Hydrolysis of haloacetonitriles: Linear free energy relationship. Kinetics and products

Article abstract of DOI:10.1016/S0043-1354(98)00361-3

The hydrolysis rates of mono-, di- and trihaloacetonitriles were studied in aqueous buffer solutions at different 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 affected 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 different buffer solutions follow first 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. The hydrolysis rates of mono-, di- and trihaloacetonitriles were studied in aqueous buffer solutions at different 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 affected 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 different buffer solutions follow first 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.

Full text of DOI:10.1016/S0043-1354(98)00361-3

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
M
*
OVADIA LEV{
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 bu€er sol-
utions at di€erent 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 a€ected 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 di€erent bu€er 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-
trile, dichloroacetonitrile, bromochloroacetonitrile
Water chlorination yields halogenated byproducts
and dibromoacetonitrile in the periodic monitoring
due to the reaction of halogens with naturally
requirements of the proposed United States'
Information Collection Rule (U.S. EPA, 1994).
occurring organics, such as humic acids (Bellar and
Lichtenberg, 1974; Rook, 1974; Johnson and
HANs are less frequently studied compared to
THMs and HAAs and the occurrence of trihaloace-
Randtke, 1983; Oliver, 1983; Ami et al., 1990). The
three most dominant families of chlorination by-
tonitriles in water is rarely reported. The most
products, in order of abundance, are the trihalo-
abundant HANs after water chlorination are
dichloroacetonitrile and its brominated analogs,
bromochloroacetonitrile and dibromoacetonitrile
methanes (THMs), halogenated acetic acids (HAAs)
and haloacetonitriles (HANs) (Bellar et al., 1974;
U.S. EPA, 1979; Oliver and Shindler, 1980; Boyce
(Oliver and Shindler, 1980; Coleman et al., 1984;
and Hornig, 1983; Urano et al., 1983; Coleman et
Reckhow and Singer, 1984; Trehy et al., 1986;
al., 1984; de Leer et al., 1985; Alouni and Seux,
Reckhow et al., 1990; Peters et al., 1990a,b) and tri-
1987; Singer et al., 1995). The latter is a product of
chloroacetonitrile (Coleman et al., 1984; Smith et
al., 1987; Koch et al., 1988; Singer et al., 1995).
the chlorination of aminoacides, proteins and other
nitrogen containing species. The toxicology of
Recently, Richardson et al. reported dibromochlor-
oacetonitrile in chlorine dioxide disinfected water,
HANs is less documented as compared to the more
abundant THMs and HAAs. For all HAN com-
though identi®cation was based on mass spectral
pounds there are no data appropriate for develop-
match and was not con®rmed by identi®cation stan-
dards (Richardson et al., 1994, 1996).
ing acceptable limits for lifetime exposure to the
chemicals though in some cases mutagenic (dibro-
Several factors complicate the investigation of the
HANs and particularly trisubstituted HANs in
chlorinated drinking water: (1) The HANs are inter-
moacetonitrile and bromochloroacetonitrile against
Salmonella) and teratogenic action (trichloroaceto-
nitrile against Long±Evans rats) were reported (Bull
mediate compounds, susceptible to further conver-
and Kop¯er, 1991). Nevertheless, the USEPA
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.
{Author to whom all correspondence should be addressed.
HANs are still not documented. (3) Some of the
HANs are still commercially unavailable, thus
quanti®cation and identi®cation require synthetic
[Tel: +972-2-6585558; Fax: +972-2-6586155; E-mail:
ovadia@vms.huji.ac.il].
1938

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
di€erences 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 di€erent 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 bu€er 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.

1940
Victor Glezer et al.
