Reactions of hydrated electrons with triazine derivatives in aqueous medium

Article abstract of DOI:10.1021/jf061916d

A study is made of the kinetics and mechanism of the reaction of radiolytically produced hydrated electron (e^-_aq) with some triazine derivatives [1,3,5-triazine (T), 2,4,6-trimethoxy-1,3,5-triazine (TMT), 2,4-dioxohexahydro-1,3,5-triazine (DHT), 6-chloro N-ethyl N-(1-methylethyl)-1,3,5-triazine 2,4-diamine (atrazine, AT), and cyanuric acid (CA)] in aqueous medium using pulse and steady-state radiolysis techniques. The second-order rate constants were determined from the pseudo first-order decay of e^-_aq in the presence of triazines at 720 nm, and the values obtained with T, TMT, AT, and CA are in the order of 10⁹ dm³ mol^-1 s^-1 and that of DHT was 10 ⁸ dm³ mol^-1 s^-1 at pH 6. The transient absorption spectra from the reaction of e^-_aq with T and TMT are characterized by their λ_max at 310 nm, and those of DHT and CA are around 280 and 290 nm, respectively. However, a very weak and featureless absorption spectrum is obtained from AT. On the basis of the spectral evidence and on the quantitative electron transfer from the transient intermediates to the oxidant, methyl viologen (MV²⁺), the intermediate radicals are assigned to N-protonated electron adducts (with the unpaired spin density at carbon) of triazines. The degradation profiles, monitored as the disappearance of parent triazine concentrations as a function of dose, obtained with AT, TMT, CA, and DHT, highlight the potential use of e^-_aq in the degradation of triazines.

Full text of DOI:10.1021/jf061916d

J. Agric. Food Chem. 2006, 54, 8171−8176 8171
Reactions of Hydrated Electrons with Triazine Derivatives in
Aqueous Medium
RANI VARGHESE,† HARI MOHAN,‡ P. MANOJ,† V. M. MANOJ,†
USHA K. ARAVIND,† K. VANDANA,† AND C. T. ARAVINDAKUMAR*,†
School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, India, and Radiation
Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre,
Mumbai 400 085, India
A study is made of the kinetics and mechanism of the reaction of radiolytically produced hydrated
electron (e-aq) with some triazine derivatives [1,3,5-triazine (T), 2,4,6-trimethoxy-1,3,5-triazine (TMT),
2,4-dioxohexahydro-1,3,5-triazine (DHT), 6-chloro N-ethyl N-(1-methylethyl)-1,3,5-triazine 2,4-diamine
(atrazine, AT), and cyanuric acid (CA)] in aqueous medium using pulse and steady-state radiolysis
techniques. The second-order rate constants were determined from the pseudo first-order decay of
e-aq in the presence of triazines at 720 nm, and the values obtained with T, TMT, AT, and CA are in
the order of 109 dm3 mol-1 s-1 and that of DHT was 108 dm3 mol-1 s-1 at pH 6. The transient absorption
spectra from the reaction of e- with T and TMT are characterized by their λmax at 310 nm, and
aq
those of DHT and CA are around 280 and 290 nm, respectively. However, a very weak and featureless
absorption spectrum is obtained from AT. On the basis of the spectral evidence and on the quantitative
electron transfer from the transient intermediates to the oxidant, methyl viologen (MV2+), the
intermediate radicals are assigned to N-protonated electron adducts (with the unpaired spin density
at carbon) of triazines. The degradation profiles, monitored as the disappearance of parent triazine
concentrations as a function of dose, obtained with AT, TMT, CA, and DHT, highlight the potential
use of e- in the degradation of triazines.
aq
KEYWORDS: Pulse radiolysis; steady-state radiolysis; second-order rate constants; electron adducts;
degradation
INTRODUCTION
slow and therefore are almost inefficient in the case of triazines
(4, 5). Burkhard and Guth reported that the rate of decomposition
of certain triazines could be increased 3-11 times with UV
light using acetone as a photosensitizer (6). Photochemical
decomposition studies of certain triazines in both methanol and
aqueous solutions have also been reported earlier (7, 8).
