4
88
Chemistry Letters Vol.34, No.4 (2005)
Degradation of p-Chlorophenol by ꢀ-Radiolysis:
Radiolytic Intermediates and Theoretical Calculations
ꢀ
y
Shao-Yang Liu, You-Peng Chen, Han-Qing Yu, and Qian-Rong Li
Department of Chemistry, University of Science & Technology of China,
Hefei, Anhui 230026, P. R. China
y
Research Center for Physics & Chemistry, University of Science & Technology of China,
Hefei, Anhui 230026, P. R. China
(Received January 11, 2005; CL-050051)
Radiolysis of p-chlorophenol (p-CP) was investigated
6
4
2
0
0
0
through experiments and theoretical calculations. Its radiolytic
intermediate products, i.e., phenol, hydroquinone, 4-chlororesor-
cinol, and 4-chloropyrocatechol, were identified using their mass
spectra through a GC/MS system. Three transition states and a
prereaction complex of the reaction between hydroxyl radical
and p-CP were found from the density functional theory (DFT)
study. Both the experimental and calculation results demonstrate
that the main p-CP degradation pathway was the formation of
B
A
827
0
3336
1511 1196
8
0
0
0
4
-chloropyrocatechol.
6
4
Within the last two decades, there has been a growing con-
2923
3435
cern related to serious environmental problems due to the in-
creasing water contamination. Among the top priority pollutants,
chlorinated phenols generated as chemical intermediates or by-
products in various industries represent an important class of wa-
ter pollutants. Since chlorophenols are resistant to conventional
3
500 3000 2500 2000 1500 1000 500
Wavelength (nm)
1
biological treatments, many efforts have been made in the
search for efficient and economical decomposition methods,
Figure 1. FTIR spectra of p-CP (A) and the extract of irradiated
samples (B).
2
3,4
5
e.g. Fenton oxidation, photocatalytic, and ultrasonic proc-
esses.
Radiation-induced degradation is a promising method
tracts of 0.2 mL were subjected to GC–MS determination and
FTIR (Magna-IR 750, Nicolet Instrument Co., USA) analysis.
p-Chlorophenol solutions with an initial concentration of
6
,7
against organic contaminations. Degradation of monochloro-
8
,9
ꢂ1
phenols by ꢀ-irradiation has been investigated. Their decom-
position and dechlorination efficiencies have been reported. For
p-CP, phenol under reductive conditions and 4-chlorocatechol
and hydroquinone under oxidative conditions were respectively
detected in radiolysis. However, the degradation immediate
products were just preliminarily determined by their HPLC re-
tention times and UV-spectra, and information about its degra-
dation mechanisms is still sparse. In the present work, ꢀ-radio-
lytic metabolites of p-CP were investigated by using GC–MS
and FTIR. Furthermore, theoretical calculations about its degra-
dation mechanisms were performed.
1.0 mmol L were saturated with high-pure argon and irradiated
6
0
in sealed Pyrex glass vessels at a Co ꢀ-ray dose rate of
49 Gy min under ambient temperatures for 2.5 h.
ꢂ1
Figure 1 illustrates the evolution of IR spectra during the
irradiation. Strong peaks, e.g. at wavenumbers of 1511, 1196,
ꢂ1
and 827 cm , appeared in spectrum B, indicating the formation
of radiolytic products. The band at a wavenumber of about
ꢂ1
3400 cm was assigned to the stretching vibration of hydroxyl
group. It shifted and broadened significantly after the irradiation,
implying that different hydroxyl groups were formed.
Figure 2 shows the GC chromatogram of the extract from
the irradiated sample. Phenol (1), hydroquinone (3), 4-chlorore-
sorcinol (4), 4-chloropyrocatechol (5), and remained p-CP (2)
were identified from their mass spectra. In the previous studies,
4-chlororesorcinol was not detected, while phenol was formed
Ethyl acetate, p-CP and anhydrous magnesium sulfate, all
purchased from Shanghai Chemical Reagent Company, were
of analytical grade. Ethyl acetate was redistilled prior to use.
Double distilled water was used throughout the experiments.
Radiolytic products of p-CP were analyzed and identified
using an Agilent 6890 GC (Angilent Inc., USA) system coupled
to a GCT–MS (Micromass Ltd., UK) through an electron impact
interface. Chromatographic measurements were performed with
a capillary column DB-5 (30 m ꢁ 0.25 mm ꢁ 0.25 mm). Irradiat-
ed samples were extracted with redistilled ethyl acetate. The ex-
tracts were merged and dried with anhydrous magnesium sulfate
and were concentrated under reduced pressure. Concentrated ex-
ꢂ
8,9
by the e attack. The presence of metabolites 3–5 indicates
aq
that the hydroxyl radicals generated during the irradiation could
attack all the positions of the benzene ring. The abundance of
4-chloropyrocatechol was much higher than those of other
metabolites. Its formation might be the main radiolysis pathway
because the sensitivities on the responses of GC–MS to the
species 1, 3, 4, and 5 are of a similar level.
Hydroxyl radical is the most active oxidative species gener-
Copyright ꢀ 2005 The Chemical Society of Japan
Liu, Shao-Yang
