Oxidation of tetrahydrofuran to butyrolactone catalyzed by iron-containing clay

Article abstract of DOI:10.1039/c4gc00997e

Thermally treated iron-containing clay was used as a greener oxidation catalyst for the conversion of tetrahydrofuran (THF) to butyrolactone (BTL). Mild liquid phase reactions were tested at 50-66 °C using hydrogen peroxide (H₂O₂) as an oxidizing agent. XRD, TGA, ESR, DR-UV, and FTIR revealed the dislodged iron oxide species formed by treating at ≥500 °C. Formation of active oxidizing species on the surface occurs on contact the dislodged Fe(III) oxide with H₂O₂. Such active species can promote the oxidation of THF, giving high yield and selectivity of BTL, whereas the iron-containing clay treated at lower temperatures (<500 °C) perform Fenton-like oxidation with lower THF conversions and non-selective products. 2-Hydroxytetrahydrofuran (THF-2-ol) was primarily produced and further oxidized to BTL with a small amount of 4-hydroxybutyric acid as a minor product. Minimal H₂O₂/THF ratio of 1.0 is sufficient for the production of BTL. Deactivation can be observed presumably due to deposition of the products despite slight leaching of the active iron species.

Full text of DOI:10.1039/c4gc00997e

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Page 1 of 16
Green Chemistry
Oxidation of tetrahydrofuran to butyrolactone
catalyzed by iron-containing clay
Artit Ausavasukhia, and Tawan Sooknoib*
Earth-abundant iron-containing clay can be applicable as an oxidation catalyst for
butyrolactone production from biomass-derived tetrahydrofuran using hydrogen
peroxide as oxidant at mild condition.

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Oxidation of tetrahydrofuran to butyrolactone catalyzed by iron-
containing clay
Artit Ausavasukhia, and Tawan Sooknoib*
aProgram in Applied Chemistry, Faculty of Sciences and Liberal Arts,
Rajamangala University of Technology Isan, Nakhon Ratchasima 30000, Thailand
bDepartment of Chemistry, Faculty of Science,
King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand
Abstract
The thermally treated ironꢀcontaining clay was used as a greener oxidation catalyst
for the conversion of tetrahydrofuran (THF) to butyrolactone (BTL). Mild liquid phase
o
reactions were tested at 50ꢀ66 C using hydrogen peroxide (H2O2) as oxidizing agent.
XRD, TGA, ESR, DRꢀUV, and FTIR revealed the dislodged iron oxide species formed
o
by treating at ≥ 500 C become active oxidizing species on the surface upon contacting
with H2O2. Such active species can promote oxidation of THF giving high yield and
selectivity of BTL. While the ironꢀcontaining clay treated at lower temperature (< 500
oC) perform Fentonꢀlike oxidation with lower THF conversion and nonꢀselective
product. 2ꢀHydroxy tetrahydrofuran (THFꢀ2ꢀol) was primarily produced and further
oxidized to BTL with small amount of 4ꢀhydroxybutyric acid as minor products.
Minimal H2O2/THF ratio as 1.0 is sufficient for production of BTL. Deactivation can be
observed presumably due to deposition of the products despite of a slight leaching of
active iron species.
Keywords: Greener oxidation, Ironꢀcontaining clay, Tetrahydrofuran, Thermal treatment
* Corresponding authors; Tel.: +668 1929 8288; Fax: +662 326 4415.
Eꢀmail address: kstawan@gmail.com

