A promising catalyst for exclusive: Para hydroxylation of substituted aromatic hydrocarbons under UV light

Article abstract of DOI:10.1039/c7gc01653k

Herein, we describe a waterborne polymer/carbon dot nanocomposite system as an efficient, resourceful and sustainable photocatalyst for para-selective hydroxylation of substituted aromatic compounds using H₂O₂ under UV light. The polymer matrix and carbon dot generate a synergistic catalytic system. A unique structural attribute of the functionalities in this catalytic system attracts the aromatic substrates into close proximity and activates them. Additionally, the flexible molecular box-like structure of the hyperbranched polymer provides the ability for favorable three-point interaction with several substrates having various sizes by means of their multiple force networks and the increased accessibility of the active sites. The catalyst can be stored on the bench top for months and is reusable without considerable loss in its activity. The reaction was exclusively selective toward para hydroxylation irrespective of the nature of the substituents (electron donating or electron withdrawing) in the aromatic hydrocarbons. Hence, it is one of the most promising catalysts for selective hydroxylation of substituted aromatic hydrocarbons.

Full text of DOI:10.1039/c7gc01653k

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: V. K. Das, S.
Gogoi, B. M. Choudary and N. Karak, Green Chem., 2017, DOI: 10.1039/C7GC01653K.
Volume 18 Number
7
7
April 2016 Pages 1821–2242
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 7
View Article Online
DOI: 10.1039/C7GC01653K
Journal Name
COMMUNICATION
A promising catalyst for exclusive para hydroxylation of
substituted aromatic hydrocarbons under UV light
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a,c
a
a
Vijay Kumar Das , Satyabrat Gogoi , Boyapati Manoranjan Choudary and Niranjan Karak *
DOI: 10.1039/x0xx00000x
www.rsc.org/
3
waterborne polymer/carbon dot reactions afforded low yields and poor selectivity. Of late,
,4
Herein, we describe
a
5
-8
nanocomposite system as an efficient, resourceful and sustainable several iron based heterogeneous catalysts have also been
photocatalyst for para-selective hydroxylation of substituted developed for hydroxylation of aromatic hydrocarbons to
2 2
aromatic compounds using H O under UV light. The polymer overcome the shortcomings of homogeneous catalysis
matrix and carbon dot generate a synergistic catalytic system. A including catalysts decomposition, tedious recovery and non-
unique structural attribute of the functionalities in this catalytic reusability. However, an excess amount of the substrate has
system attracts the aromatic substrates into the close proximity always been utilized to prevent dihydroxylation and reactions
and activates them. Additionally, the flexible molecular box like are performed at ambient temperature with low turnover
structure of the hyperbracnhed polymer provides the ability for number. More recently, hydroxylation reactions of aromatic
favorable three point interaction with several substrates having hydrocarbons are catalysed by nonheme iron in the presence
9
-13
various sizes by means of their multiple force networks and the of peroxide with low regio-selectivity.
increased accessibility of the active sites. The catalyst can be hydroxylation of aromatic compounds catalysed efficiently by
Similarly, the
1
4,15
stored on bench top for months and reusable without zeolites
have also been reported recently but never
considerable loss in its activity. The reaction was exclusively reached exclusive p-selectivity. We have also reported the
selective toward para hydroxylation irrespective of the nature of enhanced p-selective nitration of aromatic compounds at para
1
6
the substituents (electron donating or electron withdrawing) in position using the pores of zeolite beta with low Si/Al ratio.
the aromatic hydrocarbons. Hence, it is one of the most promising The catalysis by zeolite has certain drawbacks like irreversible
catalysts for selective hydroxylation of substituted aromatic adsorption or steric blockage of the products leads to its
hydrocarbons.
