molecules
Article
One-Pot Conversion of Epoxidized Soybean Oil (ESO)
into Soy-Based Polyurethanes by MoCl2O2 Catalysis
Vincenzo Pantone 1 , Cosimo Annese 2 , Caterina Fusco 2 , Paola Fini 3 , Angelo Nacci 2,4 ,
Antonella Russo 1 and Lucia D’Accolti 2,4, *
1
2
3
4
*
Greenswitch s.r.l., 75013 Ferrandina (MT), Italy; [email protected] (V.P.);
[email protected] (A.R.)
ICCOM-CNR, SS Bari, Via Orabona 4, 70126 Bari, Italy; [email protected] (C.A.);
[email protected] (C.F.); [email protected] (A.N.)
IPCF-CNR, SS Bari, via E. Orabona 4, 70125 Bari, Italy; [email protected]
Dipartimento di Chimica, Università di Bari “A. Moro”, Via Orabona 4, 70126 Bari, Italy
Correspondence: [email protected]; Tel.: +39-080-544-2068
Academic Editor: Derek J. McPhee
Received: 14 January 2017; Accepted: 17 February 2017; Published: 21 February 2017
Abstract: An innovative and eco-friendly one-pot synthesis of bio-based polyurethanes is proposed
via the epoxy-ring opening of epoxidized soybean oil (ESO) with methanol, followed by the
reaction of methoxy bio-polyols intermediates with 2,6-tolyl-diisocyanate (TDI). Both synthetic
steps, methanolysis and polyurethane linkage formation, are promoted by a unique catalyst,
molybdenum(VI) dichloride dioxide (MoCl2 O2 ), which makes this procedure an efficient,
cost-effective, and environmentally safer method amenable to industrial scale-up.
Keywords: catalysis; oxidation; bio-based polyurethane; one-pot synthesis
1. Introduction
In an era facing the depletion of fossil fuels and the increasing environmental concerns related
to their burning, much of the current efforts have been directed to the challenging search for more
sustainable sources that can ensure continuous manufacture of those commodities that have improved
the quality of human life. As an example, recent years have witnessed a rapid increase in the production
of bio-based plastics and polymers, entirely derived from renewable sources, such as starch, cellulose,
sugars, etc. [1,2]. In this context, vegetable oils, such as ricinoleic, linseed, soybean oils, etc., have also
been regarded as convenient source of renewable feedstocks to be employed in the development of
bio-based polyurethanes (PU) [3–9].
Bio-based polyurethanes are available in a wide range of hardnesses, as well as in several
formulations, to obtain different materials that allow energy savings, protect the environment, enhance
safety, lead to innovative building systems, as well as several polyurethanes that have been studied for
their preparation of composites [1,10–13].
A practical approach to PU from vegetable oils involves epoxidation of the carbon-carbon double
bonds of unsaturated fatty ester moieties and subsequent epoxide ring-opening reaction by nucleophilic
reagents, providing the hydroxyl functionalities that form the urethane network upon reaction with
isocyanates [3]. This is exemplified by the conversion of soybean oil (SO) into soy-based PU, through
preliminary epoxidation, followed by methanolysis of the epoxidized oil (ESO), and reaction of the
ensuing soy-methanol polyol 1 with suitable diisocyanates (Scheme 1).
Molecules 2017, 22, 333; doi:10.3390/molecules22020333
www.mdpi.com/journal/molecules
Molecules 2017, 22, 333
Molecules 2017, 22, 333
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2 of 13
1. Representation of a typical chemical approach to the conversion of soybean oil (SO) into
Scheme 1.
bio-based
simplicity, only
only one
one of
of the possible regioisomers
regioisomers of
of soy-methanol
soy-methanol polyol
polyol 1 is shown.
bio-based PU. For simplicity,
In this
context,
specialspecial
attentionattention
has been paid
oxidation
methods
employingmethods
organocatalysts
[14,15]
In
this
context,
hastobeen
paid
to oxidation
employing
or
based
on
mild
and
safe
oxidants,
such
as
H
2O2 [16,17] organic (hydro)peroxides [18–20] and even
organocatalysts [14,15] or based on mild and safe oxidants, such as H2 O2 [16,17] organic
O2 [21]. On the other
hand,and
typical
the use
of strong
(e.g., p-Toluene
(hydro)peroxides
[18–20]
evenprotocols
O2 [21]. prescribe
On the other
hand,
typicalBrønsted
protocolsacids
prescribe
the use of
sulfonicBrønsted
acid SA,
H3PO
4, and HBF4) to catalyze the epoxide ring-opening reaction step, while
strong
acids
(e.g.,
p-Toluene sulfonic acid SA, H3 PO4 , and HBF4 ) to catalyze the epoxide
hazardous Lewis
acids
(e.g.,
tin-,hazardous
mercury-compounds)
and/or
toxic
bases (e.g., tertiaryand/or
amines)toxic
are
ring-opening
reaction
step,
while
Lewis acids (e.g.,
tin-,
mercury-compounds)
usually
employed
the formation
of urethane
linkages
[22–24]. of urethane linkages [22–24].
bases
(e.g.,
tertiary in
amines)
are usually
employed
in the formation
In
our
ongoing
efforts
aimed
at
searching
new
green
catalytic methods
methods [25–28]
[25–28] our
our interest
interest in
in
In our ongoing efforts aimed at searching new green catalytic
the area
area is
is driven
driven by
by the
the search
search for
for an
an efficient,
efficient, cost-effective,
cost-effective, and
and environmentally
environmentally safer
safer conversion
conversion
the
of
epoxidized
soybean
oil
(ESO)
into
bio-polyol
1
and
then
into
soy-based
PU
(Scheme
1),
with the
the
of epoxidized soybean oil (ESO) into bio-polyol 1 and then into soy-based PU (Scheme 1), with
ultimate
goal
of
moving
the
whole
process
from
laboratory
bench
to
a
pilot
scale
and
then
on
to
ultimate goal of moving the whole process from laboratory bench to a pilot scale and then on to aa
manufacturing scale.
scale. Bio-polyol
it an
an
manufacturing
Bio-polyol 11 shows
shows interesting
interesting physico-chemical
physico-chemical properties
properties that
that makes
makes it
excellent
substitute
for
petrochemical
polyols
in
the
manufacture
of
some
soy-based
PUs.
excellent substitute for petrochemical polyols in the manufacture of some soy-based PUs.
In recent
been
prepared
by by
reacting
a soybean
oil-based
polyol
with
In
recent years,
years,polyurethanes
polyurethaneshave
have
been
prepared
reacting
a soybean
oil-based
polyol
different
isocyanates
to give
foams,
elastomers,
coatings,
and and
adhesives
[1,8] [1,8]
in addition,
the
with
different
isocyanates
to give
foams,
elastomers,
coatings,
adhesives
in addition,
influence
of
a
catalysts
on
gelling
and
blowing
reactions
was
studied
to
compare
the
properties
of
the influence of a catalysts on gelling and blowing reactions was studied to compare the properties of
polymers [22–24].