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1. Introduction
Because of factors such as the finite reserves of petroleum, their unequal geographic
distributions, and the environmentally motivated desire to decrease CO2 emissions,
renewable feedstocks, such as lingoꢀcellulosic biomass, have become promising
candidates for the production of renewable fuels and chemicals. One of an attractive
biomassꢀderived chemical feedstock is butyrolactone (BTL). Its demand is steadily
growing due to the major use as an important intermediate for biodegradable polymer
and a direct use as a dielectric material or a solvent. BTL is typically produced using two
processes: (i) Davy McKee process based on the hydrogenation of diethyl or dimethyl
maleate and (ii) Reppe process based on acetylene and formaldehyde.1 Alternatively,
oxidation of tetrahydrofuran (THF) can be applied for the production of BTL. The THF
can be simply obtained by decarbonylation and hydrogenation of the furfural derivatives2
found mainly in biomass pyrolysis oil.
Selective oxidation3ꢀ10 is one of the key approaches for production of BTL
from THF. The earlier reports describe the synthesis of BTL by the organometallicꢀ
catalyzed oxidation of THF, which was performed homogeneously with BTL selectivity
of 22ꢀ100% depending on the oxidant types.11ꢀ14 Although molecular oxygen (O2) is a
cheap oxidant with no waste, its oxidation potential is limited due to a long reaction time
(> 24 hours). Even though H2O2 is more expensive than the molecular oxygen, it can be
the oxidant of choice for fine chemicals because of its simplicity of operation.11ꢀ12
SalavatiꢀNiasari et.al.9 reports that bis(macrocyclic) copper(II) complexes containing
aromatic linkers can catalyze the oxidation of THF to give BTL under mild conditions.
However, the homogeneous process has some disadvantages, such as expensive catalyst.
As a comparison, heterogeneous catalytic processes serve as an environmentally benign
alternative for easy catalyst separation, regeneration, and relatively low process cost.

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Encapsulated complexes ([Cu(R2[16]aneN6)]2+/Zeolite Y)14 is example of early attempt
for heterogeneously catalytic system for this approach. However, it yields mainly 2ꢀ
hydroxytetrahydrofuran (THFꢀ2ꢀol) and insignificant amount of BTL while, with their
homogeneous counterparts, selectivity to BTL are higher.14 Titanosilicates (TSꢀ1) can be
used as heterogeneous catalyst for the oxidation of THF to BTL in moderate to good
yields in the presence of dilute aqueous H2O2 as oxidant.10 However, such catalysts in
use today are based on expensive, and methods of preparing catalysts continue to be
complicated, and laborious. Iron is the element of choice that performs a number of
chemically challenging oxidative processes. Fenton’s reagent15ꢀ16, a mixture of Fe(II)
ions and H2O2, is widely applied to oxidize organic substrates. In the last decade, several
systems based on heterogeneous Fentonꢀlike catalyst (Feꢀsupported solids), such as iron
oxides, zeolites, pillared clays, and alumina, have been investigated for use in
environmental remediation processes.15ꢀ18 Some preliminary studies using ironꢀ
containing clay based catalysts have shown the promising possibilities of this kind of
catalysts because they are natural, abundant, inexpensive, and environmental friendly.
In this research, greener oxidation using earthꢀabundant ironꢀcontaining clay as
catalyst and H2O2 as oxidizing agent is investigated for BTL production under mild
condition. The heterogeneous oxidizing sites can be generated by simple thermal
treatment at high temperature. The ESR, DRꢀUV and FTIR study permits us to detect the
active oxidizing iron species. Effects of thermal treatment and role of the oxidizing iron
species on BTL production from THF are discussed. Reaction pathway for the selective
oxidation is also generalized.

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2. Experimental
2.1. Catalyst preparation and characterization
The ironꢀcontaining clay was obtained from the SCG Chemicals. The sample was brown
color and used as received. Such parent clay possesses a relatively high wt.% of Fe (~ 5
%), which makes it ideal as oxidation catalyst. The sample was treated at 100ꢀ700 oC for
5 hours and designated as ClayꢀTemperature according to their treatment temperature.
XRD and TGA provided information on the catalyst structure and phase transformation
upon thermal treatment. BET surface areas of the all samples were also determined. The
ESR spectra was taken in the Xꢀband at 20 oC and registered at 1 mW microwave power
in the field range of 10ꢀ810 mT (one scan with a sweep time of 4 min). The diffuse
reflectance UVꢀVIS spectra of the clay samples in the form of selfꢀsupporting pellets
were recorded with BaSO4 coated integration sphere. FTIR spectra was acquired in the
transmission mode at room temperature over the wavenumber range of 4000ꢀ650 cmꢀ1.
2.2. Catalytic testing
In a typical procedure for oxidation of THF; a mixture of ironꢀcontaining clay as catalyst
(0.05ꢀ0.20 g) and THF (0.05 mol) was stirred for 30 min in a 100 mL round bottom
threeꢀnecked flask equipped with a condenser. Then 0.05 mol of the H2O2 (30% in H2O)
was added via the dropping funnel. The mixture was then heated under reaction
o
o
temperature (50 C and 66 C) for 1ꢀ8 hours. At the end of reaction, the mixture was
quenched in an ice bath and the solid catalyst was separated from the solution by coldꢀ
filtration. The remaining H2O2 residual was analyzed using iodometric titration
method.19 The cold mixture was promptly analyzed by GCꢀFID to avoid further
oxidation and the products are identified using GCꢀMS. The products containing H2O2
residual was disposed according to literature.20

