Synthesis of dipentaerythritol from pentaerythritol under acidic conditions

Article abstract of DOI:10.1021/acs.oprd.0c00269

The direct synthesis of dipentaerythritol (DPE) from pentaerythritol (PE) was studied under acidic conditions. After optimization of the reaction parameters in a batch reactor, DPE was obtained with 50% selectivity when 50% PE was converted. This process, using PE in suspension in sulfolane (PE/sulfolane ratio = 2333 g/L) at 175 °C for 60 min, required a low amount of sulfuric acid (0.5 mol %). The optimized conditions were transposed to a 140 grams scale process. Finally, DPE was isolated with 16% yield (72% gas chromatography, GC purity) for 28% conversion of PE that corresponds to 57% DPE selectivity.

Full text of DOI:10.1021/acs.oprd.0c00269

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Full Paper
Synthesis of dipentaerythritol from pentaerythritol under acidic conditions
Melissa Landart, Marc Lemaire, and Estelle Métay
Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.0c00269 • Publication Date (Web): 02 Sep 2020
Downloaded from pubs.acs.org on September 2, 2020
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Synthesis of dipentaerythritol from pentaerythritol under acidic
conditions
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a
a,
a,
Mélissa Landart , Marc Lemaire * and Estelle Métay *
a
Université de Lyon, Université Claude Bernard Lyon1, CNRS, INSA-Lyon, CPE- Lyon,
Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, (ICBMS), UMR 5246,
Equipe CAtalyse, SYnthèse et ENvironnement (CASYEN), Bâtiment Lederer, 1 rue Victor
Grignard, F-69100 Villeurbanne Cedex, France.
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Dipentaerythritol (DPE) has been prepared from a slurry of Pentaerythritol (PE) in sulfolane
catalyzed by a low amount of sulfuric acid and was isolated with 16% yield (72% GPC purity) and
5
7% isolated selectivity.
OH
OH
OH
OH
0.5 mol% H SO4
Purification
2
OH
O
OH
O
HO
HO
HO
HO
OH
OH
HO
HO
OH
OH
PE in suspensions in sulfolane
Recrystallization in water
Fractional crystallization
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175°C for 1 h
PE
28% conversion
DPE
DPE
19% titrated yield
8 % titrated selectivity
16% isolated yield
57 % isolated selectivity
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ABSTRACT: The direct synthesis of dipentaerythritol (DPE) from pentaerythritol (PE) was
studied under acidic medium. After optimization of the reaction parameters in batch
reactor, DPE was obtained with 50% selectivity when 50% of pentaerythritol was
converted. This process, using pentaerythritol in suspension in sulfolane (PE/Sulfolane
ratio=2333 g/L) at 175 °C for 60 min, required a low amount of sulphuric acid (0.5 mol%).
The optimized conditions were transposed to 140 grams scale process. Finally, DPE was
isolated with 16% yield (72% GPC purity) for 28% conversion of PE that corresponds to
57% DPE selectivity.
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KEYWORDS: Selective dimerization, Pentaerythritol (PE), Dipentaerythritol (DPE), Acid
catalysis, Dehydration, Condensation
INTRODUCTION
Dipentaerythritol (DPE) is an attractive raw material used for the production of
polyesters, polyethers, polyurethanes, alkyd resins. DPE is also employed in a wide range
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synthesis of specialty chemicals such as lubricants, coatings, adhesives, plasticizers and
cosmetics.1–5 The worldwide market value of DPE experienced a steady growth in the
past few years and attained 184.6 million USD in 2018. DPE is expected to undergo a
sustained demand until 2028. Nevertheless, to the best of our knowledge, no industrial
process is dedicated to the sole production of DPE to date. Commercially available DPE
is currently a by-product of pentaerythritol (PE) production from acetaldehyde and
formaldehyde in basic medium (scheme 1).6,7 In this process, DPE yields were low, only
reaching up to 10%.