Electrochemical reduction of triazine pesticides including pro-
pazine and prometryne at mercury electrode has been recently
reported (9-11). Advanced oxidation processes (AOPs), which
make use of the reaction of a highly oxidizing radical, the
hydroxyl radical (•OH), are becoming increasingly popular for
an effective degradation of organic pollutants, and these include
the degradation by H2O2/UV (12, 13), O3/UV (14), ultrasound
(15), Fenton reaction (16-19), and radiation chemical tech-
niques (20-22).
Triazine derivatives are among the most widely used herbi-
cides, and its main mode of action as a herbicide is the disruption
of the light reaction of photosynthesis (1). Contamination of
ground and surface water by triazines is a serious problem in
many parts of the world due to their continual use as herbicides.
The maximum permissible concentration of triazines for human
consumption is set at 0.1 ppb by the European Economic
Community (2). However, their concentrations were reported
to exceed this value in drinking water; hence, their degradation
studies in aqueous medium are of vital importance (3). Triazines
are stable compounds and are almost inert to direct photodeg-
radation because of their very weak absorption of sunlight. The
conventional methods for the removal of these pollutants from
drinking water such as flocculation, filtration, sterilization,
reverse osmosis, and adsorption on activated carbon are
inadequate to degrade the aromatic ring. Decontamination
processes using microorganisms like bacteria are relatively very
Among the various AOPs, the radiation chemical method can
be considered as a potential technique in understanding the
fundamental reactions that lead to aromatic degradation, as it
allows us to create a selective oxidizing or reducing environment
in the solution state (23, 24). The oxidizing condition is
attributed to the reaction of •OH and the reducing condition to
the hydrated electron (e-aq) [and hydrogen atom (H•)] generated
* To whom correspondence should be addressed. Fax: +91-481-
2731009. E-mail: CT-Aravindakumar@rocketmail.com.
† Mahatma Gandhi University.
‡ Bhabha Atomic Research Centre.
10.1021/jf061916d CCC: $33.50
© 2006 American Chemical Society
Published on Web 09/22/2006

8172 J. Agric. Food Chem., Vol. 54, No. 21, 2006
Varghese et al.
and was kept at 14 Gy. A low dose per pulse (6 Gy) was used to study
the electron-transfer reaction from the electron adducts to MV2+. This
oxidant was well-suited for the study of electron-transfer reactions
because of its good selectivity, its low tendency to react by addition,
and inherent high detection sensitivity due to the large extinction
coefficient at 605 nm of its semireduced form [ꢀ(MV•+
)605nm ) 12800
dm3 mol-1 cm-1] (33). The concentrations of triazines and MV2+ were
kept in such a way that most of the e-aq (g90%) reacts with triazines.
The transient absorption spectra were recorded by monitoring the
absorbance-time profiles at various wavelengths. The absorbance of
the transients was monitored using a 450 W pulsed xenon arc lamp
monochromator (Kratus GM-252) on the exit of which a Hamamatsu
R-955 photomultiplier was fixed, which was used as a detector. The
photomultiplier signal was then fed to a 100 MHz storage oscilloscope
and was transferred to a computer for kinetic analysis.
Figure 1. Structural formulas of the selected triazines.
by the radiolysis of water by γ-rays or high-energy electrons
(24).
