shown to produce a v a r i e t y of PCPPs upon reactions with hypochlorite in water. The production of these compounds is g r e a t l y dependent on the molar r a t i o s of HOCI and the reaction pH, with higher concentrations formed at moderate chlorine doses. These compounds have also been shown to decompose into the chlorinated phenolic monomers upon f u r t h e r reactions with hypochlorite in water. However, the chlorinated 4-MP dimers are p a r t i c u l a r l y i n t e r e s t i n g , as they are comparatively persistent in c h l o r i n e - t r e a t e d water and are also mutagenic substances (Onodera et a l . , 1986 b). REFERENCES B a l l a n t i n e J. A. and C. T. P i l l i n g e r (1968). Rearrangement processes in the mass spectra of substituted diphenyl ethers. Org. Mass Spectrom., I, 447-458. Duquet J. P.. B. Dussert, A. Bruchet and J. M a l l e v i a l l e (1986). The p o t e n t i a l use of ozone and peroxidase fo r removal of aromatic compounds from water by polymerization. Ozone.8, 247-260. Jensen S. and L. Renberg (1972). Contaminants in pentachlorophenols: Chlorinated dioxins and predioxins (chlorinated hydroxy-diphenyl ethers). Ambio, I, 62-65. Onodera S., K. Yamada, Y. Yamaji and S. Ishikura (1984 a). Chemical changes of organic compounds in chlorinated water. IX. Formation of polychlorinated phenoxyphenols during the reactions of phenol with hypochlorite in d i l u t e aqueous solution. J. Chromatogr., 287. 91 -I00. Onodera S., T. Udagawa, M. Tabata. S. Ishikura and S. Suzuki (1984 b). Isotachophoretic determination of chlorinated carboxylic acids formed during c h l o r i n a t i o n of phenol with hypochlorite in d i l u t e aqueous s o l u ti o n . J. Chromatogr., 287. 176-182. Onodera S.. K. Yamada, Y. Yamaji, S. Ishikura and S. Suzuki (1986 a). Chemical changes of organic compounds in chlorinated water. X. Formation of polychlorinated methylphenoxymethylphenols (predioxins) during c h l o r i n a t i o n of methylphenols in d i l u t e aqueous solution. J. Chromatogr., 354, 293-303. Onodera S.. M. Yamashita. S. Ishikura and S. Suzuki (1986 b). Chemical changes of organic compounds in chlorinated water. XI. Thin-layer chromatographic f r a c t i o n a t i o n of Ames mutagenic compounds in c h l o r i n e - t r e a t e d 4-methylphenol solution. J. Chromato~r., 360. 137-150. Rappe C. and C.-A. Nilsson (1972). An a r t i f a c t in gas chromatographic determination of impurities in pentachlorophenol. J. Chromatogr., 67, 247-253. Sandermann W., H. Stockman und R. Casten (1957). Uber die pyrolyse des pentachlorphenol. Chem. Ber.. 90. 690-692.