Preparation of functionalized castor oil derivatives with tunable physical properties using heterogeneous acid and base catalysts

Article abstract of DOI:10.1039/c5ra04154f

Functionalized castor oil derivatives namely ring-opened glyceryl ricinoleates, epoxy alkyl ricinoleates, and ring-opened alkyl ricinoleates were successfully prepared through two reaction chemistry viz., ring opening and transesterification using epoxidized castor oil (ECO) as a raw material. Amberlyst 15, the most active catalyst among several acid catalysts screened, showed a maximum conversion of 82% for ring opening of ECO with methanol. In another chemistry, 91% yield of epoxy methyl ricinoleate was achieved through transesterification of ECO with methanol using CaAl-layered double hydroxide (LDH) derived oxides as base catalyst. The scope is extendable to many nucleophiles and alcohols for both reactions respectively. Ring-opened alkyl ricinoleates were prepared both in two-pot and one-pot reactions using both acid and base catalysts together. The catalysts were recyclable and were successfully scaled at 25 g. The physical properties of these castor-based derivatives bestow the opportunity to design tailor-made materials suiting industrial needs.

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Preparation of functionalized castor oil derivatives
with tunable physical properties using heterogeneous
acid and base catalysts
Cite this: DOI: 10.1039/x0xx00000x
ab
ab
Sivashunmugam Sankaranarayanan and Kannan Srinivasan*
Received 00th March 2015,
Accepted 00th April 2015
Functionalized castor oil derivatives namely ring-opened glyceryl ricinoleates, epoxy alkyl
ricinoleates, and ring-opened alkyl ricinoleates were successfully prepared through two
reaction chemistry viz., ring opening and transesterification using epoxidized castor oil (ECO)
as a raw material. Amberlyst 15, the most active catalyst among several acid catalysts
screened, showed a maximum conversion of 82% for ring opening of ECO with methanol. In
DOI: 10.1039/x0xx00000x
www.rsc.org/
another chemistry,
91%
yield of
epoxy methyl ricinoleate was achieved through
transesterification of ECO with methanol using CaAl-layered double hydroxide (LDH) derived
oxides as base catalyst. The scope is extendable to many nucleophiles and alcohols for both
reactions respectively. Ring-opened alkyl ricinoleates were prepared both in two-pot and one-
pot using both acid and base catalysts together. The catalysts were recyclable and were
successfully scaled at 25 g. The physical properties of these castor-based derivatives bestow
opportunity to design tailor-make materials suiting industrial needs.
industrial processes for making various chemicals besides
being used for centuries for medicinal purposes. Castor oil,
being highly stable (longer shelf life) and relatively
9
Introduction
Due to limited availability, demand, vacillating cost,
geopolitical reasons and environmental concerns associated
with petroleum products, biomass has gained interest in last
two decades as an alternate source for the production of bio-
inexpensive, coupled with their unique functionality make it
10
superior over many other vegetable oils. In world, ~1.2
million tons of castor oil are produced every year and India
occupies the top place for castor production with nearly
1
based products. The term bio-based products include fuels
11
~
60% of overall production followed by China and Brazil.
as well as chemicals derived from renewable carbon sources
which are eco-friendly. Vegetable oils, one of the large-
segment category of such biomass sources, have fatty acid
triglycerides in their structure and are effectively utilized for
the production of diverse oleochemicals. Presence of
unsaturated centres in vegetable oils and their fatty
derivatives causes low cold flow and lesser oxidative4
stability that limits their use in commercial applications.
Though hydrogenation is the commonly explored
commercial option, epoxidation of double bond followed by
Presence of >85% of ricinoleic acid (a functionalized fatty
acid which has ester linkage, hydroxyl group and
unsaturated centre) makes castor oil an important raw
2
12
material for various commercial applications. Generally in
3
vegetable oils, reactions can occur at ester region (or) fatty
region and functionalization in one region without affecting
the other will leads to molecules with entirely different
physical properties.
Epoxides of oils and fatty derivatives are valuable
5
6
ring opening with alcohols (or) acids are some of the intermediates for the production of several chemicals that
1
3
interesting and potential ways to achieve the desired have many industrial applications. Owing to the presence
physical properties. Further, functionalized oil/fatty of highly active oxirane ring, fatty epoxides can easily
derivatives have huge market value and are the best undergo various chemical transformations.5, 14 The products
1
5
replacement for petroleum products which can be utilized derived from fatty epoxides are useful in bioplasticizers,
1
4a
16
either directly (or) as potential intermediate for making surfactants
derivatised chemicals thanks to their functional flexibility additives,
and
coatings,
polymers,
lubricant
1
4g
17
14d, 14e
hydraulic and dielectric fluids,
as
7
and reactivity.
antifriction/antioxidant and anti-wear in automotives
1
4j
and as lubricants. Ring opening of epoxidized oils with
In recent years, non-edible and used cooking oils have
alcohols is an interesting pathway to produce polyols that
earned impetus for producing energy8 molecules (or)
chemicals for averting food vs fuel issues. Castor oil, one of
such promising non-edible oils, is effeciently used in many
15b
are used as starting materials for polyurethane.
Besides,
thus obtained hydroxyl ethers can be further processed
18
chemically into lubricants as well.
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denoted as M(II)M(III)x-CLDH700 where M(II) & M(III)
represents divalent and trivalent cations respectively and „x‟ is
the molar ratio of M(II)/M(III). Epoxidized castor oil (ECO;
Molecular weight ~980) was provided by Jayant Agro Organics
Ltd., Mumbai, India.