[22–24].
polymers
By
taking
advantage of
of the
the high
high versatility
versatility of
of dichlorodioxo-molybdenum(VI),
dichlorodioxo-molybdenum(VI),MoCl
MoCl2O
O2, as well
By taking advantage
2 2 , as well
the direct
as Lewis
Lewisacid
acid
catalyst
describes
our in
efforts
in applying
O2 to conversion
as
catalyst
[29],[29],
this this
workwork
describes
our efforts
applying
MoCl2 O2 MoCl
to the2direct
conversion
of
epoxidized
soybean
oil
(ESO)
into
PU
in
a
one-pot
reaction
that
encompasses
the
of epoxidized soybean oil (ESO) into PU in a one-pot reaction that encompasses both the both
epoxide
epoxide ring-opening
and the subsequent
urethaneformation
linkage formation
step.
Inthe
thisadditional
way, the
ring-opening
stage andstage
the subsequent
urethane linkage
step. In this
way,
additional
steps
of acid
catalyst neutralization
andofremoval
of thesalts
ensuing
salts are completely
steps
of acid
catalyst
neutralization
and removal
the ensuing
are completely
bypassed.
bypassed.
This,with
coupled
high efficiency
and
better environmental
acceptance
MoCl
over
2O2other
This,
coupled
highwith
efficiency
and better
environmental
acceptance
of MoClof2 O
2 over
other metal-based
catalysts,
the whole
process
amenable
to industrial
scale-up.
metal-based
catalysts,
makesmakes
the whole
process
amenable
to industrial
scale-up.
2. Results and Discussion
Molybdenum is much less toxic than typical heavy metals. For this reason, molybdenum-based
compounds have found several applications as clean alternatives to heavy metals in the petroleum
petroleum
and plastic industries. In particular, MoCl2O2, and its related complexes, serve well as Lewis acid
Molecules 2017, 22, 333
3 of 13
and plastic industries. In particular, MoCl2 O2 , and its related complexes, serve well as Lewis acid
Molecules 2017, 22, 333
3 of 13
catalysts
for2017,
several
Molecules
22, 333organic transformations [29], ranging from oxidation to acylation, reduction,
3 of 13
and carbamylation
[30–32]
catalysts for several
organic transformations [29], ranging from oxidation to acylation, reduction, and
catalysts for several
organic transformations [29], ranging from oxidation to acylation, reduction, and
carbamylation
[30–32]
Reportedly,
MoCl
2 O2 can efficiently catalyze the methanolysis of a range of terminal epoxides to
carbamylation
[30–32]
Reportedly,
methanolysis
of ato
range
of reactions
terminal epoxides
to
2O2 can
β-methoxy
alcohols,MoCl
for which
5 efficiently
mol % ofcatalyze
catalystthe
generally
suffices
drive
to completion
Reportedly,
MoCl
catalyze
the
methanolysis
oftoadrive
rangereactions
of terminal
epoxides to
2O
2 can efficiently
◦
β-methoxy
alcohols,
for
which
5
mol
%
of
catalyst
generally
suffices
to
completion
within 1–5 h at 50 C or, in some cases, even at room temperature [33].
β-methoxy
5 mol
%even
of catalyst
generally suffices
to drive reactions to completion
within
1–5tohalcohols,
at 50whether
°C for
or, which
in some
cases,
at room
In
order
test
this protocol
could
be temperature
extended to[33].
the methanolysis of such internal
within
h at
°Cwhether
or, in some
evencould
at room
temperature
[33].methanolysis of such internal
In 1–5
order
to50
test
thiscases,
protocol
be extended
to the
epoxides In
as thosetooftest
ESO
(Scheme
1), we deemed
it useful to
firstmethanolysis
study the MoCl
2 Ointernal
2 -catalyzed
whether
this1),protocol
could
be extended
to thethe
of such
epoxidesorder
as those of ESO
(Scheme
we deemed
it useful
to first study
MoCl2O2-catalyzed
epoxideepoxide-ring
opening
reaction
of
methyl
oleate
epoxide
(3)
with
methanol
under
the
reported
epoxides
as those
of ESO
(Schemeoleate
1), weepoxide
deemed(3)
it useful
to first study
the the
MoCl
epoxide2O2-catalyzed
ring
opening
reaction
of methyl
with methanol
under
reported
conditions.
To
conditions.
To
this
purpose,
methyl
oleate
epoxide
(3)
was
prepared
by
reaction
of
commercial
ring purpose,
opening reaction
of methyl
oleate
(3) withby
methanol
the reported
conditions.
To
this
methyl oleate
epoxide
(3)epoxide
was prepared
reactionunder
of commercial
methyl
oleate (2)
methyl
oleate
(2)
with
H
O
/formic
acid,
according
to
a
widely-exploited
industrial
protocol
this
purpose,
methyl
oleate
epoxide
(3)
was
prepared
by
reaction
of
commercial
methyl
oleate
(2)
2
2
with H2O2/formic acid, according to a widely-exploited industrial protocol [17]. Thus, upon treatment [17].
◦ C (Scheme
Thus,of
upon
treatment
epoxide
with
5 mol % MoClindustrial
O2 in CH
OH at
2,
with
H2O
according
a widely-exploited
protocol
[17].
Thus,
upon
treatment
2/formic
epoxide
3 with acid,
5of
mol
% MoCl32to
O
2, 3route
a),50
GC-MS
analysis
of route
the a),
2 in CH3OH at 50 °C 2(Scheme
of
epoxide
3
with
5
mol
%
MoCl
O
in
CH
3
OH
at
50
°C
(Scheme
2,
route
a),
GC-MS
analysis
of
the 4 h.
GC-MS
analysis
of
the
reaction
mixture
revealed
that
substrate
conversion
reached
93%
after
2 2
reaction mixture revealed that substrate
conversion reached 93% after 4 h. Additionally, the MS and
reactiondata
mixture
revealed
that substrate
reached
afterof4methyl
h.the
Additionally,
the MS
and of
Additionally,
theofMS
and
spectral
data
of conversion
thethe
crude
product93%
displayed
characteristic
features
spectral
the
crude
product
displayed
characteristic
features
10(9)-hydroxy-9(10)spectral
data of the crude4,product
displayed
thewith
characteristic
10(9)-hydroxy-9(10)methyl
10(9)-hydroxy-9(10)-methoxy-octadecanoate
4,
which features
was
obtained
with
selectivity
≥99% as a
methoxy-octadecanoate
which was
obtained
selectivity
≥99%
asofamethyl
roughly
equimolar
mixture
methoxy-octadecanoate
4,of
which
was
obtained
with
selectivity
≥99%
as
roughly of
equimolar
mixture
of
regioisomers.
unambiguous
identification
ofunambiguous
β-methoxy
alcohol
4, aa reference
sample
was
made
roughly
equimolar For
mixture
regioisomers.
