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Ultrasonic and Catalyst-Free Epoxidation of Limonene and Other Terpenes Using Dimethyl Dioxirane in Semibatch Conditions

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Abstract

Limonene dioxide is a key intermediate molecule for the development of bio-based polycarbonates or non-isocyanate polyurethanes. In this work the epoxidation of limonene to limonene dioxide using in-situ generated dimethyl dioxirane as the oxidizing agent using both conventional agitation and ultrasound has been compared. The time required to completely convert limonene to limonene dioxide with 100% yield using ultrasound was only 4.5 min at room temperature. In comparison, when conventional agitation using magnetic stirrer is used, the required time to reach 97% yield of limonene dioxide was 1.5 h. The epoxidation of α-pinene has also been studied using both agitation techniques. Epoxidation of α-pinene to α-pinene oxide under ultrasound required only 4 min with an obtained yield of 100% while in comparison with conventional method the reaction time was 60 min. As for other terpenes, β-pinene was converted to β-pinene oxide in only 4 min whereas farnesol yield of 100% of the tri-epoxide in 8 min. Carveol, a limonene derivative, was converted to carveol dioxide with a yield of 98%. The epoxidation reaction of carvone using dimethyl dioxirane the conversion was 100% in 5 min, but only 7,8-carvone oxide was produced.
Ultrasonic and Catalyst-Free Epoxidation of Limonene and Other
Terpenes Using Dimethyl Dioxirane in Semibatch Conditions
Luc Charbonneau, Xavier Foster, and Serge Kaliaguine*
Department of Chemical Engineering, Laval University, 1065 Medecine Avenue, Quebec City, Quebec G1V 0A6, Canada
*
SSupporting Information
ABSTRACT: Limonene dioxide is a key intermediate molecule
for the development of biobased polycarbonates or nonisocyanate
polyurethanes. In this work the epoxidation of limonene to limo-
nene dioxide using in-situ-generated dimethyl dioxirane as the
oxidizing agent under both conventional agitation and ultrasound
has been compared. The time required to completely convert
limonene to limonene dioxide with 100% yield using ultrasound
was only 4.5 min at room temperature. In comparison, when con-
ventional agitation using a magnetic stirrer is used, the required
time to reach a 97% yield of limonene dioxide was 1.5 h. The
epoxidation of α-pinene has also been studied using both
agitation techniques. Epoxidation of α-pinene to α-pinene oxide
under ultrasound required only 4 min with an obtained yield of
100%, while in comparison with the conventional method the reaction time was 60 min. As for other terpenes, β-pinene was
converted to β-pinene oxide in only 4 min whereas farnesol yielded 100% of the triepoxide in 8 min. Carveol, a limonene
derivative, was converted to carveol dioxide with a yield of 98%. In the epoxidation reaction of carvone using dimethyl dioxirane
the conversion was 100% in 5 min, but only 7,8-carvone oxide was produced.
KEYWORDS: Catalyst free, Ultrasound, Epoxidation process, Limonene, Limonene derivates, Farnesol, Pinenes
INTRODUCTION
Biomass-based monomers are thought to be sustainable and
renewable alternatives to traditional oil-based monomers.
13
These new monomers will contribute to reduce our depend-
ency on fossil carbon leading to a considerable reduction of
CO2emissions in the atmosphere. Biomass-derived monomers
may be classied into four dierent categories: oxygen-rich
monomers (lactic acid, succinic acid), hydrocarbon monomers
(bio-olens), nonhydrocarbon monomer (carbon dioxide),
and nally hydrocarbon-rich monomers (vegetable oils, fatty
acids, terpenes).
4
Terpenes, carbon-rich monomers mostly
derived from essential oils, have been the subject of much
scientic research. Considerable progress has been made in the
eld of terpenes-based monomers in order to produce bio-
based polymers.
57
One of the most promising terpenes is
limonene. Its annual production is around of 70 kt per year,
mostly extracted from citrus peel wastes.
