Novel aluminium exchanged dodecatungstophosphoric acid supported on K-10 clay as catalyst: Benzoylation of diphenyloxide with benzoic anhydride

Article abstract of DOI:10.1039/c6ra05379c

A series of (20% w/w) aluminium exchanged dodeca-tungstophosphoric acids (DTP) (Al_x-DTP, x = 0.33-1) supported on montmorillonite K-10 clay were synthesized and completely characterized by sophisticated techniques. These catalysts were used for

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Novel Aluminium exchanged Dodecatungstophosphoric acid
Supported on K-10 Clay as Catalyst: Benzoylation of
diphenyloxide with benzoic anhydride
Received 00th January 20xx,
Accepted 00th January 20xx
Manishkumar S. Tiwari, Ganapati. D. Yadav*,
DOI: 10.1039/x0xx00000x
www.rsc.org/
A series of (20%w/w) aluminium exchanged dodecaꢀtungstophosphoric acid (DTP) (AlxꢀDTP, x=0.33ꢀ1)
supported on montmorillonite Kꢀ10 clay were synthesized and completely characterized by sophisticated
techniques. These catalysts were used for the selective benzoylation of diphenyl oxide with benzoic anhydride
to mono acylated product. Al0.66ꢀDTP/Kꢀ10 catalyst showed the best activity amongst other aluminium
substituted catalyst and Cs2.5H0.5PW12O40 (CsꢀDTP)/Kꢀ10. Different supports such as ZrO2, SnO2and Kꢀ10
were used to study the effect of support on the acidic property and activity of Al0.66ꢀDTP supported catalysts in
the benzoylation reaction. The order of activity was Al0.66ꢀDTP/Kꢀ10>Al0.66ꢀDTP/SnO2>Al0.66ꢀDTP/ZrO2. The
effect of benzoylating agents such as benzoic anhydride, benzoyl chloride and benzoic acid on the conversion
and rate were also studied. Benzoic anhydride showed the high reactivity. EleyꢀRideal mechanism was found
to be consistent with the data. The activation energy for benzoylation of DPO was calculated as 22 kcal/mol,
which further supports that the reaction is kinetically controlled. Al0.66ꢀDTP/Kꢀ10 was an active and robust
catalyst.
5ꢀ9
support and/or substituting the H+ ions with metal ions.2,
Introduction
Various supports used to prepare a heterogeneous catalyst by
supporting bulk heteropoly acid or substituted heteropoly acids
Heteropoly acids (HPA) and their salts, either in
10ꢀ13
include, metal oxides (ZrO2, TiO2, SnO2 and Nb2O5),
supported or unsupported form, are frequently used as solid acid
catalysts for a various industrially significant reactions.1ꢀ3 Dodecaꢀ
tungstophosphoric acid (DTP) having Keggin structure is reported
to have the highest acidity and better thermal stability amongst all
HPAs in several acid catalysed reactions. 1,2ꢀ4 Unsupported HPAs
have some basic drawbacks like very high solubility in polar
media and low surface area of salts of HPAs. The problems
associated with bulk HPAs can be overcome by the use of proper
mesoporous materials (silica, MCMꢀ41, SBAꢀ15),14ꢀ17 alumina,18
21ꢀ24
active carbon,19 graphene20 and montmorillonite Kꢀ10.3,
Various metals ions have been reported to make the exchanged
HPA and classified accordingly in two groups.25 Different metal
ions such as Na+, Al3+, Cu2+, Cs+, Ag+, Y3+, Fe3+, Bi3+, Ru3+, Al3+,
4+
Sm3+, Ti4+, Zr4+, Ti4+, Hf and Sn4+ have been studied in detail
for several reactions.6, 8, 26ꢀ30 Some metal ions act as electron pair
acceptor and hence generate Lewis acidic sites in substituted
heteropoly acid.7 Cs substituted DTP either supported or
unsupported have been explored extensively in reactions because
of higher acidity content as compared to the parent acid.3,30 The
synergistic effect of supporting DTP and its Cs substituted salts on
Department of Chemical Engineering, Institute of Chemical Technology, Matunga,
Mumbai-400 019, India; E-mail: gdyadav@yahoo.com,manishtiwari877@gmail.com
Fax: +91-22-3361-1002, +91-22-3361-1020; Tel: +91-22-3361-1001.
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3, 21ꢀ24
Kꢀ10 has been reported and used in several reactions.
The primary aim of present work was the synthesis of
different aluminium salts of dodecaꢀtungstophosphoric acid
(DTP) supported metal oxides including montmorillonite Kꢀ
10 clay catalysts with varying aluminium content and to
characterize them by different methods such as FTꢀIR, NH3ꢀ
TPD, XRD, surface area analysis, TGA and SEM. The
activity of the prepared catalysts was investigated in selective
benzoylation of diphenyl oxide with benzoic anhydride under
solvent free condition to monoacylated product including
kinetics. Different reaction parameters were optimized to
derive suitable mechanism and kinetics.
Aluminium exchanged DTP supported on titania was employed in
the reaction of anisole with benzyl alcohol which showed that Al
25
exchanged DTP are very active for the reaction.