deactivation, the unfeasibility of using their micro porosity for
the synthesis of bulky molecules. Due to greater polarity of
functional compounds in the micro porous structure of
zeolites, it is more difficult to exploit their shape selectivity. On
the other hand, exclusive selective p-hydroxylation is also
possible through enzymatic catalysis involving three-point
binding of the substrate but this reaction was confined to a
The regioselective hydroxylation of aromatic hydrocarbons is
1
one of the most demanding reactions in organic synthesis as it
gives rise to hydroxyl-arene motif which is a core unit of many
2
modern polymers, agrochemicals and pharmaceuticals. The
introduction of the hydroxyl moiety directly and selectively
into aromatic ring is a challenging task in the domain of
organic synthesis. Processes in the prior art used metal based
catalysts for the hydroxylation of aromatic rings but the
1
7
few examples. However, catalysis by enzyme offers a number
of disadvantages. It remains insufficiently stable for
commercial applications; recovery of the enzyme from the
reaction mixture for subsequent reutilization is always
troublesome, difficulty in isolating the product from the
reaction mixture which is generally present in low
concentrations. Hence, there is an unmet need to provide
commercially scalable process for the selective para-
hydroxylation in aromatic hydrocarbon that can be carried out
at ambient conditions with recoverable and reusable low-cost
metal free catalyst. In order to meet this goal under the norms
1
8
of green chemistry and to mimic enzymes, we demonstrate
here a facile yet unexplored protocol presenting carbon dot
encapsulated in waterborne dendritic polyurethane as a
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 7
View Article Online
DOI: 10.1039/C7GC01653K
COMMUNICATION
Journal Name
Figure 2. Model reaction. It involves the optimization of the reaction condition by
considering the hydroxylation of benzoic acid. Various parameters have been tested to
check the selectivity of the catalyst in the presence of visible, dark and UV light. The
optimization of the hydroxylation reaction was also observed at room temperature, 50
°C and 70 °C respectively.
Figure 1. CD@WPU catalysed hydroxylation under UV light. This route entails the
hydroxylation of aromatic hydrocarbon at para position with 100% selectivity. The
effect of electron withdrawing as well as electron donating groups on aromatic ring is
found to be negligible in providing 100% selectivity at para position which ultimately
leads to process intensification.
form 4 (Table 1, entries 1 & 2). This felt the necessity of a
catalyst and thus, CD@WPU was introduced to test the
reaction under investigation. With the addition of 5 wt% of
finely cut thin film of CD@WPU under day light at room
temperature, 50 °C and 70 °C provided trace to 23% yield of 4
promising photocatalyst for the selective hydroxylation of the
aromatic compounds at para position (Figure 1). The catalytic
1
9
activity of the dendritic polymers has been extensively
studied due to their interesting cage like structure,
heterogeneous nature and straightforward isolation from the
reaction mixture. In this context, the photocatalysis by
nanostructured materials remained in practice in the recent
(
Table 1, entries 3-5). Photo responsive CD falls in UV region
and hence, the said reaction was conducted under UV light. In
5 min and 45 min, CD@WPU gave 76% and 90% yields
1
2
0,21
time
due to the unlimited and united benefits of the
respectively (Table 1, entries 6 & 7) and maximum yield was
recorded in 1 h (Table1, entry 8). In the current process, when
the model reaction was carried out in dark, it gave no
indication of product formation (Table 1,
homogeneous as well as heterogeneous catalytic systems and
2
2
thereby making a bridge between them. With this view, nano
dimension carbon has broadly been utilized in the past few
years as a smart material with the capability to harvest photon
2
3
Table 1. Optimization of the reaction condition.
in the UV/visible spectral region
and also for the
2
4
development of advanced catalysts. In the family of nano
dimension carbon, carbon dot (CD) has been researched as a
photocatalyst in the reduction of carbon dioxide to an organic
a
b
Entry
Conditions
Yield (%)
1
2
No catalyst, RT, ground, 1 h
No catalyst, 50 °C, 12 h
c
c
2
5
26,27
acid, oxidation of benzyl alcohol to benzaldehyde,
2
d
3
*CD@WPU, RT, ground, visible light, 1 h
*CD@WPU, 50 °C, visible light, 9 h
*CD@WPU, visible light, 70 °C, 9 h
*CD@WPU, UV light, 15 min.
*CD@WPU, UV light, 45 min.
*CD@WPU, UV light, 1 h
Trace
17
23
76
90
98
c
8
cyclohexane to cyclohexanone and contributed significantly
as nanocatalyst underneath the umbrella of ‘NOSE
d
4
d
5
d
(
Nanoparticles-catalysed Organic Synthesis Enhancement)’
2
6
9,30
d
approach.