810
Direct polymeriza-
tion of limonene leads to low molecular weight polylimonene.
11
1,2-Limonene oxide, the epoxidation product of limonene,
is more promising and has been successfully used as a bio-
monomer in combination with CO2in the presence of a
catalyst, leading to the production of new green polycar-
bonates.
7,10,1215
Limonene dioxide, the double-epoxidation
product of limonene, has attracted the attention of scientists
since it has shown great potential for many applications in plas-
tic industries. This monomer can be used for the development
of epoxy resins or as a cross-linker. Limonene dicarbonate, the
product of the carbonatation of limonene dioxide, has been
successfully isolated in relatively good yield and is a very prom-
ising monomer to produce green polymers, nonisocyanate
polyurethane.
1618
Finally, limonene dioxide can be converted
by reacting the latter with a solution of ammonia in order to
produce an aminoalcohol which can also be used in the pro-
duction of isocyanate and phosgene-free polyhydroxyurethane.
19
Given the importance of limonene dioxide for the production
of new biobased polymers, it is crucial to develop a highly e-
cient epoxidation process in order to meet future industrial
needs.
One of the most widely known methods for the epoxidation
of olens is the use of peracids in organic solvents, such as
m-CPBA in CH2Cl2, also known as the Prilezhaev reaction.
20
Metal complexes are the most active catalysts for the epoxi-
dation reaction.
21
Dierent oxidizing agents can be used such
as hydroperoxides, ClO, and PhIO or molecular oxygen as
oxygen source in the presence of such catalysts as supported
metal oxides or organometallic complexes. The most employed
metals are V, Mo, W, Ti, Mn, Cr, or Co.
21,22
Hydrogen perox-
ide is a cheap and green epoxidizing agent that can be used in
the presence of dierent types of catalysts including soluble
metal oxides, metal oxides generated in situ, or organometallic
Received: June 2, 2018
Revised: July 19, 2018
Published: July 23, 2018
Research Article
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complexes in the presence of organic solvents, mostly dichloro-
methane or DMF.
23
These techniques lead generally to high
epoxide yields. From an environmental and health viewpoint
these techniques are not essentially viable at industrial scales.
Solvents such as dichloromethane or DMF and metal-based
catalysts are rather toxic and are not considered environmen-
tally friendly.
21,24
Heterogeneous epoxidation of limonene using
low-coordination titanium supported on silica using H2O2as the
oxidizing agent has attracted many scientists as an alternative,
since it only produces a water molecule as a byproduct.
2535
Epoxidation of limonene to 1,2-limonene oxide by photocatalysis
using low-coordination titanium and O2as the oxidation agent
has also been studied.
36
However, this type of catalyst has
shown a low yield of limonene dioxide which is a most prom-
ising biomonomer. The epoxide molecules are rather sensitive
and can undergo ring opening with formation of diols in the
presence of water in the hydrogen peroxide solution. Further-
more, limonene reacts with hydrogen peroxide leading to the
formation of oxidation secondary products such as carvone,
carveol, and perilyl alcohol. Finally, even with optimized pore
structure and when working in anhydrous conditions, low-
coordination titanium supported on silica was found to not be
active enough for the double epoxidation of limonene to limo-
nene dioxide.
37
Epoxidation of olens by in-situ-generated dimethyl dioxirane
(DMDO) by the reaction of acetone with potassium peroxy-
monosulfate commercially known as Oxone, in semibatch con-
ditions in the presence sodium bicarbonate as the buer is not
performed industrially. This epoxidation method is, however,
rather green, fast, highly selective, and catalyst free, works at
room temperature, and it is easy to separate the products from the
reaction medium.
21,3848
Oxone is a cheap oxidizing agent, easy
for storage, and a stable salt, and the only products generated are
the epoxides, KSHO4, acetone, sodium bicarbonate, and water.
A greener approach for the double epoxidation of limonene has
been achieved in the absence of any of catalyst using in-situ-
generated DMDO at room temperature in acetone as both
the ketone source and the solvent yielding 97% of limo-
nene dioxide.