Table 3. Taft's polar and steric constants and the corresponding
rate constant for hydrolysis of haloacetonitriles at pH 8.7
Taft equation for aliphatic compounds. The Taft equation
divides the substituent e€ects to polar and steric com-
ponents. In this work Taft equation is used to describe the
hydrolysis rate of HANs according to equation 1:
Compound
s*
ES
k
log k
6
6
6
6
6
5
5
4
4
1.05a
1.00a
1.86b
1.90b
1.94a
2.55b
2.59b
2.62b
2.65a
0.24a
0.27a
1.86a
1.70b
1.54a
2.43a
2.31b
2.19b
2.06a
1.2 Â10
2.7 Â10
4.0 Â10
5.3 Â10
5.6 Â10
4.5 Â10
8.0 Â10
2.2 Â10
3.9 Â10
5.92
5.57
5.40
5.27
5.25
4.35
4.10
3.66
3.41
R±CN ‡ H2O 4R±CONH2,
where R = X1X2X3C and X1, X2, X3 are chlorine, bromine
or hydrogen atoms.
The Taft's polar (s*) and steric (Es) substituent con-
stants can be used to predict the rate constants of hydroly-
sis reaction (equation 1) according to equation 2:
ꢀ1†
ClCH2CN
BrCH2CN
Br2CHCN
BrClCHCN
Cl2CHCN
Br3CCN
Br2ClCCN
BrCl2CCN
Cl3CCN
logꢀkR=k0† ˆ rs* ‡ dES,
ꢀ2†
aFrom /29/.bCalculated as described in text.
where k0 is the hydrolysis rate constant for unsubstituted
compound (in this case acetonitrile); kR the hydrolysis rate
constant for compound with substituent R; s* and ES are,
respectively, Taft polar and steric constants; and r and d
are empirical parameters representing the sensitivity of the
hydrolysis rate to the polar and steric factors.
Taft's polar and steric constants for all haloacetonitriles
are presented in Table 3.
The Taft polar constants (s*) for ClCH2, Cl2CH, Cl3C
and BrCH2 substituents have been reported by Taft (1956)
and Hansch et al. (1991). These constants for mixed bro-
mochlorosubstituents and di- and tri-bromosubstituents
were not available, but they could be evaluated based on
correlations describing the relationship between the induc-
tive component of the Hammett constant, sI, and Taft
polar constant, s*.
RESULTS AND DISCUSSION
Conversion of haloacetonitriles: structure and pH-
dependence
The hydrolysis of all 9 HANs was studied at pH
8.7, 7.2, 5.4 and in 0.1 N HCl. The stability of
HANs depends on their chemical structure and on
pH and can be divided into two groups, one for
neutral and basic conditions and the second for
acidic conditions. Examples of HANs disappear-
ance at pH 8.7 and pH 5.4 are presented on
Fig. 1(a) and (b). The HAN's are most stable in
weak acidic media Ð less than 50% were degraded
after 4 d at pH 5.4, while at pH 8.7 (the pH of the
Israel National Water Carrier) some of the com-
pounds, e.g. trihaloacetonitriles could not be
detected after 24 h. Faster hydrolysis of dichloroa-
cetonitrile in basic media in comparison to acidic
media was observed also by Oliver (1983) and now
it is clear that this conclusion can be extended for
all tri- and di-haloacetonitriles. The trihalo-substi-
Thus, the Taft polar constant for CH2X substituent can
be calculated by equation 3 (Lowry and Schueller
Richardson, 1987; Hansch et al., 1991).
sÃꢀCH X † ˆ sIꢀX †=0:45,
ꢀ3†
2
where sI(X) is the inductive component of the Hammett
constant and 0.45 is an empirical constant.
sI(X) of bromine and chlorine atoms were reported to be
0.47 and 0.45, respectively. Thus, using this approach
sÃꢀCH Br†=1.0 and sꢀÃCH Cl†=1.05 which coincide with the
publ2ished value of s* 2(Lowry and Schueller Richardson,
1987; Schwarzenbach et al., 1993). Extrapolation of this
approach can be used to extend equation 3 to multisubsti-
tuent groups.