Characterization
+
Acidic strength of the materials (meq H /g) was determined by
acid-base titration method. In a flask, 50 mg of material was
taken with 5 ml of water and to that 5 ml of 0.1M NaOH
solution was added. The contents in the flask were stirred well
for 15 min. 2 drops of phenolphthalein indicator was added and
then titrated against 0.1M HCl solution. Powder X-ray
Scheme 1 Preparation of functionalized castor oil derivatives
(
mainly represented as methyl derivatives).
Transesterification of vegetable oils with alcohol is a known diffraction (PXRD) of the materials was carried out on a
method for the preparation of fatty acid alkyl esters (commonly Rigaku Miniflex II system using Cu Kα radiation. The
1
9
called biodiesel) and the same process can be extended for operating voltage and current were 30 kV and 15 mA,
epoxidized oils and the resulting epoxidized fatty acid alkyl respectively. The step size was 0.04˚ with a step time of 0.2 s.
esters are useful as surfactants, fuel additives and in other
1
2
0
H NMR analysis was done using Bruker Avance DPX 200
instrument with an operating frequency of 200 MHz. FT-IR
spectra were recorded in a Perkin-Elmer Spectrum-GX
instrument using KBr pellets; 100 scans were recorded with a
industrial products. Given the abundant availability of castor
oil in India besides steady growth and considering the industrial
application potential of functionalized derivatives for oils, it is
prudent to study the value addition of castor oil or its
derivative. In recent years, heterogeneous catalysts are
preferred for industrial processes due to their well-known
advantages over homogeneous catalysts. To our best
knowledge, no report is available for the ring opening of
epoxidized castor oil as well as transesterification of epoxidized
castor oil (including for epoxidized vegetable oils) using
heterogeneous catalysts. In this work, we report the preparation
of functionalized castor oil derivatives namely ring-opened
glyceryl ricinoleates and epoxy alkyl ricinoleates with tunable
physical properties through two reaction chemistry using
epoxidized castor oil (ECO) as raw material using
heterogeneous acid and base catalysts. Furthermore, ring-
opened alkyl ricinoleates (functionalized in both regions) is also
prepared from ECO in a two-pot as well as one-pot reactions
-
1
nominal resolution of 4 cm , which were accumulated and
averaged to improve the signal-to-noise ratio. For diffuse
reflectance
measurements, neat samples were used using reflectance
accessory.
infra-red
Fourier-transformed
(DRIFT)
ESI-MS studies were carried out in Waters 2487 Q-TOF
Micro by dissolving samples in acetonitrile and diluted with
methanol. Viscosity studies were carried out using Brookfield
Viscometer (Model –LVOV-II+P) by keeping the samples at
different rpm. Oxidative stability studies were done in Metrohm
8
73 Biodiesel Rancimat.
Ring opening reaction
(
Scheme 1).
In a 25 ml round bottom flask, 500 mg of epoxidized castor oil
(
ECO) was taken along with 3 ml of toluene as solvent. To that,
known amount of methanol and catalyst were added and the
flask was kept at different temperatures in a preheated oil bath.
The contents in the flask were stirred vigorously for desired
reaction time. The reaction mixture was then allowed to cool
and the product mixture was collected by simple decantation (in
particular for resin based catalysts). Collected mixture was
subjected to rotary evaporation under reduced pressure to
Experimental
Materials
Commercial resin based materials such as Amberlite IR 120,
Amberlite 200 C, Amberlite IRA 67 and Amberlite IRA 402Cl
were purchased from sd fine chemicals limited, Mumbai, India.
Amberlyst 15 was purchased from Lancaster while Amberlyst
A 26 (OH) and zinc triflate were purchased from Sigma-
Aldrich. Sulphated zirconia was gifted from Dr. Beena Tyagi‟s
research group, CSIR-CSMCRI, Bhavnagar.
remove unreacted methanol and solvent. Finally, solvent free
1
sample (15-25 µL) was analyzed by H NMR using CDCl as
3
solvent. Duplicate experiments were conducted and the errors
in the values are ± 3%. Conversion is calculated based on the
decrease in the peak area of the oxirane ring protons of
reactants and products (by keeping the terminal -CH protons as
3
internal standard in both the samples). Ring opening of epoxy
methyl ricinoleate, epoxy ethyl linoleate and 1,2-epoxy
hexadecane were also performed similar to the above
procedure.
MgAl-LDH and CaAl-LDH were prepared by co-
precipitation under low supersaturation as reported earlier.
The as-synthesized LDHs were calcined at 700 °C in static air
in an electric furnace for 5 h and the calcined samples were
2
1
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Transesterification reaction
The catalyst was then washed well with methanol and kept in
an oven for drying at 110 °C for 4 h. In the case of
transesterification reaction, the catalyst was recovered by G3
crucible separation, washed well with methanol and kept in an
oven at 110 °C. In another experiment with an endeavor to
understand the effect of re-activation, the recovered catalyst
was recalcined at 700 °C for 5 h in static air atmosphere (as
done for as-synthesized LDH) and tested for the reaction.