49
Epoxidation of limonene by in-situ-generated
DMDO is a multiphasic process which requires strong agitation
in order to enhance the DMDO mass transfer from the aqueous
phase to the organic phase where the reaction takes place.
To resolve that situation, ultrasonic agitation may be expected to
considerably reduce the reaction time. In previous reports,
epoxidation of various olens was therefore performed under
ultrasound in the presence of a catalyst, and the published results
show a high yield of epoxides in only a few minutes, which is a
considerable gain over conventional agitation using a magnetic
stirrer or mechanical agitator.
5057
However, in the case of
limonene, the obtained limonene dioxide yield was very low.
This works aims at demonstrating the advantages of the use of
ultrasound for the epoxidation reaction of limonene to produce
limonene dioxide by using in-situ-generated DMDO as the
oxidizing agent in the absence of any catalyst. In order to
generalize this method, other terpenes such as α- and β-pinene,
farnesol, and limonene derivatives such as carveol and carvone
have also been epoxidized.
MATERIAL AND METHODS
Epoxidation of Terpenes under Semibatch Conditions Using
in-Situ-Generated DMDO. A 125 mL glass ask was initially lled
with 40 mL of acetone, 4.0 g of sodium bicarbonate, and 10 mmol of
limonene (entry 1a). A 60 mL amount of an aqueous solution of 0.52 M
of Oxone was added using a syringe pump at a constant owrate of
1 mL min1when the reaction is carried out under conventional
agitation and 10 mL min1under ultrasound. The sonotrode used for
the sonication was 7 mm in diameter (39 mm2) and 95 mm length
(Hielsher). The ultrasound nominal power applied was 50 W with a
frequency of 26 kHz. The 125 mL ask was immersed in a water bath
in order to maintain the content at room temperature. The biphasic
reaction medium was separated by liquidliquid extraction using
diethyl ether. The organic layer was dried on magnesium sulfate and
evaporated on a rotary evaporator. Other terpenes such as α-pinene
(entry 2a), β-pinene (entry 3a), (carveol entry 4a), carvone (entry 5a),
and farnesol (entry 6a) were also epoxidized in the same epoxi-
dation conditions as for limonene.
Characterization of the Reaction Medium. All reaction mix-
tures were analyzed using a CP-3800 gas chromatograph (Varian Inc.)
equipped with a ame ionization detector (FID) and a Stabilwax col-
umn (30 m ×0.53 mm ×1μm) coupled with a 5 m guard column.
The limonene conversion was determined using eq 1
=
×
nn
n
Conversion(%) 100
of
o
(limonene) (limonene)
(limonene) (1)
The yield for limonene oxide and limonene dioxide was calculated
using eq 2
n
n
Y
ield(%) 100
o
epoxide
(limonene)
(2)
Both 1,2-limonene oxide and limonene dioxide standards were pur-
chased from Sigma-Aldrich. Methoxybenzene was used as the internal
standard. To ascertain the presence of limonene dioxide, α-pinene
oxide (2b), or β-pinene oxide (3b) the reaction mixture composition
was conrmed by GC-MS. The GC-MS was a Hewlett-Packard HP
5890 series GC system and MSD Hewlett-Packard model 5970.
The GC-MS was equipped with a Zebron ZB-5MS capillary column
(30 m ×0.25 mm ×0.25 mm).
The yields for carvone, carveol, and farnesol oxides were deter-
mined by 1H NMR using a Bruker 300 MHz NMR in deuterated
chloroform. Their respective 1H NMR spectra are available in the
Supporting Information.
RESULTS AND DISCUSSION
Optimization of Reaction Conditions for the Double
Epoxidation of Limonene to Limonene Dioxide by DMDO
under Ultrasound. Limonene was the model molecule used
for optimization of reaction conditions for the synthesis of limo-
nene dioxide by in-situ-generated DMDO under semibatch
conditions coupled with ultrasound. The epoxidation reaction of
limonene was expected to yield the dierent isomers represented
on Scheme 1.