γ-Radiolysis was carried out in a 60Co-γ-chamber. The dose rate
was determined using ceric sulfate dosimetry (24). The degradation of
the parent triazines and the generation of products (determined from
the area of product peaks) after γ-radiolysis were monitored using
HPLC (Shimadzu LC10 AS) with a UV-vis detector (SPD 10A) at a
wavelength 210 nm. A methanol/water mixture (10/90) was used as
the mobile phase in a 25 cm, Supelcosil 5C-18 column at a flow rate
of 1 mL/min. The retention times for the parent triazines were as
follows: T, 3.01 min; TMT, 7.43 min; DHT, 3.55 min; AT, 5 min;
and CA, 4.40 min. All of the experiments and analyses were performed
at least twice and obtained a very good reproducibility. In the radiolysis
of water, a totally reducing condition can be achieved by the addition
of t-butyl alcohol (0.3 mol dm-3), a scavenger of OH radicals, and
H2O f •OH, e-aq, H•, H3O+, H2O2, H2
(1)
Most of the degradation studies of triazines reported so far
are based on AOPs that make use of the oxidizing property of
hydroxyl radicals. e- is one of the most powerful reducing
aq
agents with a reduction potential of 2.86 V. The rate constants
for the reaction of OH radicals as well as e-aq with a variety of
nitrogen-containing heterocycles have been reported as diffusion
controlled (25). However, only few studies have concentrated
on the degradation of organic water pollutants in aqueous
solutions under reductive conditions (26-28). Therefore, the
objective of this study is to investigate the mechanistic aspects
purging with argon or nitrogen to eliminate O2, which can convert e-
aq
into superoxide radical (34) (reactions 2 and 3).
of the reaction of e- with triazines and to explore the
aq
•OH + (CH3)3COH f (CH3)2C(•CH2)OH + H2O
(2)
(3)
possibility of its application in the degradation of triazines on
a laboratory scale. We have used a reductive environment using
the highly reducing radical, e-aq, produced by the radiolysis of
water and investigated the reaction kinetics, the properties of
the short-lived electron adducts, and the degradation reactions
of triazine and some of its substituted derivatives in aqueous
medium at near neutral pH. Both pulse and steady-state
radiolyses have been carried out. The selected triazines are 1,3,5-
triazine (T), 2,4,6-trimethoxy-1,3,5-triazine (TMT), 2,4-dioxo-
hexahydro-1,3,5-triazine (DHT), 6-chloro N-ethyl N-(1-meth-
ylethyl)-1,3,5-triazine, 2,4 diamine (atrazine, AT), and cyanuric
acid (CA), and the structures of these compounds are shown in
Figure 1. Although T is not stable for prolonged periods in
aqueous medium due to hydrolysis (29), it is selected as a basic
structure to understand the reaction mechanism. The oxidant,
methyl viologen (MV2+), has been used to demonstrate the
reducing nature of the electron adducts. To our knowledge, this
is the first report on the degradation of triazine derivatives using
a reducing radical or a radical other than hydroxyl radical.
•-
e-aq + O2 f O2
Alternatively, an oxidizing condition can be achieved by saturating
the solutions with NO2, which converts e- into OH radicals.
aq
e-aq + N2O f •OH + OH- + N2
(4)
The radiolytic yields are expressed in terms of G values, which can
be defined as the number of molecules formed or destroyed per 100
eV absorption of radiation energy, and in SI units, these yields were
G(•OH) ≈ G(e-aq) ≈ G(H3O+) ) 0.28 µmol J-1, G(H•) ) 0.062 µmol
J-1, G(H2O2) ) 0.072 µmol J-1, and G(H2) ) 0.047 µmol J-1
.