In a 25 ml round bottom flask, 5 g of ECO and 3 g of methanol
(
methanol:oil = ~ 18:1 molar ratio) was taken and to that
exactly 250 mg of CaAl2-CLDH700 (mixed oxides derived by
calcining CaAl2-LDH at 700 °C; 5 wt.% w.r.t. ECO) was
added. The flask was placed in a 65 °C preheated oil bath and
contents in the flask were stirred vigorously for 5 h. After the
reaction, the catalyst was separated from reaction mixture by
simple centrifugation and product mixture was collected. No
glycerol layer was observed; water was added to this mixture to
remove glycerol. Organic layer was extracted with hexane and
subjected for rotary evaporation to remove unreacted methanol
Results and discussion
Ring opening reaction with methanol
and hexane. Finally, solvent free sample (15-25 µL) was For the initial screening, various catalysts were chosen for the
1
analyzed by H NMR using CDCl3 as solvent. Similar ring opening of ECO with methanol (Scheme 1; Reaction A) as
procedure was extended (except water addition step) for the nucleophile at 60 °C for 4 h and the results are given in Table 1.
transesterification of EMR with higher alcohols namely Thermal heating of ECO (blank reaction) in toluene at 60 °C in
ethanol, n-propanol and iso-propanol using a alcohol:EMR the absence of catalyst showed only 2% conversion of oxirane
molar ratio of 6:1.
ring suggests the thermal stability of ECO and also supports the
authenticity of the methodology employed for calculating
conversion using H NMR spectroscopy. Reaction of ECO with
methanol in toluene in the absence of catalyst gave only 2%
conversion suggests the necessity of the catalyst for the ring
opening reaction under the conditions studied. Resin based
acidic and basic catalysts were studied that gave conversion in
the range of 9-18% except for Amberlyst 15 which gave 34%
conversion.
Yield of epoxy methyl ricinoleate (EMR) was calculated
based on the formation of new peak around 3.7 ppm for -OCH3
1
1
protons in H NMR by keeping methylene protons as internal
standard. Same procedure was adopted for the
transesterification of castor oil with methanol to obtain methyl
ricinoleate with methanol:oil molar ratio of 10:1.
In the case of epoxy alkyl ricinoleates, conversion was
calculated based on the decrease in the peak area at 3.7 ppm
and the yield was computed assuming the products formed were
only epoxy alkyl ricinoleates. The formation of transesterified
products was ascertained by the appearance of characteristic
Though Nafion is a well-known acid catalyst, gave lesser
conversion (15%) might be due to its rigid nature. Further, as
Nafion was used as „as-received‟ beads for the catalytic studies,
there is likely that the reactant molecules do not have easy
accessibility to the catalytically active sites. Solid base MgAl3-
LDH catalyst gave 12% conversion which is comparatively
lesser than Amberlyst 15. When comparing the results of
Amberlyst A 26 (OH) and MgAl3-LDH with Amberlyst 15,
one could infer that the acidity of the catalyst plays an
important role in the conversion of oxirane ring. Under the
reaction condition studied, homogeneous zinc triflate catalyst
gave 53% conversion which is slightly higher than the
1
peak at 4.2-4.1 ppm in H NMR that corresponds to -OCH2
protons in the alkyl ricinoleates.
One-pot reaction
In a 50 ml round bottom flask, 2 g of ECO and 12 g of
methanol were taken along with 10 ml of toluene as solvent. To
that exactly 200 mg of Amberlyst 15 (10 wt.% w.r.t. ECO) and
1
00 mg of CaAl2-CLDH700 (5 wt.% w.r.t. ECO) were taken
1
heterogeneous Amberlyst 15 catalyst (comparison of H NMR
together. The flask was placed in a 105 °C preheated oil bath
and contents in the flask were stirred vigorously for 5 h. The
catalyst was then separated from the reaction mixture by simple
centrifugation and the product mixture was collected. No
glycerol layer was observed; water was added to this mixture to
remove the glycerol. Organic layer was extracted with hexane
and subjected for rotary evaporation to remove unreacted
spectrum of ECO along with the reaction product mixture are
given in ESI† Fig. S1). All the resin based materials have
+
acidity in the range of 0.5-1 meq H /g whereas Amberlyst 15
+
has 4.9 meq H /g. Sulphonic acid is the main functional group
in the resin based catalysts and it was found that compared to
other resin catalysts/sulphated zirconia, Amberlyst 15 has
higher sulphur content that supported well for its higher acidity.
These results clearly show that higher acidity of Amberlyst 15
is the probable reason for the higher conversion of ECO.
Hence, Amberlyst 15 was selected as catalyst for the ring
opening of ECO with methanol for further studies.
methanol, toluene and hexane. Finally, solvent free sample (15-
1
2
5 µL) was analyzed by H NMR using CDCl as solvent.
3
Conversion of oxirane ring and yield of transesterified products
were calculated by the above mentioned calculation procedures.
Catalyst reusability studies
Parametric variation studies
To assess the reusability of the catalyst, the Amberlyst 15 was
separated from the reaction mixture by filtration. It was then
washed with toluene to remove the oily nature of the catalyst.