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3. Results and discussion
3.1. Catalytic characterization
The parent ironꢀcontaining clay shows a strong diffraction peak corresponding to
montmorillonite and magnetite (Fe3O4 or FeO⋅Fe2O3) crystallite (Fig. 1). As being a
mineral, it is expected that these two phases are separately aggregated and existed as a
o
physical mixture. Under thermal treatment ≥ 500 C, such ironꢀcontaining clay catalyst
was completely transformed into illite and hematite (Fe2O3). The TGA and DTG profile
o
of the catalyst sample showed the major weightꢀloss at 60ꢀ180 C, corresponded to
o
desorption of the physisorbed water and the minor weightꢀloss at 450ꢀ700 C, denoted
the dehydroxylation of iron hydroxide and/or clay layer (Fig. 2a). In consistent with
TGA, a noticeable decrease in the terminal hydroxyl group (SiꢀOH, AlꢀOH) is observed
by FTIR at ~3630 cmꢀ1, together with a lower intensity of bands at ~3500ꢀ3250 cmꢀ1
(Fig. 2b) and ~ 1630 cmꢀ1 (Fig. 2c) corresponded to the adsorbed water. A significant
change in BET surface area is in line with the observed phase change by thermal
treatment. While Fe content remains similar for all samples (Table 1).
o
As phase transformation take place upon calcination at ≥ 500 C, DRꢀUV reveals
different coordination of the Fe species as shown in Fig. 3a. It can be seen that Clayꢀ100
and Clayꢀ300 exhibit only two absorption edges at about λ ~263 nm and 525 nm,
corresponding to octahedral Fe(III) substituted for Al(III)21, and larger particles of Fe2O3
aggregates22, respectively. This suggests that certain amount of Fe is also present in the
clay structure, not only as separated magnetite aggregates. However, the additional
signal of the 425 nm band ascribed to the oligomeric octahedrally coordinated Fe(III)
species22, can be observed on the Clayꢀ500. This Fe species is presumably formed by
dislodgement of the substituted Fe(III) in the clay structure upon dehydroxylation, and
then segregated within the clay layer. The presence of this oligomeric Fe species is also

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evidenced as a series of ESR signals superimposed on the major resonance of Fe oxides
clusters at g = 2.323ꢀ24 as shown in Fig. 3b. Experimentally, the intensity of the ESR line
at g = 2.3 increased significantly when the parent clay was thermally treated due to the
transformation of Fe3O4 to Fe2O3. However, such a series of the superimposed signals
o
are only pronounced when the sample was treated at 500 C, in consistence with an
additionally observed UV signal at 425 nm, as discussed above.
It is worth noting that the weak ESR signal at g = 4.2 assigned to the presence of
isolated Fe(III)23ꢀ24 in the tetrahedral or octahedral coordination is observed for all
sample. For the clay minerals, this corresponds to the Fe located in the interior of the
clay sheets (iron substituting aluminum in the octahedral layers).
3.2. Oxidation of tetrahydrofuran
Table 2 shows the activity of various thermally treated ironꢀcontaining clay catalyst in
the oxidation of THF to BTL. The Clayꢀ500 exhibits relatively higher activity, as
compared to those from the Clayꢀ100, Clayꢀ300, and Clayꢀ700. It is clear that the
oxidation activity is generally increased with treating temperature. However, the lower
activity observed in the reaction using Clayꢀ700 as the catalyst is presumably due to the
o
significant loss of catalyst surface area (Table 1) by further dehydroxylation at 700 C.
This is consistent with the TGA/DTG, and FTIR results (Fig. 2) that show the
dehydroxylation of clay layer.
With respect to the same range of catalyst surface area (72ꢀ85 m2/g), the increase in
activity with the treatment temperature can be accounted for the degree of
dehydroxylation and hence the formation of oligomeric octahedrally coordinated Fe(III)
species formed by dislodgement of the substituted Fe(III) in the clay structure, as
evidenced by TGA, FTIR, DRꢀUV, and ESR. This is speculated from a linear