Therefore it
was planned to investigate the effect of support as well as content
of aluminium in exchanged DTP on acidity and activity in Friedelꢀ
Crafts acylation reaction. Benzophenone are very important class
of fine chemicals which can be produced from acylation of
different aromatic ethers (such as anisole, veratrole, diphenyl
oxide) with benzoyl chlorides, alcohols and olefins having vast
area of application in industries like fragrance, pharmaceuticals,
31ꢀ34
dyes and as heat transfer fluids.
However, the use benzoyl
chloride causes the corrosion of process equipment because of
HCl generated during reaction and makes process uneconomical.
Further these reactions are catalyzed by different homogenous
Lewis and Bronsted acid catalyst which requires neutralization
and presents several environmental and economic issues. 10, 23
Experimental section
Chemicals and Catalysts
The list of chemicals procured was as follow: Diphenyl
oxide, dodecaꢀtungstophosphoric acid hexahydrate, benzoic
anhydride, benzoic acid, nꢀdodecane, aluminium nitrate (AR
grade; S. D. Fine Chem. Ltd, Mumbai, India), cesium chloride, Kꢀ
10 clay (Aldrich, USA).
Benzoylation of diphenyl oxide with benzoyl chloride
produces 4ꢀphenoxybenzophenone which is used as intermediate
34
and as a heat transfer fluid. Sawant et al
have reported the
benzoylation of diphenyl oxide with benzoyl chloride over
DTP/ZrO2, which gives 97% selectivity of 4ꢀ
Catalyst Synthesis
phenoxybenzophenone along with only 39.3 % conversion of
benzoyl chloride after 3 h under optimum conditions. Overall
yield of product is still very low. Further the use of acid chloride
has disadvantage in terms of economic and environmental as
discussed above.
Preparation of 20%w/w AlxDTP / K-10
Supported aluminium exchanged heteropoly acid catalyst,
20%w/w AlxꢀDTP over Kꢀ10 montmorillonite (AlxDTP/Kꢀ10) was
synthesized by wet impregnation method as that reported for Csꢀ
DTP/Kꢀ10 in our laboratory. 21ꢀ24, 37
Benzoic anhydride as a benzoylating agent has been used in
various benzoylation reactions of alkyl benzenes, aromatic ethers
etc.35The activity of benzoic anhydride was compared with
benzoyl chloride and found to be better in case of benzoylation of
veratrole to 3, 4ꢀdimethoxybenzophenoene over HꢀY zeolites. 35
The better activity of benzoic anhydride was explained on the
basis of its strong adsorption on the catalytic surface due to higher
molecular weight of benzoic anhydride as compared to benzoyl
chloride. 36The co product formed with use of benzoic anhydride is
benzoic acid, which can be easily recovered and used for other
purposes. Benzoylation of diphenyl oxide using benzoic anhydride
is so far not reported in literature and advantage discussed above
makes it an alternative for the green synthesis of the acylated
product. This is first time we are reporting the use of benzoic
anhydride as acylating agent for acylation of diphenyl oxide.
The preparation involves two steps of impregnation. Firstly,
aluminium with varying amount was loaded on Kꢀ10. Around 5 g
of support (Kꢀ10) was dried for 3 h in oven at 120°C to remove
moisture. The required quantity of aluminium nitrate was
dissolved in methanol (5 ml)and then added in small amount
(approximately 1 ml)each time as an aluminium source to 4 g of
Kꢀ10 and kneaded and dried in air to get free flowing solid. The
obtained solid material was again dried at 120°C for 4h to remove
the entire methanol from the impregnated solid.
In second step, the desired amount of DTP was dissolved in
methanol and added to dry powder of aluminium loaded Kꢀ10 clay
descried before resulting in formation of slurry which was dried as
stated above to get a nearly dry solid material. The resultant
material was dried at 120° C for 12 h followed by calcination at
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O
OH
O
O
O
O
O
+
+
O
Diphenyl oxide
Benzoic anhydride
4ꢀPhenoxy benzophenone
Benzoic acid
Scheme 1 Benzoylation of diphenyl oxide with benzoic anhydride
300 °C for 3h to get active 20%w/w AlxDTP/Kꢀ10, where x
represents the number of aluminium ions, which was varied from
0.33 to 1. 20 %(w/w) Cs2.5ꢀDTP/Kꢀ10was synthesized by the same
method as described by us for cesium chloride as a source of Cs.
AlꢀDTP supported on different supports (ZrO2 and SnO2) were
prepared by same procedure as described above.
BET surface area analysis
The textural characteristics of the catalysts are given in Table1.
The adsorptionꢀdesorption isotherms of different aluminium
substituted and supported catalyst are shown in Fig. 1. Surface
area of Kꢀ10 supports decreases after loading of DTP which
suggests the filling of pores by DTP particles. However on
aluminium substitution, the salt formation of aluminium with DTP
results in increase in surface area which is due to the dense porous
network formed by the salts of DTP with aluminium as same
explained by the Moffat et al.38 Pore sizes of all catalyst are in the
range of 5 nm to 7.5 nm and show a type IV hysteresis loop,
representative of mesoporous material. Also all samples show a
negligible amount of micropore volume which further confirms
the mesoporous nature of samples. The amount of N2 adsorbed at
the highest P/P0 is also tabulated in Table 1. Kꢀ10 has maximum
nitrogen adsorption capacity which decreases when DTP and Alꢀ
DTP are loaded. Decrease in the surface area supports that long
range pores are hindered or blocked making N2 adsorption
possible only in most accessible pores and hence the surface area
decreases.39 The closure point of hysteresis loops of Kꢀ10 and
DTP/Kꢀ10 took place when the value of P/P0 reaches to 0.5, while
in the case of Al substituted catalyst it shifted towards high P/P0
value which indicates the presence of more macrospores as
compared to Kꢀ10 and DTP/Kꢀ10.