sÃꢀCHX X † ˆ AꢀsIꢀX † ‡ sIꢀX ††=0:45,
ꢀ4†
1
2
1
2
where A is a correction factor for the disubstituted com-
pound. The constant A can be evaluated based on the
known value of Taft's s*-constant for CHCl2 substituent tuted compounds were the least stable and the most
reported to be 1.94 (Taft, 1956). So, A can be calculated
from the expression A=sÃꢀCH Cl†/(2sI(Cl)/0.45). Thus,
sensitive to pH changes. Under basic conditions
decrease of trihaloacetonitriles can be observed
already after 1 h, while in acid media there was no
signi®cant change in trihaloacetonitriles concen-
2
A = 1.94/(2*0.47/0.45) = 0.93. Similarly, the constant for
trisubstituted radical can be represented by,
sÃꢀCX X X † ˆ BꢀsIꢀX † ‡ sIꢀX † ‡ sIꢀX ††=0:45:
ꢀ5†
1
2
3
1
2
3
tration even after 24 h. Figure 2 compares the rela-
tive stability of the HANs at the various pH levels.
The percent of each of the HANs that remain after
96 h hydrolysis is described as a function of pH.
For most compounds optimal stability of the triha-
loacetonitriles is obtained at pH 5.4. Much faster
hydrolysis occurs at higher pH with exception for
chloroacetonitrile which remains in high concen-
tration also after 96 h. Comparison of hydrolysis
rates at pH 5.4 and pH 1 shows that the di€erences
in degradation rate vs. pH are less pronounced in
acidic media as compared to basic solutions.
Generally the stability of HANs is on the same
level or even slightly improved at pH 5.4, except for
trichloroacetonitrile which was more stable in 0.1 N
HCl. Mono- and di-substituted HANs are very
The correction coecient, B, can be evaluated by the ratio
of Taft's s*-experimental value, reported for sÃꢀCCl † to be
2.65 and the constant's value calculated based on3the ex-
pression for 3 chlorine atoms: sÃꢀCCl †=3sI(Cl)/0.45. This
3
approach yields B = 2.65/(0.47*3/0.45) = 0.85. The values
of the correction coecients A and B show that the contri-
butions of the halogen substituents are almost additive.
The steric constants, Es, for ClCH2, BrCH2 , Cl2CH,
Br2CH, Cl3C and Br3C substituents were reported (Taft,
1956; Hansch et al., 1991). Es values for other substituents
were not reported, but they can be calculated considering
that the constants for di- and tri-halosubstituents are com-
prised of the sum of the speci®c contributions of the corre-
sponding halogen substituents. The contribution of one
chlorine substituent equals 1.54:2 = 0.77 for dihalo-
compounds and 2.06:3 = 0.69 for trihalo-compounds.
The contribution of each bromine radical can be calcu-
lated in a similar way to give 0.93 and 0.81 for the
double and triple halosubstituted compounds, respectively. stable in acid media and only after 48 h some

Hydrolysis of haloacetonitriles
1941
Fig. 1. Hydrolysis of haloacetonitriles at pH 8.7 (a) and at pH 5.4 (b).
decrease in their concentrations could be increases for the series Cl3CCN±BrCl2CCN±
observed, while the stability of the trisubstituted Br2ClCCN±Br3CCN.
compounds was much inferior. The nature of the
Hydrolytic pathways of trihaloacetonitriles
halogen atom in substituent in¯uences also the
HANs hydrolysis rate. Subsequent substitution of
Under all pH conditions, the decrease in concen-
chlorine with bromine atoms in trichloroacetoni- tration of trihaloacetonitriles is accompanied by
trile increases HANs stability. The in¯uence appearance of new chromatographic peaks. These

1942
Victor Glezer et al.