The epoxidation reaction by in-situ-generated DMDO is a
multiphasic reaction comprising an organic phase, which is a
mixture of acetone and limonene, an aqueous phase com-
prising an Oxone solution, which is added using a syringe
pump at a constant owrate in the reaction vessel, an aqueous
acetone solution, and nally a solid phase composed of sodium
bicarbonate as the buer. The complete epoxidation process of
limonene by DMDO is illustrated in Scheme 2.
Scheme 1. Limonene Oxide Isomers
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B
KHSO5reacts in the aqueous phase by a nucleophilic attack,
and one atom of oxygen is transferred to acetone, leading to
the formation of DMDO and KHSO4. Following that step
DMDO is transferred from the aqueous phase to the acetone
phase, reacting with limonene, the latter being insoluble in
water, and produces the limonene dioxide. The other product
of DMDO reacting with limonene is acetone, which in our case
is also the solvent of the reaction.
The epoxidation of limonene using in-situ-generated
DMDO requires a strict control of the reaction conditions
such as the owrate of the aqueous solution of Oxone, the pH
of the reaction medium, and the Oxone/limonene stoichio-
metric ratio. The eect of Oxone solution feed owrate on the
conversion and yield of limonene dioxide has been studied,
and the results are reported in Figure 1.
The maximum feed owrate of the 0.52 M aqueous solution
of Oxone for the epoxidation of limonene by DMDO gener-
ated in situ under ultrasound in order to obtain 100% of limo-
nene dioxide yield should be 20 mL min1. At higher owrate
both conversion and yield start decreasing due to the catalytic
decomposition of HSO5
by the already produced DMDO,
with the reaction represented in Scheme 3.
The epoxidation of olens by in-situ-generated DMDO as
the oxidizing agent should be carried out over a narrow pH
range between 7 and 9. At pH lower than 7 the oxidation of
ketones by the BayerVillager reaction was shown to be
favored over the epoxidation of alkenes. By opposition, when
the pH of the reaction medium is higher than 9, the auto-
decomposition process of Oxone takes place, leading to a
reduction in epoxide yield to only 12% or even less.
48
One of
the easiest ways to maintain the pH of the reaction medium is
to use sodium bicarbonate as the buer in its solid form. The
stability of sodium bicarbonate as the buer of the reaction has
been studied, and the results are presented in Figure 2.
The conditions for the test described in Figure 2 are 4 g of
sodium bicarbonate, 40 mL of acetone, 60 mL of 0.52 aqueous
Oxone solution under a owrate of 20 mL min1at room
temperature, and 50 W of nominal ultrasound power for a
reaction time of 10 min in the absence of limonene. Prior to
adding the 0.52 M aqueous Oxone solution to the reaction
vessel, the pH of the mixture of acetone with sodium bicar-
bonate is about 9.85. This is due to the low solubility of
NaHCO3in acetone corresponding to 0.02 wt %.
58
After 15 s,
the pH started to rapidly decrease to a value of 7.57, reaching
8.0 after only 1 min. After complete addition of the 0.52 M
aqueous solution of Oxone, the pH of the mixture is relatively
stable and is maintained at a value of 8. Finally, a mixture of
60 mL of 0.52 M aqueous solution of Oxone and acetone has
slowly increased to a pH value of 8.2 after 10 min under
ultrasound. The obtained experimental results are shown in
Figure 2, indicating the stability of sodium bicarbonate as the
buer under ultrasound.
For stoichiometric considerations, an Oxone/limonene
molar ratio of 2:1 is required to completely epoxidize the two
unsaturations of limonene to limonene dioxide. This ratio was
therefore optimized, and the results are reported in Table 1.
The results presented in Table 1 show that at a molar ratio
of 2:1, the double epoxidation is not complete with a partial
conversion of Oxone to epoxide of 86%, while at a molar ratio
of 2.60:1, the two double bonds of limonene are completely
epoxidized with a partial conversion of Oxone of 77%.