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relationship between the catalyst activity (conversion) and the UV absorbance at 425 nm
that corresponded to such Fe(III) species as shown in Fig. 4. It is expected that the
dislodged Fe(III) oxide species would possess higher degree of coordinative
unsaturation, as compared to those in the bulk oxide. Hence, H2O2 can readily react with
such Fe(III) species forming high valence ironꢀoxo, peroxo or superoxo species (Surfaceꢀ
Fe=O, SurfaceꢀFe(OꢀO) or SurfaceꢀFeOOꢀ⋅)25ꢀ28 that acts as oxidizing species. As higher
o
extent of dehydroxylation was observed when treated at 500 C, higher fraction of
dislodged Fe(III) oxide species and hence higher activity could be expected.
The presence of active oxidizing species generated by reaction of H2O2 and the
dislodged Fe(III) oxide can be further supported by FTIR spectroscopy. From Fig. 5, the
band at ~1000 cmꢀ1 were assigned to FeꢀOꢀH overlapped with SiꢀOꢀAl in
montmorillonite29, while the signal at and 916 cmꢀ1 can be referred to Al2ꢀOH.30
Interestingly, a new signal at 1050 cmꢀ1 become pronounced when H2O2 is introduced
into Clayꢀ500. This relatively high frequency signal is generally attributed to OꢀO
stretching of endꢀon superoxo or peroxo complexes.31ꢀ34 Hence, it is proposed in this
work to be derived from the formation of highꢀvalence ironꢀsuperoxo or peroxo species
(FeꢀOꢀOꢀ⋅ or Fe(OꢀO)) on the surface of dislodged Fe oxide via surface oxidation by
H2O2. This species may well be an active oxidizing species, or may also be a precursor of
a hydroxylhydroperoxyl Fe species (Fe(OH)(OOH))28, 35 that promote oxidation of THF.
It is important to emphasize that this additional signal at 1050 cmꢀ1 is particularly
obtained only for the clay treated at high temperature (Clayꢀ500 and Clayꢀ700). Without
a certain degree of dehydroxylation and hence the presence of dislodged Fe oxide
species, the bulk Fe oxide and substituted Fe in the clay structure may be too stable to
interact with H2O2 to form such Fe superoxo or peroxo species. The formation of the
active site can be proposed as follows;

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Fe(III) oxide in the framework
SurfaceꢀFe(III) + H2O2
ꢀ
ꢀ
ꢀ
SurfaceꢀFe(III) (Dislodged species)
Eq. (1)
Eq. (2)
Eq. (3)
ꢀ⋅
SurfaceꢀFe(III)ꢀO2
SurfaceꢀFe(IV)(OH)(OOH)
ꢀ⋅
SurfaceꢀFe(III)ꢀO2 + H2O
One could expect that the Fentonꢀtype oxidation36ꢀ37 would be also responsible for
the observed activity. This may be true in the case of ironꢀcontaining clay treated at low
temperature (Clayꢀ100 or Clayꢀ300) since a larger fraction of Fe(II) oxide species is
present in these samples. However, a relative lower conversion of THF was obtained
from the reaction over Clayꢀ100 or Clayꢀ300. This is because the Fenton process
involves the reaction of Fe(II) with H2O2, giving rise to hydroxyl radicals (●OH) (Eq.
(4)). This catalytic cycle can be completed by the reduction of Fe(III) to Fe(II) (Eq.
(5)).37
SurfaceꢀFe(II) + H2O2
SurfaceꢀFe(III) + H2O2
ꢀ
ꢀ
SurfaceꢀFe(III) + ●OH + OHꢀ
SurfaceꢀFe(II) + ●OOH + H+
Eq. (4)
Eq. (5)
Since the reduction of Fe(III) to Fe(II) by H2O2 is extremely slow38ꢀ40, the Fe(III)
would be accumulated in the system and that would result in a low activity.41 Therefore,
the observed higher activity for the catalyst treated at higher temperature (Clayꢀ500)
suggests that the active oxidizing center would be derived from the highꢀvalence ironꢀ
oxo species that is formed by interaction of H2O2 with the dislodged Fe(III) oxides,
rather than the Fentonꢀtype species. For all catalysts, butyrolactone (BTL) is the main
product from THF oxidation. Major coꢀproducts include 2ꢀhydroxytetrahydrofuran
(THFꢀ2ꢀol) and 4ꢀhydroxybutyric acid (4ꢀHBA). Furanone and polyhydroxy derivatives

