Hydrolysis of haloacetonitriles
Table 1. GC retention times of haloacetonitriles
1939
capabilities. In fact, the mass spectra of some
HANs, like bromochloroacetonitrile, bromodichlor-
oacetonitrile, dibromochloroacetonitrile and tribro-
moacetonitrile are not reported in the MS libraries.
This manuscript describes systematic studies of
the hydrolysis products and the rate of the hydroly-
sis of all 9 possible HANs as a function of pH. We
demonstrate that linear free energy relationships
can be used to predict the hydrolysis and oxidation
kinetics of the various HANs.
Compound
Abbreviated
name
Retention
time
(min)
Relative
retention
time
1. ClCH2CN
2. Cl3CCN
Cl1
Cl3
Cl2
Br1
BrCl2
BrCl
Br2
Br2Cl
Br3
4.47
4.88
5.79
8.05
10.69
11.59
17.81
18.01
23.26
19.03
0.23
0.26
0.30
0.42
0.56
0.61
0.94
0.95
1.22
1.00
3. Cl2CHCN
4. BrCH2CN
5. BrCl2CCN
6. BrClCHCN
7. Br2CHCN
8. Br2ClCCN
9. Br3CCN
IS-CH2ClCHClCH2Cl
MATERIALS AND METHODS
Equipment and instrumentation
trile exhibited shorter retention time than the bromochlor-
oacetonitrile. These changes can be explained by the
dierences in the polarity of the haloacetonitriles. Using
these GC-conditions all 9 acetonitrile compounds could be
resolved by a single run using extracting ion chromato-
grams. The 6 main MS-peaks and 3 MS-peaks, which
were selected for EI-MSD-SIM detection, are presented in
Table 2. The standard deviation for analysis of the HANs
(for 20 ppm solutions) was <10% for consecutive analy-
sis. The relative change of the retention time vs. the in-
ternal standard (1,2,3-trichloropropane) was always less
than 0.1 min.
Hewlett-Packard GC-MS system using GC 5890 and
5971 Mass Selective Detector operated in EI (electron ion-
ization) mode equipped with Altech Heli¯ex AT-1 capil-
lary column (30 m long, 0.32 mm i.d., 0.25 mm ®lm
thickness) was used. The mass detector temperature was
2808C, the injection port was operated at 1808C, the GC
temperature program was: initial temperature 358C, 9 min
hold time; 28C/min ramp to 428C; a second ramp at 58C/
min to 1608C; third ramp at 308/min to 2208C and ®nally
4 min hold at 2208C.
Haloacetic acids were quantitated by a conventional
standard methods procedure (APHA, 1995). The pro-
cedure includes sample acidi®cation till pH 1, extraction
with MTBE and further methylation with diazomethane.
Acidi®cation without methylation resulted in formation of
the corresponding haloform by thermal decarboxylation in
the injector. This was con®rmed by injection of the
extracts of model trichloro- and tribromoacetic acids
under the same chromatographic conditions, which gave
chloroform and bromoform artifact peaks, respectively.
Chemicals
Analytical reagents were used unless otherwise speci®ed.
Commercial standards including chloroacetonitrile, bro-
moacetonitrile, dichloroacetonitrile, dibromoacetonitrile,
trichloroacetonitrile and 2,2,2-trichloroacetoamide were
purchased from Aldrich. Bromochloroacetonitrile, bromo-
dichloroacetonitrile, dibromochloroacetonitrile and tribro-
moacetonitrile were synthesized by bromination of
chloroacetonitrile and dichloroacetonitriles according to
reported
procedures
(Hechenbleikner,
1946).
Bromochloroacetonitrile and bromodichloroacetonitrile
were isolated as individual compounds, puri®ed by distilla-
tion under reduced pressure and used as standards. In the
case of dibromochloroacetonitrile and tribromoacetonitrile
rich fractions of these compounds were obtained by frac-
tional distillation of the bromochloroacetonitrile synthesis
product. Pure compounds were not obtained and these
compounds could only be used as reference materials but
not for accurate quantitation. Quantitation of these com-
pounds is reported in this article relative to trichloroaceto-
nitrile MSD response.
Application of linear free energy relationship (LFER) for
hydrolysis of HANs
Quantitative description of the in¯uence of substituents
in organic molecules on their reactivity was for ®rst
demonstrated by Hammett for the dissociation of substi-
tuted benzoic acids in 1937. Later, this approach was suc-
cessfully developed for dierent classes of organic
compounds and now it is well known as linear free energy
relationship (LFER) (Taft, 1956; Lowry and Schueller
Richardson, 1987; Hansch et al., 1991). LFER allows one
to explain the in¯uence of molecular structure on the ther-
modynamic and kinetic parameters of chemical reactions,
to interpret IR-, UV-, NMR-spectra and also to predict
the structure-activity relationships in medical chemistry
and electrochemistry. The LFER approach penetrates
slowly also into water and environmental chemistry
(Schwarzenbach et al., 1993). LFER is manifested in the
Hammett equation for aromatic compounds and in the
Chromatographic analysis
Acetonitrile (Fluka) was used as solvent for the prep-
aration of stock solutions instead of acetone that is tra-
ditionally the recommended solvent for HANs studies
(U.S. EPA, 1988). Quenching of free chlorine with NH4Cl
dechlorinator forms chloramine. The latter interacts with
acetone, forming 2-chloroiminopropane, which yields an
additional chromatographic peak. Subsequently, phos-
phate buer solutions Ð pH 5.4, 7.2, 8.7 and 0.1 N HCl
Ð were used for preparation of the HANs water sol-
utions. HANs ®nal concentration ranged between 20±
50 ppm. Solutions were stored in a thermostat at 208C and
analyzed after 1, 3, 24, 48 and 96 h. Methyl-tert-buthyl
ether (MTBE) (Sigma, HPLC grade) was used for liquid
extraction, 50 ml of aqueous phase was extracted with
3 ml of organic phase in the presence of 10 g of NaCl
(Frutarom, Israel). Extracts were dried over sodium sul-
fate. Retention times of all 9 haloacetonitriles, under the
above-mentioned conditions, are presented in Table 1. The
retention times followed the molecular weight order with
two exceptions: trichloroacetonitrile had shorter retention
time than dichloroacetonitrile and bromodichloroacetoni-
Table 2. Main MS Ð peaks and relative abundances of haloace-
tonitriles
1. ClCH2CN
2. BrCH2CN
3. Cl2CHCN
77(23), 75(100), 50(22), 48(67), 47(10), 40(25)
121(97), 119(100), 94(11), 81(50), 79(24), 40(75)
84(44), 82(65), 76(33), 74(100), 48(9), 47(25)
4. BrClCHCN 155(27), 153(21), 81(12), 79(12), 76(33), 74(100)
5. Br2CHCN 201(23), 199(46), 197(26), 120(100), 118(100), 81(22)
6. Cl3CCN
112(11), 110(68), 108(100), 82(11), 73(14), 47(15)
7. BrCl2CCN 154(26), 152(21), 112(11), 110(67), 108(100), 73(17).
8. Br2ClCCN 198(10), 156(22), 154(100), 152(76), 81(10), 79(12).
9. Br3CCN
200(48), 198(100), 196(52), 119(11), 117(12), 79(12).
Italic values were used for SIM analysis. Values in brackets rep-
resent relative abundance.