The active site accessibility aspect of montmorillonite for ketone yield in ester rearrangement

Article abstract of DOI:10.1039/c4cy01356e

The removal of Al from the octahedral layer of montmorillonite by organic acid treatment results in increased microporosity generating a material with different surface features from the virgin clay. The micropores thus generated are found to be responsible for ester to ketone transformation. Various parameters of the newly generated pores such as the pore diameter, pore structure, pore volumes and acidity by pyridine-FTIR were evaluated with respect to ester to ketone formation. The best correlation was found between the volume accessibility factors (VAF) and the ketone yield. The VAF reflects the extent of volume space available around the acid site for the reactant to orient in a specific way for the transformation to occur within the pore to form a specific product. This acid site accessibility aspect was further verified by extending to micropores with large VAF generated by treatment with phenoldisulfonic acid (PDSA).

Full text of DOI:10.1039/c4cy01356e

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Active Site Accessibility Aspect in Montmorillonite for Ketone Yield in Ester
Rearrangement
N.J Venkatesha, B.S. Jai Prakash, Y.S. Bhat*
Chemistry Research Centre, Bangalore Institute of Technology, K.R. Road,
Bangalore 560 004, India
*Corresponding author: Eꢀmailꢀbhatys@yahoo.com,
Tel.: +91 80 26615865; fax: +91 80 26426796.
Abstract:
Removal of Al from the octahedral layer of montmorillonite by organic acid treatment results in increased
microporosity generating a material with different surface features from the virgin clay. Micropores thus
generated are found to be responsible for ester to ketone transformation. Various parameters of the newly
generated pores such as, pore diameter, pore structure, pore volumes and acidity by pyridineꢀFTIR were
evaluated with respect to ester to ketone formation. Best correlation was found between volume
accessibility factors (VAF) and the ketone yield. The VAF reflects the extent of volume space available
around the acid site for the reactant to orient in a specific way for the transformation to occur within the
pore to form a specific product. This acid site accessibility aspect was further verified by extending to
micropores with large VAF generated by treatment with phenoldisulfonic acid (PDSA).
Keywords: micropore, accessibility, acidity, ester rearrangement, citric acid, pꢀtoluenesulfonic acid,
phenoldisulfonic acid.
1. Introduction
Solid acid catalysts are widely used in the acylation of phenolic compounds with carboxylic acids.
Phenolic esters and aromatic ketones find use in the synthesis of fragrances and pharmaceuticals1ꢀ4. The
acylation reaction involves the formation of acylium ion by the protonation of carboxylic acid with
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subsequent dehydration5. In the industrial practice, acylation reactions are carried out using corrosive,
homogenous acid catalysts, such as FeCl3, SnCl4, TiCl4, AlCl3, HF, BCl3 and ZnCl2, in stoichiometric
amounts invariably generating waste products.6ꢀ9 Efforts have also been made to use, ecoꢀcompatible,
reusable, heterogenous catalysts for acylation. Heteropoly acids,1,6 acidic zeolites,10,11 metal oxides,12,13
cationꢀexchange and acid treated clays are the most studied heterogeneous catalysts.9,14 Activity and
selectivity of these catalysts have been investigated in the direct acylation as well as rearrangement of
several organic substrates such as aromatic ethers (anisole, thioanisole, veratrole, and 2ꢀmethoxy
naphthalene), heterocyclic compounds (thiophene and benzofuran), phenolic compounds (phenol, pꢀ
cresol, naphthol and resorcinol) and aromatics15ꢀ20 (toluene, biphenyl and naphthalene).
Acidic clays are promising solid acid catalysts for aromatic acylation owing to their easy modification
and generation of acidity, cation exchange capacity and unique layered structure. Modification of layered
clays involves interlayer cation exchange,21ꢀ24 acid treatment,15, 25ꢀ27 surfactant treatment and pillaring.28ꢀ30
One of the commonly used surface modifications is treatment with mineral and organic acids to generate
acid sites. Mineral acid treatment results in decrease in the cation exchange capacity and increase in
surface area but severe treatment results in the removal of structural elements leading to the collapse of
the layered structure. Treatment with organic acids, however, results in a layered clay material with
increased surface area having altered pore structure exhibiting higher acid characteristics without much
change in the cation exchange capacity.15,25,31 It will be of interest to exploit such enhancement in the
surface and acid characteristics for improving the yield of the desired products.