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of the aboves are also observed. It is clear from Fig. 6 that the conversion is increased
together with yields of all products when both catalyst content and reaction time is
increased, suggesting that the reaction is catalytically controlled. As BTL and THFꢀ2ꢀol
appears to form in parallel, these products may well be derived from the decomposition
of the parent hydroperoxide intermediate (in a manner similar to ketoneꢀalcohol from the
decomposition of alkyl hydroperoxide). However, it is noticed that THFꢀ2ꢀol yield start
to level off while yields of BTL and 4ꢀHBA are steadily increased with conversion. This
also suggests that THFꢀ2ꢀol may well be primarily produced from the oxidation of THF
and become a precursor of BTL and 4ꢀHBA (Scheme 1). In the mechanistic point of
view, the Hꢀabstraction at from the carbon adjacent to the oxygen in THF can be most
likely promoted and hydroxylation at this position readily leads to formation of THFꢀ2ꢀ
ol. This product is prone to be further oxidized to BTL. It is possible that the BTL is
formed either by (i) direct oxidation of THFꢀ2ꢀol while the ring is kept intact or by (ii)
ring opening of THFꢀ2ꢀol to 4ꢀhydroxybutanal that is subsequently oxidized to 4ꢀHBA.
This ωꢀhydroxy acid can also undergo selfꢀesterification to form BTL. Although 4ꢀHBA
is actually found as evidence for the ring openingꢀoxidation (ii), it is unlikely that selfꢀ
esterification of 4ꢀHBA to form BTL is the case in the reaction with large amount of
water present. Moreover, selectivity of 4ꢀHBA is relatively small and it is increased
together with BTL selectivity while THFꢀ2ꢀol selectivity is reduced with increased
conversion (Fig. 7). This suggests that BTL and 4ꢀHBA may be produced in paralleled,
presumably from the oxidation of THFꢀ2ꢀol. It is also worth noting that BTL is relatively
stable under the reaction condition and no hydrolysis of BTL to 4ꢀHBA was observed
when BTL was used as feed in a separate test (not shown). The overall reaction pathway
can be proposed as shown in Scheme 1.

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As also seen in Fig. 7, small amounts of other products, such as 2ꢀfuranone and
3,4ꢀdihydroxytetrahydrofuran were obtained with increased catalyst content and time.
However, no significant change in the selectivity can be observed at lower temperature
(Table 2). These coꢀproducts may be the result of further oxidation of CꢀH bond at
different positions on the major products. However, the selectivity of these products is
particularly high in the reaction using Clayꢀ100 and Clayꢀ300 as catalysts despite lower
conversions were obtained (Table 2). This is presumably because there is much less
amount of dislodged Fe(III) oxide present in these samples, and hence less number of
active Fe superoxo or peroxo species as discussed earlier. Nevertheless, the oxidation of
THF can be somewhat facilitated via •OH radical mechanism that is promoted by
decomposition of H2O2 over Fe(II) oxide surface. Although, they are less active as
compared to the Clayꢀ500, the •OH radical initiates a radical chain reaction by randomly
abstracting hydrogen atom from THF. This leads to the generation of carbon radicals that
undergo oxidation to various oxygenated products.
From Fig. 6b, it can be seen that the activity is gradually declined over the course of
the reaction. This can be accounted either for (i) limit of the oxidant, H2O2 or (ii)
deactivation of the catalysts. Accordingly, the effect of H2O2/THF ratio was investigated
and it is clear that the decline activity observed in Fig. 6b is not due to the limit of H2O2.
As seen from Fig. 8, no significant increase in activity is obtained when H2O2/THF ratio
was raised to 2. This suggested that H2O2/THF ratio of 1 is sufficient for the oxidation of
THF to BTL and shall not restrain the activity as observed in Fig. 6b. Although the
excess H2O2 does not strongly effect the conversion, selectivity of 4ꢀHBA and other
products are slightly increased with H2O2/THF ratio while THFꢀ2ꢀol selectivity is
decreased. This indicates that further oxidation of THFꢀ2ꢀol can be promoted when H2O2
is in excess.