For
identification
β-methoxy
alcohol
of regioisomers.
For unambiguous
identification
oftoβ-methoxy
alcohol
4, a reference
sample was made
available
upon
subjecting
methyl
oleate
epoxide
(3)
conventional
methanolysis
by
tetrafluoroboric
acid
4, a reference sample was made available upon subjecting methyl oleate epoxide (3) to conventional
available
upon subjecting methyl oleate epoxide (3) to conventional methanolysis by tetrafluoroboric acid
(HBF
4) catalysis, according to route b of Scheme 2 [34–36].
methanolysis
by tetrafluoroboric acid (HBF4 ) catalysis, according to route b of Scheme 2 [34–36].
(HBF4) catalysis, according to route b of Scheme 2 [34–36].
Scheme
2. MoCl
a)a)
vs.vs.HBF
(routeb)b)methanolysis
methanolysis
of methyl
oleate
epoxide
Scheme
2. MoCl
O2-(route
-catalyzed (route
of methyl
oleate
epoxide
(3) (3)
HBF44-catalyzed
2 O22-(route
Scheme
2.alcohol
MoCl
a) vs. HBF4-catalyzed (route b) methanolysis of methyl oleate epoxide (3)
2O
to β-methoxy
4.2-(route
to
β-methoxy
alcohol
4.
to β-methoxy alcohol 4.
Next, we turned to check whether the reaction conditions adopted were optimal for the case at
Next,Next,
we turned
to check
whether
the
conditionsadopted
adopted
were
optimal
for case
the case
to check
whether
thereaction
reaction
were
optimal
formol
the
at at
hand. Thus,we
theturned
reaction
was studied
under
variableconditions
conditions of catalyst
loading
(1–5
%) and
hand.hand.
Thus,Thus,
the reaction
was
studied
under
variable
conditions
of
catalyst
loading
(1–5
mol
%)
and
the reaction
wasfixed
studied
under
variable
conditions
of catalyst
loading
(1–5ofmol
%) and
temperature (20–65
°C) at the
reaction
time
of 4 h. Results
are collected
in the
diagram
Figure
1.
◦
temperature
(20–65
C)°C)
at the
fixed
of44h.h.Results
Results
collected
indiagram
the diagram
of Figure
1.
temperature
(20–65
at the
fixedreaction
reaction time
time of
areare
collected
in the
of Figure
1.
Figure 1. Diagram of the substrate conversion (%) vs. catalyst (MoO2Cl2) loading and temperature in
Figure
1. Diagramofof
the substrate
(%) vs. catalyst (MoO2Cl2) loading and temperature in
the
methyl
oleateconversion
3.conversion(%)
Figure
1.methanolysis
Diagram
of the
substrate
vs. catalyst (MoO2 Cl2 ) loading and temperature in
the methanolysis of methyl oleate 3.
the methanolysis of methyl oleate 3.
Molecules
Molecules 2017,
2017, 22,
22, 333
333
44 of
of 13
13
As shown in Figure 1, substrate conversion is directly correlated to catalyst loading and temperature.
The GC-MS
analysis
of the reaction
mixtures
revealedisthat,
in thecorrelated
range of temperatures
and catalyst
As shown
in Figure
1, substrate
conversion
directly
to catalyst loading
and
loading
explored,
productanalysis
selectivity
was
retained,
beingrevealed
always that,
higher
thanrange
99%.ofOverall,
these
temperature.
The GC-MS
of the
reaction
mixtures
in the
temperatures
results
pointloading
out thatexplored,
an increase
in temperature
for always
the decrease
catalyst
and catalyst
product
selectivity can
wascompensate
retained, being
higherofthan
99%.loading,
Overall,
without
significantly
product in
selectivity.
Thiscan
means
that as long
as decrease
the temperature
is
these results
point outaffecting
that an increase
temperature
compensate
for the
of catalyst
increased,
the amount
of catalyst
can beproduct
reduced,
which isThis
oftenmeans
the most
for the
loading, without
significantly
affecting
selectivity.
thatdesirable
as long ascondition
the temperature
development
of economical
Forbeinstance,
using
3 mol
% of the
MoCl
65 °C allows
reaction
is increased, the
amount of processes.
catalyst can
reduced,
which
is often
most
desirable
condition
for
2O2 at
◦ C allows
thereach
development
of economical
processes.
For instance,
using
3 mol
% ofthe
MoCl
O
at
65
to
94% conversion
after 4 h (Figure
1), which
is the same
result
as when
methanolysis
is
carried
2 2
reaction
totypical
reach 94%
conversion
after 42,hroute
(Figure
out
under
conditions
(Scheme
b).1), which is the same result as when the methanolysis
is carried
outof
under
conditions
route b). to be employed in the methanolysis of
In light
thesetypical
results,
MoCl2O2(Scheme
appears 2,well-suited
In
light
of
these
results,
MoCl
O
appears
well-suited
to be employed
incatalytic
the methanolysis
of
epoxidized fatty esters, as an alternative
to explore its
performance
2 to
2 HBF4. Therefore, we turned
epoxidized
fattyring-opening
esters, as anreaction
alternative
to HBF
. Therefore,
we turned
its catalytic
in
the epoxide
of ESO
by 4methanol.
Instructed
by to
theexplore
new experimental
performance
in
the
epoxide
ring-opening
reaction
of
ESO
by
methanol.
Instructed
by
the new
conditions found for the methanolysis of methyl oleate epoxide (Figure 1), we performed
all
experimental
conditions
found
for
the
methanolysis
of
methyl
oleate
epoxide
(Figure
1),
we
performed
experiments at 65 °C, while catalyst loading was varied from 1 up to 3 mol %. 1H-NMR analysis of
◦ C, while catalyst loading was varied from 1 up to 3 mol %. 1 H-NMR analysis of
all experiments
at 65was
reaction
mixtures
preferred over GC-MS techniques, allowing us to estimate substrate
reaction mixtures
was preferred
over
GC-MS
techniques,
allowing
estimate substrate
conversion
conversion
and product
identity,
using
the reference
spectral
datausoftobio-polyol
1 as obtained
from
and product
identity, using
the reference
data
bio-polyol
1 as
obtained
from typical
typical
HBF4-catalyzed
methanolysis
of ESOspectral
at 65 °C for
2 hof[36,37].
Shown
in Figure
2, methanolysis
HBF
of ESO
at 65 ◦ Coffor
2 h [36,37].
