An efficient ring opening reaction of methyl epoxystearate promoted by synthetic acid saponite clays

Article abstract of DOI:10.1039/b900863b

The acid-catalysed reaction of methyl 9,10-epoxystearate ring opening using synthetic saponite acid clay as catalyst, has been studied for the first time. In the presence of methanol, 90% of the epoxide substrate is converted after 5 min and the main reaction product is the vicinal hydroxyether, methyl methoxyhydroxystearate, with 84% of selectivity. In the absence of alcohol the ring opening reaction proceeds slower, leading to a mixture of methyl 9- and 10-oxostearate as main products, and a 9,10-epoxystearate conversion of 66% after 1 h. The performance of acid saponite, an environmentally benign catalyst, is exceedingly higher than those of strong mineral acids, such as H ₂SO₄, widely used for this reaction.

Full text of DOI:10.1039/b900863b

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PAPER
www.rsc.org/greenchem | Green Chemistry
An efficient ring opening reaction of methyl epoxystearate promoted by
synthetic acid saponite clays†
Matteo Guidotti,*a Rinaldo Psaro,a Nicoletta Ravasio,a Maila Sgobba,a Fabio Carniato,b Chiara Bisio,*b
Giorgio Gattib and Leonardo Marcheseb
Received 15th January 2009, Accepted 23rd April 2009
First published as an Advance Article on the web 15th May 2009
DOI: 10.1039/b900863b
The acid-catalysed reaction of methyl 9,10-epoxystearate ring opening using synthetic saponite
acid clay as catalyst, has been studied for the first time. In the presence of methanol, 90% of the
epoxide substrate is converted after 5 min and the main reaction product is the vicinal
hydroxyether, methyl methoxyhydroxystearate, with 84% of selectivity. In the absence of alcohol
the ring opening reaction proceeds slower, leading to a mixture of methyl 9- and 10-oxostearate as
main products, and a 9,10-epoxystearate conversion of 66% after 1 h. The performance of acid
saponite, an environmentally benign catalyst, is exceedingly higher than those of strong mineral
acids, such as H2SO4, widely used for this reaction.
optimized the synthesis of epoxidized fatty acid methyl esters
Introduction
using titanium silica catalysts (Scheme 1, from 1 to 2).8
The diminishing fossil reserves and the awareness of global en-
In this report, we focus our attention onto the ring opening of
vironmental problems have made the exploitation of alternative
renewable resources an urgent goal.1 In this strategy, oleochem-
methyl 9,10-epoxystearate (2) in the presence of a solid catalyst
(Scheme 1). The tests were performed on the epoxy FAME
istry plays a major role in the great challenge represented by
synthesized from methyl oleate over a Ti-MCM-41 catalyst in
the chemistry of renewable raw materials as building blocks to
obtain fine chemicals and biofuels.2
The functionalisation of double bonds of unsaturated fatty
acid methyl esters (FAMEs) provides an interesting tool for
the presence of tert-butylhydroperoxide (TBHP), as previously
described.8 With this methodology, the conversion attains 95%
after 24 hours of reaction, with selectivity >95% to methyl 9,10-
epoxystearate.
the preparation of molecules containing different functional
Epoxide ring opening is typically performed under acid con-
groups. The formation of oxirane rings on double bonds is
ditions with nucleophilic molecules, such as water or alcohols.
a well-established industrial reaction,3 generally used for the
The transformation leads to diols and hydroxyethers derivatives,
preparation of epoxidised oils as additives for plastic materials.4
respectively (Scheme 1). Rearranged epoxides bear a castor
Epoxidised fatty acid methyl esters (epoxy FAMEs) are key
oil-like structure and can find applications similar to those
intermediates in the synthesis of fatty acid derivatives, since
where ricinoleic derivatives are used, namely as precursors of
by ring opening or rearrangement they can give rise to a
biopolymers, lubricants, polyurethane foams and casting resins.
broad variety of valuable compounds with functionalised alkyl
In particular, diol derivatives of FAMEs find application in
chains.5,6 In the last few years, the use of heterogeneous catalysts
the preparation of polyols for bio-based polymers9 or in the
in the epoxidation of fatty acid methyl esters have received
synthesis of fine chemicals.10 Hydroxyether derivatives can be
great attention. Large-scale processes based on heterogeneous
used as components for alternative mineral additive-free base
catalysts are desirable, because they do not need difficult
lubricants,11 for casting resins12 or as additives for biofuels.13 Up
separation and recycling steps. In addition, the use of selective
to now, strong mineral acids have been employed as catalysts
solid catalysts can lead to a global reduction in the production
for this reaction, but the set-up of an efficient heterogeneous
of wastes thanks to the formation of less undesired by-products
catalytic process could lead to more sustainable technologies.