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1) NaOH solution (16wt%)
5°C for 25 min
OH
OH
O
O
2
OH
OH
OH
O
OH
O
OH
OH
4
+
HO
HO
+
+
HO
HO
OH
OH
HO
HO
O
OH
H
H
H
2) 35-40°C for 25 min
OH
PE
yield 87%
DPE
yields=1-10%
TPE
yields=1-10%
Scheme 1: Synthesis of PE from acetaldehyde and formaldehyde in basic conditions
This lack of efficient process threw up a challenge to develop new methods of DPE
synthesis that are economically viable and environmentally friendly. Analysis of the
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literature revealed that DPE could be prepared from PE under acidic conditions according
to three strategies (scheme 2).
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Dimerization without solvent
from melted PE
Way 1
Way 2
Way 3
2-10%
titrated
Acidic catalysts of which H PO (0.4-1 mol% ) yields
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220-260°C
Dimerization without solvent
from solid PE
OH
OH
OH
OH
O
2
HO
HO
+ H2O
2-22%
HO
HO
OH
OH
titrated
yields
H PW12O40 (1 mol%)
3
PE
170°C
DPE
Dimerization with solvent
5-15%
titrated
yields
Acidic catalysts of which H SO (0.01 mol%)
2
4
200°C
Scheme 2: Direct synthesis of DPE with acid catalysts
In the first strategy, dehydration of PE is performed from melted PE.8–11 A range of
inorganic acid catalysts such as phosphoric acid, sulfuric acid, titanium phosphate,
zirconium phosphate and P MxSi
type catalyst (x=V, Sn, Ti, Pb) have been reported
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0-10
for the dimerization with melted PE. Synthesis carried out at 240 °C for 1 h with
phosphoric acid (0.5 mol%) converted from 13 to 16% of PE whereas DPE was obtained
with 9% DPE titrated yield and thus 55-69% DPE selectivity.8,10 In the same way,
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synthesis performed with zirconium phosphate converted from 14 to 17.6% of PE and
produced 10% of DPE titrated yield with 56-71% of DPE selectivity.8,10 Nakajima Taro et
al. demonstrated that high DPE selectivity (from 68 to 80%) could be achieved when PE
conversion was very low (from 2 to 8%). These results were obtained when the reaction
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was performed at 260 °C for 20 min with 3 to 6 wt% of P MxSi
type catalyst (x=V, Sn,
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Ti, Pb).11 Among the processes involving melted PE, the best result concerning DPE
selectivity (80%) was obtained when a low amount of PE (3%) was converted with the
use of P Pb Si .
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Concerning the second strategy, only one reference in the literature describes the
synthesis of DPE from solid PE without solvent. Toshio Okuhara et al. proposed the
selective dimerization of the polyol with the use of heteropoly acids such as
phosphotungstic acid (H PW O ) and silica-supported 12-tungstosilicic acid
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12 40
12
(
H SiW O /SiO ). Syntheses performed with those acid catalysts (without solvent) at
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12 40
2
170 °C for 24 h converted respectively 81.6% of PE for 22.7% of DPE titrated yield and
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7% of PE for 22.8% DPE titrated yield. Among all the acids described in the literature,
those heteropoly acid are considered the best catalysts in terms of PE conversion and
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DPE selectivity.
The third strategy consists in realizing the selective oligomerization of PE in solvents.12–
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In this route, 46.5% of PE was converted giving a 22% DPE titrated selectivity with the
use of water (PE/water ratio=4000 g/L) and phosphoric acid (0.9 mol%). While syntheses
performed using sulfuric acid (0.01 mol%) in sulfolane (PE/sulfolane ratio=1260 g/L) and
tridecane (PE/tridecane ratio=756 g/L) weakly converted PE (<30%) into 43% and 46%
DPE titrated selectivity. The best DPE titrated selectivity reported in the literature, 77%,
was obtained when only 13% of PE was converted in tetralin (PE/tetralin ratio=970 g/L).15
Notably, selective dimerization of PE into DPE could be achieved at low conversion of PE
(10-30%).