Shownofin85%
Figure
4 -catalyzed
of
ESO
catalyzedmethanolysis
by HBF4 attains
a maximum
substrate
conversion
at 2 2,h, methanolysis
as estimated
of
ESO
catalyzed
by
HBF
attains
a
maximum
of
substrate
conversion
of
85%
at
2
h,
estimated
4
1
based on signal integration of residual epoxide protons (3.15–2.74 ppm) in the H-NMRas
spectrum
of
1
based on signal
integration
of residual with
epoxide
(3.15–2.74
ppm)
in the H-NMR
spectrum of
of
bio-polyol
1 (Figure
3b) in comparison
the protons
corresponding
signal
integrations
in the spectrum
bio-polyol
1
(Figure
3b)
in
comparison
with
the
corresponding
signal
integrations
in
the
spectrum
of
ESO (Figure 3a). The singlet at 3.65 ppm in the spectrum of Figure 3b can be assigned to the resonance of
ESO (Figure
3a). The
singlet
atmethyl
3.65 ppm
in the
spectrum
of Figure
can be assignedistoconcomitant
the resonance
methoxyl
protons
of fatty
acid
esters
(~7%),
suggesting
that 3b
transesterification
to
of
methoxyl
protons
of
fatty
acid
methyl
esters
(~7%),
suggesting
that
transesterification
is
concomitant
the epoxide ring-opening reaction. Yet, it is seen that longer reaction times cause transesterification
of
to the epoxidetoring-opening
it is seen that
reaction
times cause
triglycerides
take place atreaction.
a rate of Yet,
approximately
2%longer
of fatty
acid methyl
esterstransesterification
formed per each
of
triglycerides
to
take
place
at
a
rate
of
approximately
2%
of
fatty
acid
methyl
esters
formed per each
additional hour of reaction.
additional hour of reaction.
Figure 2.
2. Conversion
Conversionofofsubstrate
substrateasasfunction
functionofof
time
and
catalyst
HBF
or MoCl
O2mol
(1 mol
%
4 (or) MoCl
Figure
time
(h)(h)
and
catalyst
HBF
4 (●)
2O22(1
% (×),
(2×mol
), 2 %
mol
%
(
♦
),
3
mol
%
(
))
in
the
methanolysis
of
ESO.
(◊), 3 mol % (□)) in the methanolysis of ESO.
◦ C, the maximum
Figure
the MoCl
MoCl22O22-catalyzed
Figure 2 shows that, in the
-catalyzed methanolysis
methanolysisof
of ESO
ESO at
at 65
65 °C,
substrate conversion achievable is
still
as
high
as
85%–86%,
regardless
of
catalyst
loading
is still as high as 85%–86%, regardless
loading and
and reaction
time.
%%
ofof
MoCl
requires
as long
as 24ash24
to h
allow
conversion
to reach
80%,
2O22 O
time. However,
However,the
theuse
useofof1 1mol
mol
MoCl
as long
to allow
conversion
to reach
2 requires
while
on
doubling
or
tripling
the
catalyst
concentration,
85%
conversion
can
be
smoothly
reached
80%, while on doubling or tripling the catalyst concentration, 85% conversion can be smoothly reached
within 4 or 6 h, respectively.
respectively.
In all of the cases examined, reactions led to the selective conversion of ESO into bio-polyol 1, as
one can judge from the comparison of 1H-NMR spectral profiles of 1 obtained by HBF4 (Figure 3b) or
Molecules 2017, 22, 333
5 of 13
Molecules
2017,
333cases
In all
of22,
the
5 of 13
examined, reactions led to the selective conversion of ESO into bio-polyol
1,
1
as one can judge from the comparison of H-NMR spectral profiles of 1 obtained by HBF4 (Figure 3b) or
1
MoCl
MoCl22O
O22 (2
(2mol
mol%,
%,Figure
Figure 3c).
3c). In
Inthe
the 1H-NMR
H-NMRspectrum
spectrumof
ofFigure
Figure 3c,
3c, the
the signal
signal at
at 3.65
3.65 ppm
ppm indicates
indicates
the
presenceofofminor
minor
amounts
(~3%)
of methyl
side products.
case
with
HBF4
the presence
amounts
(~3%)
of methyl
esterester
side products.
UnlikeUnlike
the casethe
with
HBF
4 catalyst,
catalyst,
their was
amount
was
to not increase
appreciably
for prolonged
reaction
times, consistent
their amount
found
tofound
not increase
appreciably
for prolonged
reaction times,
consistent
with the
with
the
weak
propensity
of
MoCl
2
O
2
to
catalyze
transesterification
reactions
[31,38].
weak propensity of MoCl2 O2 to catalyze transesterification reactions [31,38].
1 H-NMR (CDCl , 400 MHz) spectrum of (a) ESO; (b) bio-polyol 1 from HBF -catalyzed
Figure 3.
Figure
3. 1H-NMR
(CDCl33, 400 MHz) spectrum of (a) ESO; (b) bio-polyol 1 from HBF44-catalyzed
methanolysis of
of ESO
ESO at
at 22 h,
O22-catalyzed
-catalyzed methanolysis
methanolysis of
of ESO
ESO at
at 22 h.
h.
methanolysis
h, and
and (c)
(c) from
from MoCl
MoCl22O
Other hints of the
the conversion
conversion of
of ESO
ESOinto
intobio-polyol
bio-polyol11ininthe
thereaction
reactionwith
withCH
CH
3OH/MoCl22O22
3 OH/MoCl
come from
fromthe
themeasurement
measurement
of
physicochemical
properties,
such
as
density,
viscosity,
the
of physicochemical properties, such as density, viscosity, and the and
average
average
of hydroxyl
and
epoxy functionalities
number number
of hydroxyl
and epoxy
functionalities
(Table 1).(Table 1).
Table
Table 1. Physical and chemical characteristics of bio-polyol 1.
#
#
1 from HBF4
fromMoCl
HBF2O
42
1 1from
1 from
MoCl2 O2
a
Density
Density
(Kg/dm3)3
(Kg/dm )
1.001761
1.001761
1.003678
1.003678
Viscosity
Viscosity
(cP)
(cP)
4551
4551
4567
4567
n. OH a
n. OH a
(mg of KOH/g)
(mg of KOH/g)
191
191
188
188
n.
n.
OH/Molecule
OH/Molecule
3.45
3.45
3.40
3.40
n. Epoxy/
E-Factor b b
n.
Molecule
E-Factor
Epoxy/Molecule
---1.45
—1.45
---0.24
—-
0.24
mg of KOH required to neutralize 1 g of polyol treated with excess acetic anhydride, according to
mg of KOH required to neutralize 1 g of polyol treated with
excess acetic anhydride, according to ASTM, D4274.
b
ASTM, D4274. For additional info,
b please refer [39] See experimental section for calculation.
a
For additional info, please refer [39] See experimental section for calculation.
Data reported in Table 1 indicate that it is possible to obtain the bio-polyol 1 with 3.45 hydroxyl
Data
in Table
1 indicate
that it isexpect
possible
to obtain
bio-polyol
1 with
3.45 hydroxyl
groups
perreported
molecule,
instead
of 4, as would
based
on thethe
average
number
of epoxy
groups.
groups
per molecule,
4, asexplained
would expect
basedofon
thepresence
average of
number
of epoxy
This
discrepancy
has instead
already of
been
as result
the
ethereal
bonds groups.
due to
This discrepancy
has already
beenring-opening
explained as(cross-linking
result of theprocess).
presence of ethereal bonds due to
concurrent
intramolecular
epoxide
concurrent
intramolecular
ring-opening
process).