Fig. 2. The in¯uence of pH on stability of haloacetonitriles. Remaining percentage after 96 h.
were identi®ed as the corresponding trihaloaceta- (2.1%)/M+/; 205 (1.4%), 207 (2.8%), 209 (1.8%)/
mides. The commercial standard of trichloroaceta- CBr2Cl/+; 170 (2.0%), 172 (3.5%), 174 (1.0%)/
mide was available and the compound was CBr2/+; 154 (1.1%), 156 (1.4%), 158 (0.2%)/
identi®ed both by matching chromatographic reten- CBrClCO/+; 142 (2.5%), 144 (3.5%), 146 (0.7%)/
tion time and by spectral matching. For other triha- CBrClNH2/+; 126 (5.0%), 128 (6.7%), 130 (1.0%)/
loacetamides the library mass-spectra were not CBrCl/+; 91(2.8%), 93 (2.8%)/CBr/+; 79 (3.5%),
available and they were identi®ed based on their 81 (3.9%)/Br/+; 47 (3.5%), 49 (1.1%)/CCl/+; 44
MS-spectra fragmentation. In the case of dibromo- (100%)/CONH2/+. Small relative abundances of all
chloroacetamide the following peaks correspond to mass-spectra peaks in comparison with the base
the EI fragments, their relevant chemical structure peak, 44 corresponding to the ion /CONH2/+ was
is given in brackets: 249 (0.7%), 251 (2.1%), 253 typical also for trichloroacetamide.
Fig. 3. Products formation by the hydrolysis of trichloroacetonitrile at pH 8.7: (1) trichloroacetonitrile,
(2) trichloroacetamide, (3) trichloroacetic acid (detected in ester form) and (4) sum of 1 + 2 + 3.

Hydrolysis of haloacetonitriles
1943
Table 4. Retention time of the hydrolysis products of trihaloaceto-
nitriles
Hydrolysis of the HANs under basic conditions
yielded also the corresponding haloacetic acids as
demonstrated for trichloroacetonitrile (Fig. 3). The
haloacetic acids were determined as the correspond-
ing methylester by MTBE extraction in acidic sol-
Compound
Retention time (min)
1. Cl3CCOOCH3
2. BrCl2CCOOCH3
3. Br2ClCCOOCH3
4. Cl3CCONH2
5. BrCl2CCONH2
6. Br2ClCCONH2
7. Br3CCONH2
19.71
23.70
27.21
29.10
32.29
35.02
37.10
ution
and
subsequent
methylation
with
diazomethane. The chromatographic retention times
for all trihaloacetonitriles hydrolysis products are
presented in Table 4. In basic solution, the molar
sum of haloacetonitrile + haloacetamides + haloa-
cetic acids was time invariant (Fig. 3). In acid and
neutral solutions the sum of haloacetamide and
Table 3 also depicts the values of the hydrolysis
rate constants of the HANs at pH 8.7. The hydroly-
haloacetonitrile was conserved demonstrating that sis rate constants depend on the number of halogen
these are indeed the only, or at least the dominant
hydrolysis products.
atoms in the HAN molecule. The trihaloacetoni-
triles are less stable than mono- and di-substituted
compounds. Thus, the expected quantitative depen-
dence between the chemical structure and the reac-
tivity of the HAN molecules can be described by
linear free energy relationship (LFER), demonstrat-
ing the in¯uence of structural changes in the or-
ganic molecule on its chemical characteristics, using
the constants of Table 3.
Taft equation for haloacetonitriles hydrolysis
The hydrolysis of the trihaloacetonitriles obeyed
®rst order kinetics as demonstrated for the hydroly-
sis of trichloroacetonitrile. The kinetic coecient
can be obtained from the linear ln(C) vs. t depen-
dence (Fig. 4). The C and 1/C vs. t dependencies
were not linear showing that zero order and second
order kinetics can be ruled out. The hydrolysis rate
constants of the trihaloacetonitile compounds at
di€erent pH-values are presented in Table 5. The
qualitative conclusions that were derived earlier
based on Figs 1 and 2, that rate constants (k)
increase with pH and depend on the nature of the
substituents can now be con®rmed based on the
quantitative kinetic data of Table 5. For the triha-
loacetonitrile molecules, consecutive substitution of
bromine atoms by chlorine increases the stability of
the trihaloacetonitriles.