RESULTS AND DISCUSSION
Pulse Radiolysis. The hydrated electron has a well-defined
absorption spectrum with a maximum around 720 nm (24). The
second-order rate constants for the reaction of e-aq with triazines
at pH 6 were determined from the decay of e- at 720 nm at
aq
MATERIALS AND METHODS
different concentrations of triazines, along with its own decay
in the absence of triazines. The decay of e- was best fitted
aq
The triazine and its derivatives [T (97%), TMT (95%), DHT (99%),
AT (98%), and CA (97%)] were purchased from Aldrich Chemical
Co. (United States) and were used without further purification. The
initial concentration of triazines was kept at 10-3 mol dm-3 (i.e., T )
81.08 mg/L; TMT ) 171.16 mg/L, DHT ) 115.09 mg/L, AT ) 215.6
mg/L, and CA 129.06 mg/L). All of the solutions were prepared in
either triply distilled water or water purified by Millipore Milli-Q
system. T was added just before the pulse irradiation as it can undergo
hydrolysis in aqueous medium (29). However, in the case of steady-
state radiolysis experiments, the time required to irradiate and finally
to analyze the sample by HPLC was close to about 2 h; a significant
decay of T had been observed (see Steady-State Radiolysis).
for a first-order kinetics, and this decay has shown a concentra-
tion dependence. Therefore, the pseudo first-order rate constants
(kobs) vs concentration plots were found to be linear with very
good correlation coefficients (g0.98, and the maximum devia-
tion observed in the linear regression plots was within 10%). A
typical kobs vs concentration plot obtained in the case of T is
shown in Figure 2. The decay traces obtained in the presence
as well as in the absence of T are also shown in Figure 2. The
kobs vs concentration plots obtained with all of the triazines have
intercepts in the Y-axis (for a typical plot, see Figure 2) that
corresponds to the self-decay of e-aq, most likely due to its
reaction with trace amount of impurities. Such intercepts in the
case of the reactions of e-aq have been reported in a number of
earlier studies (35, 36). The second-order rate constants obtained
A linear accelerator that delivered 7 MeV electron pulses of 50 ns
duration was used to carry out pulse radiolysis experiments (30). The
dose per pulse was determined using KSCN dosimetry taking a Gꢀ500
nm value of 2.15 × 10-4 m2 J-1 in aerated aqueous solution (31, 32)

Hydrated Electrons with Triazine Derivatives
J. Agric. Food Chem., Vol. 54, No. 21, 2006 8173
Figure 3. Transient absorption spectra recorded at pH 6 in argon-saturated
Figure 2. Plot of pseudo first-order rate constant obtained for the decay
millimolar solutions of T (
O
), TMT (
[
), DHT (
×
), and CA (
2
) containing
-
of e
of e
at 720 nm (kobs) vs concentration of T. Inset: The decay traces
-
t-butyl alcohol (0.3 mol dm 3) at 3
µ
s after the pulse (dose/pulse )
14
aq
aq
-
-
4
-
at 720 nm (a) in the presence of T (2
×
10 mol dm 3) and (b)
•+
Gy). Inset: Absorption build-up of MV resulted from the electron-transfer
reaction of the intermediate obtained from TMT to MV2 (dose/pulse
in the absence of T.
+
) 6
Gy).
Table 1. Kinetic and Spectral Parameters Obtained from the Reaction
-
of e
with Triazines at pH 6 Using Pulse Radiolysis
viologen radical cation (MV•+) was monitored at 605 nm. A
well-defined build-up of MV•+ is observed with all of the
triazines. A typical trace showing the build-up of absorption
due to MV•+ is given in Figure 3. The G(MV•+) and the second-
order rate constants (approximate) for the electron-transfer
reactions of the electron adducts to MV2+ are compiled in Table
1. The G values were calculated by taking a typical ꢀ value of
MV•+ as 12800 dm3 mol-1 cm-1 at 605 nm (33).