After the screening of catalysts, several reaction parameters
such as methanol:ECO molar ratio, catalyst wt.%, time,
temperature and solvent were varied to improve the conversion
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Table 1 Preliminary catalyst screening and catalyst characterization for the ring opening of ECO
a
c
Catalyst
Conversion of oxirane
ring (%)
Acidity
(meq H /g)
Sulphur content (%)
+
b
d
Blank reaction
2
-
-
-
e
Nil
2
-
Amberlite IR 120
Amberlite 200 C
Amberlyst 15
14
11
34
18
16
9
1
8.5
11
12.9
0.2
0.2
0
0.6
4.9
0.8
0.9
0
Amberlite IRA 67
Amberlite IRA-402 Cl
Amberlyst A-26 (OH)
Sulphated zirconia
Nafion
22
15
12
53
2.4
-
3.9
-
MgAl3-LDH
0.6
5.9
-
f
Zinc triflate
-
a
b
ECO = 0.5 g, Methanol:ECO = ~60:1 molar ratio, Toluene = 3 ml, Catalyst = 5 wt.% w.r.t. ECO, Temp. = 60 °C, Time = 4 h; Acid-
c
d
e
base titration; Based on CHNS analysis; Reaction of ECO in Toluene in the absence of catalyst; Reaction of ECO and methanol in
toluene in the absence of catalyst; Homogeneous reaction.
f
(
(ESI† Fig. S4; although the sample is nearly amorphous
(
ESI† Fig. S2; A-F). A maximum oxirane conversion of 82%
irrespective of the physical state – bead or powdered) and
DRIFT measurements (ESI† Fig. S5) showed an increase in the
intensity of –OH and –S-Ostr vibration bands for the crushed
sample suggest crushing might have increased the number of
available sites and thus improved the conversion.
was achieved with methanol:ECO molar ratio of ~180:1, 10
wt.% catalyst at 105 °C in 4 h using toluene as solvent. FT-IR
spectra of ECO and methoxylated castor polyol (MCP; ring-
opened glyceryl ricinoleate) are given in ESI† Fig. S3. The
bands present around 840 and 1250 cm for ring C-O-C
stretching band in ECO were almost disappeared for the ring-
opened MCP confirms the conversion of oxirane ring. The band
appeared at 1220 cm in MCP represents the C-O vibration of
ether indicates the product formation. In both ECO and MCP,
the band appeared at 1750 cm corresponds to the ester
carbonyl of glyceride moiety suggests the retention of glyceryl
moiety. The bands appeared around 3500 cm are attributed
to OH vibration present in both ECO and MCP. Though,
maximum conversion was achieved at 105 °C, some of the
studies were carried out at 60 °C to discern more scientific
information at which 70% conversion was ECO was observed.
-
1
Methanol used in the studies has (≤0.2%) water content and
is well-known that epoxides (also castor oil due to the presence
of -OH) are sensitive to react with moisture. To find out the
role of water/moisture, reaction was performed with dry
methanol that showed 81% conversion confirms its detrimental
role on the conversion. To further confirm, studies were
extended in presence of different concentrations of water
-
1
str
-
1
-1
(
keeping the total nucleophile amount constant; Reaction
conditions: ECO = 0.5 g, Methanol and water = 3 g, Toluene =
ml, Catalyst = 10 wt.% w.r.t. ECO, Temp. = 60 °C, Time = 4
3
h). Reaction without water gave 70% conversion while it
decreased to 24 and 16% when 1 g (33 wt.%) and 2 g (66 wt.%)
of water present in the system respectively. Reaction only with
water gave 6% conversion suggests diol formation is less
favourable than hydroxyl ether under the conditions studied. In
addition, the presence of -OH group in ricinoleate may interfere
strongly in the case of water as nucleophile and in turn result
poorer conversion.
Activity of Amberlyst 15 in water
Interestingly, the conversion of ECO (70%) increased to 76 and
7
h) and by powdering the catalyst respectively suggests the
influence of physical state of the material on the conversion.
PXRD patterns showed a subtle increase in the crystallinity
4% upon pre-treating the catalyst in reactant methanol (for 3
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Table 2 Ring opening ECO with different nucleophiles
a
1
Nucleophile
Conversion of oxirane ring
Characteristic proton peaks in H NMR
b
(
%)
(δ in ppm)
Methanol
Ethanol
82
60
51
47
49
69
39
24
4
3.5-3.4 (t, -OCH ;ether)
3
3.8-3.6 (q, -CH ;ether)
2
n-propanol
Iso-propanol
3.7-3.5 (q, -CH ;ether)
2
4.0-3.9 (q, -CH ;next to -OH)
3.66-3.35 (s, -OH ;diol)
c
Water
Acetic anhydride
Acetone
3.4-3.5 (t, -OCH ;ester)
3
1.4 (s, -CH ;ketal)
3
Diethyl amine
2.7-2.8 (q, -CH ;amine)
2
Sodium azide/water
-
a
ECO = 0.5 g, Nucleophile: ECO = ~180:1 molar ratio, Toluene = 5 ml, Catalyst = 10 wt.% w.r.t. ECO, Temp. = 105 °C, Time = 4 h;
Supports the yield of products. White gel like material.