For pH 8.7 the LFER equation is best ®tted by
equation 6:
log kR
ˆ
8:4420:26 ‡ ꢀ2:9120:50†sÃ
‡ ꢀ1:3620:40†ES:
ꢀ6†
The standard deviations of the coecients are given
in the regular brackets in equation 6. The linear
correlation coecient was r = 0.97 and the number
of degrees of freedom was n = 6. Graphic presenta-
tions of equation 6 are given in Fig. 5(a), (b) for ES
and s* parameters, respectively. Comparison of
Fig. 4. ln(C) vs. time dependence for the hydrolysis of trichloroacetonitrile at pH 8.7 (correlation coe-
cient, R = 0.99, degrees of freedom, n = 5).

1944
Victor Glezer et al.
Table 5. Hydrolysis rate constants (s 1) of trihaloacetonitriles
constant s* increases the hydrolysis rate constants,
while increasing the absolute value of the steric con-
stant, Es, decreases the hydrolysis rate constant.
Thus, the increase of amount of halogen atoms in a
HAN molecule increases log k due to larger rs*
contribution which is more signi®cant than the
change in dEs. Inside a group of the same number
of halogen atoms the substitution of chlorine by
bromine atoms decreases the hydrolysis rate
because the polar constant, s* decreases and the
absolute values of the steric constant, Es, increases.
The hydrolysis rate constants also depend on the
pH 5.4
pH 7.2
pH 8.7
6
6
6
6
4
5
5
5
4
4
4
4
Cl3CCN
2.0 Â 10
1.3 Â 10
1.0 Â 10
0.7 Â 10
1.5 Â 10
1.2 Â 10
0.9 Â 10
1.6 Â 10
3.9 Â 10
2.2 Â 10
0.8 Â 10
0.4 Â 10
BrCl2CCN
Br2ClCCN
Br3CCN
Taft's sensitivity constants r and d in equation 6
shows that the hydrolysis rate is more sensitive to
the polar than to the steric constant. These con-
stants have opposite signs and in¯uence the log k-
values in opposite directions. Increasing the polar pH of the media Ð lowering the pH diminishes the
Fig. 5. Projections of the linear free energy relationship for haloacetonitriles hydrolysis at pH 8.7:
(a) Dependence of Taft steric constants ES, (b) Dependence of Taft polar constants s*.

Hydrolysis of haloacetonitriles
hydrolysis rates (Fig. 2) and decreases the value of presented by equation 10:
1945
the coecients in equation 2. This is demonstrated
for pH 7.2 (equation 7) and pH 5.4 (equation 8):
log kR
ˆ
8:6520:28 ‡ ꢀ2:7320:53†sÃ
‡ ꢀ1:3120:41†ES,
ꢀ7†
ꢀr ˆ 0:97, n ˆ 6†,
log kR
ˆ
8:4720:14 ‡ ꢀ1:7020:27†sÃ
‡ ꢀ0:8120:21†ES,
ꢀr ˆ 0:97, n ˆ 6†:
ꢀ8†
The hydrolysis of haloacetonitrile compounds
under basic conditions yields the corresponding
acetamides, which in basic media can be further
hydrolyzed to the corresponding acid. During the
extraction with MTBE the trihaloacetic acid anions
remain in the aqueous phase and can not be ident-
i®ed by GC-MS analysis, whereas acidi®cation
yields the acidic form, which can be extracted to
the organic phase and further methylated. The hy-
drolysis of trihaloacetamides is a much slower pro-
cess as compared to the hydrolysis of the starting
compound (see Fig. 3) and it is carried out only
under basic solutions. In acid solutions the hydroly-
sis process is terminated by formation acetamides
which are stable under acidic conditions. Based on
these observations it can be concluded that preser-
vation of HAN samples between sampling and
analysis, can be best accomplished by adjusting the
pH to weakly.
Comparison of equations 6)±(8) suggests that the
log kR values be twice more sensitive to substi-
tuent's polar constants as compared to the steric
constants.