Next, we
turned our epoxide
attention
to the “step(cross-linking
2” of the one-pot
MoCl2O2-catalyzed soy-based
Next, we turned our attention to the “step 2” of the one-pot MoCl2 O2 -catalyzed soy-based
polyurethane production, i.e., the reaction of bio-polyol 1 with toluene 2,6-diisocyanate (2,6-TDI)
polyurethane production, i.e., the reaction of bio-polyol 1 with toluene 2,6-diisocyanate (2,6-TDI)
(Scheme 3).
(Scheme 3).
Brückner and coworkers have recently studied catalytic activity of MoCl2O2 and related
complexes in the formation of mono-, di-, tri-, and tetracarbamates from a variety of alcohols and
isocyanates [30]. They found that these reactions proceed to completion at room temperature in few
minutes using as little as 0.1–1 mol % of the catalyst in chlorinated solvents.
Molecules 2017, 22, 333
6 of 13
Polyurethanes were prepared according to a reported procedure in the experimental section,
where each polyol obtained by methanolysis reaction with 1–5 mol % of catalyst on respect to
epoxide,2017,
after
in vacuo of methanol, was mixed in a plastic cup with 2,6-TDI for6 30
Molecules
22, evaporation
333
of 13s
using a high-speed mixer. The gel times at room temperature for each compound were 4–12 min.
Molecules 2017, 22, 333
6 of 13
Polyurethanes were prepared according to a reported procedure in the experimental section,
where each polyol obtained by methanolysis reaction with 1–5 mol % of catalyst on respect to
epoxide, after evaporation in vacuo of methanol, was mixed in a plastic cup with 2,6-TDI for 30 s
using a high-speed mixer. The gel times at room temperature for each compound were 4–12 min.
Scheme 3.
3. One-Pot
One-Pot preparation
preparation of
of soy-based
soy-based bio-PU
bio-PU from
from ESO
ESOby
bymeans
meansof
ofMoCl
MoCl2O
O2 catalysis.
Scheme
2 2 catalysis.
Polyurethanes obtained from the polyols were quite similar, which was reflected in their
Brückner and coworkers have recently studied catalytic activity of MoCl2 O2 and related
physical and mechanical properties.
complexes in the formation of mono-, di-, tri-, and tetracarbamates from a variety of alcohols and
The thermal properties of polyurethane samples, obtained using different amounts of catalyst,
isocyanates [30]. They found that these reactions proceed to completion at room temperature in few
were analyzed by DSC seven days after their synthesis (Figure 4). No thermal evidence of melting,
minutes using as little as 0.1–1 mol % of the catalyst in chlorinated solvents.
crystallization or decomposition were detected in the studied range of temperature from −80 °C to
Polyurethanes were prepared according to a reported procedure in the experimental section,
120 °C. It turned out that all samples were in an amorphous state and thermally stable.
where each polyol obtained by methanolysis reaction with 1–5 mol % of catalyst on respect to epoxide,
Scheme 3. One-Pot preparation of soy-based bio-PU from ESO by means of MoCl2O2 catalysis.
after evaporation in vacuo of methanol, was mixed in a plastic cup with 2,6-TDI for 30 s using a
high-speed mixer. The gel times at room temperature for each compound were 4–12 min.
Polyurethanes obtained from the polyols were quite similar, which was reflected in their
Polyurethanes obtained from the polyols were quite similar, which was reflected in their physical
physical and mechanical properties.
and mechanical properties.
The thermal properties of polyurethane samples, obtained using different amounts of catalyst,
The thermal properties of polyurethane samples, obtained using different amounts of catalyst,
were analyzed by DSC seven days after their synthesis (Figure 4). No thermal evidence of melting,
were analyzed by DSC seven days after their synthesis (Figure 4). No thermal evidence of melting,
crystallization or decomposition were detected in the studied range of temperature from −80 °C to
crystallization or decomposition were detected in the studied range of temperature from −80 ◦ C to
120 °C. It turned out that all samples were in an amorphous state and thermally stable.
120 ◦ C. It turned out that all samples were in an amorphous state and thermally stable.
Figure 4. DSC curves for bio-PU made with bio-polyol 1 and (a) 1 mol %; (b) 2 mol %; (c) 3 mol % and
(d) 5 mol % catalysts MoCl2O2.
Thermal events attributable to glass transitions were observed only for samples prepared at
lower catalyst quantity, 1 mol % and 2 mol %, with midpoints in the range between 9.4 and 10.5 °C
(Figure 4a,b). These glass transition temperatures (Tg) indicate that polyurethane samples prepared
using the one-pot synthesis herein reported with 1 mol % and 2 mol % of catalyst are rubbery at room
temperature.
Figure
4.
DSCexperiment,
curves for
for bio-PU
bio-PU
made with
bio-polyol
11 and
11 mol
%;
(b)
(c)
mol %
%
andbased
As a control
we prepared
same bio-PU
using
the
procedure
[36]
Figure
4. DSC
curves
made
withthe
bio-polyol
and (a)
(a)
mol
%;literature
(b) 22 mol
mol %;
%;
(c) 33 mol
and
(d)
5
mol
%
catalysts
MoCl
O
.
2
2
O2. case, heating of the mixture for 24 h at 110 °C was necessary to
(d) thermal
5 mol % catalysts
MoCl
on the
catalysis.
In 2this
complete the polymerization reaction, and a rubbery polymer with a Tg of 20 °C was obtained.
eventsofattributable
to glass transitions
wereofobserved
only method
for samples
Thermal
attributable
at
Another piece
evidence supporting
the suitability
the proposed
was prepared
obtained by
◦
quantity, 11,mol
mol
%,HBF
with
midpoints
the
range
between
°C
lower
catalystbio-polyol
% andwith
2 mol
%,
with
midpoints
in the
and210.5
C
polymerizing
achieved
the
the presence
ofrange
fresh 2between
mol % of9.4
MoCl
O2. The
4, in
(Figure 4a,b). These glass transition temperatures (Tg) indicate that polyurethane samples prepared
with
1 mol
% and
2 mol
% of%
catalyst
are rubbery
at room
using the
the one-pot
one-potsynthesis
synthesisherein
hereinreported
reported
with
1 mol
% and
2 mol
of catalyst
are rubbery
at
temperature.
room
temperature.
As a control experiment, we prepared the same bio-PU using the literature procedure [36] based
on the thermal catalysis. In this case, heating of the mixture for 24 h at 110 °C was necessary to
complete the polymerization reaction, and a rubbery polymer with a Tg of 20 °C was obtained.