The practical difficulty associated with CD in
7
d
8
effective photocatalysis is the solubility in aqueous phase or in
alcohol which gives rise to its tedious isolation from the
d
9
*CD@WPU, dark, 3 days
h
57
1
0
*CD (5 mL), UV light, 2 h
reaction medium. In this connection, application of
a
d
1
1
2
WPU, 50 °C, 3 h
13
94
88
82
54
65
80
90
10
32
98
polymeric matrix as a smart support paves the best way to
promote the photo catalytic activity of CD on account of
prohibiting solid state quenching and permitting
straightforward catalyst isolation. The polymer matrix as a
e
f
1
1
*CD@WPU, UV light, 1 h
3
*CD@WPU, UV light, 1 h
g
1
1
1
4
5
6
*CD@WPU, UV light, 1 h
d
d
d
d
i
CD@WPU, UV light, 1 h
3
1
support also affords mechanical strength to CD which is
suitable for catalytic stability. In this context, the polymeric
nanocomposites bestowed a novel model in material discovery
j
CD@WPU, UV light, 1 h
k
17
18
CD@WPU, UV light, 1 h
l
CD@WPU, UV light, 1 h
3
2
d,m
due to their enormous feasibility in various applications. The
physico-chemical properties of these polymeric
19
*CD@WPU, UV light, 1 h
*CD@WPU, UV light, 1 h
*CD@WPU, UV light, 1 h
*CD mixed with WPU, UV light, 2 h
WPU, UV light, 3 h
d,n
2
2
0
d,o
d
1
nanocomposites show a considerable distinction from their
bulk counterparts which can be subjected to architect such
h
2
2
74
d
3
3
23
c
c
materials with tuneable features.
We first optimized the reaction condition by considering
the hydroxylation reaction of benzoic acid (3) with H as a
model reaction (Figure 2) under UV light at room temperature
using waterborne hyperbranched polyurethane/CD
2
4
No catalyst, UV light, 5 h
a
Reaction condition: Benzoic acid 3 (1 equivalent, 122 mg), H
2 2
O (3
2 2
O
equivalent, 30%, 102 mg, 0.09 mL) are homogeneously ground for the
b
c
proper mixing in day light. Isolated yield.* 2 wt% CD in WPU. No
d
e
f
reaction. 5 wt% (11 mg) catalyst. 10 wt% (22 mg) catalyst. 15 wt%
3
4
g
h
nanocomposite (CD@WPU) prepared earlier . In this case 2
wt% CD on WPU was considered. The results are summarized
(
34 mg) catalyst. 20 wt% (45 mg) catalyst. Mixture of ortho and para
i
j
k
hydroxy benzoic acid. 0.5 wt% CD in WPU. 1 wt% CD in WPU. 1.5
l
m
n
in Table 1. The neat reaction of 3 with H
at 50 °C did not
2
O
2
(30% v/v) heated
wt% CD in WPU. 2.5 wt% CD in WPU.
1 equivalent H
2
O
2
.
2
o
equivalent H
2
O
2
.
4 equivalent H
2
O
2
.
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 7
Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins
View Article Online
DOI: 10.1039/C7GC01653K
Journal Name
COMMUNICATION
entry 9) even after continuing the reaction for 3 days. Again, about exclusive para selectivity in hydroxylation reaction.
when the reaction was conducted only in the presence of CD Furthermore, WPU brings an extra profit by producing ionic
(Table 1, entry 10) under UV light furnished a mixture of ortho centers along the polymer chains which perform like ionomers
and para products whereas WPU alone at 50 °C could produce with potent electron transfer ability. Thus, WPU has been
selectively 4 in lower yield (Table 1, entry 11). Hence, CD as found to be a very effective support for photocatalytic activity
3
6,37
well as WPU alone was not very effective and selective for of CD compared to the conventional polymers.
hydroxylation of 3 and found to be highly active as well as Additionally, both CD and CD@WPU possess suitable band gap
3
7
selective in collaboration i.e., the synergistic effect of WPU on of 3.4 eV and 3.2 eV respectively and applicable for the light
CD. Thus, the complex architecture and interior as well as harvesting capacity in the UV region. Hence, the current
3
5
exterior functionality of WPU led to the increased selectivity.
reaction underwent in the presence of UV light and remained
Catalyst loading was also optimized and results were tabulated inactive in dark.