Mechanism of trihaloacetonitrile hydrolysis
The hydrolysis of trihaloacetonitriles can be
either acid or base catalyzed (Schaefer, 1970). The
mechanism of basic hydrolysis involves nucleophilic
addition of OH (Schaefer, 1970):
RCN ‡ OH
‡H2O
4RCꢀOH †.N
4RCONH2,
4
RCꢀOH †.NH
OH
ꢀ9†
where R = CH3 nXn, n = 1,2,3 and X = Cl, Br or
their combination.
Chlorination of haloacetonitriles
The mechanism of HANs chlorination was
suggested by Peters et al. (1990b), equation 11. It
may followed either direct chlorination by HOCl,
forming the corresponding N-chloroamides (route
A) or an indirect route through hypochlorite cata-
lyzed hydrolysis of the cyano group producing an
amide that reacts with HOCl to give the corre-
sponding N-chloramide (route B). The proposed
mechanisms of HAN chlorination are analogous to
HAN hydrolysis, which allows use of the LFER
approach also for this case.
The main products of this process are the aceta-
mides and further basic hydrolysis of these forms
the corresponding carboxylic acids. The acid-cata-
lyzed process starts with protonation of the nitro-
gen atom in the nitrile group (Schaefer, 1970) and
is slower than in basic media. The di€erences
between pH 1 and pH 5 can be explained by
increase of hydrolysis rate in more acidic media.
The general scheme of haloacetonitriles hydrolysis
followed by determination of the corresponding
esters after methylation by diazomethane can be

1946
Victor Glezer et al.
Fig. 6. Disappearance of haloacetonitriles in the presence of 30 ppm chlorine at pH 7.2.
Degradation of the HANs by chlorination is much reaction as well. The stability increases with increas-
faster compared to their hydrolysis. For example, at ing number of bromine atoms in the molecule.
pH 7.2 only 2 of the 4 starting trihaloacetonitriles
The successful application of LFER in describing
remained in solution after 1 h (Fig. 6) and after the hydrolysis of the HANs stimulated the appli-
24 h only the monohaloacetonitriles remained unde- cation of the LFER and the Taft's parameters to
graded. The stability ranking observed for the hy- describe the chlorination of the HANs as well. This
drolysis step was preserved for the chlorination is of course relevant as an end in itself and as a
Fig. 7. Stability of haloacetonitriles at pH 7.2 in the presence of chloramine (see text).

Hydrolysis of haloacetonitriles
1947
further supports for the linear approach taken to can be adequately described by LFER approach.
derive the missing Taft's constants, though unlike The stability of haloacetonitriles for both hydrolysis
hydrolysis chlorination is a second order process:
and chlorination reactions decreased for larger
number of halogen substituents and increased upon
replacing chlorine with bromine. Under acid con-
ditions the hydrolysis of haloacetonitriles gave
haloacetoamides and in basic media further hy-
drolysis to the corresponding trihaloacetic acid was
observed.
log k ˆ 1:6920:16 ‡ ꢀ1:0520:47†sÃ
‡ ꢀ0:4820:33†ES,
ꢀr ˆ 0:93†:
ꢀ12†
Equation 12 describes the best ®t second order reac-
tion kinetic coecient of chlorination at pH 7.2.
The comparison of equation 12 and equation 7,
describing the kinetic coecients of hydrolysis
under the same pH, reveal that the independent
constant is much larger for chlorination as com-
pared to hydrolysis while the steric and polar
dependencies are somewhat less signi®cant for
chlorination as compared to the hydrolysis. Thus,
the overall stability of unsubstituted acetonitrile is 6
orders of magnitude larger for hydrolysis as com-
pared to its stability in the presence of the speci®ed
chlorination conditions. Interestingly, the polar con-
stant was found to be twice larger than the steric
constants for all the hydrolysis and chlorination test
cases. This again point on the mechanistic similarity
of hydrolysis and chlorination.
A practical conclusion that arise from the studies
is that HAN samples are best preserved (between
sampling and analysis) under weak acid conditions
due to their superior stability under such con-
ditions. Weak acid conditions are also optimal for
preservation of chlorinated samples after am-
monium chloride quenching of the oxidant.