Another piece of evidence supporting the suitability of the proposed method was obtained by
polymerizing bio-polyol 1, achieved with the HBF4, in the presence of fresh 2 mol % of MoCl2O2. The
Molecules 2017, 22, 333
7 of 13
As a control experiment, we prepared the same bio-PU using the literature procedure [36] based
on the thermal catalysis. In this case, heating of the mixture for 24 h at 110 ◦ C was necessary to
complete the polymerization reaction, and a rubbery polymer with a Tg of 20 ◦ C was obtained.
Another
Molecules
2017, 22,piece
333 of evidence supporting the suitability of the proposed method was obtained
7 ofby
13
polymerizing bio-polyol 1, achieved with the HBF4 , in the presence of fresh 2 mol % of MoCl2 O2 .
PU thus
obtained
displayed
a Tg value
very close
thatto
ofthat
the polymer
achieved
using the
one-pot
The
PU thus
obtained
displayed
a Tg value
very to
close
of the polymer
achieved
using
the
method. method.
one-pot
TGA curves
curves of
of polyurethane
polyurethane samples
samples obtained
obtained using
% and
and 22 mol
mol %
% of
of Mo
Mo catalyst
catalyst and
and
TGA
using 11 mol
mol %
literature
procedure,
analyzed
by
the
first
derivative
(DTG),
showed
a
multistep
decomposition
literature procedure, analyzed by the first derivative (DTG), showed a multistep decomposition pattern
◦ C the
pattern
in agreements
with literature
5) At
[40–43].
At temperature
lower
200
°C theloss
weight
in
agreements
with literature
(Figure 5)(Figure
[40–43].
temperature
lower than
200 than
weight
was
loss
was
due
to
small
molecule
products
(not
reacted
isocyanates,
water,
ethers,
etc.).
due to small molecule products (not reacted isocyanates, water, ethers, etc.).
Figure 5. TGA curves for bio-PU made with bio-polyol 1 and 1 mol % (blue color), 2 mol % (red color)
MoO22Cl22 catalysts
catalysts and
and literature
literature procedure
procedure (grey color) [36].
The urethane
urethane bond
bond groups
groups break
break up
up into
into isocyanates
isocyanates and
and polyols
polyols from
from 200
200 ◦°C.
The
C. At
At the
the same
same time,
time,
the
polyols
segments
decompose
to
same
kinds
of
aliphatic
alcohols
and
the
products
become
more
the polyols segments decompose to same kinds of aliphatic alcohols and the products become more
complex as
as the
the evolved
evolved products
products interact
interact with
with each
each other.
other. At
At temperature
temperature above
above 350
350 ◦°C,
primary and
and
complex
C, primary
secondary amines,
amines, vinyl
vinyl ethers,
ethers, CO
CO22,, HCN,
nitriles are
are the
the decomposition
decomposition products
products [42,43].
[42,43].
secondary
HCN, and
and nitriles
The
values
of
degradation
temperatures
for
5%
weight
loss
(T
d5%
),
for
70%
weight
loss
(Td70%
), for
The values of degradation temperatures for 5% weight loss (Td5% ), for 70% weight loss
(Td70%
),
90%90%
weight
lossloss
(Td90%
), the), maximum
degradation
temperature
(Tmax)
andand
the the
charchar
yield
at 700
°C
for
weight
(Td90%
the maximum
degradation
temperature
(Tmax)
yield
at 700
◦are
shown
in Table
2. 2.
C are
shown
in Table
Table 2.
2. The thermal properties
properties of
of the
the polyurethane
polyurethane samples.
samples.
Material
d90% (°C)
Mresidue
◦ TmaxT(°C) (◦T
◦ C)
Material
Td5% (◦ C) Td5%T(°C)
C)d70% (°C)
Td90% (T
Mresidue
(%) (%)
max ( C)
d70%
Literature procedure
272.1
378.3
401.02
465.98
5.4
Literature procedure
272.1
378.3
401.02
465.98
5.4
BIO
PUR
with
BIO PUR with 1 mol %
242.0312.4
312.4401.02 401.02 540.0 540.0
242.0
0.5 0.5
1 mol
MoCl%
2O2 catalyst
2 OMoCl
2 catalyst
BIO PUR
with
2 mol
%
BIO
PUR
with
231.5
6.3
231.5291.7
291.7408.0 408.0 609.0 609.0
6.3
MoCl2 O2 catalyst
2 mol % MoCl2O2 catalyst
These results indicate that the polyurethane sample prepared using the literature procedure is
initially the most stable. In fact, the 5% degradation weight loss is obtained at 272.1 °C, thirty and
forty degrees above the weight loss temperatures observed for Bio-PU samples deriving from 1 mol %
and 2 mol % catalyst. Moreover, temperatures at which the degradation process shows the maximum
rate follow the same order: 291.7 °C for 2 mol % Bio-PU sample, 312.4 °C for 1 mol % Bio-PU sample
and 378.3 °C for literature samples.
Molecules 2017, 22, 333
8 of 13
These results indicate that the polyurethane sample prepared using the literature procedure is
initially the most stable. In fact, the 5% degradation weight loss is obtained at 272.1 ◦ C, thirty and forty
degrees above the weight loss temperatures observed for Bio-PU samples deriving from 1 mol % and
2 mol % catalyst. Moreover, temperatures at which the degradation process shows the maximum rate
follow the same order: 291.7 ◦ C for 2 mol % Bio-PU sample, 312.4 ◦ C for 1 mol % Bio-PU sample and
378.3 ◦ C for literature samples.
At about the 70% weight loss the situation changes. The literature polyurethane sample
becomes less stable than polyurethane samples prepared using the one-pot synthesis herein reported.
In particular, the Bio-PU with 2 mol % MoCl2 O2 catalyst has the highest temperature at which
the 90% degradations weight loss is obtained. However, the shapes of the weight loss curves of
all polyurethanes are almost identical, and overall differences in thermal stability appear to be
small [44,45].
3. Experimental Section
3.1. Material and Methods
NMR spectra were recorded on a Varian Inova 400 MHz (Agilent company, Santa Clara, CA,
USA) or on an Agilent Technologies 500 MHz spectrometer (Agilent company); the 1 H-NMR spectra
(400 MHz) were referenced to residual isotopic impurity of CDCl3 (7.26 ppm). GC/MS experiments
were run on a Shimadzu GLC 17-A instrument connected with a Shimadzu ITALIA GLC/MS QP5050A
selective mass detector (Shimadzu, Milan, Italy) using a SLB-5MS column (30 m × 0.25 mm id,
film thickness 0.25 µm). Mass spectra were performed in EI mode (70 eV). FTIR spectra (Perkin Elmer,
Milan, Italy) are relative to KBr pellets or films (deposited on KBr plates).