REACTION OF LIMONENE EPOXIDATION
The time evolutions of limonene conversion and epoxide yields
were monitored with both conventional agitation using a mag-
netic stirrer and under ultrasound at optimized conditions, and
the results are reported in Figure 3.
Scheme 2. Limonene Epoxidation Process
Figure 1. Eect of owrate of the aqueous solution of Oxone on the
conversion of limonene and limonene dioxide yield.
Scheme 3. DMDO Decomposition by Oxone
Figure 2. Stability of sodium bicarbonate as the buer of the reaction.
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The time required to reach 100% conversion of limonene
and 97% yield of limonene dioxide by conventional agitation is
90 min. This reaction time was considerably reduced to only
4.5 min under ultrasonic agitation, yielding 100% of limonene
dioxide. Furthermore, no diol and no oxidation secondary
products such as carvone or carveol by oxidation of the limo-
nene ring were found in the reaction medium, which is not the
case when H2O2is used as the oxidizing agent. The only reac-
tion intermediate detected by gas chromatography using in-
situ-generated DMDO by both conventional and ultrasound
agitation was the 1,2-limonene oxide.
The 8,9-limonene oxide isomer (see Scheme 2)wasnot
detected as an intermediate in the reaction medium during the
epoxidation of limonene to limonene dioxide by in-situ-generated
DMDO using both conventional and ultrasonic agitation. The
absence of 8,9-limonene is rather odd, since the 8,9-limonene
oxide was detected when low-coordination titanium supported
on silica was used as the catalyst using tert-butyl hydroperoxide as
the oxidizing agent.
37
The absence of 8,9-limonene oxide isomer
is not limited to the epoxidation of limonene under the present
conditions using in-situ-generated DMDO in semibatch con-
ditions. Michel et al. also observed the same phenomenon for the
same epoxidation reaction when hydrogen peroxide was used
as the oxidizing agent catalyzed by methyltrioxorhenium (MTO)
in homogeneous conditions at room temperature.
59
Under these
conditions limonene was completely converted to 1,2-limonene
oxide after 5 min of reaction time. Thereafter, the 1,2-limonene
oxide was slowly reacted with hydrogen peroxide to produce
limonene dioxide with a yield of 90% over a period of 24 h.
Michel et al. mentioned that the only by-product was
1,2-limonene oxide.
59
On the basis of these observations, the
epoxidation of limonene to limonene dioxide by in-situ-gen-
erated DMDO is considered to be a two-step successive reaction.
This proposed reaction mechanism is represented in Scheme 4.
In kinetic terms, the 1,2 position of limonene is considered to
be more reactive being trisubstituted than the 8,9 position which
is disubstituted (see Scheme 2). In general, the trisubstituted
double bond is epoxidized roughly 7 times faster than a
disubstituted one. During the epoxidation process 1,2-limonene
oxide is the rst isomer formed by reaction of limonene with the
already produced DMDO. Following this step the second epoxi-
dation occurs, leading to the production of limonene dioxide. It is
proposed that the rst oxygen added to the 1,2 of the limonene
position could induce a steric rearrangement, allowing the
Table 1. Eect of the Total Amount of Oxone Fed to the Reactor at Constant Flowrate
a
Oxone/limonene
ratio pH of Oxone solution conversion
b
(%) 1,2-limonene oxide yield
b
(%) limonene dioxide yield
b
(%) oxone conversion to epoxide
(%)
2.00 1.43 99 24 75 86
2.60 1.30 100 0 100 77
a
A 10 mmol amount of of limonene, 40 mL of acetone, 4 g of sodium bicarbonate, various amounts of Oxone dissolved in 60 mL of water were
added to the ask at a constant owrate of 20 mL min1, room temperature, and total reaction time 10 min.
b
Limonene conversion and yields were
determined by GC-FID after purication.
Figure 3. Time evolution of the conversion of limonene and the yield of limonene dioxide under conventional agitation and under ultrasound (US)
(uncertainties on the conversion and yields are within 5%).