AcknowledgementsÐThis research was supported by the
Avicennia initiative of the European Community; German
Federal Ministry of Education, Science, Research and
Technology (BMFT) and the Israeli Ministry of Science
(MOS) and U.S. EPA.
REFERENCES
Alouni Z. and Seux R. (1987) Cinetiques et mechanismes
de l'action oxydative de l'hypochlorite sur les acides a-
amines lors de la desinfection des eaux. (Kinetics and
mechanisms of hypochlorite oxidation of a-amino acids
at the time of water chlorination). Water Res. 21, 335±
343.
Termination of the chlorination reaction by chlorami-
nation
Nieminski et al. (1993) demonstrated that termin-
ation of the chlorination step can be best achieved
by addition of ammonium chloride which captures
e€ectively the active chlorine. Unlike sul®te, thiosul-
fate and hexacyanoferrate, ammonium ions do not
reduce the HAN compounds concentration.
It was, therefore, interesting to verify the stability
sequence of HANs in the presence of monochlora-
mine. These tests were conducted in the presence of
chloramine (NaClO was added in the presence of
NH4Cl) at pH 7.2. The rate of disappearance of
HANs under these conditions was best ®tted by
equation 13:
Ami G. L., Thompson J. M., Tan L., Davis M. K. and
Krasner S. W. (1990) Evaluation of THM precursor
contributions from agricultural drains. J. AWWA 82,
57±64.
APHA (1995) Standard Methods for the Examination of
Water and Wastewater. 19th edn., pp. 6±69. American
Public Health Association, Washington, DC.
Bellar T. A. and Lichtenberg J. J. (1974) Determining vol-
atile organics at microgram-per-litre levels by gas chro-
matography. J. AWWA 66, 739±744.
Bellar T. A., Lichtenberg I. J. and Kroner R. C. (1974)
Occurrence of organohalides in chlorinated drinking
waters. J. AWWA 66, 703±706.
Boyce S. D. and Hornig J. F. (1983) Reaction pathways
of trihalomethane formation from the halogenation of
dihydroxyaromatic model compounds for humic acids.
Environ. Sci. Technol. 17, 202±211.
Bull R. J. and Kop¯er F. C. (1991) Health E€ects of
Disinfectants and Disinfection By-Products. AWWA,
Research Foundation, Denver, CO.
Coleman W. E., Munch J. W., Kaylor W. H., Streicher R.
P., Ringhand H. P. and Meier J. P. (1984) Gas chroma-
tography/mass spectroscopy analysis of mutagenic
extracts of aqueous chlorinated humic acid. A compari-
son of the by-products to drinking water contaminants.
Environ. Sci. Technol. 18, 674±681.
Hansch C., Leo A. and Taft R. W. (1991) A survey of
Hammett substituent constants and resonance and ®eld
parameters. Chem. Rev. 91, 165±195.
Hechenbleikner I. (1946) Halogen substituted acetonitriles.
U.S. Patent 2,394,912.
log k ˆ 7:9020:29 ‡ ꢀ2:3820:55†sÃ
‡ ꢀ1:1520:44†ES,
ꢀr ˆ 0:94, n ˆ 6†:
ꢀ13†
The rate of disappearance of haloacetonitriles in the
presence of chloramine is slightly higher compared
to nonchlorinated media (equation 7) and (Fig. 7),
but it is still much smaller as compared to the
degradation in the presence of hypochlorite
(equation 12).
Johnson D. E. and Randtke S. J. (1983) Removing nonvo-
latile organic chlorine and its precursors by coagulation
and softening. J. AWWA 75, 249±253.
CONCLUDING REMARKS
Koch B., Crofts E. W., Schimp€ W. K. and Davis M. K.
(1988) Water Qual. Technol. Conf. (Publ. 1989) 16,
429±456.
The disappearance of haloacetonitriles (hydrolysis
under di€erent pH conditions and by chlorination)

1948
Victor Glezer et al.
ducts in drinking water. Environ. Sci. Technol. 30, 3327±
3334.
