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Hydrolysis of Haloacetonitriles: Linear Free Energy Relationship, Kinetics and Products

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Hydrolysis of Haloacetonitriles: Linear Free Energy Relationship, Kinetics and Products Wat. Res. Vol. 33, No. 8, pp. 1938±1948, 1999 # 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain PII: S0043-1354(98)00361-3 0043-1354/99/$ - see front matter HYDROLYSIS OF HALOACETONITRILES: LINEAR FREE ENERGY RELATIONSHIP, KINETICS AND PRODUCTS VICTOR GLEZER*, BATSHEVA HARRIS, NELLY TAL, BERTA IOSEFZON and OVADIA LEV{*M Division of Environmental Sciences, Fredy and Nadine Herrmann School of Applied Science, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel (First received September 1997; accepted in revised form August 1998) AbstractÐThe hydrolysis rates of mono-, di- and trihaloacetonitriles were studied in aqueous buer sol- utions at dierent pH. The stability of haloacetonitriles decreases and the hydrolysis rate increases with increasing pH and number of halogen atoms in the molecule: The monochloroacetonitriles are the most stable and are also less aected by pH-changes, while the trihaloacetonitriles are the least stable and most sensitive to pH changes. The stability of haloacetonitriles also increases by substitution of chlorine atoms with bromine atoms. The hydrolysis rates in dierent buer solutions follow ®rst order kinetics with a minimum hydrolysis rate at intermediate pH. Thus, haloacetonitriles have to be preserved in weakly acid solutions between sampling and analysis. The corresponding haloacetamides are formed during hydrolysis and in basic solutions they can hydrolyze further to give haloacetic acids. Linear free energy relationship can be used for prediction of degradation of haloacetonitriles during hydrolysis in water solutions. # 1999 Elsevier Science Ltd. All rights reserved Key wordsÐhaloacetonitriles, hydrolysis, LFER, chlorination products INTRODUCTION included 4 of the HANs, namely, trichloroacetoni- Water chlorination yields halogenated byproducts trile, dichloroacetonitrile, bromochloroacetonitrile due to the reaction of halogens with naturally and dibromoacetonitrile in the periodic monitoring occurring organics, such as humic acids (Bellar and requirements of the proposed United States' Lichtenberg, 1974; Rook, 1974; Johnson and Information Collection Rule (U.S. EPA, 1994). Randtke, 1983; Oliver, 1983; Ami et al., 1990). The HANs are less frequently studied compared to three most dominant families of chlorination by- THMs and HAAs and the occurrence of trihaloace- products, in order of abundance, are the trihalo- tonitriles in water is rarely reported. The most methanes (THMs), halogenated acetic acids (HAAs) abundant HANs after water chlorination are and haloacetonitriles (HANs) (Bellar et al., 1974; dichloroacetonitrile and its brominated analogs, U.S. EPA, 1979; Oliver and Shindler, 1980; Boyce bromochloroacetonitrile and dibromoacetonitrile and Hornig, 1983; Urano et al., 1983; Coleman et (Oliver and Shindler, 1980; Coleman et al., 1984; al., 1984; de Leer et al., 1985; Alouni and Seux, Reckhow and Singer, 1984; Trehy et al., 1986; 1987; Singer et al., 1995). The latter is a product of Reckhow et al., 1990; Peters et al., 1990a,b) and tri- the chlorination of aminoacides, proteins and other chloroacetonitrile (Coleman et al., 1984; Smith et nitrogen containing species. The toxicology of al., 1987; Koch et al., 1988; Singer et al., 1995). HANs is less documented as compared to the more Recently, Richardson et al. reported dibromochlor- abundant THMs and HAAs. For all HAN com- oacetonitrile in chlorine dioxide disinfected water, pounds there are no data appropriate for develop- though identi®cation was based on mass spectral ing acceptable limits for lifetime exposure to the match and was not con®rmed by identi®cation stan- chemicals though in some cases mutagenic (dibro- dards (Richardson et al., 1994, 1996). moacetonitrile and bromochloroacetonitrile against Several factors complicate the investigation of the Salmonella) and teratogenic action (trichloroaceto- HANs and particularly trisubstituted HANs in nitrile against Long±Evans rats) were reported (Bull chlorinated drinking water: (1) The HANs are inter- and Kop¯er, 1991). Nevertheless, the USEPA mediate compounds, susceptible to further conver- sion to their corresponding haloacetic acids. (2) Even in disinfectant-free water the HANs undergo *Present address: Public Health Laboratory of Ministry of further hydrolysis and the hydrolysis rates of most Health, Abu Kabir, Tel Aviv 61082, Israel. HANs are still not documented. (3) Some of the {Author to whom all correspondence should be addressed. [Tel: +972-2-6585558; Fax: +972-2-6586155; E-mail: HANs are still commercially unavailable, thus [email protected]]. quanti®cation and identi®cation require synthetic 1938 Hydrolysis of haloacetonitriles 