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D
oxidizing agent to epoxidize the second unsaturation at position
8,9, thus producing the limonene dioxide. This hypothesis
requires further investigations by theoretical calculations in order
to reach a better understanding of the reaction intermediates.
EPOXIDATION OF α-PINENEANDOTHERTERPENES
On the basis of the results obtained for the epoxidation of
limonene to limonene dioxide, the epoxidation α-pinene (2a)
to α-pinene oxide (2b) was also studied (Scheme 5).
The epoxidation of α-pinene to α-pinene oxide has been
performed under the same conditions optimized for the epoxi-
dation of limonene. The obtained results are summarized in
Figure 4.
The results presented in Figure 4 show that for a conventional
agitation the required time to completely convert α-pinene to
α-pinene oxide is 60 min, allowing a yield of 100%. In compari-
son, when ultrasound is applied in the reaction medium, the
time required is only 4 min to completely convert pinene, yield-
ing 100% of pinene oxide. Furthermore, similar to the epoxi-
dation of limonene, no oxidation products of the pinene ring
such as verbenone and verbenol have been observed. The very
signicant eect of ultrasound on epoxidation reaction rates
depicted in Figures 3 and 4result from several factors. First, the
interdependence of the mass transfer of the DMDO is greatly
accelerated by the emulsifying eect of the acoustic wave
through the intervention of the cavitation and microjets. More-
over, it may be hypothesized that the oxygen transfer from
DMDO to the double bonds of terpenes is favored by the local
temperature rise due to the cavitation.
Other terpenes were also epoxidized by in-situ-generated
DMDO in semibatch conditions coupled with ultrasound. The
dierent structures of the reactants and their epoxidation
products are presented in Scheme 6.
The obtained results for the epoxidation of terpenes are
summarized in Table 2.
β-Pinene, one of the most abundant terpenes in nature, was
completely epoxidized with a yield of 100% of β-pinene oxide over
only 4 min, similar to the required time for α-pinene. Farnesol, a
sesquiterpene, bearing three unsaturations, has also been com-
pletely epoxidized (for 1H NMR, see Supporting Information).
Scheme 5. Epoxidation of α-Pinene
Scheme 4. Epoxidation Mechanism of Limonene to
Limonene Dioxide by DMDO
Figure 4. Time evolution of the conversion of α-pinene and yield of α-pinene oxide between conventional agitation and under ultrasound (US)
(uncertainties on the conversion and yields are within 5%).
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E
The conversion of carveol was determined by GC-FID analysis
and reached 100% with a yield of 99% of carveol dioxide. The
minor by-products are the two monocarveol oxides (4b, 4c).
Furthermore, the Oxone from the solution oxidized the alcohol
function to ketone, converting carveol to carvone, the latter
having been detected via 1H NMR by the presence of small
a peak with a chemical shift at 6.74 ppm (see Supporting
Information).
Finally, epoxidation using in-situ-generated DMDO assisted
by ultrasound reached its limitation when carvone was used as
the substrate. Carvone has a carbonyl group at the beta posi-
tion, reducing the electronic density of the double bond at
position 1,2. Furthermore, this double bond is in resonance
with the carbonyl group, which is represented in Scheme 7.
The 1H NMR spectrum of carvone (see Supporting
Information) displays one peak at 6.75 ppm corresponding
to a multiplet of the β-proton of the enone moiety. The two
1H NMR signals at δ= 4.75 and 4.80 ppm are corresponding
to the two geminal vinyl protons of the isopropenyl group.
The two 1H NMR spectra of carvone before and after the epoxi-
dation reaction using DMDO were recorded (see Supporting
Information). After 6 min of reaction, the two peaks at 4.75
and 4.80 ppm corresponding to the 7,8 position have com-
pletely disappeared but the peak at 6.75 is still there, allowing one
to conclude to the formation of only one epoxide isomer. The
same situation has also been observed when meta-chloroperben-
zoic acid had been used as the oxidizing agent.