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Due to the few studies reporting the direct dimerization of PE under acidic conditions,
analysis of the literature was expanded to other industrially polyols such as
trimethylolpropane (TMP), trimethylolethane (TME) and glycerol (GLY). To our
knowledge, there also have been very few studies about dimerization of those polyols
under acidic conditions (scheme 3).
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OH
PTSA (0,8 wt%)
xylene 200°C
2
HO
OH
+ H O
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HO
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OH
OH
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TMP
di-TMP
No example
HO
OH
HO
O
2
2
+ H O
2
HO
HO
HO
TME
di-TME
Nafion or Lewis acid
or Aquivion PFSA PW98
OH
OH
OH
+ H O
2
HO
OH
HO
O
OH
150°C
GLY
di-GLY
yields=21-68%
Scheme 3: Dimerization reactions under acidic conditions regarding TMP, TME and GLY
Malec Robert E. proposed a reactive distillation process for the preparation of a mixture
containing a substantial amount of ditrimethylolpropane (di-TMP).16 The reaction was
performed in xylene at 200 °C with 0.8 wt% of p-toluene sulfonic acid (PTSA) until 7 wt%
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of water was distillated. The exact quantity of synthesized di-TMP was not provided since
the reaction medium was directly put in oxidative conditions in order to convert the alcohol
functions into acids, which will be then esterified for lubricant applications.
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Manfred Richter et al. proposed to selectively synthesize di-glycerol (di-GLY) from
glycerol (GLY) under acidic conditions by the use of a falling film reactor equipped with a
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roll-like package of Nafion®. The dimerization was performed at 150 °C for 12 h under
reduce pressure (4 mbar). The optimized conditions allowed converting 93% of GLY,
giving 68% di-GLY yield. In addition, François Jérôme et al. described two routes to
selectively produce the dimer under acidic conditions. The first one used a Lewis acid,
aluminum bis(trifluoromethanesulfonyl)imide Al(TFSI) (1.4 mol%), at 150 °C for 4 h. In
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these conditions, GLY was converted at 58% for 31% di-GLY yield. The second strategy
involved a heterogeneous catalyst, Aquivion® PFSA PW98 (1.4 mol%), for 6 h at 150
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C. In that way, 82% of GLY was converted into 21% di-GLY yield. According to the
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authors, this heterogeneous catalyst could be recycled 10 times without appreciable
decrease of activity and selectivity.19
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Researches developed for the dimerization of GLY into di-GLY could represent a source
of inspiration to the selective dimerization of PE into DPE under acidic conditions.
However, PE and GLY physico-chemicals properties are totally different which make the
syntheses much more difficult to transpose. Indeed, PE is a white crystalline powder,
mostly non-soluble in usual organic solvents and melts at 260 °C. Furthermore, another
challenge regarding the selective DPE synthesis from PE is suggested by the literature.
Competitive oligomerizations of polyols throughout dimerization reaction are promoted
under acidic conditions and conduce to molecules of high molecular weight (superior then
trimer).
In order to synthesize DPE form PE under acidic conditions, we performed several
attempts without and with solvent. We also detailed the screening of the reaction
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parameters with solvent. Once the optimized conditions found, DPE selective gram-scale
synthesis was achieved.
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RESULTS AND DISCUSSION
The first studies concerning synthesis of dipentaerythritol (DPE) from pentaerythritol
(PE) were performed without additional solvent under acidic conditions. In table 1 are
presented the best conditions (temperature, reaction time) for each catalyst. The best
conditions, reported in table 1, correspond to the reaction conditions required to obtain
the highest DPE selectivity for 50 % minimum PE conversion. The target was fixed to
these values for economic reasons and in order to further effectively separate the polyols.