Rook J. J. (1974) Formation of haloforms during chlori-
nation of natural waters. Water Treat. Exam. 23, 234±
243.
Schaefer F. C. (1970) Nitrile reactivity. In The Chemistry
of the Cyano Group, ed. Z. Rappoport. Interscience
Publishers, New York, p. 256.
Schwarzenbach R. P., Gschweno P. M. and Imboden D.
M. (1993) Environmental Organic Chemistry. Wiley,
New York, p. 681.
Singer P. C., Obolensky A. and Greiner A. (1995) DBPs
in chlorinated North Carolina drinking waters. J.
AWWA 87, 83±92.
Smith M. K., George E. L., Zenick H., Manson J. M. and
Stober J. A. (1987) Developmental toxicity of haloge-
nated acetonitriles: drinking water by-products of chlor-
ine disinfection. Toxicology 46, 83±93.
Taft R. W., Jr. (1956) Separation of polar, steric, and res-
onance e€ects in reactivity. In Steric E€ects in Organic
Chemistry, ed. M. S. Newman. Wiley, New York, p.
556.
Trehy M. L., Yost R. A. and Miles C. J. (1986)
Chlorination byproducts of amino acids in natural
waters. Environ. Sci. Technol. 20, 1117±1122.
Urano K., Wada H. and Takemasa T. (1983) Empirical
rate equation for trihalomethane formation with chlori-
nation of humic substances in water. Water Res. 17,
1797±1802.
de Leer E. W. B., Damste J. S. S., Erkelens C. and de
Galan L. (1985) Identi®cation of the mediates leading to
chloroform and C4-diacids in the chlorination of humic
acids. Environ. Sci. Technol. 19, 512±522.
Lowry T. H. and Schueller Richardson K. (1987)
Mechanism and Theory in Organic Chemistry. Harper
and Row Publications, New York, p. 152.
Nieminski E. C., Chaudhuri S. and Lamoreaux T. (1993)
The occurrence of DBPs in Utah drinking waters. J.
AWWA 85, 98±105.
Oliver B. G. (1983) Dihaloacetonitriles in drinking water:
algae and fulvic acids as precursors. Environ. Sci.
Technol. 17, 80±83.
Oliver B. G. and Shindler D. B. (1980) Trihalomethanes
from the chlorination of aquatic algae. Environ. Sci.
Technol. 14, 1502±1505.
Peters R. J. B., de Leer E. W. B. and de Galan L. (1990a)
Dihaloacetonitriles in Dutch drinking waters. Water
Res. 24, 797±800.
Peters R. J. B., de Leer E. W. B. and de Galan L. (1990b)
Chlorination of cyanoethanoic acid in aqueous medium.
Environ. Sci. Technol. 24, 81±86.
Reckhow D. A. and Singer P. C. (1984) The removal of
organic halide precursors by preozonation and alum co-
agulation. J. AWWA 76, 151±157.
Reckhow D. A., Singer P. C. and Malcolm R. L. (1990)
Chlorination of humic materials: byproduct formation
and chemical interpretations. Environ. Sci. Technol. 24,
1655±1664.
Richardson S. D., Thruston A. D., Collete T. W.,
Patterson K. S., Lykins B. W., Jr., Majetich G. and
Zhang Y. (1994) Multispectral identi®cation of chlorine
dioxide disinfection by-products in drinking water.
Environ. Sci. Technol. 28, 592±599.
U.S. EPA (1994) Monitoring requirements for public
drinking water supplies; Proposed rule, Federal
Register, 40 CFR part 141, Vol. 59, N28.
U.S. EPA (1979) National Interim Primary drinking water
regulations: control of trihalomethanes in drinking
water. Fed. Reg. 44 (231): 68624.
Richardson S. D., Thruston A. D., Collete T. W.,
Patterson K. S., Lykins B. W., Jr. and Ireland J. C.
(1996) Identi®cation of TiO2/UV disinfection by-pro-
U.S. EPA (1988) Determination of chlorination disinfec-
tion by-products and chlorinate solvents in drinking
water.