1939 capabilities. In fact, the mass spectra of some Table 1. GC retention times of haloacetonitriles HANs, like bromochloroacetonitrile, bromodichlor- Compound Abbreviated Retention Relative oacetonitrile, dibromochloroacetonitrile and tribro- name time retention moacetonitrile are not reported in the MS libraries. (min) time This manuscript describes systematic studies of 1. ClCH2CN Cl1 4.47 0.23 the hydrolysis products and the rate of the hydroly- 2. Cl3CCN Cl3 4.88 0.26 sis of all 9 possible HANs as a function of pH. We 3. Cl2CHCN Cl2 5.79 0.30 demonstrate that linear free energy relationships 4. BrCH2CN Br1 8.05 0.42 5. BrCl2CCN BrCl2 10.69 0.56 can be used to predict the hydrolysis and oxidation 6. BrClCHCN BrCl 11.59 0.61 kinetics of the various HANs. 7. Br2CHCN Br2 17.81 0.94 8. Br2ClCCN Br2Cl 18.01 0.95 9. Br3CCN Br3 23.26 1.22 IS-CH2ClCHClCH2Cl 19.03 1.00 MATERIALS AND METHODS Equipment and instrumentation trile exhibited shorter retention time than the bromochlor- Hewlett-Packard GC-MS system using GC 5890 and oacetonitrile. These changes can be explained by the 5971 Mass Selective Detector operated in EI (electron ion- dierences in the polarity of the haloacetonitriles. Using ization) mode equipped with Altech Heli¯ex AT-1 capil- these GC-conditions all 9 acetonitrile compounds could be resolved by a single run using extracting ion chromato- lary column (30 m long, 0.32 mm i.d., 0.25 mm ®lm thickness) was used. The mass detector temperature was grams. The 6 main MS-peaks and 3 MS-peaks, which were selected for EI-MSD-SIM detection, are presented in 2808C, the injection port was operated at 1808C, the GC Table 2. The standard deviation for analysis of the HANs temperature program was: initial temperature 358C, 9 min (for 20 ppm solutions) was <10% for consecutive analy- hold time; 28C/min ramp to 428C; a second ramp at 58C/ sis. The relative change of the retention time vs. the in- min to 1608C; third ramp at 308/min to 2208C and ®nally ternal standard (1,2,3-trichloropropane) was always less 4 min hold at 2208C. than 0.1 min. Chemicals Haloacetic acids were quantitated by a conventional standard methods procedure (APHA, 1995). The pro- Analytical reagents were used unless otherwise speci®ed. cedure includes sample acidi®cation till pH 1, extraction Commercial standards including chloroacetonitrile, bro- with MTBE and further methylation with diazomethane. moacetonitrile, dichloroacetonitrile, dibromoacetonitrile, Acidi®cation without methylation resulted in formation of trichloroacetonitrile and 2,2,2-trichloroacetoamide were the corresponding haloform by thermal decarboxylation in purchased from Aldrich. Bromochloroacetonitrile, bromo- the injector. This was con®rmed by injection of the dichloroacetonitrile, dibromochloroacetonitrile and tribro- extracts of model trichloro- and tribromoacetic acids moacetonitrile were synthesized by bromination of under the same chromatographic conditions, which gave chloroacetonitrile and dichloroacetonitriles according to chloroform and bromoform artifact peaks, respectively. reported procedures (Hechenbleikner, 1946). Bromochloroacetonitrile and bromodichloroacetonitrile were isolated as individual compounds, puri®ed by distilla- Application of linear free energy relationship (LFER) for tion under reduced pressure and used as standards. In the hydrolysis of HANs case of dibromochloroacetonitrile and tribromoacetonitrile Quantitative description of the in¯uence of substituents rich fractions of these compounds were obtained by frac- in organic molecules on their reactivity was for ®rst tional distillation of the bromochloroacetonitrile synthesis demonstrated by Hammett for the dissociation of substi- product. Pure compounds were not obtained and these tuted benzoic acids in 1937. Later, this approach was suc- compounds could only be used as reference materials but cessfully developed for dierent classes of organic not for accurate quantitation. Quantitation of these com- compounds and now it is well known as linear free energy pounds is reported in this article relative to trichloroaceto- relationship (LFER) (Taft, 1956; Lowry and Schueller nitrile MSD response. Richardson, 1987; Hansch et al., 1991). LFER allows one to explain the in¯uence of molecular structure on the ther- Chromatographic analysis modynamic and kinetic parameters of chemical reactions, Acetonitrile (Fluka) was used as solvent for the prep- to interpret IR-, UV-, NMR-spectra and also to predict aration of stock solutions instead of acetone that is tra- the structure-activity relationships in medical chemistry ditionally the recommended solvent for HANs studies and electrochemistry. The LFER approach penetrates (U.S. EPA, 1988). Quenching of free chlorine with NH4Cl slowly also into water and environmental chemistry dechlorinator forms chloramine. The latter interacts with (Schwarzenbach
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