in Table 1 (Entries 11-14). It was observed that 5 wt% catalyst
Encouraged with these results, we next moved to the
loading with respect to the substrate (Table 1, entry 8) was exploration of the scope of CD@WPU catalysed selective
sufficient for photo hydroxylation of benzoic acid. On hydroxylation of substituted aromatic hydrocarbons by
2 2
increasing the catalyst loading from 10 wt% to 20 wt%, the treating with H O under UV light under the optimized reaction
yield of 4 started to decrease by keeping the reaction time conditions. As demonstrated in Table 2, CD@WPU has been
constant which might be attributed to the strong adsorption of established as a robust and sustainable photo catalyst for the
reactants on the catalyst surface which did not react further to hydroxylation of substituted aromatic hydrocarbons furnishing
form the product (Table 1, entries 12-14). The strong the selective hydroxylated products in good to high yields
adsorption of reactants on the catalyst surface due to increase (Table 2, Entries 1-9). It was noteworthy to mention that under
in loading was confirmed by the UV-visible analysis of the the present reaction condition, the catalyst was found to be
reaction mixture where the concentration of the reactants less effective in the hydroxylation of benzene into phenol (7%
started to decrease than whatever it was. The model reaction
was also tested by considering various loading (0.5 wt%, 1
wt%, 1.5 wt% and 2.5 wt%) of CD in WPU (the entire CD@WPU
loading was 5 wt%) for a duration of 1 h. It was observed that
a
Table 2. CD@WPU catalyzed selective hydroxylation of aromatic hydrocarbons .
Entry
1
Product
Time
(min.)
Yield
(%)
Melting
point (°C) /
Lit. m.p.)
b
the hydroxylated product
4
formed in low yield at 0.5 wt%, 1
Ref.
(
wt%, and 1.5 wt% loading (Table 1, entries 15-17) and due to
aggregation of CD on WPU at higher loading (Table 1, entry
60
60
98
92
212.7-214.5
213-215)
3
9
(
1
8). The hydroxylation reaction was less effective on using 1
and 2 equivalents of H with respect to 3 (Table 1, entries
9, 20) but when 4 equivalent of H was used it gave same
2 2
O
2
3
4
5
223.8-226.4
225-227)
4
0
1
2 2
O
(
yield (Table 1, entry 21) akin to 3 equivalent. No further
oxidation of 4 was seen when the reaction was continued for
more than 1 h. Thus, it was established that 1 and 2
90
70
88
76
60
114.3-115.8
(114-116)
4
1
2 2
equivalents of H O could not generate enough hydroxyl free
radicals needed for the reaction whereas 3 and 4 equivalents
did, but then low amount was preferred in order to follow
green chemistry approach. Besides CD encapsulated in CD,
when CD mechanical mixed with WPU used as a catalyst (Table
114.7-115.6
115-116)
4
2
(
100
171.6-173.4
43
(
173)
1, entry 22), it gave a mixture of ortho and para products
(
57%) wherein the ratio of ortho one (53%) was higher. It
6
7
8
9
60
90
58
80
70
189.1-190.8
might be due to the presence of WPU which could work well
when CD would have been encapsulated in its matrix instead
44
(187-191)
of using a mixture of the two. When
3
was treated with H
2
O
2
130
150
180
111.2-112.7
4
5
(110-112)
under UV light in presence of WPU, no hydroxylation was
observed (Table 1, entry 23). Blank experiment using UV light
also could not lead the reaction toward product formation
43.8-45.2
46
(44-45)
(Table 1, entry 24).
In general, the hydroxylation was found to be clean and
31.6-33.4
4
7
only para selective (100%) using 5 wt% CD@WPU in UV light
and no side product formation took place. The homogeneous
distribution of CD over the entire polymer matrix helps light
harvesting capacity of CD@WPU nanomaterial and polymer in
the same media. Here, CD is the photoactive component which
can absorb UV light, while WPU provides the requisite
mechanical support and its unique structural attribute brings
(32-33)
a
Reaction condition: Substrate (1 mmol), H O (3 mmol), CD@WPU (5
wt%), UV light. Isolated yield. The products were characterized by H and
C NMR and also by comparing the melting points from the literature.