Acetone and other common solvents were purified by standard methods. Commercial starting
materials were purchased in highest purity available from scientific chemicals suppliers (Aldrich,
Milan, Italy) and were used without purification. Soybean oil was provided by Valsoia (iodine number
of 130 g I2 /100 g).
A Viscometer Cannon-Fenske reverse flows YNT instrument (Koehlerinstrument, NY, USA) was
used to determine the viscosity using the standard method ASTM D445 (Standard Test Methods for
Kinematic Viscosity of Transparent and Opaque Liquids). The determination of density was obtained
with the pycnometer method EN ISO 1675.
Iodine number value, oxirane number (ON) and hydroxyl number of pre-polymers were
determined by EN ISO 661, ASTM D 1652, and ASTM D4274 methods, respectively [36,37].
3.2. Synthesis of the Epoxide of Methyl Oleate (3)
The epoxide was prepared using H2 O2 /HCOOH and phosphoric acid as catalyst. To a stirred
solution of methyl oleate (2) (34.6 g) at 60 ◦ C, and 75% aqueous phosphoric acid (1.14 g) was added
50% hydrogen peroxide, H2 O2 (18.11 g), in mixture with 85% formic acid (2.53 g) at regular intervals
over two h. Then, the solution was heated at 75 ◦ C and left to react for two h. Next, the temperature
was lowered to 64 ◦ C and 1.85 g of aqueous NaOH (24.9%) was added dropwise during 1 h, and the
temperature slowly raised to 85 ◦ C. Then, oxalic acid (0.12 g) was added and the mixture was left
to react for 30 min. Next, reaction mixture was transferred into a separating funnel, and layered for
1 h. Finally, the aqueous phase was removed and the epoxide 3 was dried in vacuo at 98 ◦ C for 1 h.
Chemical properties of 3 were reported: number of oxirane oxygen: 5.3 g O2 /100 g; number of epoxy
groups: 1 per molecule; and amount of iodine: 1.1 g I2 /100 g. The spectral data of epoxide 3 was in
agreement with the literature [34,35].
3.3. Synthesis of 10(9)-Hydroxy-9(10)-methoxy-octadecanoate (4)
Starting from the corresponding epoxides, methanolysis reaction was performed using HBF4 as
the catalyst, following a procedure from the literature [36,37]. The molar ratio of epoxy groups to
Molecules 2017, 22, 333
9 of 13
OH was 1:11. The catalyst loading was 0.2% with respect to the total weight of the reaction mixture.
Chemical properties of methyl 10(9)-hydroxy-9(10)-methoxy-octadecanoate (4) were reported: the
number of epoxy groups: 0.03 per molecule; the amount of –OH: 161 mg KOH/g; and fn (hydroxyl
functionality/molecule): 1. The spectral data of 4 were in agreement with the literature [34,35,37].
3.4. Synthesis of ESO
To a stirred solution of soybean oil (110.31 g) and 75% aqueous phosphoric acid (1.21 g) heated at
63 ◦ C, a mixture of 50% hydrogen peroxide H2 O2 (71.31 g) and 85% formic acid (9.89 g) was added at
regular intervals of 4 h. Then, the solution was warmed at 75 ◦ C for 2 h and, subsequently, an aqueous
solution of NaOH at 25% was added dropwise for 1 h while the temperature was raised slowly up
to 85 ◦ C. Then, oxalic acid (0.29 g) was added and the mixture was left to react for 30 min. Then,
the mixture was transferred into a separating funnel, and layered for 2 h. Finally, the aqueous phase
was removed and the ESO was dried in vacuo at 98 ◦ C for 1 h. The spectral data of ESO were in
agreement with the literature [36] and with an authentic sample provided by Greenswitch Industry
(Greenswicht, Ferrandina (MT), Italy).
Chemical properties of ESO were reported: amount of oxirane oxygen: 6.3 g O2 /100 g; number
of epoxy groups: 4 per molecule; amount of iodine: 1.5 g I2 /100 g; and the number of double
bonds/molecule: 0.05.
3.5. Methanolysis of ESO Using HBF4
Methanol 151.10 g (4.72 mol) and 1.11 g of 48% aqueous solution of HBF4 (0.006 mol) were
added to a 500-mL, three-necked flask equipped with a refluxing column, a mechanical stirrer, and a
thermometer [14]. To the refluxing mixture, heated with a water bath, 97.80 g of ESO (oxirane oxygen
6.3 g O2 /100 g) were added and left to react for 2 h. After cooling to room temperature, aqueous
ammonia (30%) was added to neutralize the catalyst and avoid hydroxylation. The mixture was
washed with water and then purified on a rotary evaporator under a low vacuum at 98 ◦ C for 1.5 h [14],
yielding 102 g of bio-polyol 1. Finally, the E-factor was determined using the Sheldon rules. [46,47].
Estimation of the E-factor:
Mass of reactants: 48% aqueous HBF4 : 0.5328 g (solvent (water) has been excluded from this
calculation); 30% aqueous NH3 : 0.225 g (solvent (water) has been excluded from this calculation);
CH3 OH: 151.1 g; ESO: 97.8 g; total amount of reactants: 0.5328 g + 0.225 g + 151.1 g + 97.8 g = 249.6578 g.
Mass of product: bio-polyol 1: 102 g; total amount of final products: 102 g.
Amount of waste: (249.6578 − 102): 147.6578 g.
E-Factor = Amount of waste/Amount of product = 147.6578/102 = 1.45.
3.6. Synthesis of Methyl 10(9)-Hydroxy-9(10)-methoxy-octadecanoate (4) Using MoCl2 O2
The following procedure was representative for methanolysis of 3. To a stirred solution of methyl
oleate epoxide (3) (1.0 g, oxirane oxygen value with 5.3 g O2 /100 g) in methanol (1.2 g, 37.5 mmol)
heated at 65 ◦ C, 32 mg of MoCl2 O2 (5 mol % respect to epoxide) were added in one portion. The reaction
progress was monitored by GC/MS. After 4 h (conv. 98%), the solvent was removed in vacuo at 98 ◦ C
for 1.5 h, thus obtaining methyl 10(9)-hydroxy-9(10)-methoxy-octadecanoate (4) [34,35] as a colorless
oil (number of oxirane oxygen: 0.04 g O2 /100 g; number of epoxy groups: 0.02 per molecule; amount
of –OH: 164 mg KOH/g; fn (hydroxyl functionality/molecule): 1).