aq
•+
k2a (dm3
λmax
(nm)
ꢀ
(dm3
G(MV
µ
)
k′
b (dm3
-
-1
-
-1
-
1
-
-1
triazines
mol 1 s
)
mol 1 cm
)
(
mol J
)
mol 1 s
)
T
5.2
3.75
1. 07
4.8
×
×
×
×
×
109
109
108
109
109
310
310
280
360
290
1099
1714
1861
-
0.28
0.27
0.28
-
4.3
2.8
2.3
×
×
×
109
109
109
TMT
DHT
AT
-
×
CA
1.4
1109
0.27
2.1
109
In general, e- undergoes addition at the highly electron
aq
a Second-order rate constant for the reaction of e
with triazines. b Second-
-
aq
affinic nitrogen in the heterocyclic ring as observed in the case
of purines and pyrimidines (37, 38). The resulting radical anion,
being highly proton affinic, can get protonated by water. The
protonation and deprotonation reactions at a heteroatom are
faster than at carbon (36, 37). We propose a similar electron
addition at nitrogen centers of triazine ring with all of the
selected triazines. Because all three nitrogens in T are identical,
an electron adduct with the negative charge at one of the
nitrogens is proposed.
order rate constant for the reaction of protonated electron adducts of triazines
+
•+
with MV2 (these are calculated from the absorption build-up of MV at 605 nm).
for T, TMT, AT, and CA are in the order of 109 dm3 mol-1
s-1, and for DHT, it is 108 dm3 mol-1 s-1 (Table 1).
As can be seen from Table 1, the second-order rate constants
obtained with T, TMT, AT, and CA are diffusion-controlled
because of the high electron affinity of the triazine ring.
However, a slight reduction in the rate constant values was
observed on going from T to CA, which can be attributed to
the increased electron density in TMT and CA due to the
presence of -OCH3 and -OH groups leading to the electrostatic
effect. The second-order rate constant obtained for DHT was
by an order lower in magnitude as compared to the other three
compounds, likely due to the nonaromatic nature of DHT.
The optical absorption spectra of the intermediates resulting
from the reaction of e-aq with T, TMT, DHT, AT, and CA were
recorded at pH 6. Among these triazine, the transient absorption
spectrum obtained for AT was very week and featureless. All
other triazines resulted in well-defined transient absorption
spectra on reaction with e-aq. The time-resolved spectra obtained
with these compounds were found to undergo a second-order
decay (2k ∼ 109 dm3 mol-1 s-1). The transient spectra measured
at 3 µs after the pulse are given in Figure 3. In the case of T
and TMT, the absorption spectra are characterized by their λmax
at 310 nm. The absorption spectrum obtained with CA has a
H2O
(5)
T + e-aq 98 T•- y z T•H(6/-6)
OH-
The electron adducts of triazines are expected to be stronger
bases and hence can be rapidly protonated by water (reaction
6). The protonation of T•- is therefore likely to be very fast as
observed with purine electron adducts (35-37) where the rate
of protonation at the heteroatom is of the order of 108 s-1
.
Therefore, it is logical to assume that the triazine electron adduct
gets protonated at nearly equal (or higher) rate due to the
presence of three equivalent nitrogens in the triazine ring. It
follows that the transient intermediate characterized by its
absorption spectrum with λmax at 310 nm must be a protonated
electron adduct of T as the protonation could be complete much
before the detection time of the initial spectrum (i.e., 3 µs after
the pulse).
The results obtained with MV2+ further support the structural
assignment of the protonated electron adducts. The observed G
value for MV•+ at pH 6 was 0.28 µmol J-1. This follows that
there is a quantitative electron transfer from the protonated
electron adduct (where its G value is expected as 0.28 µmol
J-1) to MV2+. This is understandable from the proposed
structure of the protonated electron adduct of T as shown in
reaction 7 in which the unpaired spin density is at one of the
λ
max close to 290 nm and that with DHT to 280 nm along with
a shoulder around 360 nm. The absorption traces below 280
nm were not recorded due to poor S/N ratio. The spectral
parameters are summarized in Table 1.
In order to understand the nature of the electron adducts, we
have investigated the electron-transfer reaction of the electron
adducts with the oxidant, MV2+. The formation of methyl

8174 J. Agric. Food Chem., Vol. 54, No. 21, 2006
Varghese et al.
Scheme 1
carbon atoms in the triazine ring (C-yl radicals). Such carbon-
centered radicals are known to be able to transfer one electron
to reducing agents such as MV2+ and pNAP (para-nitroac-
etophenone) (35, 39).