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According to the study on the effect of H2O2, it appears that the observed decline in
activity after 4 hours would be resulted from the catalyst deactivation. This may be due
to adsorption of products on the catalyst surface or leaching of the active iron species.
However, it is clear from Fig. 9 that severe catalyst leaching is not the case. This is
because, as the catalyst recovered from THF oxidation experiment was tested under
similar condition for another three cycles, the catalytic activity is reproducible in
consecutive experiments without a remarkable drop in the efficiency. This again
indicates the absence of significant deactivation of the catalyst due to iron leaching, but
presumably due to the adsorption of products and the washing with THF or appropriate
solvent, can easily regenerate the catalyst.
Conclusions
Butyrolactone can be successfully produced via a greener oxidation of THF using
earthꢀabundant ironꢀcontaining clay as catalysts. The active oxidizing species can be
o
obtained by thermal treatment at temperature ≥500 C. The dehydroxylation of the clay
structure leads to partial dislodgement of the iron oxide species that can react with
hydrogen peroxide. Spectroscopic evidences suggest the formation of Fe superoxo or
peroxo upon contacting hydrogen peroxide with the dislodged Fe oxide species, which is
also well correlated with the observed activity. It appears that 2ꢀhydroxytetrahydrofuran
(THFꢀ2ꢀol) is a primarily product from THF oxidation. This product is further oxidation
of butyrolactone (BTL), 4ꢀhydroxy butyric acid (4ꢀHBA) and other oxidized products.
Up to 70% selectivity of BTL is obtained over Clayꢀ500 catalyst. H2O2/THF ratio of 1.0
is sufficient for BTL production and no significant leaching of the active species can be
observed. The catalyst can be simply regenerated by washing with the feed, THF, and reꢀ
used at least 4 cycles without significant drop in activity.

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Acknowledgments
This work was financially supported by the Thailand Research Fund (Grant No. TRGꢀ
5780177).
References
1
2
U. R. Pillai, E. S. Demessie and D. Young, Appl. Catal. B, 2003, 43, 131ꢀ138.
S. Sitthisa, T. Pham, T. Prasomsri, T. Sooknoi, R. G. Mallinson and D. E. Resasco,
J. Catal., 2011, 280, 17ꢀ27.
3
4
C. Jia, T. Kitamura and Y. Fujiwara, Acc. Chem. Res., 2001, 34(8), 633ꢀ639.
R. A. Periana, O. Mironov, D. Taube, G. Bhalla and C. J. Jones, Science, 2003,
301, 814ꢀ818.
5
6
S. Pradhan, J. K. Bartley, D. Bethell, C. A. Frederick, C. Marco, G. Stanislaw, H.
Matthew, J. R. Leyshon, L. Rhys and H. G. John, Nat. Chem., 2012, 4, 134ꢀ139.
P. Stavropoulos, R. CelenligilꢀCetin and A. E. Tapper, Acc. Chem. Res., 2001, 34,
745ꢀ752.
7
8
9
D. H. R. Barton, Tetrahedron, 1998, 54, 5805ꢀ5817.
D. H. R. Barton and D. Doller, Acc. Chem. Res., 1992, 25, 504ꢀ512.
M. SalavatiꢀNiasari and M. Bazarganipour, Inorg. Chem. Comm., 2006, 9, 332ꢀ
336.
10 M. Sasidharan and A. Bhaumik, J. Mol. Catal. A, 2011, 338, 105ꢀ110.
11 M. Sommovigo and H. Alper, J. Mol. Catal., 1994, 88, 151ꢀ158.
12 P. Li and H. Alper, J. Mol. Catal., 1992, 72, 143ꢀ152.
13 L. Metsger and S. Bittner, Tetrahedron, 2000, 56, 1905ꢀ1910.
14 M. SalavatiꢀNiasari, Inorg. Chem. Comm., 2006, 9, 628ꢀ633.