The aim of the present investigation is to study the role of the micropore generated by the displacement of
structural Al in the organic acid treated montmorillonite on the ketone selectivity in the acylation of pꢀ
cresol with decanoic acid in solventꢀless liquid phase microwave irradiation.
2. Experimental
2.1Catalyst preparation
The used montmorillonite obtained from Bhuj area, Gujarat, India supplied by Ashapura Group of
Industries, India. The clay was treated with 1 M NaCl solution to convert sodium form. The composition
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was found using ICPꢀOES to be 42.86% SiO2, 10.14% Al2O3, 6.08% Fe2O3, 1.69% MgO, 1.91%Na2O,
with idealized structural formula Si4[Al1.432 Fe0.416 Mg0.266] O10 (OH)2Na(0.318)
.
Acid treated montmorillonite clay catalyst was prepared by treating with different acids. Typical
procedure for acid treatment followed is discussed elsewhere.15,25,27 Briefly, the method involved
treatment of 10 g Montmorillonite clay with 100 ml of 1M solution of pꢀtoluenesulfonic acid (pꢀTSA)
0
and stirring the mixture at 110 C for 30 min under the microwave irradiation, centrifuged, washed with
deionized water to remove excess of acid from the clay and dried in hot air oven at 120 0C. Diꢀsodium salt
of ethylenediaminetetraacetic acid (EDTA), citric acid (CA) and phenoldisulfonic acid (PDSA) treatment
were also carried out for comparison and the resulting samples were labeled as pꢀTSAꢀclay, EDTAꢀclay,
CAꢀclay and PDSAꢀclay. Clay samples treated with different concentration of pꢀTSA ranging from
0.1M, to 0.5M pꢀTSA were prepared and named as 0.1pꢀTSAꢀclay, 0.3pꢀTSAꢀclay and 0.5pꢀTSAꢀclay.
For the preparation of ionꢀexchange clay with Al, reported procedure was followed.21ꢀ24. The procedure
involved stirring 10 g clay with 100 ml 1M aluminium chloride for 24 hours, then centrifuged and washed
0
with distilled water to remove the chloride ions. The sample was dried at 120 C for 5 hours in hot air
oven, then ground and labelled as Alꢀclay. The catalytic activities of all the prepared catalyst samples
were evaluated for acylation followed by rearrangement.
2.2 Characterization
The prepared catalysts were characterized using pyridineꢀFTIR, XRD, TEM and BET surface area.
Acidity was measured by FTIR spectroscopy using pyridine as probe molecule. All the samples were
activated by degassing at 110 0C for 2 h and then saturated with pyridine. The catalyst samples were then
evacuated at 120 0C for 1 h to remove physisorbed pyridine. The amount of pyridine adsorbed on the acid
sites of the clay samples was determined gravimetrically which was taken as a measure of the total
acidity. FTIR spectra of the samples were then recorded in the range 1400–1600 cmꢀ1 using IRAffinityꢀ1
spectrometer having resolution of 4 cmꢀ1 with 40 scans.15ꢀ17 The Brønsted and Lewis acidity were
quantified based on the peak areas of the two sites with respect to the total acidity. The acidity was
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expressed in micromole per gram of clay. The molar extinction coefficient of the pyridine adsorbed on the
acid sites was found to be 5.8 x 104 kg molꢀ1 cmꢀ1.
Surface area and porosity measurements were carried out using Quanta chrome Novaꢀ1000 surface
analyzer under liquid nitrogen temperature. N2 adsorptionꢀdesorption isotherm measurements were done
in order to study the evolution of porosity and textural properties of the acid treated and ionꢀexchange
clay samples. Full adsorptionꢀdesorption cycles were determined up to the saturation vapor pressure of
0
nitrogen at ꢀ196 C. Pore size distribution was calculated from adsorption data using BJH and deBoer tꢀ
method.26,32, 33, 34
Structural integrity of the catalyst samples was checked by powder XRD. The data were recorded by step
scanning at 2θ= 0.0200 per second from 30 to 800 on PANalytical X’Pert PRO MPD Xꢀray diffractometer
with graphite monochromatized Cu Kα radiation (λ = 0.15406 nm).
Morphology of montmorillonite before and after PDSA modification was recorded using TecnaiꢀG2
Transmission Electron Microscope (TEM) under 120KV, transmission mode.