b
c
catalyst, 60 °C, 4 h) ECO gave 34% conversion whereas the
same for EMR was 76% (ESI† Fig. S8). This shows that
compared to viscous ECO, its corresponding methyl ricinoleate
derivative can easily undergo epoxide ring opening probably
due to the hindrance offered by glyceryl moiety present in
Leaching and hot filtration studies over Amberlyst 15
Calculated amount of water was taken along with catalyst (pH of the
medium: 4.6) and stirred well at 60 °C for 4 h. Collected water (pH
=
2.6) was used for the ring opening of ECO withmethanol at 60 °C
for 4 h in the absence of catalyst which showed 22% conversion
similar to when the reaction was carried out in presence of catalyst
with same wt. % of water in methanol; vide supra) while the
recovered catalyst (dried) showed 45% conversion. This
former. Under identical conditions (Epoxide
= 0.5 g,
Methanol:substrate = ~45:1 molar ratio, Toluene = 3 ml,
Catalyst = 10 wt.% w.r.t. substrate, Temp. = 60 °C, Time = 4
h), EMR, epoxidized ethyl linoleate (EEL) and 1,2-epoxy
hexadecane showed 39, 64 and 75% conversion of oxirane ring
respectively. These results suggest simple fatty epoxides and
terminal epoxides can easily undergo ring opening reaction than
functionalized fatty epoxides. The only structural difference
between EMR and EEL is the presence of -OH group instead of
unsaturated centre in the former. To further understand the
variation in the activity, Amberlyst 15 was treated with EMR
and EEL under neat condition at 60 °C for 4 h and the catalysts
were recovered and FT-IR was recorded. A sharp decrease in S-
(
suggests homogeneous contribution of the reaction when aqueous
methanol was used probably due to leaching of acidic moieties of
Amberlyst 15. To unravel further, hot filtration studies were carried
wherein the catalyst was removed by filtration at different time
under hot conditions and the reaction was allowed further to
continue in the absence of catalyst for 4 h (ESI† Fig. S6). A
conversion of 11, 18 and 22% was observed in 4 h for the catalyst-
removed at 0.5, 1 and 2 h filtrates respectively while 24% was
observed in the presence of catalyst. This further confirms the
significant homogeneous contribution of leached acidic moieties
under the reaction conditions. Furthermore, FT-IR spectra of the
water-treated Amberlyst 15 showed a sharp decrease in the intensity
-
1
Ostr vibration (at 1200 cm ) was observed for EMR treated
catalyst (ESI† Fig. S9) indicates strong interaction of sulphonic
groups with -OH group of EMR that in turn lead to lesser
conversion.
-
1
of the band around 1200 cm
that corresponds to the S-Ostr
vibration corroborates the observed decrease in the activity (ESI†
Fig. S7).
Ring opening reaction with different nucleophiles
For scientific curiosity and expanding the scope, ring opening
of ECO with different nucleophiles were studied and the results
are given in Table 2. Increase in the chain length of alcohols
Role of glyceryl moiety and the functional group
In order to find out the role of glyceryl moiety present in the
ECO, ring opening reaction was carried out for epoxidized
methyl ricinoleate (EMR) with methanol. Under identical
conditions (~60:1 molar ratio of methanol:substrate, 10 wt.%
(
C -C ) resulted a decrease in the conversion of ECO. Ring
1 3
opening of ECO with water to produce polyol (diol formation
in the place of oxirane) gave 49% conversion. The product
mixture became white gel like material and FT-IR spectra
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Table 3 Two-pot reactions for the preparation of ring-opened alkyl ricinoleates
Entry
No.
Pathway
Reaction
Conversion of
oxirane ring (%)
Yield of transesterified
product (%)
(
as per Scheme 1)
a
1
2
3
a
.
.
.
Ring opening of ECO with methanol followed by
transesterification of methoxylated castor polyol
Reaction A
81
b
Reaction C
83
91
(MCP) with methanol
c
Transesterification of ECO with methanol followed
by ring opening of epoxy methyl ricinoleate (EMR)
with methanol
Reaction B
d
Reaction C‟
76
47
e
a
Ring opening of ECO with iso-propanol followed
by transesterification of isopropoxylated castor
polyol (IPCP) with methanol
-
b
-
81
Alcohol:ECO = ~ 180:1 molar ratio, Toluene = 5 ml, Catalyst (Amberlyst 15) =10 wt.% w.r.t. ECO, Temp. = 105 °C, Time = 4 h;
Methanol:Alkoxylated castor polyol (MCP/IPCP) = ~ 18:1 molar ratio, Catalyst (CaAl2-CLDH700) = 5 wt.% w.r.t. oil, Temp. = 65
C, Time = 5 h; Conditions same like (b) except Methanol: ECO = ~ 18:1 molar ratio; Conditions same like (a) except Methanol:
b
c
d
°
e
EMR = ~ 60:1 molar ratio; Isopropanol as nucleophile for ring opening reaction.
supported the conversion of oxirane ring as well as formation of -OH chain length alcohols which results fatty acid alkyl esters with
group (ESI† Fig. S10). Ring opening of ECO with acetic anhydride different properties. Transesterification of ECO with ethanol
resulted 69% conversion which is comparatively higher in shorter (or) propanol did not work under the optimized reaction
1
4j
time than a recent report. Ring opening of ECO with acetone gave conditions adopted for methanol (reactions were carried out at
9% conversion with the formation of ketals while ring opening of reflux temperature). In order to synthesize epoxidized alkyl
3
ECO with diethyl amine gave 24% conversion which resulted ricinoleates, epoxidized methyl ricinoleate (EMR) was further
aminated polyols. Sodium azide along with water is known for the transesterified with different alcohols (Scheme 1; Reaction D)
1
4b
preparation of nitrogen containing oil derivatives; but gave only such as ethanol, n-propanol and iso- propanol which showed
1
4
% conversion under the studied reaction conditions. H NMR 49, 35 and 23% yield of corresponding epoxidized alkyl
profile of ring opening of ECO with different nucleophiles are given ricinoleates respectively (ESI† Table S1). In other words, an
in ESI† Fig. S11 and S12.
increase in the chain length decreased the yield of epoxidized
alkyl ricinoleates as elucidated from the appearance of
characteristic peak at 4.2-4.1 ppm in H NMR that corresponds
1
Transesterification reaction
to -OCH protons (ESI† Fig. S15).