TMT, being a highly symmetric heterocycle similar to T, a
very similar electron adduct, followed by its protonation by
water, is proposed. Once the radical anion is formed, its
protonation would be faster than in the case with T due to the
presence of three -OCH3 groups that make the radical anion
more basic. Therefore, the spectra characterized by its λmax at
310 nm are attributed to the N-protonated electron adduct of
TMT (carbon centered radical). The well-defined build-up of
Figure 4. Degradation profiles (HPLC analyses) of T (
O
), TMT (
using γ-radiolysis. Inset:
aq
)), DHT
-
(
×
), and CA (
4
) from the reaction of e
degradation profile of AT (The degradation of T is a combined effect of
both radiolysis and its hydrolysis; see the text).
reducing nature of this radical [G(MV•+) ) 0.27 µmol J-1; see
Table 1] can be understood as in the previous cases.
MV•+ and the quantitative G(MV•+) value (i.e., 0.27 µmol J-1
)
Steady-State Radiolysis. In order to look at the reaction of
are clearly in line with the proposed protonated electron adduct
of TMT with the unpaired electron density at carbon.
On the basis of the well-established properties of the electron
e- in an environmental perspective, the degradations of T,
aq
TMT, AT, CA, and DHT at pH 6 have been investigated by
monitoring their decrease in concentration at different times of
γ-irradiation. In all of these experiments, the initial concentra-
tions of triazines were kept at 10-3 mol dm-3 (except of AT,
which has a concentration of 10-4 mol dm-3) and t-butyl alcohol
at 0.3 mol dm-3. The degradation profile obtained by HPLC as
a function of dose absorbed is shown in Figure 4. This indicated
a nearly complete disappearance of T at 3.2 kGy. However,
when the G(-T) value was calculated from the initial decrease
in concentration of T, a very high value of 3.9 µmol J-1 was
obtained. As the maximum expected G(-T) is around 0.28 µmol
J-1 [equal to G(e-aq)], such a value must be the result of some
other reactions. A detailed investigation has shown that T
undergoes a self-decay [due to hydrolysis (29), as expected]
during the experimental time scale (which was about 2 h).
Obviously, this is the reason for the high G(-T) value; hence,
this degradation profile is a combined effect of both radiation
and thermal degradations. It is, therefore, not very useful data
for the understanding of the reductive degradation of triazines.
Similar HPLC analyses in the case of TMT, DHT, AT, and
CA were carried out, and it was found that none of these
compounds have undergone thermal decay during the experi-
mental time scale. A clear dose-dependent decay was also
observed in the case of TMT, and the HPLC analysis showed
its complete disappearance at 10.1 kGy (Figure 4). From the
initial disappearance of TMT, a G(-TMT) value of 0.20 µmol
J-1 was calculated. Similarly, DHT showed a high degree of
degradation (more than 70%) and a relatively low G(-DHT)
value of 0.11 µmol J-1 has been obtained. Examination of the
product peaks showed the presence of two major products at
the λmax of DHT (data not shown) whose structural details could
not be determined using HPLC due to the lack of standards.
AT has also shown a clear dose-dependent decay and a G(-
AT) of 0.26 µmol J-1 is calculated from its initial decay. Its
decay was nearly complete after about 8 kGy (Figure 4). CA
has not shown a significant decay of its initial concentration in
the initial stage as can be seen from Figure 4. However, at a
adducts of uracil (39, 40), it is proposed that the e- can
aq
efficiently add to one of the >CdO groups in the case of DHT
(Scheme 1). As both >CdO groups are in the same environ-
ment, the resulting electron adducts could have the same
absorption spectra. As this radical anion is highly proton affinic,
its fast protonation can be justified at pH 6 similar to uracil
radical anion (39, 40) where oxygen protonation occurs very
fast with a pK value of 7.3. The oxygen-protonated carbon-
centered radical situated in the middle of two -NHs in the case
of uracil has an absorption spectrum with a maximum around
290 nm (40). The situation is very similar with DHT where the
protonated electron adducts (reactions 8 and 9) have >C•-OH
between two -NHs. The absorption spectra with maximum
around 280 nm are, therefore, attributed to the protonated
electron adduct of DHT.