60
The results
obtained for the epoxidation of carvone by in-situ-generated
DMDO suggest that DMDO has an oxidizing capacity com-
parable to m-CPBA but in a greener way, being unable to
epoxidize low electron density double bonds.
CONCLUSION
This work has shown the advantages of using ultrasonic agi-
tation compared to traditional agitation for the epoxidation of
limonene and other terpenes using in-situ-generated DMDO as
the oxidizing agent. The main advantages of the procedure are
the green aspect of the oxidizing agent and the reaction time
reduction obtained by performing this oxidation under ultra-
sound agitation. This epoxidation method allowed reaching
100% conversion of limonene with a 100% yield of limonene
dioxide in only 4.5 min compared to 90 min when traditional
agitation is used. Furthermore, no oxidation products of limo-
nene, such as carvone, carveol, and perrilyl alcohol, were found
Scheme 6. Terpenes and Their Epoxidation Products
Table 2. Epoxidation of Natural Products Using in-Situ-
Generated DMDO under Ultrasound
a
substrate no. of
instaurations conversion
b
(%) reaction time
(min) epoxides
yield (%)
β-pinene (3a) 1 100 5 100
carveol (4a)
c
2 100 6 >95
carvone (5a)
c
,
d
2 100 6 100
farnesol (6a)
c
3 100 8 100
a
Reaction conditions: 10 mmol of olen (farnesol, 6.6 mmol), 40 mL
of acetone, 4.0 g of sodium bicarbonate, 60 mL of 0.52 M Oxone
solution under a owrate of 20 mL min1, ultrasound power of 50 W,
room temperature.
b
Conversion was determined by GC-FID after
purication.
c
Yield was determined by 1H NMR spectroscopy after
purication.
d
100% of 8,9-carvone oxide; the double epoxidation did
not occur.
Scheme 7. Resonance of the Carvone Double Bond
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F
in the reaction medium. The epoxidation of α-pinene under
ultrasound required only 4 min, yielding 100% of α-pinene
oxide without oxidation of the ring. Other terpenes such as
β-pinene, farnesol, and carveol have also been oxidized, leading
to very high epoxide yields. The only observed exception is for
carvone, which was only converted to a 7,8 carvone oxide, a
monoepoxide. Further work should consider performing this
reaction in a continuous ow reactor which could be scaled up
to industrial size.
ASSOCIATED CONTENT
*
SSupporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acssuschemeng.8b02578.
1H NMR spectra before and after the epoxidation of
limonene, carvone, carveol, and farnesol (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: serge.kaliaguine@gch.ulaval.ca.
ORCID
Serge Kaliaguine: 0000-0002-4467-2840
Notes
The authors declare no competing nancial interest.
ACKNOWLEDGMENTS
Financial support from the Natural Sciences and Engineering
Council of Canada (NSERC). Oxone is a registered trademark
of E. I. du Pont de Nemours and Company. In this article, we
do not display trademark logos in accordance with the
American Chemical Society style guidelines.
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... A catalytic system consisting of a combination of mild mixing resulting from highfrequency ultrasonic irradiation (800 kHz) with precise temperature regulation of the double jacketed sonochemical reactor has achieved a higher yield of cyclooctene oxide (C 8 H 14 O) (96%) and selectivity (98%) within 30 min in the epoxidation of 1-octene mediated by H 2 O 2 and H 2 WO 4 compared with silent conditions (Scheme 10) [122]. Similarly, ultrasonic-assisted limonene epoxidation using in situ generated dimethyl dioxirane, C 3 H 6 O 2 (DMDO), as the oxidising agent, achieved 100% yield of the limonene dioxide product within 4.5 min, compared to 97% yield obtained in the reaction conducted using conventional agitation with a magnetic stirrer after 1.5 h [123]. A proposed two-step mechanism for the reaction is presented in Scheme 11. ...