Characterization of catalysts
Different characterization techniques were employed to
characterize the fresh and used catalyst. The detail methodology is
given in ESI.
Reaction procedure
Experiments were conducted in a glass reactor (volume 50 cm3)
having 6ꢀbladed pitchedꢀturbine impeller. The setup was kept in a
thermostatic oil bath provided with PID controller. The reaction
was started by taking the appropriate quantities of reactants and
internal standard nꢀdodecane (usually 3%v/v) and the temperature
was set to the known value and agitated. In controlled reaction we
have used Benzoic anhydride 0.0057 mol, Diphenyl oxide
0.057mol, catalyst loading 0.03 g/cm3, temperature 130°C, speed
of agitation 800rpm. The zero hour sample was taken once the
mixture reached the desired temperature and the catalyst was
added and the stirring started again. Clear samples were taken at
regular time interval for analysis. The samples were centrifuged
and analyzed by using BPꢀ1 column in GC 6810 having FID
detector. Samples were quantified by using internal standard
method.
The surface area analysis of used and fresh catalyst was also
compared in order to see the any changes in surface area of the
reused catalyst (Fig. 1; Table 1)There is a marginal decrease in the
overall surface are of the reused catalyst; however, other
Results and Discussion
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properties remain the same which indicate the reusability of
catalyst.
loading of DTP on Kꢀ10 may result in change in overall XRD
patterns shown by the Kꢀ10. The loading of DTP and
Total Amount of N2
Sr.
No
Surface area
(m2/g)
Pore diameter
(nm)
Pore Volume
(cm3/g)
Catalyst
adsorbed (cm3/g STP)
6.4
7.1
6.4
6.0
6.1
5.9
6.1
1
2
3
4
5
6
7
Montmorillonite Kꢀ10
20% (w/w) DTP/Kꢀ10
245.7
139.6
183.3
188.5
196.3
232.1
183.3
227.1
110.6
168.9
180.2
183.6
205.8
176.4
0.36
0.31
0.29
0.27
0.28
0.29
0.27
20% (w/w) Al0.33ꢀDTP/Kꢀ10
20% (w/w) Al0.66ꢀDTP/Kꢀ10
20% (w/w) Al1ꢀDTP/Kꢀ10
20%(w/w)CsꢀDTP/Kꢀ10
Reused 20% (w/w) Al0.66ꢀDTP/Kꢀ10
Table 1: Surface area pore volume and pore diameter analysis
aluminium exchanged DTP on the Kꢀ10 results in decrease in
the intensity shown by Kꢀ10 and there are no distinct peak
shown by DTP related to its crystalline nature is seen. This
indicates high dispersion of these materials on the surface and
their interaction with the support. 40 The XRD pattern of used
and fresh catalyst was also compared to see the fidelity of
catalyst composition after the use. There is no difference in
the XRD pattern which confirms the stability of catalyst after
4th reuse.
Fig. 1 N2 adsorptionꢀdesorption isotherms of (a) Kꢀ10 clay, (b)
DTP/Kꢀ10,(c) Al0.33ꢀDTP/Kꢀ10 (d) Al0.66ꢀDTP/Kꢀ10 (e) Al1ꢀDTP/Kꢀ
10 (f) Reused Al0.66ꢀDTP/Kꢀ10
X-ray powder diffraction (XRD)
The XRD diffraction patterns of all catalysts are shown in
Fig. 2. The observed sharp peaks in the diffractogram of Kꢀ
10 are due to the quartz and other impurities. 40 Despite of
sharp peaks shown by these impurities two broad 2θ peaks
at 20° (due to 110 diffraction) and 35° (due to 105
diffraction) of montmorillonite Kꢀ10 can be easily found in
the XRD pattern. DTP is crystalline in nature as reported
earlier; 23 hence the
Fig. 2 XRD of different catalysts (a) Kꢀ10 clay, (b) DTP/Kꢀ10,(c)
Al0.66ꢀDTP/Kꢀ10 (d) ReusedAl0.66ꢀDTP/Kꢀ10
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Fourier transforms infrared spectroscopy (FT-IR)
The montmorillonite Kꢀ10 also show theses peaks as it is an
acid treated clay and hence possess not only weak but also
strong acidic sites (Fig. 4). Strength of moderate and strong
acidic sites varies with the change in the content of
aluminium (Table 2); however, the total replacement of
protons of heteropoly results in increase in weak acidic site
but the strong site concentration decreases. The overall
acidity possessed by the aluminium exchanged supported
catalyst were more as compared to DTP/Kꢀ10 and Csꢀ
DTP/Kꢀ10 which may be due to Lewis acidity possess by
aluminium.