and to simpler purification protocols.7 In previous works, we
The optimisation of a heterogeneous solid acid is still a challenge
and many reports in open and patent literature focus on this
topic.14–16
aIstituto di Scienze e Tecnologie Molecolari and IDECAT CNR Unit,
Saponite clays are layered hydrous silicates of aluminium and
Via G. Venezian 21, Milano, Italy. E-mail: m.guidotti@istm.cnr.it;
magnesium and show interesting features. They have a marked
Fax: +39 02 5031 4405; Tel: +39 02 5031 4428
acidity, generated by isomorphous substitution of Si(IV) by
Al(III) ions in tetrahedral sheets, and a good thermal stability.
There are many advantages in the use of natural acid-activated
saponite clays, thanks to their large availability and low price,
but their use for technological applications requires several
extensive purification steps, due to their extremely variable
bDipartimento di Scienze e Tecnologie Avanzate and Nano-SISTEMI
Interdisciplinary Centre, Universita` del Piemonte Orientale
“A. Avogadro”, Via Bellini 25G, 15100, Alessandria, Italy. E-mail: chiara.
bisio@mfn.unipmn.it; Fax: +39 0131 360 250; Tel: +39 0131 360 262
† Electronic supplementary information (ESI) available: Materials,
characterization techniques and tests on methyl epoxystearate from
Prileshajew process. See DOI: 10.1039/b900863b
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Scheme 1 Synthetic pathway for ring opening of methyl 9,10-epoxystearate from methyl oleate.
chemical composition and the presence of impurities. Different
simple and less time-consuming methods for the preparation of
synthetic clays with controlled chemical composition for tailored
purposes have therefore been developed.17 Here we report on the
epoxide-ring opening of a fatty acid methyl ester using synthetic
acid saponites as catalysts, and compare their performance with
both solid acids having different structure and acid strength and
a solution of highly concentrated sulfuric acid.
(see also ESI).† Zeolite H-BEA, having a Si/Al ratio of 13,
was provided by Polimeri Europa S.p.A. in its acidic form after
template removal at 550 ◦C in air. A commercial sample of
amorphous SiO2–Al2O3 (14.7 wt% Al2O3, 475 m2 g-1 surface
area; 0.79 mL g-1 pore volume; grade 135 Sigma Aldrich) and
montmorillonite K10 (Sigma Aldrich) were also tested as solid
acid catalysts and used without any further modification. H2SO4
(98%, 6 mL corresponding to 0.22 mmol H+ in the reaction
medium) was purchased from Prolabo.
The concentration of Brønsted acid sites calculated by FT-IR
of adsorbed NH3 by using the equation C = A/(er), where A is
Experimental
the integrated intensity of the FT-IR band at 1445 cm-1 (d NH4
+
The synthesis of methyl 9,10-epoxystearate (2) starting from
methyl oleate (1) was performed using Ti-MCM-41 (1.8 wt% Ti;
950 m2 g-1 surface area; 2.5 nm pore diameter), in the presence
of anhydrous tert-butylhydroperoxide (TBHP; Aldrich, 5 M
solution in decane) as oxidant.8 Methyl oleate (Aldrich, 99%)
was used as received. Ti-MCM-41 was prepared by grafting
titanocene dichloride, Ti(Cp)2Cl2 (Fluka, purum >95%) onto
MCM-41.18 Ethylacetate (Carlo Erba, RPE, 10 mL) was used
as solvent for the epoxidation. After filtration of Ti-MCM-
41 catalyst, the final solution was evaporated overnight under
vacuum.
Synthetic saponite sample Na-SAP with a gel composition
of 1SiO2 : 0.835MgO : 0.056Al2O3 : 0.056Na2O : 20H2O and a
nominal cationic exchange capacity (CEC) of 104.9 meq/100 mg
was prepared and optimized in our laboratory, as reported in
the literature.19 Part of the Na-SAP material was exchanged in
three HCl aqueous solutions of different concentrations, 0.01M,
0.1M and 1M, and have been named H-SAP (A), H-SAP (B)
and H-SAP (C), respectively19 (see also ESI).† A further series
of tests was carried out over another H-SAP material obtained
by exchanging a second batch of Na-SAP clay in a 0.01 M
hydrochloric acid solution. The results confirmed a very good
reproducibility of the synthesis procedure of the heterogeneous
catalyst.
ions), e is the extinction coefficient (e = 13.0 cm mmol-1)21 and r
is the pellet density (g cm-2).