2 2
b
1
13
yield, 9 h) and naphthalene into naphthol (2% yield, 15 h). This
was because of the lack in substituents (electron withdrawing
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 7
View Article Online
DOI: 10.1039/C7GC01653K
COMMUNICATION
Journal Name
th
or donating) in the aromatic ring. Also, hydroxylation of intensity was observed 5 cycle onwards (Figure S1, ESI). This
cinnamic acid and styrene did not take place under the current indicated some extent of dissolution (though not substantial)
th
reaction condition which might be due to the π-π interaction of CD after 5 cycle. Further, comparison of TEM images of
th
with CD of the catalyst. In general, the yield of the product was fresh catalyst and spent catalyst after 4 cycle (Figure S2, ESI),
found to be good to high when the benzene ring was revealed some extent of clustering of the nanomaterial in the
substituted with electron withdrawing group (EWG) and later. Thus, we believe that dissolution as well as movement of
electron donating group (EDG) which activated the ring toward CD within the polymer matrix to cause aggregation deactivated
hydroxylation. In order to drive the catalyst selectivity for the efficiency of the catalyst. In order to avoid the use of
ortho position, the reaction was carried out by considering excess amount of catalysts and to clarify the recyclability of
para phenylene diamine (para position was blocked) under the CD@WPU, the reaction condition with a low yield as
optimized condition. In this case, instead of hydroxylation mentioned in entry 15 of Table 1 was carried out and the
3
8
product, it gave azobenzene-4,4'-diamine as a coupling outcome for this event was also akin to Table 4 (Table S1, ESI).
product (50% yield, 16 h). Thus, CD@WPU has been found to
be highly active, stable and 100% selective towards para
hydroxylation of aromatic hydrocarbons which has been
a
Table 4. Recyclability of CD@WPU .
b
Entry
Run
Time (min)
Yield (%)
9
-17
lacked in the previously reported catalysts.
The hydroxylation reaction of aromatic hydrocarbons
mentioned in Table 3) was repeated using only CD as a
1
2
3
4
5
6
Fresh
60
60
98
st
1
98
nd
(
2
60
98
rd
catalyst to check the amount of ortho, meta and para
hydroxylated product formation. It was found that carbon dot
could only produce a mixture of ortho and para products
3
60
98
th
4
60
98
th
5
80
98
th
7
6
100
98
(
Table 3, entries 1-9). However, only nitrobenzene furnished
meta hydroxylated product along with ortho and para isomers
Table 3, entry 3). It can be seen from this table that the
a
2 2
Reaction condition: 3 (5 mmol, 610 mg), H O (15 mmol, 510 mg),
b
CD@WPU (5 wt%, 56 mg), UV light. Isolated yield.
(
hydroxylation reaction was uncontrolled leading to the
production of mixture of ortho, meta and para isomer. In this
case, no selectivity at para position was seen. This may be due
to non-selective nature of CD.
The mechanism of the reaction is not very clear. However,
on the basis of above results, a very probable free radical
mechanistic pathway (Figure 3) has been proposed. At the very
outset, under UV light irradiation, CD in CD@WPU acts as the
electron reservoirs to entrap photo-induced electrons from
the conduction band which assists the efficient partition of
a
Table 3. CD catalysed hydroxylation of aromatic hydrocarbons
-
+
electrons (e ) and holes (h ) enhancing the photo catalytic
Entry
Time
Ortho
(%)
33
8
Meta
Para
(%)
24
7
Net yield
4
8
b
activity. The proposed plausible mechanism may proceed in
different paths for aromatic ring substituted with electron
donating (EDG) and electron withdrawing groups (EWG). In
case of EDG, the ortho and para positions (I) of the aromatic
(min)
(%)
(%)
1
2
3
4
5
6
7
8
9
60
-
-
57
15
26
17
14
11
6
60
90
7
15
-
4
4
9
70
6
11
4
ring are rich in partial negative charges i.e. electron density.
+
100
60
10
4
-
The electron deficient h may interact at these positions and
expels one electron out of it. But three point interaction of the
-
7
5
0
130
150
180
2
-
4
molecular box like structure of dendritic polymer with the
EDG containing aromatic ring, blocks the ortho position and
keeps the para position (II) available for the incoming hydroxyl
radical (OH·) to form para-hydroxylated product (III) thereon.
On the other hand, electron snatching nature of EWG
generates partial positive charges at ortho and para positions
11
5
-
13
3
24
8
-
a
2 2
Reaction condition: Substrate (1 mmol), H O (3 mmol), CD (5 wt%), UV
b
1
13
light. Isolated yield. The products were characterized by H and
C
NMR and also by comparing the melting points from the literature.