Indeed, separation would be more efficient if the reaction medium contains the highest
amount of dimer and the lowest amount of PE oligomers (oligo-PE). Those conditions
were obtained from optimization studies (available in supporting information) regarding
loadings catalysts (trials from 0.25 to 1 mol% catalyst), temperature (from 100 to 200°C)
and time (from 4 min to 6 h).
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Table 1: Outcome regarding direct dimerization of PE under acidic conditions without
additional solventa
OH
OH
OH
50 mol% catalyst
OH
HO
HO
+ H2O
HO
HO
O
OH
OH
without solvent
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5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
PE
DPE
PE
DPE
DPE
selectivity
(%)c
Entry
Catalyst
Conditions
conversion
(%)b
yield
(%)b
1
2
CH -SO H
180 °C for 10 min
47
48
30
25
64
52
3
3
120 °C for 240
H SO
2
4
min
Armstrong’s
acid
3
140 °C for 30 min
50
27
54
SO H
3
. 4H O
2
SO H
3
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1
20 °C for 120
4
CF -SO H
47
36
77
3
3
min
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
a
Reaction conditions: Sealed tube (15 mL), PE (7.34 mmol, 1 g), catalyst (50 mol%). b
c
Determined by GPC following the method detailed in supporting information. DPE
퐷푃퐸 푦푖푒푙푑
푃퐸 푐표푛푣푒푟푠푖표푛
selectivity is calculated from
.
) × 100
(
Synthesis performed with methanesulfonic acid at 180 °C for 10 min converted 47% of
PE for 64% DPE selectivity (table 1, entry 1). In milder conditions, at 120 °C for 240 min
using sulphuric acid and 140 °C for 30 min catalysed by Armstrong’s acid (naphthalene-
1
,5-disulfonic acid), PE was half converted for 52 and 54% DPE selectivity (table 1,
entries 2 and 3). The best DPE selectivity, 77%, was obtained when 47% of PE was
converted at 120 °C for 120 min in triflic acid (table 1, entry 4). This overview of the
reaction conditions that furnished the bests results regarding DPE selectivity when 50%
of PE was converted come from a screening of conditions available in supporting
information.
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Nevertheless, solvent-free direct dimerization of PE in acid conditions was not pursued.
Indeed reproducibility issues were encountered because of physic aspect of the reaction
medium. Systems without solvent were usually very viscous and difficult to stir.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
However, the first experimentation highlighted factors which could limit both PE
conversion and DPE production during the synthesis. The first one was related to the
physicochemical properties of polyols. PE has a higher melting point (260 °C) than DPE
(220 °C). This parameter has directly an impact on the heating demand for solvent-free
dimerization from melted PE. As previously observed, the process implementation of
solvent-free dimerization could be complicated through physic aspect of the system
(viscosity).
The second factor was DPE reactivity throughout the synthesis. In order to get a better
understanding of this reactivity over time, the solvent-free dimerization was studied at 120
°
C, using 50 mol% of sulphuric acid (figure 1). Taking samples in the same reaction
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medium over time was difficult due to the viscosity and fast solidification of the system.
Consequently, we carried out separate experiments and stopped at different times.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
9
0
7
7
80
7
0
5
7
60
5
2
2
5
4
3
2
1
0
0
0
0
0
0
3
8
48
39
2
9
26
26
5
24
2
2
2
0
1
0
7
0
1
2
3
4
5
6
7
t (h)
PE conversion
DPE yield
DPE selectivity
Figure 1: PE conversion and DPE selectivity over time. Reaction conditions: Sealed tube,
PE (7.34 mmol, 1 g), without solvent, H SO (50 mol%), 120 °C. The conversion of PE
2
4
and yield of DPE were determined by CPG following the method detailed in supporting
information.