2
Transesterification of epoxidized castor oil with methanol
(
Scheme 1; Reaction B) in presence of 700 °C calcined CaAl-
Two-pot reactions
layered double hydroxides (CaAl2-CLDH700) as heterogeneous
base catalyst rendered 91% yield of epoxidized methyl Ring-opened alkyl ricinoleates can be prepared by ring opening
ricinoleate (ESI† Fig. S13). Under identical conditions of epoxidized castor oil followed by transesterification of
(
Alcohol:oil = ~18:1 molar ratio, Catalyst = 5 wt.% w.r.t. ECO, derived ring-opened glyceryl ricinoleate (Scheme 1; Reaction
Temp. = 65 °C, Time = 5h), mixed oxides derived from C) (or) transesterification of epoxidized castor oil followed by
MgAl3-LDH gave only 22% yield of transesterified product. ring opening of derived epoxy alkyl ricinoleate (Scheme 1;
This indicates the presence of sites having higher basic strength Reaction C‟). In the current study, both the pathways were
range and higher density of basic sites in CaAl-LDH derived studied and the results are given in Table 3 (Entry No. 1& 2). In
mixed oxides play a crucial role in the transesterification both the cases, conversions of oxirane ring towards ring-opened
2
1
reaction. Transesterification of castor oil with methanol products were 81 and 76% whereas the yields of transesterified
methanol:oil = ~12:1 molar ratio) using the same active products were 83 and 91% respectively. These results bestow
catalyst showed 74% yield of methyl ricinoleate at 65 °C in 5 h that ring-opened alkyl ricinoleates (methoxylated methyl
(
(
ESI† Fig. S14).
ricinoleate; MMR) can be effectively prepared by carrying the
above mentioned reactions in a two-pot synthesis. Reaction C
was also extended for transesterification of isopropoxylated
castor polyol (IPCP) with methanol (Table 3; Entry No. 3) for
the preparation of isopropoxylated methyl ricinoleate (IPMR).
Depending on the availability of alcohol feedstock,
transesterification reaction can be performed with different
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Table 4 Physical properties of neat and blended castor oil, epoxidized castor oil and ring-opened glyceryl ricinoleates
a
b
Property
CO
ECO
CO +
ECO
Ring-opened glyceryl ricinoleates
c
d
e
f
g
MCP
IPCP
MCP+
HCP
ACP
c
IPCP
Appearance
Golden
yellow
Pale
yellow
Pale
yellow
Pale
yellow
Pale
yellow
Pale
yellow
(liquid)
Milky
white
(gel)
Brown
Yellow
(liquid)
m
(liquid) (liquid) (liquid) (liquid) (liquid)
Chemical formula
C
57
H
104
C
57
H
104
-
C
60
H
116
C
66
H
128
-
C
57
H
110
O
C H N
69 137 3
O9
O12
O15
O15
O12
15
h
Molecular weight (g/mol)
~933
0.94
16.0
0
~981
1.03
3.1
-
~1077
0.97
2.4
~1161
0.98
-
~1035
~1200
0.95
2.7
3
Density (kg/m )
0.99
11.6
1.3
0.99
3.4
-
2.9
2.9
0.59
-
i
Iodine number
2.5
i
Oxirane group content (%)
4.0
0.9
2.3
1.0
1.2
i
Relative oxirane conversion
0
0.81
4625
0.26
972
4951
15.0
7.3
0.18
1020
42552
43.9
18.6
0.46
0.20
1644
1298
3.2
0.25
370
-
j
Viscosity (Cp)
360
3581
118.7
77.6
4007
112016
61.1
k
l
Oxidative stability at 30 °C (h)
-
-
k
k
l
Oxidative stability at 110 °C (h)
Oxidative stability at 120 °C (h)
-
-
194.4
l
l
-
23.9
1.5
-
-
a
b
c
d
e
f
Castor oil; Epoxidized castor oil; Blended in 1:1 w/w%; Methoxylated castor polyol; Isopropoxylated castor polyol; Hydroxylated
g
h
i1
j
k
castor polyol; Aminated castor polyol; Maximum molecular weight is given; H NMR analysis; at 25 °C; Rancimat analysis;
l
m
Occurrence of solidification of sample restricted the analysis; Nitrogen content is 2% (based on CHNS analysis).
Physical property measurements
Scale-up studies
Various physical properties were measured for neat, ring
Ring-opened glyceryl ricinoleates were successfully prepared
up to 25 g (MCP and IPCP were prepared on 100 g scale) using
various nucleophiles. Epoxy alkyl ricinoleates and ring-opened
alkyl ricinoleates were also prepared up to 25 g (EMR and
MMR were prepared on 50 and 250 g scale respectively). On
higher scale for the ring opening reactions, alcohol:oil molar
ratio was fixed as ~60:1 (except for hydroxylated castor
polyol (HCP) preparation where ratio was 100:1). For
transesterification reaction, methanol:oil molar ratio was fixed
as ~18:1 and 12:1 for ECO and CO respectively. In all the
cases, conversion/yield of the products were similar as that of
normal reaction scale (0.5/5 g) that substantiate good efficacy
of the catalysts even while working at higher scale. CO, ECO
and formed products are confirmed by ESI-MS analysis (ESI†
Fig. S16-S26) and interestingly in the case of transesterification
reaction, along with EMR and MR diglycerides were also
present which shows partial completion of reaction (suggest
requirement of harsher reaction conditions).