It is clear from Table 1 that the electrostatic effect due to
the increased electron density in the triazine ring in the case of
CA decreases the rate constant value on going from T to CA.
Therefore, the rate of protonation of the electron adduct of CA,
undoubtedly, will be higher as compared to T due to the
increased basicity of the electron adduct. The protonated electron
adduct has a >C•-OH radical site similar to the protonated
electron adduct of DHT, which is essentially responsible for
the absorption spectrum. A λmax at shorter wavelengths is,
therefore, anticipated, similar to the case with DHT (the structure
CA•H is given below).
On the basis of this understanding, the spectrum characterized
by its λmax around 290 nm is attributed to the N-protonated
electron adduct with the unpaired spin density at carbon. The

Hydrated Electrons with Triazine Derivatives
J. Agric. Food Chem., Vol. 54, No. 21, 2006 8175
However, a fully convincing explanation for this behavior could
not be given at this stage as it requires further studies on the
exact nature of the intermediate (unstable) products.
In conclusion, the kinetic and mechanistic details of the
diffusion-controlled reaction of e-aq with triazines are presented.
Such reduction reactions of triazine derivatives are reported for
the first time. The comparison of the degradation profile of TMT
induced by e- and OH radicals highlights the potential
aq
application of the reaction of e-aq in the degradation of triazines.
However, it must be noted that the contaminated water normally
contains oxygen and nitrate, which can effectively react with
e-aq, and this may evoke a competition for e-aq. In this context,
additional steps may be required to minimize such competition
reactions. Therefore, more work is needed to fully explore the
applicability of this reaction in natural conditions. On the other
hand, radical-mediated reductive degradation of these com-
pounds provides an additional detoxification channel, which
must be intensively explored.
Figure 5. Comparison of the degradation profile obtained from the reaction
-
of e
([) and of OH radicals (taken from ref 21) (O) with TMT.
aq
higher time of irradiation (i.e., more than 6 kGy), the concentra-
tion of CA has shown a considerable decrease similar to other
triazines.
ACKNOWLEDGMENT
We are thankful to the Rubber Research Institute of India (RRII),
Kottayam, Kerala, for providing the γ-radiolysis facility.
These degradation studies have been carried out to understand
the efficiency of degradation of triazines under reductive
environment, as most of the known studies are under oxidative
conditions, mostly using OH radicals (12-22). The results
obtained in this study demonstrate that the degradation profile
of the parent triazines is well comparable to that induced by
OH radicals (22). A comparison between the decay of TMT
induced by OH radicals from the previous report (22) and by
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e- in the present study is shown in Figure 5. In the reaction
aq
of TMT with OH radicals, a complete degradation was obtained
after 5 kGy (22). In both cases, TMT was irradiated under the
same conditions. Interestingly, the yield of e-aq is only half the
yield of OH radicals under this condition according to reaction
4. Even then, a nearly similar decay of TMT is observed using
both of the reactions. This comparison clearly establishes the
potential role of e- in the degradation of triazines similar to
aq
OH radicals.
It must, however, be noted that a complete degradation of
the aromatic ring may not be taking place under the present
experimental conditions. It can be only understood that there is
a transformation of the triazines to some of their products on
reaction with e-aq. As indicated in the Pulse Radiolysis section,
the immediate intermediate after the attack of e- with all of
aq
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Received for review July 10, 2006. Revised manuscript received August
3, 2006. Accepted August 8, 2006. Part of the financial support for this
study is from the Board of Research In Nuclear Sciences (BRNS),
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