The amount of interlayer aluminium in different acid treated clay samples was estimated by the method
0
reported elsewhere.35 It involved treatment of 2 g of clay sample with 0.1M HCl for 60 min at 60 C.
After treatment, the mixture was centrifuged and the solid was repeatedly washed with deionized water.
Al was estimated in the centrifugate by aluminon reagent method spectrophotometrically using Chemito
UVꢀ2100 Spectrophotometer.25, 36
2.3 Catalytic activity tests
The activity of catalysts was studied under microwave irradiation, using microwave lab station “STARTꢀ
S” model from Milestone, Italy, having software which enables the control of reaction mixture and
temperature with aid of infrared sensor by regulation of microwave power output in such a way that the
reaction mixture was exactly in line with infrared sensor that monitors the temperature. Variable power up
to 1200 W was applied by microprocessorꢀcontrolled singleꢀmagnetron system.
Ten mmol of pꢀcresol (PC) and five mmol of decanoic acid (DA) were mixed with 1 g catalyst in a
microwave reactor vessel with magnetic stirring bar. Reactor vessel was kept in microwave reactor and an
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0
initial power of 1200 W was applied for 1 minute to attain the reaction temperature of 190 C. The
reaction temperature was then maintained for 59 minutes to get maximum conversion. The mixture was
then cooled for 10 minutes, and the mixture of reactants and products was extracted by stirring with 10
mL of toluene for 30 minutes and filtered to remove the catalyst. The reaction mixture was analyzed using
Chemito GCꢀ1000 gas chromatograph with TRꢀWax capillary column of length 30 m, 0.32 mm thickness
and 0.55 ꢁm internal diameter with flame ionization detector. The ester product, pꢀcresyldecanoate (Oꢀ
acylation) and the ketone product 1ꢀ(2ꢀhydroxyꢀ5ꢀmethylphenyl) decanꢀ1ꢀone (Cꢀacylation) were
analyzed using nꢀheptane as internal standard.The products were also confirmed by GCꢀMS analysis.15,26
Catalytic activity, measurement of acidity and surface characteristics were performed three times on each
sample and the mean of the measurements were used for calculating the standard deviation (< ±2.3).
3. Results and discussion
3.1 Acylation with ionꢀexchange and acid treated montmorillonite clay catalyst samples
Acylation involves formation of ester in the initial stages. The ester formed subsequently undergoes
transformation into ketone through rearrangement as shown in scheme 1. Under the experimental
conditions, interphase and intraparticle heat and mass transfer as calculated using KorosꢀNovak, Mears
and Weiszꢀ Prater criteria were negligible.37, 38 The Alꢀclay and the acid treated clays showed different
behavior in the formation of products. These are discussed below.
Al-exchange clay: Under optimized reaction conditions, acylation reaction was carried out with Alꢀclay
and the per cent conversion of DA and yields of ester and ketone were recorded. While untreated clay was
ineffective, the conversion of DA in presence of Alꢀclay was found to be quite high (68%). It was
observed that the ester (62%) was the major product accompanied by small amounts of ketone (6%), the
latter formed due to subsequent rearrangement of the former.
Alꢀclay had a CEC 0.83 meq/g, surface area 28ꢀ32 m2/g, average pore diameter (50.27 Ǻ) and micropore
volume (0.011 cm3/g). These surface features were not different from the untreated clay, but the acidity
was very much higher than the untreated clay, 150 µmol/g as measured by pyridineꢀFTꢀIR method.15,21,22
Ionꢀexchange clays are known to accelerate the rate of acidꢀcatalyzed reactions through their Brønsted
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acid sites present in the form of polarized hydrated cations on the edge sites. In the same way, the
conversion of DA is also catalyzed by the polarized water molecules of the hydrated Al cations.
Although high amounts of ester were formed, the Alꢀclay was not effective in bringing about the ester’s
conversion to ketone through rearrangement, both reactions being known to be catalyzed by acid
catalysts. Ketone formation is not assisted by the mesopores is clearly seen in the case of Alꢀclay as
shown by its BJH curve (Fig.1). Apparently, rearrangement of the ester to ketone is not facilitated by the
mesopores.