opened glyceryl ricinoleates, epoxy alkyl ricinoleates, ring
opened alkyl ricinoleates and their blended forms whose values
are summarized in Table 4 and 5. Density of castor oil is 0.94
3
kg/m whereas the obtained products showed variable densities
3
from 0.87-1.03 kg/m . Decrease in the iodine number of the
functionalized castor derivatives compared to CO/MR further
confirmed the participation of double bonds in the epoxidation
reaction. Functionalized derivatives showed almost similar
iodine number values as that of ECO/EMR while a decrease in
the oxirane group (epoxy oxygen) content values were observed
indicates the formation of ring opened products. ECO and MCP
showed 12.8 and 2.8 times higher viscosity than CO whereas
ACP showed almost same viscosity like CO. Interestingly,
IPCP showed only 1.2 times lesser viscosity than ECO and may
be due the presence of higher epoxide (lesser conversion of
ECO). EMR (transesterified product) showed 96 times lesser
viscosity than ECO and MR (transesterified product) showed
16.3 times lesser viscosity than CO. Ring-opened alkyl
ricinoleates showed 1.5 to 4 times higher viscosity than MR
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Table 5 Physical properties of neat and blended methyl ricinoleate, epoxidized alkyl ricinoleate and ring-opened alkyl ricinoleates
a
Property
MR
Epoxidized alkyl
ricinoleates
Blended epoxy
ricinoleates
Ring-opened alkyl ricinoleates
b
c
e
f
EMR
EPR
MR+
EMR
EMR+
EPR
MMR
IPMR
MMR+
IPMR
d
d
d
Appearance
Golden
yellow
Pale
yellow
(liquid)
Pale
yellow
(liquid)
Pale
yellow
(liquid)
Pale
yellow
(liquid)
Golden
yellow
(liquid)
Pale
yellow
(liquid)
Golden
yellow
(liquid)
(liquid)
Chemical formula
C H O
C H O
-
-
-
C H O
C H O
22 44 5
-
1
9
36
3
19 36
4
20 40
5
g
Molecular weight (g/mol)
~312
0.87
15.4
0
~328
0.91
0.6
~356
0.96
0.4
-
-
~360
0.95
0.4
~388
0.91
0.5
-
3
Density (kg/m )
0.90
11.5
1.95
0.40
24
0.95
0.5
0.94
0.4
h
Iodine number
h
Oxirane group content (%)
3.95
0.81
48
3.66
0.75
60
3.56
0.73
72
0.78
0.16
91
0.50
0.10
70
0.63
0.13
103
21.3
20.6
20.5
h
Relative oxirane conversion
0
i
Viscosity (Cp)
22
j
Oxidative stability at 30 °C (h)
342
2.9
1.6
5221
22.9
11.6
27067
263.2
147.5
5051
194.4
129.4
34510
270.4
147.5
195
93865
34.8
13.0
j
j
Oxidative stability at 110 °C (h)
Oxidative stability at 120 °C (h)
194.4
194.3
a
f
b
c
d
e
Methyl ricinoleate; Epoxy methyl ricinoleate; Epoxy propyl ricinoleate; Blended in 1:1 w/w%; Methoxylated methyl ricinoleate;
g
h1
i
j
Isopropoxylated methyl ricinoleate; Maximum molecular weight is given; H NMR analysis; at 25 °C; Rancimat analysis.
which may be due to the occurrence of intramolecular functional
and epoxy derivatives. These studies show that glyceride moiety
group reactions (e.g. estolides formation) that might facilitate
present in the CO/ECO is the reason for their higher viscosity than
methyl ricinoleate (or) epoxy ricinoleates (or) ring-opened alkyl
ricinoleates. Interestingly, compared to CO/MR, their corresponding
epoxide derivatives showed higher viscosity suggests presence of
degradation of the molecules. However at higher temperature, the
oxidative stability of ring-opened alkyl ricinoleates improved than
methyl ricinoleate, epoxy alkyl ricinoleates and glyceryl ricinoleates.
oxirane ring enhances the viscosity of the oils/fatty derivatives. It One-pot reaction
was also observed that an increase in the chain length in fatty region/
Ring-opened alkyl ricinoleates are interesting molecule which can
ester region increased the viscosity of the derivatives except in the
case of IPMR and it may be due to lesser oxirane content in it
compared to EMR. Blended derivatives (1:1 w/w%) showed
viscosity between the range of the individual derivatives suggests
that viscosity can be altered by blending the derivatives in different
ratios. Oxidative stability of MCP and IPCP improved 12 and 31%
respectively than CO indicating the importance of functionalization
of castor oils which can then be effectively utilized for industrial
applications. On the other hand, oxidative stability of these
derivatives decreased drastically than CO at higher temperature
indicates the potential influence of atmosphere for faster degradation
possibly due to free radical formation. Oxidative stability of epoxy
alkyl ricinoleates is ~15 times greater than methyl ricinoleate
whereas ring-opened alkyl ricinoleates exhibited lesser stability at 30
beprepared by earlier discussed two different reaction chemistries.
Instead of two-pot reaction, this molecule can be prepared by one-
pot reaction by taking both heterogeneous acid and base catalysts
together (Scheme 1; Reaction E). Results of one-pot reaction for the
preparation of methoxylated methyl ricinoleate (MMR) are given in
ESI† Table S2. Reaction performed for 5 h reaction time resulted
6
1% conversion of ECO and 59% yield of transesterified products.