Green Chemistry
Page 14 of 16
View Article Online
DOI: 10.1039/C4GC00997E
15 H. J. H. Fenton, Chem. News, 1876, 33, 190ꢀ200.
16 H. J. H. Fenton, J. Chem. Soc. Proc., 1894, 10, 157ꢀ158.
17 J. H. Ramirez, F. J. MaldonadoꢀHodar and A. F. PerezꢀCadenas, Appl. Catal. B,
2007, 75, 312ꢀ323.
18 G. Calleja, J. A. Melero, F. Martinez and R. Molina, Water Res., 2005, 39, 1741ꢀ
1750.
19 C. Kormann, D. W. Bahnemann and M. R. Hoffmann, Environ. Sci. Technol.,
1988, 22, 798ꢀ806.
20 W. Liu, S. A. Andrews, M. I. Stefan and J. R. Bolton, Water Res., 2003, 37, 3697ꢀ
3703.
21 M. N. Timofeeva, S. T. Khankhasaeva, Y. A. Chesalov, S. V. Tsybulya, V. N.
Panchenko and E. T. Dashinamzhilova, Appl. Catal. B, 2009, 88, 127ꢀ134.
22 S. Caudo, G. Centi, C. Genovese and S. Perathoner, Appl. Catal. B, 2007, 70, 437ꢀ
46.
23 A. Kucherov and M. Shelef, J. Catal., 2000, 195, 106ꢀ112.
24 E. Gue´lou, J. Barrault, J. Founier and J. M. Tatiboue¨t, Appl. Catal. B, 2003, 44,
1ꢀ8.
25 W. C. Bray and M. H. Gorin, J. Am. Chem. Soc., 1932, 54, 2124ꢀ2125.
26 E. Kim, M. E. Helton, I. M. Wasser, K. D. Karlin, S. Lu, H. Huang, P. Moenneꢀ
Loccoz, C. D. Incarvito, A. L. Rheingold, M. Honecker, S. Kaderli and A. D.
Zuberbuhler, Proc. Natl. Acad. Sci. USA, 2003, 100(7), 3623ꢀ3628.
27 M. Newcomb, P. F. Hollenberg and M. J. Coon, Arch. Biochem. Biophys., 2003,
409, 72ꢀ79.
28 H. Mimoun, I. Seree de Rochm and L. Sayas, Bull. Soc. Chim. France, 1969, 5,
1481ꢀ1492.

Page 15 of 16
Green Chemistry
View Article Online
DOI: 10.1039/C4GC00997E
29 P. Yuan, F. AnnabiꢀBergaya, Q. Tao, M. Fan, Z. Liu, J. Zhu, H. He and T. Chen, J.
Colloid Interface Sci., 2008, 324, 142ꢀ149.
30 J. Madejova, Vib. Spectrosc., 2003, 31, 1ꢀ10.
31 Y. M. Lee, S. Hong, Y. Morimoto, W. Shin, S. Fukuzumi and W. Nam, J. Am.
Chem. Soc., 2010, 132, 10668ꢀ10670.
32 J. Annaraj, Y. Suh, M. S. Seo, S. O. Kim and W. Nam, Chem. Commun., 2005, 36,
4529ꢀ4531.
33 J. Cho, S. Jeon, S. A. Wilson, L. V. Liu, E. A. Kang, J. J. Braymer, M. H. Lim, B.
Hedman, K. O. Hodgson, J. S. Valentine, E. I. Solomon and W. Nam. Nature,
2011, 478, 502ꢀ505.
34 J. U. Rohde, J. H. In, M. H. Lim, W. W. Brennessel, M. R. Bukowski, A. Stubna,
E. Münck, W. Nam and L. Que Jr. Science, 2003, 299, 1037ꢀ1039.
35 J. L. Fillol, Z. Codola`, I. GarciaꢀBosch, L. Gomez, J. J. Pla and M. Costas, Nature
Chem., 2011, 3, 807ꢀ813.
36 R. Matta, K. Hanna and S. Chiron, Sci. Total Environ., 2007, 385(1ꢀ3), 242ꢀ251.
37 W. P. Kwan and B. M. Voelker, Environ. Sci. Technol., 2003, 37, 1150ꢀ1158.
38 W. G. Barb, J. H. Baxendale, P. George and K. R. Hargrave, Nature, 1949, 163,
692ꢀ694.
39 W. G. Barb, J. H. Baxendale, P. George and K. R. Hargrave, Trans. Faraday Soc.,
1951, 47, 462ꢀ500.
40 W. G. Barb, J. H. Baxendale, P. George and K. R. Hargrave, Trans. Faraday Soc.,
1951, 47, 591ꢀ616.
41 C. Jiang, Z. Gao, H. Qu, J. Li, X. Wang, P. Li and H. Liu, J. Hazard. Mater., 2013,
250ꢀ251, 76ꢀ81.

Green Chemistry
Page 16 of 16
View Article Online
DOI: 10.1039/C4GC00997E