Organic acid treated clays: The picture, however, is different in the presence of acid treated clay
catalysts. Organic acid treated clays, unlike Alꢀexchange clay, showed more amount of ketone formation
resulting from the rearrangement of the ester. In order to understand the formation of ketone, it was
necessary to look at the surface characteristics and acidity after acid treatment. Acid treatment of
montmorillonite clay brings about many types of changes in (i) surface area (ii) pore size and pore
volume (iii) CEC and (iv) acidity. It is reported that organic acids and chelating agents remove the
structural Fe, Al and Mg from the octahedral layer of the untreated (Naꢀ) clay resulting in micropores on
the clay surface enhancing its surface area. The structural elements that get dislodged forming complex
species hydrolyze, on subsequent washing, releasing a part of the cations into the interlayer. The hydrated
Al and Fe ions, which displace the sodium ions in the interlayer, act as Brønsted acid sites thus enhancing
the acidity.25 Removal of structural elements would create voids in the structure resulting in increase in
porosity, pore volume and surface area. It is known that when structural aluminium is removed, there is
no reduction in CEC while the removal of isomorphously replaced Fe and Mg causes a reduction in CEC.
Tables1 and 2 give the structural elements and their amounts removed from the clay samples along with
the increase in surface area and pore volume after the acid treatment. It can be seen from Table 2, that pꢀ
TSA and PDSA remove more Al, but very little structural Fe and Mg than CA and EDTA. Hence the
CECs of the former two treated clays were not very much different (0.70ꢀ0.72) from the untreated clay
(0.83). Among the acids used for treatment, PDSA removed more structural Al (1.04 meq/g) generating
more porous regions and higher amounts of interlayer Al than the other acids. On the other hand, CA and
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EDTA removed more Fe and Mg than Al resulting in a considerable reduction in CEC (≈0.2 to 0.4). As a
result, the interlayer Al was much less and proportionate to the reduced CEC in these two treated clays.
CA however removed relatively a large quantity of Fe resulting in a clay material with high surface area
(156 m2/g) and micropore volume (0.031 cm3/g) but having a low CEC value (0.42 meq/g) and
consequently low interlayer Al. Most of the Al that is removed has migrated to the interlayer in CAꢀclay.
Among the acids used, EDTA was able to remove the least amount of structural elements. In this case
almost all the Al removed has migrated to the interlayer resulting in a material having relatively low
surface area and pore volume.
Table 2 shows the CEC calculated based on the loss of structural Fe and Mg. CEC, as calculated based
on the total amount of Fe and Mg leached out, was in agreement with the experimentally determined CEC
values within experimental errors.
Decrease in average pore diameter on acid treatment clearly shows the formation of micropores on the
surface (Table1). This could also be seen in Figs.1 and 2, where the nitrogen adsorptionꢀdesorption
isotherms and BJH plots show the pore size distribution curves of the acid treated clays. TEM images in
fig.3 show surface morphology of the clay before and after the PDSA treatment.
The acidity of clays was dependent on the interlayer Al after the acid treatment. It was almost the same
for the pꢀTSA and PDSA treated clays with similar interlayer Al which was around 0.70 meq/g, but the
CAꢀclay and EDTAꢀclay showed much less interlayer Al (0.36 meq/g and 0.22 meq/g respectively).
Consequently the acidity values of the latter two clays were low (Table 3).
In order to study the effect of generated porosity and enhanced acidity on the catalytic activity, the
acylation reaction studies were considered with different acid treated clay catalysts that is, PDSAꢀclay,
CAꢀclay, pꢀTSAꢀclay and EDTAꢀclay. Fig.4 summarizes the DA conversion which increases from
EDTAꢀclay to pꢀTSAꢀclay catalyst. Clay catalysts treated with different concentration of pꢀTSA showed
increased surface area, interlayer Al and decreased average pore diameter.25 In addition, the present study
showed an increased micropore volume, mesopore volume and pyridine FTꢀIR acidityas the concentration
of pꢀTSA used for treatment was increased from 0.1 to 0.5 M (Table 3).
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Among the three treated clays, DA conversion (Fig.4) was found to increase in the order EDTAꢀ
clay<CAꢀclay< pꢀTSAꢀclay though the formation of ketone which follows the ester rearrangement
indicated variation in its yield. pꢀTSAꢀclay showed higher ketone yield (32% ) than the other two
(EDTAꢀclay 4% ; CAꢀclay 14% ). Variation in the ester rearrangement to form ketone may be attributed
to higher acidity and the generated porosity of the acid treated clay catalyst samples.