Keggin structure of supported dodecaꢀtungstophosphoric
acid and aluminium exchanged catalysts were confirmed by
comparing their FTꢀIR spectra (Fig.3). The characteristic
peaks (between 700 and 1100 cmꢀ1) related to Keggin
structure of DTP i.e. at 1081 cmꢀ1, 984 cmꢀ1, 897 and 812 cmꢀ
1
were assignable respectively to the vibration of ν(P
W) and edgeꢀsharing ν
W). 5,37Overall spectral of the supported catalysts are
–O),
terminal ν (W= O), corner ν (W
(W
–O–
–O–
quite similar to that shown by Kꢀ10. The peaks related to
DTP and metal exchanged DTP have got superimposed on
those of support suggesting that the structure remains
unaltered even after interacted with Kꢀ10. 40, 23 The FTꢀIR of
spent catalyst was compared with the fresh catalyst to
confirm the stability of exchanged DTP after the reaction.
Fig. 3 shows the all characteristic peaks related to Keggin
structure in the spent catalyst as shown by the Fresh catalyst,
once again supporting the stability of catalyst and its activity
was not affected during reaction.
Fig.4 NH3ꢀ TPD patterns of different catalysts (a) Kꢀ10 clay,
(b) DTP/Kꢀ10,(c) Al0.33ꢀDTP/Kꢀ10 (d) Al0.66ꢀDTP/Kꢀ10 (e)
Al1ꢀDTP/Kꢀ10 (f) Reused Al0.66ꢀDTP/Kꢀ10
TGA Analysis
TGA analysis of different samples i.e. montmorillonite Kꢀ10,
DTP/Kꢀ10 and Al0.66ꢀDTP/ Kꢀ10 was done to study the
thermal stability (Fig.5). DTP is supposed to decompose
around 465°C; 1hence, supporting DTP on proper support and
/or replacement of protons will further increase its thermal
stability.5 TGA profile reveals that supporting DTP on Kꢀ10
increases it thermal stability as there is only marginal loss of
3% after 300 °C. The weight loss of total 12% of support is
due to the loss water which is physically adsorbed and
present in interlayer and also due to –OH group destruction
of the montmorillonite Kꢀ10.41 Further its substitution with Al
results in increase in thermal stability and is in good
agreement with
Fig 3 FTꢀIR spectra of catalysts (a) DTP, (b) Kꢀ10 clay,
(c)DTP/Kꢀ10,(d) Al0.33ꢀDTP/Kꢀ10 (e) Al0.66ꢀDTP/Kꢀ10 (f)
Al1ꢀDTP/Kꢀ10 (g) Reused Al0.66ꢀDTP/Kꢀ1
NH3-TPD
The NH3ꢀTPD of Kꢀ10, DTP and AlꢀDTP/Kꢀ10 was
conducted during 50 to 650°C (Fig. 4; Table 2). All
supported catalyst showed two different desorption peak of
ammonia in the range of 100ꢀ300°C and from 450ꢀ600°C.
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Table 2: Acid strength distribution of K-10 supported catalyst
Acidity (mmol/g)
Moderate/Strong
No
1
Catalyst
Kꢀ10
Weak
0.53
Total
0.99
0.46
2
3
4
5
6
7
20% (w/w) DTP/Kꢀ10
20% (w/w) Al0.33ꢀDTP/Kꢀ10
20% (w/w) Al0.66ꢀDTP/Kꢀ10
20% (w/w) Al1ꢀDTP/Kꢀ10
20% (w/w) CsꢀDTP/Kꢀ10
0.75
0.82
0.80
0.88
0.36
0.79
1.12
1.14
1.33
1.27
1.15
1.30
1.87
1.96
2.13
2.16
1.51
2.09
Reused 20% (w/w) Al0.66ꢀDTP/Kꢀ10
Fig 6 SEM Images of (a) Fresh Al0.66ꢀDTP/Kꢀ10, (b) Reused
Al0.66ꢀDTP /Kꢀ10
Efficacy of various solid acid catalysts
The activity of different catalysts, namely, Kꢀ10, 20%w/w
DTP/Kꢀ10,20%w/w CsꢀDTP/Kꢀ10 and 20%w/w AlxꢀDTP/Kꢀ
10 in solvent free benzoylation of diphenyl oxide was studied
with benzoic anhydride (Fig. 7). The result shows highest
activity of Al0.66ꢀDTP/Kꢀ10 catalyst as compared to others
due to its highest acidity (Table 2). The aluminium
exchanged catalysts were found to be more active in
comparison of CsꢀDTP/Kꢀ10, DTP/Kꢀ10 and Kꢀ10. The
acidity of the catalysts determined by ammonia TPD is in
Fig 5: TGA analysis of (a) Kꢀ10 clay, (b) DTP/Kꢀ10, (c)
Al0.66ꢀDTP/Kꢀ10
different literature which reported increase in thermal
stability of metal ion exchanged heteropoly acid. 7ꢀ9, 23
SEM
The surface morphology of the sample was evaluated from
SEM analysis. Fig. 6 shows formation of agglomerates after
loading of Al exchanged DTP on supports. The morphology
of Al exchanged catalyst shows a smooth surface as same
reported for CsꢀDTP/Kꢀ10. 37 The fresh and reused catalyst
shows no difference in the morphology which confirms the
reusable nature of catalyst.
following order: Al1DTP/Kꢀ10
≅
Al0.66DTP/Kꢀ10
>
Al0.33DTP/Kꢀ10 > DTP/Kꢀ10 > CsꢀDTP/Kꢀ10 > Kꢀ10. The
activity of these catalysts towards conversion of benzoic
anhydride under solvent less condition was also in the same
order as mentioned above as: Al1DTP/Kꢀ10≅ Al0.66DTP/Kꢀ
10 >Al0.33DTP/Kꢀ10 > DTP/Kꢀ10 > CsꢀDTP/Kꢀ10 > Kꢀ10.