4
9
(
IV) of the aromatic ring. But the three point interaction of
Under the norms of green chemistry, recycling is a key
concern in catalysis. Hence, the recycling potency of CD@WPU
catalyst has also been tested using the model reaction (Figure
the dendritic polymer with the aromatic ring leaves only para
-
position (V) unmasked. Hence, the e from electron-hole pair
gets driven toward only available para position wherein the
OH· radical attacks thereof to produce expectedly
hydroxylated product (VI). In the entire scene, OH· radical is
2) under the optimized condition. The data obtained as
presented in Table 4 demonstrate that CD@WPU has been
th
recycled from fresh up to the 4 run without loss in its action.
5
1
generated from H
Actually, WPU having surface functional groups –NH-C(=O)-
O-, -O-C=O, -OH, -NH facilitates a strong interaction with CD
2 2
O under UV light.
However, slightly longer reaction time was required
afterwards to achieve the desired yield of
4 because the finely
2
sliced thin film of CD@WPU slightly stuck amongst each other
th
after 4 run. Also, the activity of the catalyst decreased in the
to provide a unique box like structure which in turn acting as
the binding sites for the reactants. Similarly, graphitic CD with
passivated surface states (which include –C=O, -OH, -O-C-O-) is
fifth cycling. The UV-Visible analysis confirmed apparently no
th
change in intensity up to 4 cycle, however, slight decrease in
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 7
Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins
View Article Online
DOI: 10.1039/C7GC01653K
Journal Name
COMMUNICATION
electron withdrawing groups in the aromatic hydrocarbons.
The selectivity as well as light harvesting tendency of
CD@WPU catalyst was imparted when CD was immobilized on
the polymer matrix (WPU) in the aqueous media rendering
extra stability to it and making the material resourceful in
photo catalysis. The protocol bequeaths various advantages
such as high yields of the hydroxylated products, safe to
handle, experimental ease, using commercially available
2 2
greener H O , no byproduct formation, unfussy recoverability
and reusability of the metal free catalyst making it sustainable,
beneficial and benevolent alternate over the existing tactics.
Therefore, as disclosed herein, we are expectant that the UV
light active heterogeneous catalysts would find tremendous
applications for new chemical transformations.
Notes and references
The authors thank SAIC, Tezpur University, India for the
instrumental assistance.
Figure 3. (a) Insight into the plausible reaction mechanism for the selective
hydroxylation of aromatic hydrocarbons at para-position catalyzed by CD@WPU. (I) =
1
2
3
4
5
6
7
8
9
1
1
Alonso, D. A., Najera, C., Pastor, I. M. & Yus, M. Chem.–Eur. J.
010, 16, 5274-5284.
Tyman, J. H. Synthetic and natural phenols, Elsevier,
Amsterdam, 1996.
Lücke, B., Narayana, K.V., Martin, A. & Jhnisch, K. Adv. Synth.
Catal. 2004, 346, 1407-1424.
Tani, M., Sakamoto, T., Mita, S., Sakaguchi, S. & Ishii, Y.
Angew. Chem. Int. Ed. Engl. 2005, 44, 2586-2588.
Raba, A., Cokoja, M., Herrmann, W. A. & Kuhn, F. E. Chem.
Commun. 2014, 50, 11454-11457.
Makhlynets, O. V. & Rybak-Akimova, E. V. Chem.–Eur. J.
2010, 16, 13995-14006.
Taktak, S., Flook, M., Foxman, B. M., Que, Jr. L. & Rybak-
Akimova, E. V. 2005, Chem. Commun. 2005, 42, 5301-5303.
Bianchi, D., Bortolo, R., Tassinari, R., Ricci, M. & Vignola, R.
Angew. Chem. 2000, 112, 4491-4493.
Thibon, A., Jollet, V., Ribal, C., Sénéchal-David, K., Billon, L.,
Sorokin, A. B. & Banse, F. Chem.-Eur. J. 2012, 18, 2715-2724.
0 Kang, M. J., Song, W. J., Han, A. R., Choi, Y. S., Jang, H. G. &
Nam, W. J. Org. Chem. 2007, 72, 6301-6304.
1 Sahu, S., Widger, L.R., Quesne, M. G., De Visser, S.P.,
Matsumura, H., Moënne-Loccoz, P., Siegler, M.A. &
Goldberg, D. P. J. Am. Chem. Soc. 2013, 135, 10590-10593.