Ring opening of epoxystearate (0.500 mL, >95%) was carried
out in a glass batch reactor (stirring rate 500 rpm) at 363 K using
toluene as solvent (puriss., Riedel de Hae¨n, 3 mL), previously
dried on molecular sieves (Siliporite, 3A). All solid catalysts
(50 mg) were pretreated at 150 ◦C for 1 h in vacuo, before
running catalytic tests. Methanol (0.100 mL) used for reactions
as in Table 1 was purchased from Fluka (>99.8%). Samples
were taken after a reaction time of 5, 10, 15, 30 min and 1 h, and
reaction products were determined by GC analysis (HP5890;
HP-5 column, 30 m ¥ 0.25 mm; temperature programme: 60 ◦C
◦
◦
0 min, 40 C min-1 to 140 ◦C 0 min, 8 C min-1 to 195 ◦C
30 min; FID or MS detectors, head pressure 160 kPa). The
products were identified by comparison with standards (2) or
by the analysis of the MS fragmentation patterns (3 to 6).
Separation of oxostearates and epoxystearate (retention times:
16.9 min and 17.2 min) was also confirmed by single ion
chromatography on the GC-MS. Standard deviations were
2% and 3% in conversion and selectivity values, respectively.
n-Decane (Janssen Chimica, 99.8%) was used as internal stan-
dard.
A conventional, montmorillonite K10 clay,14,15 was tested
under the same conditions and used as a reference material.
This clay, from natural origin, shows a lower initial rate and a
longer time of reaction to reach the complete conversion of
epoxystearate with respect to the synthetic H-SAP (A) clay.
An aluminium-containing SBA-15 mesoporous silica was pre-
pared with a Si/Al ratio of 20 following the procedure reported
in the literature.20 Triblock poly(ethylene oxide)–poly(propylene
oxide)–poly(ethylene oxide) (P123), was purchased from Aldrich
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However, a direct comparison between the catalytic performance
of synthetic saponite and natural montmorillonite is difficult
because of their different chemical composition, structure and
morphology. This comparison is beyond the scope of the present
manuscript.
Due to the presence of some tert-butanol in the batch of
methyl epoxystearate synthesized using TBHP as oxidant, in
all reactions of Table 1 and Table 2 tert-butoxyhydroxystearate
(1–4% yield) was always detected as side-product in epoxide
ring opening. Methyl 9,10-dihydroxystearate was a side-product
obtained in 1–2% yield in all the presented tests. No detectable
amounts of oligomerized or polymerized species have been
observed in solution under the reaction conditions used here.
exchanged with more concentrated acid solutions (0.1 and 1 M
HCl solutions) are characterised by an increasing amount of
amorphous phase, as indicated by the broad signal in the
20–30 2q degrees range in the XRD patterns (Fig. 1A, b–c). This
effect is due to a progressive collapse of the saponite framework,
leading to the formation of an amorphous silica phase.19,22
The concentration of the catalyst acid sites was estimated by
using FT-IR spectroscopy of adsorbed NH3 at room tempera-
ture. IR spectra of NH3 adsorbed on all samples are reported in
Fig. 1B.