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Change in the amount of aluminium substitution in catalyst
increases the concentration of acidic sites from week to
strong sites as shown in Fig.4. The activity shown by the Al
substituted catalysts supported on Kꢀ10 are greater as
compared to that shown by CsꢀDTP/Kꢀ10, DTP/Kꢀ10, which
is due to the high acidity of the Alꢀexchanged catalyst as that
of other catalysts. This also indicates that aluminium helps to
enhance the overall acidity of theses catalyst because of the
Lewis acidity of Al. However, after the Al0.66DTP/Kꢀ10;
there is no distinct difference in conversion with Al1DTP/Kꢀ
10 (Fig.7). This is due to marginal difference in the acidity
possessed by these catalysts. Hence all further experiments
and studies were carried out with Al0.66DTP/Kꢀ10 catalyst.
possessed by these catalyst were found in following order
Al0.66ꢀDTP/Kꢀ10> Al0.66ꢀDTP /SnO2> Al0.66ꢀDTP /ZrO2
which is in the same order as obtained for the conversion of
benzoic anhydride with these catalyst. The SnO2 supported
catalyst shows mainly a strong acidic site and very few weak
acidic sites; however, the total acidity is still very low as
compared to that of Kꢀ10 supported catalyst which has both
strong and weak sites (Table 3). The high acidity of Kꢀ10 as
compared to other metal oxide is the most probable reason
behind the high activity and acidity shown by the
Al0.66DTP/Kꢀ10 catalyst. Further surface area may be another
reason as we can see from Table 3, the surface area of
different catalyst are in following order, Al0.66ꢀDTP/Kꢀ10>
Al0.66ꢀDTP /SnO2> Al0.66ꢀDTP /ZrO2. Large surface area
results in better dispersion of active catalyst surface. High
acidity of Kꢀ10 supported catalyst along with better
dispersion could be the reason for its high activity in
benzoylation reaction. Hence for further reaction, Kꢀ10 was
selected as the support in order to get the maximum yield of
product.
100
80
60
40
20
0
Effect of different benzoylating agent
Benzoylation of diphenyl oxide was carried out using three
different benzoylating agents i.e. benzoic acid, benzoic
anhydride and benzoyl chloride (Table 4), the benzoylation
reaction with benzoic acid shows no conversion at 130 °C
which support the fact that there is no reaction of benzoic
acid towards formation of benzoylated product formed during
reaction with benzoic anhydride. The reaction with benzoyl
chloride gives 56.6% conversion and 96% selectivity towards
4ꢀphenoxybenzophenone. Hence, overall yield of desired
product is found to be 54.5 %, while reaction with benzoic
anhydride gives the 72.1% conversion and 100% selectivity
of desired product resulting in overall yield of 72% which is
considerably high as compared to the yield obtained from
benzoyl chloride after 2 h. The strong adsorption of benzoic
anhydride due to its higher molecular weight as in case of
zeolite and other solid acid catalyst 23, 35can be applied here
as a most probable reason for the superior activity shown by
the benzoic anhydride amongst the different benzoylating
agents used for reaction. Apart from reactivity, the green part
of synthesis using benzoic anhydride is the formation of
benzoic acid (coꢀproduct) as compared to HCl generated
during use of benzoyl chloride, which makes the benzoic
Catalysts
Fig 7 Effect of various catalysts on conversion of benzoic anhydride.
Benzoic anhydride 0.0057mol, Diphenyl oxide 0.057mol, catalyst
loading 0.03 g/cm3, temperature 130°C, speed of agitation 800rpm,
total volume 10.1 cm3, reaction time 120 min
.
Effect of different supports on benzoylation activity
The activity of Al0.66DTP supported on three different
supports i.e. ZrO2, SnO2 and Kꢀ10 prepared by the same
method as described above were evaluated to understand the
role of support. The conversion of benzoic anhydride was
found to be in following order for these catalyst as Alꢀ
DTP/Kꢀ10> AlꢀDTP /SnO2> AlꢀDTP /ZrO2 (Fig.8). The
acidity of these catalysts was evaluated by using ammonia
TPD in the range of 50°C to 650 °C (Fig.9) and the
calculated acid site strength are given in Table 3. The acidity
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anhydride more preferable benzoylating agent not only in
Fig 9 NH3ꢀ TPD patterns of different supported catalysts (a)
terms of reactivity but also in terms of green synthesis
Al0.66ꢀDTP/ZrO2, (b) Al0.66ꢀDTP/SnO2, (c) Al0.66ꢀDTP/Kꢀ10
process.