2
reactant, (II)
aromatic hydrocarbons substituted with electron donating group (EDG). (IV)
reactant, (V) reaction intermediate and (VI) = hydroxylated product in case of
= reaction intermediate and (III) = hydroxylated product in case of
=
=
electron withdrawing group (EWG). Free radical mechanistic pathway. (b) three point
interaction of the substrate by polymer. Molecular recognition was possible only by
three point binding as in enzymes.
capable of absorbing UV-visible light and thus functions as a
photo catalytic module in the hydroxylation reaction (Figure
S3, ESI). Therefore, this unprecedented work demonstrated
unambiguously that our system, hyperbranched polyurethanes
encapsulated carbon dot displays 100% molecular recognition
possibly only by three point binding as in enzymes for the first
time in the annals of chemistry for all varied and diversified
substrates as described in this manuscript. Traditionally, the
regioselective electrophilic substitution depends on
ortho/para or meta positions for the electronic donating and
electronic withdrawing groups already present on aromatic
rings, respectively. None of these variations are observed with
respect to selectivity and yields in the current hydroxylation 12 Ansari, A.; Kaushik, A.; Rajaraman, G. 2013, 135, 4235.
Ansari, A., Kaushik, A. & Rajaraman, G. J. Am. Chem. Soc.
013, 135, 4235-4249.
reaction, but always provide
p-hydroxylated products
2
exclusively, possible only through free radical mechanism by
induction of molecular recognition in the cavities of polymer
matrix.
1
1
1
1
3 Latifi, R., Tahsini, L., Nam, W. & de Visser, S. P. Phys. Chem.
Chem. Phys. 2012, 14, 2518-2524.
4 Kharitonov, A. S., Sobolev, V. I. & Panov, G. I. Russ. Chem.
Rev. 1992, 61, 1130-1139.
5 Mukherjee, P., Bhaumik, A. & Kumar, R. Ind. Eng. Chem. Res.
2007, 46, 8657-8664.
6 Choudary, B. M., Sateesh, M., Kantam, M. L., Rao, K. K.,
Prasad, K. R., Raghavan, K. V. & Sarma, J. A. R. P. Chem.
Commun. 2000, 1, 25-26.
7 Ullrich, R. & Hofrichter, M. Cell. Mol. Life Sci. 2007, 64, 271-
2
8 Anastas, P. T. & Williamson, T. Green Chemistry, Frontiers in
Benign Chemicals Synthesis and Processes, Oxford Science
publications, NewYork, 1998.
Conclusions
In summary, we devised a fruitful protocol for the one pot
hydroxylation of substituted aromatic hydrocarbons under UV
light catalyzed by novel, environmentally benign, metal free
1
1
93.
and
biodegradable
waterborne
hyperbranched
polyurethane/carbon dot nanocomposite based catalyst
system (CD@WPU) catalyst system. The reactions were found
to be clean and no side product formation was observed. The 19 Astruc, D. & Chardac, F. Chem. Rev. 2001, 101, 2991-3024.
2
0 Füldner, S., Mild, R., Siegmund, H. I., Schroeder, J. A., Gruber,
M. & König, B. Green Chem. 2010, 12, 400-406.
1 Ibhadon, A. O. & Fitzpatrick, P. Catalysts 2013, 3, 189-218.
reaction was completely selective toward para hydroxylation
irrespective of the nature of the electron donating as well as
2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 7
View Article Online
DOI: 10.1039/C7GC01653K
COMMUNICATION
Journal Name
2
2
2
2
2 Astruc, D., Lu, F. & Aranzaes, J. R. Angew. Chem, Int. Ed.
005, 44, 7852-7872.
3 Wang, X., Qu, K., Xu, B., Ren, J. & Qu, X. J. Mater. Chem.
011, 21, 2445-2450.
4 Su, D. S., Perathoner, S. & Centi, G. Chem. Rev. 2013, 113,
782-5816.
5 Sahu, S., Liu, Y., Wang, P., Bunker, C. E., Fernando, K. S.,
Lewis, W. K., Guliants, E. A., Yang, F., Wang, J. & Sun, Y. P.
Langmuir 2014, 30, 8631-8636.