A further increase in the reaction time to 48 h did not have any
influence on the conversion of ECO whereas the yield of
1
transesterified product slightly increased to 67%. Comparison of H
NMR spectra of MMR prepared by two-pot as well one-pot reactions
are given ESI† in Fig. S27. The peaks appeared at 3.7 ppm
corresponds to terminal methoxy (-OCH ) protons confirms the
3
occurrence of transesterification reaction whereas the peaks at 3.5-
°C. Ring-opened glyceryl ricinoleates gave lesser oxidative stability
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3
.3 corresponds to internal methoxy protons confirms the ring
91
opening reaction. The peaks appeared at 3.2-2.8 ppm in one-pot
reaction suggests lesser conversion of ECO.
80
ESI-MS analysis was done for the mixture obtained from
one-pot reaction (5 h reaction time; as per the data Table S2; Entry
No. 1) and the mass fragmentation patterns are given in ESI† Fig.
S28. Molecules such as ECO, EMR and MMR showed intense
6
0
6
0
Active
catalyst
Recalcined
catalyst
40
+
signals corresponds to [M+Na] rather than their original expected
2
7
+
m/z values. Intense signal appeared at 1078 corresponds to [M+1]
20
Recovered
catalyst
for MCP. Also, m/z values appeared at 680-700 represents the
presence of diglyceride in the mixture which indicates incomplete
transesterification reaction. Oxirane group content and relative
oxirane conversion are 1.57 and 0.32% respectively for the mixture
obtained through one-pot reaction. These values are in between the
values of ECO and MCP which supports lesser conversion of ECO
to MCP under the studied conditions.
0
1
2
3
Cycle, Number
Fig. 2 Reusability studies of CaAl2-CLDH700 for transesterification
of ECO with methanol. Methanol:ECO = 18:1, Catalyst = 5 wt.%
w.r.t. ECO, Temp. = 65 °C, Time = 5 h.
Recycle studies
Amberlyst 15 was recycled up to 4 cycles for the ring opening
Reusability studies of the catalyst recovered from one-pot
of ECO with methanol under the optimized reaction conditions reaction (8 h reaction time; as per the data Table S2, Entry no.
with slight change in its activity (Fig. 1). Acidity measurements 2) resulted 29% conversion of ECO with 5% yield of
+
showed almost no change after every cycle (4.9 & 4.4 meq H /g transesterified product. This result suggests that the activity of
in fresh catalyst & after first use); however, interestingly a the acid and base catalysts decreases drastically after first run
subtle increase in the pH of the medium was observed after first when they were used together.
cycle which was almost constant for subsequent cycles (pH of
st
the medium before reaction for 1 cycle: 2.3; remaining all
Conclusions
cycles: ~ 6).
Among various heterogeneous acid catalysts screened,
8
2
7
6
5
4
3
2
1
0
Amberlyst 15 is the most efficient catalyst for the ring opening
of ECO with methanol. The high activity of this catalyst was
attributed to its higher acidity. By optimizing the parameters, a
maximum conversion of 82% was achieved at 105 °C in 4 h
using toluene as solvent. The catalyst was successfully recycled
up to 4 cycles with slight loss in its activity. The scope of this
reaction was extended to various nucleophiles such as alcohols,
acetone, diethyl amine and water with moderate conversion
80
70
60
50
40
30
20
10
0
7
2
6
5
6
3
Acidity
4.7
4.6
4
.6
4.4
2.2
2.2
2.1
pH
(
24-70%). Transesterification of ECO with methanol gave 91%
0
.7
yield of EMR using mixed oxides derived from CaAl-LDH as
heterogeneous base catalyst within 5 h at 65 °C without
affecting oxirane ring. Transesterification of EMR with higher
alcohols such as ethanol (or) n-propanol/iso-propanol rendered
49-23% yield of alkyl ricinoleates. This catalyst showed a
decrease in its activity while recycling and could partially be
restored by recalcining at 700 °C for 5 h. MMR was prepared
from ECO and methanol with 61% conversion of oxirane ring
and 59% yield of transesterified product by using both these
acid and base catalysts together in a one-pot reaction. The
physical properties measured for these ring opened and
transesterifed derivatives suggest the possibility of tailoring the
values by suitably choosing the appropriate nucleophiles,
besides simple blending of them. The reaction chemistry
presented here along with the propensity of modifying the
physical properties endorse the potential use of these castor-
based derivatives in industrial application in the field of
lubricants, plasticizers and in rheology.
1
2
3
4
Cycle, Number
Fig. 1 Reusability studies of Amberlyst 15 for ring opening of ECO
with methanol. Methanol:ECO =~180:1, Catalyst = 10 wt.% w.r.t.
ECO, Toluene = 5 ml, Temp.=105 °C, Time =4 h.
Reusability studies of recovered CaAl2-CLDH700 gave 27%
yield of epoxy methyl ricinoleate during the second run. It was
reported that recalcination of the recovered catalyst can
improve the transesterification efficacy. To retain the activity,
the recovered catalyst was recalcined at 700 °C for 5 h in static
air atmosphere. Reaction performed using the recalcined
catalyst showed 60% yield of epoxy methyl ricinoleate during
the third run (Fig. 2).
2
2
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Acknowledgements
9
A. Nezihe, D. Elif, Y. Ozlem and E. A. Tuncer, Ind. Eng.
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CSIR-CSMCRI Communication No. 077/2014: Authors thank
CSIR, New Delhi for financial support under the network
project Indus MAGIC (CSC-0123). Authors thank “Analytical
Division and Centralized Instrumental Facilities” for providing
instrumentation facilities. Authors also thank M/s Jayant Agro
Organics Ltd., Mumbai for providing castor oil derivative
samples.
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