80
Table 4: Reactivity of different benzoylating agent
60
40
20
0
Selectivity of 4ꢀ
Conversion
No.
1
Acylating agent
Phenoxybenzophenone
(%)
(%)
Benzoyl
chloride
56.6
96
Benzoic
2
3
72.1
100
ꢀ
anhydride
Benzoic acid
No conversion
Conditions: Diphenyl oxide /benzoylating agent (mole ratio) = 10,
catalyst loading= 0.03 g/cm3, temperature= 130°C, speed of agitation
800rpm, reaction time= 120 min.
Catalysts
Fig 8 Benzoylation activity of Al0.66DTP supported on different
supports. Benzoic anhydride 0.0057mol, Diphenyl oxide 0.057mol,
catalyst loading 0.03 g/cm3, temperature 130°C, speed of agitation
800rpm, total volume 10.1 cm3, reaction time 120 min.
Stability of catalyst
The heterogeneity of catalyst in a reaction system was
investigated to confirm the stability of prepared catalyst in
the reaction system. The catalyst was removed by simple
filtration method after 1 h of initial reaction time and reaction
was started again without addition of catalyst in the same
reactor (reactor was washed to get rid of trace of catalyst
attached to glass surface) with the same reaction condition.
After 2 h the reaction was stopped and the analysis of the
reaction sample showed no more conversion of benzoic
anhydride indicating the heterogeneous nature of catalyst.
Table 3: Acid strength distribution and surface property
of Al0.66-DTP supported on different supports
Acidity
Surface area
(m2/g)
N
o
Catalyst
(mmol/g)
20% (w/w) Al0.66
DTP/Kꢀ10
ꢀ
ꢀ
1
2
3
2.13
1.22
1.33
205.8
49.6
20% (w/w) Al0.66
DTP/ZrO2
20% (w/w) Al0.66ꢀ
DTP/SnO2
102.6
Effect of Different reaction parameters:
Various reaction parameters were studied in detail to
optimize the conversion of benzoic anhydride and rate of
formation of benzoylated product.
Speed of agitation
Fig. 10 shows that with increase in agitation speed from
400 to 800 rpm the conversion seems to increase and thereafter
remains constant which indicates the negligible effect of mass
transfer resistance on rate of benzoylation. Hence 800 rpm was
selected as optimum speed of agitation for further reaction. The
details about the theoretical calculation of mass transfer resistance
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effect on reaction rate have been explored and detailed in some of
our recent literature.21ꢀ23 Only calculation part is reported in ESI to
confirm the negligible mass transfer resistance effect on reaction.
100
80
60
40
20
0
(a)
100
80
60
40
20
0
0
30
60
90
120
150
180
Time(min)
1.8
1.5
1.2
0.9
0.6
0.3
0
(b)
0
30
60
90
120
150
180
R² = 0.9913
Time(min)
Fig 10 Effect of speed of agitation on conversion of benzoic
anhydride. Benzoic anhydride 0.0057mol, Diphenyl oxide
0.057mol, catalyst loading 0.03 g/cm3, temperature 130°C,
total volume 10.1 cm3.
(
) 400rpm, ( ) 600rpm, ( ) 800rpm, ( ) 1000rpm
Effect of the catalyst loading
0
0.01
0.02
0.03
0.04
0.05
The catalyst loading was changed from 0.01g/cm3 to 0.04 g/cm3
(Fig. 11 (a)). The plots were made for different catalyst loading vs.
initial rate to see a linear relationship (Fig. 11 (b)). It is due to the
increase in vacant surface for the benzoylation reaction with
increase in the catalyst loading which results in the initial reaction
rate enhancement. We also did the theoretical calculation and
found that WietzꢀPrater modulus (Cwp) is far less than unity
Catalyst Loading (g/cm3)
Fig 11 Effect of catalyst loading on (a) conversion of benzoic
anhydride. (b) Initial rate of Benzoylation of DPO.
Benzoic anhydride 0.0057mol,
Diphenyl oxide 0.057mol,
temperature 130°C, speed of agitation 800rpm, total volume
10.1 cm3.
(Cwp=0.0026), hence the reaction is supposed to be kinetically
(
) 0.01 g/cm3, ( ) 0.02 g/cm3, ( ) 0.03 g/cm3, ( ) 0.04 g/cm3,
42
controlled
which was confirmed by the activation energy
calculation.
(ꢀꢀꢀꢀꢀꢀꢀ) Predicted values
Effect of the mole ratio
of diphenyl oxide by keeping constant moles of benzoic anhydride
provides a better and enhanced conversion and rate. The most
probable reason is attributed to the solubility of the formed
products (desired along with benzoic acid) in the diphenyl oxide.
The increase in the mole ratio, results in excess moles of diphenyl
oxide which helps to solubilise the product formed and helps to
free the catalytic site for further reaction. At 1: 10 mole ratio good
The ratio of two reactants were varied in range of 1:2 to 1:15
(benzoic anhydride to diphenyl oxide) maintaining the other all
reaction variable constant (Fig. 12). The reaction was found to be
greatly dependent on the change in mole ratio of the benzoic
anhydride with diphenyl oxide. The increase in number of moles
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conversion was obtained and hence it was selected as optimum
mole ratio for further study.