3.7. Methanolysis of ESO Using MoCl2 O2
To a stirred solution of ESO (1.0 g, oxirane oxygen value 6.3 g O2 /100 g) in methanol (1.4 g,
40 mmol) heated at 50 ◦ C, 8.48–42.3 mg of MoCl2 O2 (1–5 mol % with respect to epoxide) were added
in one portion. The reaction progress was monitored by 1 H-NMR. After 4 h (conv. 98%), the solvent
Molecules 2017, 22, 333
10 of 13
was removed in vacuo at 98 ◦ C for 1.5 h, thus obtaining bio-polyol 1 (1.11 g); amount of OH: 191 mg
KOH/g; fn (hydroxyl functionality/molecule): 3.45; number of epoxy groups: 0.03 per molecule;
oxirane oxygen value: 0.05; density at 25 ◦ C: 1.001761 (kg/dm3 ); kinematic viscosity at 25 ◦ C: 4543 (cSt);
dynamic viscosity at 25 ◦ C: 4551 (cP) [12]. The same reaction was repeated with 100 g of ESO, yielding
110 g of bio-polyol 1, and 84 g of methanol was recovered using the column with structured packing
MellapakPlus™. The E-factor was determined using the Sheldon rules. [46,47].
Estimation of the E-Factor:
Mass of reactants: MoCl2 O2 : 1.7 g (2 mol %); CH3 OH: 140 g; ESO: 100 g; total amount of reactants:
1.7g + 140 g + 100 g = 241.7 g.
Mass of products: bio-polyol 1: 110 g; MoCl2 O2 : 1.70 g; CH3 OH: 84 g; total amount of final
product: 110 g + 1.70 g + 84 g = 195.7 g.
Amount of waste: (241.7 − 195.7) = 46 g.
E-Factor = amount of waste/amount of product = 46/195.7 = 0.24.
3.8. One-Pot Synthesis of Bio-Based PU
The consecutive steps of methanolysis of ESO and the reaction of the polyolic products with
2,6-TDI were performed in a one-pot manner as follows: (a) methanolysis of ESO according to the
previous procedure using the desired MoCl2 O2 catalyst concentration (1–5 mol %); (b) reaction of the
as prepared bio-polyol 1 (containing the catalyst) by mixing with 2,6-TDI at room temperature in a
-NCO/-OH molar ratio of 1.1: 1. Reaction mixture was left to react at room temperature, without
stirring, for 24 h, yielding the Bio-PU, which was characterized by DSC (Q200 TA Instruments, Perkin
Elmer, Milan, Italy) and TGA (Pyris 1 Perkin Elmer, Milan, Italy) analysis under N2 atmosphere with
heating rate of 20 ◦ C/min (Tg 10–12 ◦ C are better evident in the second heating scan). The thermal
analysis of all samples were performed 7 days after their synthesis in order to have consistent results.
3.9. Synthesis Bio-Based PU without Catalyst
Bio-PU was prepared using bio-polyol 1 and 2,6-TDI in a NCO/OH molar ratio of 1.1:1. The polyol
and the isocyanate components were stirred for 2 min, then the mixture was poured into a mold and
the unit was left in vacuo to evacuate bubbles (5 min at 60 ◦ C). The sample was put into an oven
for 24 h at 110 ◦ C to complete the reaction. The sample was then cooled to room temperature and
remolded. The Tg after seven days was found to be equal to 20 ◦ C, unlike what is reported in literature
(ca. 50 ◦ C) [37].
4. Conclusions
In conclusion, an atom-economical, cascade, one-pot, and two-step method for polyurethane
synthesis has been developed using the inexpensive and environmentally friendly catalyst
MoCl2 O2 , [10], as also confirmed by the safety data given in databases of ECHA (European CHemistry
Agency) [48]. Physicochemical properties of PURs obtained with this method are quite similar to those
of materials prepared by procedures in the literature.
Other important advantages of the present method are summarized as follows:
•
•
•
The synthesis of PU is carried out in a short time and at room temperature, a great advantage
when compared with reactions carried out without catalysts;
The efficiency and selectivity of the methanolysis step provides a pure polyol intermediate,
which could be used directly in subsequent reactions, avoiding the costly and time-consuming
purification procedures that are necessary when using the classical method based on HBF4 ; and
Methanol can be easily recovered and reused, thus increasing the atom economy of the process.
The E-factor for these reactions is completely different [46,47] indeed, the MoCl2 O2 allows
Molecules 2017, 22, 333
11 of 13
the recovery of methanol (purity 99.9%), which can be recycled (see experimental section for
each procedure).
The final
of
Molecules
2017,goal
22, 333
this work is the construction of a pilot apparatus located at Greenswitch S.r.l.
11 of 13
Company in Ferrandina (ITALY), of which only a part is shown in Figure 6 [49].
Figure 6. Pilot apparatus [49].
Figure 6. Pilot apparatus [49].
Acknowledgments: This research was supported by: Regione Puglia MIUR PON Ricerca e Competitività 20072013
Acknowledgments:
researchProject
was supported
by: Regione
Puglia
MIUR PON
Ricerca
e Competitività 20072013
Avviso 254/Ric. delThis
18/05/2011,
PONa3 00369
“Laboratorio
SISTEMA”,
Project
PON03PE_00004_1,
“MAIND”
Avviso 254/Ric. del 18/05/2011, Project PONa3 00369 “Laboratorio SISTEMA”, Project PON03PE_00004_1,
MAteriali eco-innovativi e tecnologie avanzate per l’INDustria Manifatturiera e delle costruzioni. Thanks to
“MAIND” MAteriali eco-innovativi e tecnologie avanzate per l’INDustria Manifatturiera e delle costruzioni.
Salvatore
Pepe, owner
Greenswitch,
for the “PIANI
SVILUPPO
INDUSTRIALI
attraverso PACCHETTI
Thanks
to Salvatore
Pepe,ofowner
of Greenswitch,
for thedi“PIANI
di SVILUPPO
INDUSTRIALI
attraverso
INTEGRATIINTEGRATI
di AGEVOLAZIONE
(PIA) Regione (PIA)
Basilicata
codiceBasilicata
progetto 227179”
Thanks
to Lucia
Vurro
PACCHETTI
di AGEVOLAZIONE
Regione
codice fund.
progetto
227179”
fund.
Thanks
to Lucia
Vurro (manager
for chemical
safety,
of Bari) for
helpful discussions
regarding
the
(manager
for chemical
safety, University
of Bari)
forUniversity
helpful discussions
regarding
the environmental
data.
environmental data.
Author Contributions: V.P. and A.R. performed the experiments, C.A., C.F., A.N., analyzed the NMR and MS
Author Contributions: V.P. and A.R. performed the experiments, C.A., C.F., A.N., analyzed the NMR and MS
data and conceived and designed the experiments, P.F. analyzed the DSC and TGA data, L.D. conceived and
data and conceived and designed the experiments, P.F. analyzed the DSC and TGA data, L.D. conceived and
designed
experiments
wrote
paper.
designed
thethe
experiments
andand
wrote
thethe
paper.
Conflicts
of Interest:
authors
declare
no conflict
of interest.
Conflicts
of Interest:
TheThe
authors
declare
no conflict
of interest.
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Pilot apparatus designed by Eng. Luciano Vassallo—Piazza Fontana 14/H, 23868 Valmadrera (LC).
Sample Availability: Samples of the compounds bio-polyol 1 and Bio-PU are available from the authors.
© 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).