3.2 Role of porosity and acidity in ester rearrangement.
In order to understand the role of acidity and porosity in the ester rearrangement to form ketone, a sample
of the prepared phenolic ester mixed with different modified clay catalyst samples was separately
subjected to microwave irradiation. The results in Table 3 show that pꢀTSAꢀclay was more effective in
ester conversion into ketone. The rearrangement of the ester into ketone on the surface of the catalysts
was apparently influenced by the pores and the acidity of the catalyst samples. This is based on the fact
that (i) ketone formation was accelerated only after the formation of pores (shown by the increased pore
volumes) due to acid treatment and (ii) that the ketone formation requires acid sites. This is substantiated
by the results in Table 3. Alꢀclay, having almost the same acidity as pꢀTSAꢀclay with relatively small
pore volume showed less conversion. On the other hand, CAꢀclay showing a high pore volume, but
having low acidity, yielded less ketone than pꢀTSAꢀclay, the latter having both high acidity and pore
volume. The results show clearly that rearrangement of the ester to ketone is the resultant of both pore
volume and acidity. Apparently, the newly generated pores facilitate the orientation of the ester
molecules in such a fashion to access the acid sites thus accelerating the conversion to ketone. This is
supported by the average turnover frequency (TOF) for ketone (Table 3).
3.3 Volume Accessibility Factor (VAF):
Correlation factor (r) was calculated between the amounts of ketone formed, pore volumes and the
different types of acidities for the Alꢀclay and acid treated clays. The results are given in Table 3.The
objective was to evaluate the role played by the different types of acidities, Brønsted (B) at 1550 cmꢀ1 and
Lewis (L) at 1445 cmꢀ1(fig 5), the combination of the acidities and also the mesopore and micropore
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volumes. This would throw light on the mechanism of the orientation of the ester molecule to form
ketone within the pore.
The results in table 3, 4 and 5 reveal very poor correlation between the different types of acidities and
pore volumes with the amount of ketone formed, clearly showing that neither the micropore and
mesopore volumes, nor the acidity, when individually considered facilitate the ketone formation. Among
the correlations, best correlation (r= 0.77) was shown by micropore volume and a poor correlation
(r=0.32) was shown by mesopore volume. Since, micropores alone cannot bring about the rearrangement,
possibly a combination of micropore and acidities are involved in the process. A factor called Volume
Accessibility Factor (VAF), therefore, was obtained by multiplying the micropore volume with the
different types of acidities. VAF was correlated with the amounts of ketone formed for all the clay
catalyst samples which developed pores upon acid treatment and also with Alꢀclay which had negligible
micropores.
To further establish the relation between the ketone yield and VAF, the ketone yield was measured under
different conditions of temperature, reaction time and catalyst amount (shown by R1, R2 and R3 in Table
6). The purpose was to find the relation between VAF and the formation of ketone under different
conditions. 10 mmol of the ester (pꢀcresyldecanoate) was irradiated with MW radiations for 30 min at
160 0C with 0.5 g of the catalyst (R1), 0.5 g catalyst for 60 min at 190 0C (R2) and with 1 g of the catalyst
for 30 min at 190 0C (R3). The yield of ketone was measured and found to increase with the temperature,
reaction time and the amount of catalyst. Table 6 shows the correlation between VAF, product of
micropore volume and Brønsted (B), Lewis (L) and (B+L) with the ketone yield. VAF(B+L) calculated by
multiplying microporosity with combination of Brønsted and Lewis acidities (B+L) showed a better
correlation with the yield of ketone for all the sets of experiments conducted at different reaction
conditions. This clearly suggests involvement of both the Brønsted and Lewis acid sites. There are several
reports on the ester to ketone transformation catalyzed by both Brønsted and Lewis acid sites [39, 40]. In
the present study the ester to ketone transformation involves acid sites which are made accessible through
micropores. Based on this, a mechanism, as shown in scheme 2 is proposed involving both the Lewis and
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Brønsted acid sites. The micropores apparently make way for the ester molecules to rearrange to ketone
where in the ester is coordinately bonded either to the Lewis acid sites or get protonated at the Brønsted
sites. Thus the pores formed due to dealumination provide access for the ester molecules to reorient
within the pore facilitating the rearrangement process to form ketone. Access to both Lewis and Brønsted
acid sites are scarcely available on the surface of the clay, as for instance on Alꢀexchange clay which
explains its low effectiveness in the ketone formation when compared with the dealuminated clays with
more pores. XRD patterns of the clays after the reaction did not show any change in the d(001) reflection
indicating no layer swelling and therefore no intercalation of reactant or product molecules into the
interlayer.Thus, volume accessibility factor, VAF of micropore provides a parameter to interpret the
mechanism of reactions that take place within the pores which possibly could find application in
micropore acidꢀbase catalyzed reactions.