... A proposed two-step mechanism for the reaction is presented in Scheme 11. Furthermore, epoxidation of α-pinene (C 10 H 16 ) to α-pinene oxide (C 10 H 16 O) under ultrasound conditions by DMDO yielded 100% after 4 min, and took 60 min to achieve a similar yield using the traditional method [123]. ...
... A catalytic system consisting of a combination of mild mixing resulting from high-frequency ultrasonic irradiation (800 kHz) with precise temperature regulation of the double jacketed sonochemical reactor has achieved a higher yield of cyclooctene oxide (C8H14O) (96%) and selectivity (98%) within 30 min in the epoxidation of 1-octene mediated by H2O2 and H2WO4 compared with silent conditions (Scheme 10) [122]. Similarly, ultrasonic-assisted limonene epoxidation using in situ generated dimethyl dioxirane, C3H6O2 (DMDO), as the oxidising agent, achieved 100% yield of the limonene dioxide product within 4.5 min, compared to 97% yield obtained in the reaction conducted using conventional agitation with a magnetic stirrer after 1.5 h [123]. A proposed two-step mechanism for the reaction is presented in Scheme 11. ...
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Oxidation and subsequent catalytic carbonation of limonene, gained from orange peels, afford high purity limonene dicarbonate (LC) as a versatile building block for tailoring linear and cross-linked non-isocyanate polyurethanes (NIPU) from renewable resources. Spectroscopic investigations reveal so far unknown highly colored carbonation byproducts which are successfully removed to yield crystalline LC. Melt-phase polyaddition of a dimer fatty acid based diamine and its diamine-terminated LC-prepolymers with carbonated 1,4-butanediol diglycidyl ether (BDGC) produces 100% bio-based linear NIPU thermoplastics. Side-reactions occurring during polymerization account for decreasing molar mass with increasing LC content. Curing carbonated pentaerythritol glycidyl ether (PGC)/LC blends with 1,5-diaminopentane, gained from lysine, enables tailoring of 100% bio-based NIPU thermosets exhibiting unconventional property profiles. The incorporation of small amounts high purity LC substantially improves NIPU glass temperature, stiffness, and strength without sacrificing elongation at break. High purity LC prevents color formation of LC-based NIPU coatings.
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Fully biobased poly(limonene carbonate)s (PLCs) have been prepared by copolymerization of limonene oxide with CO2, using a β-diiminate zinc-bis(trimethylsilyl)amido complex as the polymerization catalyst, and subsequent transcarbonation reactions using 1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD) as the catalyst, combined with 1,10-decanediol as the transcarbonation agent. Quantitative partial post-modification of these polycarbonates was fulfilled via thiol-ene chemistry using two mercaptoalcohols with different chain lengths, viz. 2-mercaptoethanol and 6-mercaptohexanol. The thermal properties and hydroxyl values (OHVs) of the resulting hydroxyl PLCs were modulated by controlling the type and amount of incorporated thioether species. The curing kinetics of these PLCs with blocked/non-blocked multifunctional isocyanates was studied by ATR-FTIR followed by the solvent casting and curing under the optimal conditions. The good acetone resistance and high transparency and hardness of the coatings demonstrated that the fully bio-based PLCs with adequate molecular weights and OHVs are promising resins for coating applications .
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The imminent depletion of resources derived from fossil fuels is a major concern for today’s society. 300 Mt of polymers are used every year in the form of plastics, most commonly derived from fossil fuels, hence the necessity to find new materials based on renewable resources. This review explores the utilisation of monoterpenes and terpenoids – a family of abundant and inexpensive natural products – as promising renewable monomers. Terpenes can be directly used in polymerisations or converted into bespoke monomers through organic transformations. The use of terpenes for the production of renewable plastics has been a prevalent topic of research for the past few decades. Early research focused on cationic polymerisation of terpenes by way of their alkene moieties; however, more recently terpenes are being functionalised to incorporate handles for a larger range of polymerisation techniques. Herein an assessment of the future prospects for the use of these small functional molecules to synthesise novel an...