The IR spectrum of H-SAP (A) (Fig. 1B, a) in the 1800–
1300 cm-1 range is dominated by an intense band at 1445 cm-1
with a shoulder at 1505 cm-1, accompanied by weak absorptions
at 1675 and 1615 cm-1. The bands at 1445 and 1505 cm-1 are
+
attributed to an asymmetric bending of NH4 ions, while the
Results and discussion
band at 1675 cm-1 is related to the symmetric bending mode
+
of NH4 . This suggests that Brønsted acid sites strong enough
Preparation and characterization of saponite catalysts
to give a proton transfer to ammonia molecules are present on
the saponite surface upon treatment under acid conditions, as
already reported in ref. 19. The absorption at ca. 1615 cm-1 can
be assigned to the bending mode of ammonia adsorbed on Lewis
acid centers and/or interacting with silanol groups.23
Fig. 1B shows that the intensity of the bands related to
ammonium ions decreases progressively as the concentration
of the HCl solution used for the ion exchange increases. This
behaviour indicates that the acid treatment in 0.1 and 1 M HCl
solutions leads to a modification of the surface acid sites of the
sample. The band at 1555 cm-1, especially observed for samples
treated in more acidic media (0.1 and 1 M HCl solutions), are
due to Si-NH2 species formed by NH3 reaction with distorted
siloxane bridges, which can be formed during the activation
treatment by condensation of vicinal silanols.24
Three different H-exchanged saponites (H-SAP (A), H-SAP (B)
and H-SAP (C)) were obtained from one batch of parent Na-
containing synthetic saponite (Na-SAP) by cationic exchange
with an aqueous solution of 0.01, 0.1 and 1.0 M hydrochloric
acid, respectively.19
While the ionic exchange under mild conditions does not alter
significantly the structure of saponite (Fig. 1A, curve a), samples
The total concentration of Brønsted acid sites can be esti-
mated from the IR data of adsorbed NH3 using the extinction
coefficient reported in the literature.21 It was calculated that
H-SAP (A) contains ca. 0.32 mmol g-1 of Brønsted surface acid
sites, whereas in H-SAP (B) and H-SAP (C) the amount of these
sites is reduced to 0.16 and 0.06 mmol g-1, respectively (Table 1).
The use of CO as FTIR probe molecule allowed us to have
a scaling of the acidity of surface sites of the different saponite
samples (Fig. 2).
The IR data indicated that the activation under mild acid
conditions (H-SAP (A)) leads to the formation of Brønsted
sites whose acidity is comparable to that of the most acid
Table 1 Transformation of methyl 9,10-epoxystearate over saponite
catalysts in the presence of methanola
Sd (%) 5 Se (%) 3
Entry Catalyst
[H+]b/mmol g-1 Cc (%) and 6
and 4
1
2
3
4
H-SAP(A)
H-SAP(B)
H-SAP(C)
Na-SAP
0.32
0.16
0.06
n.d.
98
53
22
21
14
34
27
35
84
61
50
48
Fig. 1 A: XRD pattern of (a) H-SAP (A), b) H-SAP (B) and (c) H-SAP
(C). B: IR spectra of NH3 adsorbed on (a) H-SAP (A), (b) H-SAP
(B) and (c) H-SAP (C). Spectra collected upon admission of NH3
(90 mbar) and subsequent outgassing at r.t., are reported after sub-
traction of the spectrum of bare samples, i.e. prior NH3 adsorption,
used as reference.
a Catalyst (50 mg) pre-treated at 150 ◦C for 1 h in air; Me-epoxystearate
(500 mL); methanol (100 mL); toluene (3 mL); 85 ◦C. b Concentration
of Brønsted acid sites (see Experimental). c Conversion after 1 h.
d Selectivity to 10-oxostearate and 9-oxostearate (5 and 6) at 1 h.
e Selectivity to methoxyhydroxystearate (3 and 4) at 1 h.
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Table 2 Transformation of methyl 9,10-epoxystearate using different
acid catalysts in the presence of methanola
Sc (%) 5
[H+]/mmol g-1 Cb (%) and 6
Sd (%) 3
and 4
Entry Catalyst
1
5
6
7
8
9
H-SAP(A)
SiO2-Al2O3 0.66
H-BEA 0.77
Al-SBA-15 0.66
0.32
>98
60
58
58
26
14
—
3
—
59
—
84
85
85
88
39
—
e
H2SO4
—
—
No catalyst
>2
a Solid catalyst (50 mg) pre-treated at 150 ◦C for 1 h in air; Me-
epoxystearate (500 mL); methanol (100 mL); toluene (3 mL); 85 ◦C.
b Conversion after 1 h. c Selectivity to 10-oxostearate and 9-oxostearate
(5 and 6) at 1 h. d Selectivity to methoxyhydroxystearate (3 and 4) at 1 h.
e 6 mL H2SO4 98% corresponding to ca. 0.22 mmol H+.
Fig. 2 IR spectra of CO adsorbed at 100 K (60 mbar) on (a) H-SAP
(A), (b) H-SAP (B) and (c) H-SAP-(C) samples. Spectra are reported in
the ranges 3800–3000 cm-1 (frame A) and 2300–2000 cm-1 (frame B).