The role of mesopores in the formation of ketone is of less consequence is shown by the poor correlations
of the VAFs obtained by multiplying mesopore volumes with acidities (Table 5). This can be clearly
seen in the case of Alꢀclay which shows the least ester transformation to ketone which could be attributed
to higher proportion of mesopores that do not facilitate the accessibility to acid sites. Thus the acid site
accessibility and the number of acid sites apparently determine the transformation which indicates that a
linear increase in the two favours the transformation till thermodynamic equilibrium of the reaction is
attained, whereas in cases where one of the parameters is high and the other is low, the lower parameter
limits the transformation of the ester to ketone.This suggests a limiting range of a relation linking the acid
sites and their accessibility for the rearrangement of the ester.
Limiting factor: Large micropore volumes (0.203 cm3/g) for PDSAꢀclay upon treatment with PDSA,
showed a moderate increase in the ketone formation (Table 7). Apparently, the ketone formed reaches a
maximum value, determined by the acidity factor, irrespective of the pore volume. This could be
mathematically presented as
ꢂ × ꢃꢄꢅ,
ꢂ × ꢃꢄꢅ(ꢋꢇꢌ),
0 < ꢆ < ꢆ(max) ꢇꢈꢉ 0 < ꢊ < ꢊ(ꢋꢇꢌ)
ꢆ ≥ ꢆ(max) ꢇꢈꢉ ꢊ ≥ ꢊ(max)
ꢀ = ꢁ
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Where, y = percent product formed, VAF = maximum pore volume v × acidity z , z(max) = maximum
acidity and k is a proportionality constant characteristic of the catalyst.
Conclusion:
In the present study, there is evidence for the micropore to accelerate the ester rearrangement to form
ketone. Favorable factors such as accessibility to the acid sites and number of acid sites facilitate the
ester to reorient it to transform to ketone. A new term called volume accessibility factor, VAF which is
the product of micropore volume and different types of acidities showed improved correlations with the
amount of ketone formed. Experimental results suggest that volume accessibility factor may possibly be
used to throw light on the organic transformations occurring exclusively in porous catalysts.
Acknowledgements
The authors would like to extend their thanks to the Principal and Members of Governing Council of
Bangalore Institute of Technology for the facilities provided and VTU for financial support. The authors
also thank Prof. Prashanthakumar, Department of Mathematics, BIT for assisting in deriving
mathematical equation.
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(21) Jha, A.; Garade, A.C.; Shirai, M.; Rode, C.V. Appl. Clay Science. 2013, 74, 141.
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Figures:
12
11
10
9
a
b
c
d
e
8
7
6
5
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90 100 110 120
Pore Diameter (Aο)
Fig.1 BJH plots of (a) Alꢀclay (b) EDTAꢀclay (c) CAꢀclay (d) pꢀTSAꢀclay and (e) PDSAꢀclay catalysts.
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225
200
175
150
125
100
75
d
c
b
50
a
25
0
0.0
0.2
0.4
0.6
0.8
1.0
P/Po
Fig.2BET N2 adsorption isotherm plots of (a) EDTAꢀclay (b) pꢀTSAꢀclay (c) CAꢀclay and (d) PDSAꢀclay
catalysts
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Fig.3 TEM images of montmorillonite clay (a) before treatment (b) after treatment with PDSA
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80
70
60
50
40
30
20
10
0
DA conversion
Yield of Ester
Yield of Ketone
EDTA-Clay
CA-Clay
p-TSA-Clay
Fig.4 Effect of different acid treated montmorillonite clay catalyst on the acylation of PC with DA.
Reaction condition: mole ratio PC: DA, 2:1; reaction time, 60 min; temperature 1900C; catalyst amount, 1
g.