100
80
60
40
20
0
100
80
60
40
20
0
0
30
60
90
120
150
180
Time(min)
Fig 13: Effect of temperature on conversion of benzoic anhydride.
Benzoic anhydride 0.0057mol, Diphenyl oxide 0.057mol, catalyst
loading 0.03 g/cm3, speed of agitation 800rpm, total volume 10.1
cm3, reaction time 120 min.
0
30
60
90
120
150
180
Time (min)
Fig 12 Effect of mole ratio on conversion of benzoic anhydride.
Catalyst loading 0.03 g/cm3, temperature 130°C, speed of
agitation 800rpm, total volume 10.1 cm3.
(
) 110°C, ( ) 120°C, ( ) 130°C, ( ) 140°C, (ꢀꢀꢀꢀꢀꢀꢀ) Predicted
values
(
) 1:2, ( ) 1:5, ( ) 1:10, ( ) 1:15, (ꢀꢀꢀꢀꢀꢀꢀ) Predicted values
80
Effect of temperature
The temperature of the reaction was changed from 110°Cꢀ 140°C
to see its effect and to prove that the reaction is only kinetically
controlled and all other resistance have been successfully avoided.
The final conversion of limiting reactant (i .e. benzoic anhydride)
increased with change in temperature (Fig. 13), which supports
that the reaction was kinetically controlled.
60
40
20
0
3.7. Catalyst reusability studies
Fresh
1st Reuse 2nd Reuse 3rd Reuse 4th reuse
The catalyst robustness was studied through reusability four times.
The separated catalyst mixed with 30 ml of methanol and acetone
mixture (50:50 v/v) at reflux condition for 1 h and then separated
by using filter paper and dried at 120°C for 4 h. Makeup of
catalyst loss during the regeneration was done to reach the
optimized catalyst loading value. There was a very negligible
decrease in the final conversion of benzoic anhydride (Fig. 14).
Recovered catalyst after the 4th reuse was characterized by
different techniques and found to be the same in the nature as the
fresh one. Hence catalyst is reusable.
Fig 14:Reusability of catalyst. Benzoic anhydride 0.0057mol,
Diphenyl oxide 0.057mol, catalyst loading 0.03 g/cm3,
temperature 130°C, speed of agitation 800rpm, total volume 10.1
cm3, reaction time 180 min.
3.8 Development of Theoretical Model
A detailed kinetic model was developed by using above
results. The EleyꢀRideal mechanism was supposed to be the best
suited model based on the preliminary analysis. Consider D
(diphenyl oxide),
B (benzoic anhydride), product E (4ꢀ
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phenoxybenzophenone) and F (coꢀproduct benzoic acid). The
detail of derivation of the model is reported in some of our work
23, 42 and hence the derivation part is given in ESI.
For the validation of derived mathematical model (equation 2), we
have calculated the theoretical or predicted conversion by using
the obtained rate constant and adsorption constant for different
reaction condition. These conversion values are then plotted in the
Figs 11 (catalyst loading effect), 12 (mole ratio effect) and 13
(Temperature effect) as dotted line along with the experimental
value of conversion. The plot shows the best fitting of the
theoretical value and the experimentally obtained value, hence
validates the model very well.
Considering, the surface reaction between the chemisorbed BS
and reactant D as the rate limiting step. The rate of benzoylation
of diphenyl oxide based on the conversion of benzoic anhydride B
is given as:
dCB
dt
kKBwCDCB
(1)
−
=
= rD = rB
(CF + KBCB )
Table 5: Kinetics parameters of benzoylation of DPO at different
temperature.
We know that,
Activation
(1a)
(1b)
(1c)
CB = CB (1− XB )
0
energy (E)
T (K)
k (cm6mol−1g−1s−1
)
KB (cm3/mol)
(kcal/mol)
CD = C −C XB = C (M − XB )
D0
B0
B0
No.
383
393
403
413
0.038
0.079
0.166
0.302
0.14
0.11
0.09
0.07
CF = CB X B
1
2
3
4
0
Substituting in terms of XB and integrating the Equation 1, we
have,
22
M − X
M

B 
(2)
−ln 1− X − K (M −1) − M ) ln
= kK (M −1)wt
(
)
[
]
[
]
B
B
B




The experimental data obtained at optimized conditions were used
to validate the predicated model. Using Polymath 6.0 Software
constants were calculated and the results are presented in Table 5.
The Arrhenius plot was also made (Fig. 15) to get apparent
activation energy as 22kcal/mol. It further supports the fact of
kinetically controlled benzoylation of diphenyl oxide.