2
2
5
2
2
2
2
3
6 Li, H., Liu, R., Lian, S., Liu, Y., Huang, H. & Kang, Z. Nanoscale
2
7 Mosconi, D., Mazzier, D., Silvestrini, S., Privitera, A., Marega,
C., Franco, L. & Moretto, A. ACS nano 2015, 9, 4156-4164.
8 Liu, R., Huang, H., Li, H., Liu, Y., Zhong, J., Li, Y., Zhang, S. &
Kang, Z. ACS Catal. 2013, 4, 328-336.
013, 5, 3289-3297.
9 Das, V. K., Harsh, S. N. & Karak, N. Tetrahedron Lett. 2016,
5
7, 549-553.
0 Das, V. K., Devi, R. R., Raul, P. K. & Thakur, A. J. Green Chem.
012, 14, 847-854.
2
3
3
1 De, B., Voit, B. & Karak, N. RSC Adv. 2014, 4, 58453-58459.
2 Scholz, M. S., Blanchfield, J. P., Bloom, L. D., Coburn, B. H.,
Elkington, M., Fuller, J. D., Gilbert, M. E., Muflahi, S. A.,
Pernice, M. F., Rae, S. I., Trevarthen, J. A., White, S. C.,
Weaver, P. M. & Bond, I. P. Compos. Sci. Technol. 2011, 71,
1
791-1803.
3
3
3 Gogoi, S. & Karak, N. RSC Adv. 2016, 6, 94815-94825.
4 Gogoi, S., Kumar, M., Mandal, B. B. & Karak, N. Composites
Sci. Technol. 2015, 118, 39-46
3
3
3
5 Kirkorian, K., Ellis, A. & Twyman, L. J. J. Chem. Soc. Rev. 2012,
4
1(18), 6138-6159.
6 Gogoi, S. & Karak, N. ACS Sustainable Chem. Eng. 2014, 2,
730-2738.
2
7 Yang, Y., Kong, W., Li, H., Liu, J., Yang, M., Huang, H., Liu, Y.,
Wang, Z., Wang, Z., Sham, T.K. & Zhong, J. ACS Appl. Mater.
Interfaces 2015, 7, 27324-27330.
3
3
4
4
4
8 Farhadi, S., Zaringhadam, P. & Sahamieh, R. Z. Acta Chim.
Slov. 2007, 54, 647-653.
9 Wei, B. M., Zhang, Z. Y., Dai, Z. Q. & Zhang, K. C. Monatsh.
Chem. 2011, 142, 1029-1033.
0 Ghosh, S., Bag, P. P. & Reddy, C. M. Crystal Growth & Design
2
011, 11, 3489-3503.
1 Gaber, A. E. A. M., Muathen, H. A. & Taib, L. A. J. Anal. Appl.
Pyrolysis 2011, 91, 119-124.
2 Bird, C. W. & Chauhan, Y. P. S. Org. Prep. Proc. Int. 1980, 12,
2
01-202.
4
4
3 Algi, F., & Balci, M. Synth. Commun. 2006, 36, 2293-229.
4 Nasrollahzadeh, M., Sajadi, S. M., Rostami-Vartooni, A.,
Alizadeh, M. & Bagherzadeh, M. J. Colloid Interface Sci. 2016,
4
66, 360-368.
4
4
5 Masjed, S. M., Akhlaghinia, B., Zarghani, M. & Razavi, N.
Aust. J. Chem. 2017, 70, 33-43.
6 Xu, J., Wang, X., Shao, C., Su, D., Cheng, G., & Hu, Y. Org. Lett.
2
010, 12, 1964-1967.
4
4
7 Hoffmann, R. W. & Ditrich, K. Synthesis 1983, 2, 107-109.
8 Yu, H., Zhao, Y., Zhou, C., Shang, L., Peng, Y., Cao, Y., Wu, L.-
Z., Tung, C.-H. & Zhang, T. J. Mater. Chem. A 2014, 2, 3344-
3
351.
9 Brown, A. C. & Gibson, J. J. Chem. Soc. Trans. 1892, 61, 367-
69.
0 Karak, N. & Maiti, S. Dendrimers and hyperbranched
polymers; Synthesis to applications, MD Publications Pvt.
Ltd., Daryaganj, New Delhi, 2008.
4
5
3
5
1 Baxendale, J. H. & Wilson, J. A. Trans. Faraday Soc. 1957, 53,
3
44-356.
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C7GC01653K
1
5x5mm (300 x 300 DPI)