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a
b
c
d
e
Lewis (L)
Bronsted (B)
B-L
1600
1580
1560
1540
1520
1500
1480
1460
1440
1420
1400
Wave number cm-1
Fig.5 Pyridine FTꢀIR acidity plots of (a) EDTAꢀclay (b) CAꢀclay (c) pꢀTSAꢀclay (d) PDSAꢀclay and (e)
Alꢀclay montmorillonite clays.
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Tables
Table.1 CEC, surface area, average pore diameter and micropore volume of different acid treated clays.
Acid treated CEC Surface Average Pore Micropore Mesopore
clay samples (meq/g) area (m2/g) diameter (Ǻ) volume (cm3/g) volume (cm3/g)
Untreated
EDTAꢀclay
CAꢀclay
0.83
0.64
0.42
0.72
0.71
28
80
50.3
46.9
32.2
35.3
24.0
0.011
0.017
0.031
0.026
0.203
0.067
0.073
0.159
0.094
0.140
156
135
276
pꢀTSAꢀclay
PDSAꢀclay
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Table.2 CEC, Interlayer Aluminium and ICP elemental analysis of untreated and Acid treated clay
samples
Elements
Unteated
clay (Wt%)
Amount of elements removed by acid treatment
(meq/g)
EDTAꢀclay CAꢀclay pꢀTSAꢀclay PDSAꢀclay
Al
10.14(Al2O3)
6.08 (Fe2O3)
1.69 (MgO)
0.83
0.235
0.046
0.103
0.68
0.463
0.242
0.187
0.404
0.97
0.044
0.022
0.760
1.04
0.058
0.044
0.720
Fe
Mg
CEC (calculated)
(meq/g)
CEC (experimental)
(meq/g)
Interlayer Al,
(meq/g)
0.83
ꢀ
0.64
0.22
0.42
0.36
0.72
0.70
0.71
0.71
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Table.3 Correlation between amounts of ketone formed, micropore volume and acidity factors for ester
rearrangement.
Catalysts
Micropore Ketone
Pyridine FTꢀIR acidity
(µmol/g)
Average
volume
yield
(%)
TOF(minꢀ1)
(cm3/g)
B
L
B+L
Alꢀclay
EDTAꢀclay
CAꢀclay
pꢀTSAꢀclay
0.1pꢀTSAꢀclay
0.3pꢀTSAꢀclay
0.5pꢀTSAꢀclay
Correlation factor, r
0.011
0.017
0.031
0.026
0.015
0.019
0.024
0.77
6
74
12.2
18.02
70
30
49
70
20.8
66
68
26
44
63
0.41
144
33
84.02
138
56
93
130
0.39
0.04
0.32
0.47
0.58
0.29
0.24
0.55
ꢀ
10
22
32
15
21
30
ꢀ
67
0.31
r = correlation factor between yield of ketone and other factors
TOFs were calculated for yield of ketone with B+L Pyridine FTꢀIR acidity
Reaction conditions; 10mmol of pꢀcresyldecanoate; reaction time, 30 min; temperature 1900C; catalyst
amount, 0.5 g.
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Table.4 Correlation between amounts of ketone formed with micropore volume and volume accessibility
factor.
Catalysts
Micropore Ketone
Volume Accessibility Factor
(VAF)
volume
yield
(%)
(cm3/g)
Pyridine FTꢀIR acidity
B
L
B+L
1.58
0.56
2.61
3.59
0.84
1.77
3.12
0.86
Alꢀclay
EDTAꢀclay
CAꢀclay
pꢀTSAꢀclay
0.1pꢀTSAꢀclay
0.3pꢀTSAꢀclay
0.5pꢀTSAꢀclay
Correlation factor, r
0.011
0.017
0.031
0.026
0.015
0.019
0.024
0.77
6
0.81
0.21
0.56
1.82
0.45
0.93
1.61
0.79
0.77
0.35
2.05
1.77
0.39
0.84
1.51
0.74
10
22
32
15
21
30
Reaction conditions; 10mmol of pꢀcresyldecanoate (ester); reaction time, 30 min; temperature,1900C;
catalyst amount, 0.5 g.
*r = Correlation factor between ketone formed and VAF
*VAF = (micropore volume × acidity, (eg. for Alꢀclay, VAFꢀB = 0.011 x 74 = 0.81)
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Table.5 Correlation between amounts of ketone formed with mesopore volume, total pore volume and
volume accessibility factor of mesopore volume.