CONCLUSION
Aluminium
exchanged
DTP
supported
on
montmorillonite Kꢀ10 with varying amount of Al content (0.33 to
1) was prepared and characterized by different techniques. The
catalysts were tested for the selective preparation of 4ꢀ
phenoxybenzophenoen using benzoic anhydride as benzoylation
agent. Al0.66DTP/Kꢀ10 was the most active catalyst among the
prepared catalysts. Effect of different supports on the activity of
Al0.66 DTP for benzoylation of diphenyl oxide were studied and its
0
ꢀ0.5
y = ꢀ11071x + 25.63
ꢀ1
R² = 0.99
ꢀ1.5
activity was found in the following order Al0.66DTP/Kꢀ10> Al0.66
ꢀ
ꢀ2
ꢀ2.5
ꢀ3
DTP /SnO2> Al0.66ꢀDTP /ZrO2. The surface area and acidity of the
supports plays an important role for their activity in benzoylation
reaction. The detailed investigation of various reaction parameters
was done and optimized to get the maximum yield of the product
reported so far. The catalyst stability was also investigated and
found to be heterogeneous in nature. Using benzoic anhydride as
benzoylating agent not only results in better yield of product but
also helps to avoid the use of acid chloride, hence making process
ꢀ3.5
0.0024 0.00245 0.0025 0.00255 0.0026 0.00265
1/T (K-1)
Fig. 15: Arrhenius plot for Benzoylation of diphenyl oxide
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green and economical. The kinetic modelling was done based on
the EleyꢀRideal mechanism and the apparent activation energy
was 22kcal/mol.
[3] G. D. Yadav, Cat. Surveys Asia; 2005, 9 (2), 117ꢀ
137.
[4] G.D. Yadav, H.G. Manyar, Micropor. Mesopor.
Mater. 2003, 63, 85ꢀ96.
ACKNOWLEDGEMENT
[5] F. Su, L. Ma, D. Song, X. Zhang, Y. Guo,
M.S. Tiwari acknowledges University Grants Commission (UGC)
for the award of BSR Senior Research Fellowship under its SAP
program in Chemical Engineering. G.D. Yadav acknowledges
support from R.T. Mody Distinguished Professor Endowment and
J.C. Bose National Fellowship of Department of Science and
Technology, Govt. of India.
Green Chem., 2013,15, 885ꢀ890.
[6]
K.ꢀI. Shimizu, H. Furukawa, N. Kobayashi, Y.
Itaya, A. Satsuma, Green Chem. 2009, 11, 1627–
1632.
[7] K. Shimizu, K. Niimi, A. Satsuma, Catal. Commun.
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[8] G.D. Yadav, MS Krishnan, Ind. Eng. Chem. Res.
1998, 37 (8), 3358ꢀ3365
Conflict of Interest Statement
The authors declare no conflict of interest.
[9] G.D. Yadav, P.K. Goel, AV Joshi, Green Chem
2001, 3 (2), 92ꢀ99.
.
Nomenclature
[10] B.M. Devassy, F. Lefebvre, S.B. Halligudi, J. Catal.
2005, 231, 1–10.
B
reactant species B, benzoic anhydride
Chemisorbed B
BS
D
[11] R.M. Ladera, M. Ojeda, J. L. G. Fierro, S. Rojas,
Catal. Sci. Technol., 2015, 5, 484ꢀ491.
reactant species D, Diphenyl oxide
4ꢀPhenoxybenzophenone
E
[12] M. Srinivas, , G. Raveendra, G. Parameswaram, PS
Sai Prasad, and N. Lingaiah, J Mol. Cat. A:Chem,
2016, 413,7ꢀ14
F
benzoic acid
B0
CB
CD
CF
k
concentration of B in bulk liquid phase, (mol/cm3)
concentration of B, (mol/cm3)
concentration of D, (mol/cm3)
concentration of F in, (mol/cm3)
reaction rate constant (cm6mol−1g−1s−1)
adsorption equilibrium constant for B (cm3/mol)
mole ratio of A to B
[13] K. Srilatha, N. Lingaiah, B.L.A. Prabhavathi Devi,
R.B.N. Prasad, S. Venkateswar, P.S. Sai Prasad,
Appl. Catal. A: Gen., 2009, 365 , 28–33.
[14] E. Rafiee, M. Khodayari, S. Shahebrahimi, M.
KB
M
w
Joshaghani, J. Mol. Catal. A: Chem., 2011, 351
,
204–209.
catalyst loading(g/cm3)
[15] K.You, R. Deng, J. Jian, P. Liu,Q. Ai , H.A.Luo,
RSC Adv 2015, , 73083ꢀ73090
XB
fractional conversion of B
.
,
5
[16] W. Zhang, P. Jiang, Y. Wang, J. Zhang, P.
Zhang,
Acronyms
Kꢀ10
Montmorillonite clay
Catal. Sci. Technol., 2015,
[17] T. Pinto, V. Dufaud and F. Lefebvre, Appl. Catal.,
, 2014, 483, 103.
5, 101ꢀ104.
CsꢀDTP/K10
Cs2.5H0.5PW12O40 supported on
montmorillonite acid treated clay Kꢀ10
AlxH (3ꢀx) PW12O40 supported on
montmorillonite acid treated clay Kꢀ10
A
Al ꢀDTP/K10
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Castanheiro, Catal. Commun. 2011, 12 ,573–576.
[20] E Rafiee, M. Khodayari RSC Adv., 2016,6, 36433ꢀ
36440
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GRAPHICAL ABSTRACT
Novel Aluminium exchanged Dodecatungstophosphoric acid Supported on K-10 Clay
as Catalyst: Benzoylation of diphenyloxide with benzoic anhydride
Manishkumar S. Tiwari, Ganapati D. Yadav*
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