A fraction of oxostearates 5 and 6 was always observed with a
selectivity of ca. 15%.
zeolites, accompanied with the presence of sites with medium
acidity (Al–OH), in agreement with the literature.19 When
the samples are treated under more severe acid conditions
(H-SAP (B) and H-SAP (C)) the distribution of surface OH
groups appeared significantly modified: a progressive decreasing
of strong Brønsted acid sites was observed, in fact, as the
concentration of HCl solution increases, while Al–OH sites
with medium acidity were formed. The different acid behaviour
of H-SAP materials can be explained on the basis of the
structural modification occurring to the saponite framework
upon exchange under different acid conditions (Fig. 1A). It
is worth pointing out that the destructuration phenomena are
also accompanied by progressive dealumination of the saponite
framework.19 The Si/Al ratio of H-SAP samples indeed passes
from about 11 for H-SAP (A) to 71 for the sample treated under
the most acid conditions (H-SAP (C)).
The data obtained over H-SAP(A) have been compared with
those recorded over a series of conventional and widely-used
solid catalysts (Table 2), namely a commercial silica–alumina
mixed oxide, SiO2–Al2O3 (entry 5), a protonic beta zeolite
(H-BEA, entry 6) and a mesoporous ordered aluminosilicate
Al-SBA-15 prepared in our laboratory (entry 7). In Table 2 the
results obtained in the presence of H2SO4 (entry 8), used as
industrial catalyst for this reaction, are also shown.
Entries 5, 6 and 7 (Table 2) show that the three reference solid
catalysts all give similar results and have a poorer performance
than H-SAP (A). In particular, Fig. 3 shows the most relevant
differences in epoxide conversion throughout the reaction time
for a selection of catalysts. 90% of the epoxide is already
converted over H-SAP (A) after 5 minutes. It is worth noting
that H-SAP (A) shows results that are outstandingly higher
than those obtained in the presence of H2SO4 under comparable
conditions. As a matter of fact, under the conditions and with
the methanol to epoxy FAME ratio here tested, H2SO4 leads to
conversion values as low as those obtained on H-SAP (B) and
H-SAP (C) (Table 2), but with a poorer selectivity to vicinal
hydroxyethers 3 and 4. In the presence of an amount of H+
species that is ca. 14 times as high as the amount introduced with
H-SAP (A) (i.e. 0.22 mmol H+ for 6 mL H2SO4 vs. 0.016 mmol
Transformation of methyl epoxystearate
The catalytic ring-opening of methyl 9,10-epoxystearate 2 was
studied in the presence of methanol over H- and Na-containing
saponites (Table 1, entries 1–4). H-SAP (A) shows the best
catalytic activity, leading to almost complete conversion of the
epoxide after 1 hour. This is in accordance with the results
observed by FT-IR spectroscopy of adsorbed NH3 and CO
probe molecules: cationic exchange with H+ species under mild
conditions (0.01 M aq. HCl) maximizes the number of strong
Brønsted acid sites. H-SAP (B) and H-SAP (C), prepared
under strong acid conditions show a lower catalytic activity and
H-SAP (C) gives almost the same conversion value after 1 hour
as Na-SAP itself. Such loss in catalytic activity is strictly related
to the decrease of Brønsted acid sites in the saponite clays
(Table 1), as described above (Fig. 1B and Table 1, column 3).
The reaction products found under the tested conditions are
shown in Scheme 1 and selectivities to these compounds are
presented in Table 1. The main product was in all cases methyl
methoxyhydroxystearate (3 and 4). 10-Oxostearate (5) and
9-oxostearate (6) products were obtained by isomerisation of
the epoxide ring, catalysed by Brønsted acid sites.
Attempts to force the production of 3 and 4 by increasing the
amount of methanol in the reaction mixture (5 : 1 mol mol-1
stoichiometric ratio CH3OH : epoxy FAME) were unsuccessful.
Fig. 3 Profile of methyl 9,10-epoxystearate conversion vs. reaction time
for a selection of catalysts in the presence of methanol. H-SAP(A) (᭜),
H-SAP(B) (ꢀ), H-SAP(C) (ꢀ), H-BEA (᭹) and H2SO4 (ꢀ).
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H+ for 50 mg H-SAP (A)), methyl oxostearate (mixture of 9- and
10-isomers) is the product obtained preferentially.