Catalysts
Ketone Mesopore Total pore Volume Accessibility Factor (VAF)
yield
(%)
6
volume
(cm3/g)
0.067
0.073
0.159
0.094
0.068
0.074
0.076
0.32
volume
(cm3/g)
0.078
0.090
0.190
0.120
0.083
0.093
0.100
0.41
FTꢀIR Acidity × mesopore volume
B
L
B+L
9.65
2.41
13.36
12.97
3.81
6.88
9.88
0.57
Alꢀclay
EDTAꢀclay
CAꢀclay
pꢀTSAꢀclay
0.1pꢀTSAꢀclay
0.3pꢀTSAꢀclay
0.5pꢀTSAꢀclay
Correlation
factor, r
4.95
0.88
2.86
6.58
2.04
3.63
4.79
0.57
4.69
1.52
10.49
6.39
1.77
3.26
4.33
0.43
10
22
32
15
21
30
Reaction conditions; 10mmol of pꢀcresyldecanoate (ester); reaction time, 30 min; temperature,1900C;
catalyst amount, 0.5 g.
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Table.6 Correlation between volume accessibility factor (VAF) and yield of ketone from ester
rearrangement reaction at different reaction conditions.
Catalyst
Ketone yield (%)
VAF
Pyridine FTꢀIR Acidity
R2
11
19
36
24
31
44
46
ꢀ
R1
4
R3
9
B
L
B+L
Alꢀclay
0.81
0.21
0.56
0.45
0.93
1.61
1.82
0.83
0.74
0.79
0.77
0.35
2.04
0.39
0.84
1.51
1.77
0.74
0.77
0.74
1.58
0.56
2.60
0.84
1.77
3.12
3.59
0.88
0.85
0.86
EDTAꢀclay
CAꢀclay
8
16
28
19
24
39
41
ꢀ
16
10
14
25
27
ꢀ
0.1pꢀTSAꢀclay
0.3pꢀTSAꢀclay
0.5pꢀTSAꢀclay
pꢀTSAꢀclay
Correlation factor, r(R1)
r(R2)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
r(R3)
ꢀ
*VAF = FTIR acidity x micropore volume
Reaction conditions:
R1: 10 mmol of pꢀcresyldecanoate (ester) reaction time 30 min, temperature 160 0C, catalyst amount 0.5 g
R2: 10 mmol of pꢀcresyldecanoate (ester) reaction time 60 min, temperature 190 0C, catalyst amount 0.5 g
R3: 10 mmol of pꢀcresyldecanoate (ester) reaction time 30 min, temperature 190 0C, catalyst amount 1 g
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Table.7 Amount of ketone formed, acidity and average TOF for PDSAꢀclay catalyzed ester
rearrangement.
Catalyst
Micropore
volume
(cm3/g)
0.203
Total
acidity
(µmol/g)
140
Brønsted
acidity
(µmol/g)
72
Lewis
acidity
(µmol/g)
68
Ketone yield Average TOF
(%)
(minꢀ1)
PDSAꢀclay
48
0.76
Reaction conditions; 10mmol of pꢀcresyldecanoate; reaction time, 30 min; temperature 1900C; catalyst
amount, 0.5 g.
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Schemes
O
O
O H
O
1g, modified montꢀclay
MW, 60min, 190 °C
H
O
+
H O
+
2
Decanoic acid
p-cresyldecanoate (O-acylation)
p-Cresol
O
O H
1-(2-hydroxy-5-m ethylphenyl)decan-1-one
Scheme 1: reaction carried out using modified clay catalysts samples.
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R
R
R
R
-
H
+
O
-
O
Mont Clay
O
O
O
Mont Clay
3+
O
O
O
OH2
3+
H
H
Al
Al
H
H
Al3+
H
O
Lewis site
H2O
Bronsted site
H
OH2
R=C9H19
-
Mont Clay
-
Mont Clay
OH2
3+
Al
Al+
OH2
H
O
O
O
O
OH
O
O
H
O
+
C
R
R
H
H
R
H
O
OH
R
Scheme 2: Possible reaction mechanism for the rearrangement catalyzed by both Brønsted and Lewis acid
sites.
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Abstract Graphics:
A new term Volume Accessibility Factor (VAF), product of micropore volume and acidity correlates with
ketone formation in modified montmorillonite.
1