Table 3 Transformation of methyl 9,10-epoxystearate using different
catalysts in the absence of methanola
The layered material prepared under mild acid conditions
(H-SAP (A)) displays Brønsted acid sites which are strong and
accessible at the same time, whereas these two features are
not present together in the other solid catalysts employed in
this work (Table 2). As derived by FT-IR spectroscopy of CO
adsorbed at 100 K, H-BEA zeolite shows Brønsted acid sites
whose acidity is lower than that of H-SAP(A), the downward
shift of the OH stretching vibration upon CO interaction
(DnOH) being around 300 and 340 cm-1, respectively.25,19 The acid
strength of Brønsted acid sites of H-SAP (A) is similar to that
observed in most acid zeolites (see for instance H-Mordenite26).
NH3 adsorption indicates that H-BEA zeolite contains a
larger number of Brønsted acid sites with respect to H-SAP(A)
material (Table 2, entry 6). However, the microporous nature
of zeolitic materials limits the accessibility of the epoxystearate
molecules to the catalytic sites. This justifies the lower catalytic
activity of H-BEA with respect to H-SAP (A). On the other
hand, the mesoporous Al-SBA-15 is characterized by large pores
(around 8 nm) and is able to easily accommodate epoxystearate
molecules. Nevertheless, even though Al-SBA-15 contains an
amount of Brønsted acid sites that is almost twice as high than
those of H-SAP (A) (Table 2, entry 7), the weak nature of its
surface acid sites27 (the downward shift of the OH stretching
vibration upon CO interaction at 100 K (DnOH) being around
150–200 cm-1), in comparison to H-SAP (A) and protonic
zeolites, limits its catalytic activity.
Entry
Catalyst
Cb (%)
Sc (%) 5 and 6
10
11
12
13
H-SAP(A)
SiO2–Al2O3
66
12
50
<2
87
50
70
—
d
H2SO4
no catalyst
a Catalyst (50 mg) pre-treated at 150 ◦C for 1 h in air; Me-epoxystearate
(500 mL); no alcohol; toluene (3 mL), 85 ◦C. b Conversion after 1 h.
c Selectivity to 10-oxostearate and 9-oxostearate (5 and 6) at 1 h. d 6 mL
H2SO4 98%.
of epoxide is slower, but, also in this case, H-SAP (A) is the best
catalyst, with a 9,10-epoxystearate conversion of 66% (entry 10).
Conclusions
Synthetic saponite clays proved to be interesting heterogeneous
acid catalysts and a possible alternative to strong mineral acids
in the ring-opening of methyl 9,10-epoxystearate. In particular,
in the presence of methanol, 90% of methyl epoxystearate
conversion is obtained in only 5 minutes and good selectivities
to vicinal hydroxyethers are obtained from epoxidised FAMEs.
A combination of spectroscopic and catalytic results show that
the conversion is strictly related to both the concentration and
strength of accessible Brønsted acid sites on saponite materials.
The catalytic sites of protonic saponites have an acid strength
comparable to that of the most acidic zeolites, together with
a high accessibility, similar to that of mesoporous materials.
Such features pave the way to the use of these strongly acid
materials in other acid-catalysed transformations of bulky and
richly functionalised molecules, such as those used in fine and
specialty chemistry.
The role of Brønsted acid site of saponites during the ring-
opening reaction is evident in Fig. 4, where a clear dependence
of the conversion (both after 5 and 60 min) on the concentration
of protonic sites is reported. Analogously, a diminution of the
amount of acid sites in the reaction mixture, by using, for
instance, a lower amount of catalyst, implies a proportional
diminution in the epoxide conversion.
Acknowledgements
The authors acknowledge financial support from MIUR (PRIN
Project “Progettazione e sintesi di Silsesquiossani Poliedrici
Multifunzionali per Compositi Polimerici Innovativi Termica-
mente Stabili”) and from IDECAT European NoE.
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Fig. 4 Dependence of activity on concentration of H+ acid sites.
Conversion after 5 min (᭜) and 60 min (ꢀ). Reaction conditions as
in Table 1; entry 1, 2 and 3.
Acid-catalysed rearrangement of epoxystearate in the absence
of methanol gives a mixture of methyl 10- and 9-oxostearate
(5 and 6) as the main product. This reaction was performed
with H-SAP (A) (Table 3, entry 10), SiO2–Al2O3 (entry 11) and
H2SO4 (entry 12). In the absence of alcohol, the rearrangement
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