In those conditions of reaction, from 1 to 4 h, both PE conversion and DPE selectivity
increased respectively from 29 to 48% and from 24 to 52%. After 4 h, once 50% of PE
was converted, DPE selectivity fell down from 52% to 26%. This study shown also that
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8
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
even at low PE conversion, DPE selectivity was not total and side-reactions occurred
since the beginning of the synthesis and among the major side products, TPE was
detected (in GPC).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Following observations and comments, we propose a reaction mechanism in order to
explain the evolution of DPE yield and selectivity (figure 2).
HO
HO
HO
HO
OH
H
OH
HO
HO
H
HO
+ H O + HO
HO
+ H O + HO
OH
O
O
H
O
OH
OH
H
OH
OH
2
+ H O
OH
OH
2
2
OH
Thorpe ingold
Effect
OH
HO
(2)
O
OHOH
(3)
H
(1)
(4)
HO
HO
HO
HO
HO
HO
OH
OH
OH
OH
HO
O
O
OH
H
H
O
....
O
OH + H2O
HO
OH + H2O
HO
HO
Thorpe ingold
Effect
OH
O
O
n
OH
OH
OH
(7)
O
O
HO
HO
H
HO
OH
OH
(5)
(6)
oxetanes
Figure 2: Proposed mechanism for DPE synthesis under acidic conditions
Under acidic conditions, PE (1) could be dehydrated into 3,3-bis(hydroxymethyl)oxetan-
1-ium (2) named oxonium-oxetane-PE. Compound (2) was observed in our reaction
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media and prepared separately to confirm our observations. This species is highly
reactive due to the protonation of the oxygen within the cycle and due to its cycle
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
20
tension. BHMO oxonium oxetane (2) could rapidly react either with PE (1) in order to
form DPE (3), or with DPE (previously produced) to be transformed into TPE (5). It could
also react, with another equivalent of (2) thereby resulting in the formation of oligomers
(7). Indeed, polymerization of oxetanes in acid conditions is thoroughly reported in the
literature.20–22 Experimentally, we observed that in acidic aqueous conditions, oxetane (2)
and (4) can also give PE and DPE. Once DPE (3) is produced, it could also be dehydrated
into its oxonium oxetane derivative (4). This oxetane could react with PE (1) to produce
TPE (5), or with itself or with BHMO oxonium oxetane (2) resulting in the formation of
oligomers (7). TPE (5) could also be transformed into its corresponding oxonium oxetane
(6).
Assumptions are that formation of oxetane-TPE (6) should be faster than the formation
of oxetane-DPE (4), which should itself be faster than the formation of oxetane-PE (2),
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
due to Thorpe Ingold effect. These hypotheses could explain the facts observed for all
the syntheses performed. Even at very low conversion of PE, selectivity of DPE was low.
These side reactions appearing from the beginning of the reaction essentially lead to the
high reactivity of the oxonium-oxetane-PE (2) and then due to rapid formation of oxonium-
oxetane of DPE (4) and TPE (6). It appeared that a maximum was reached when 50% of
PE was converted with a maximum of 50% DPE selectivity. Beyond this point, DPE
selectivity rapidly decreased. This could be explained by the fact that at this maximum,
the reaction medium is composed of a mix of polyols and oxonium-oxetanes species
which rapidly react with each other in order to form molecules with higher molecular
weight than the trimer (7). The main challenge of DPE selectivity improvement is
essentially due to the formation of those oxetanes throughout the DPE synthesis in acid
conditions.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
In order to optimize this process, it was necessary to consider both chemical and physical
aspects of the polyols. Performing the selective dimerization in solvent could require less
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heating and solved reproducibility issues encountered in free-solvent dimerization. Thus,
several experiments were undertaken to identify a solvent for the production of DPE from
PE. These polyols were insoluble in acetonitrile, ethyl acetate, acetone, diethyl ether,
PEG 200, cyclopentyl methyl ether (CPME); 2-methylbutan-2-ol, N-methyl-2-pyrrolidone
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(NMP),
1,3-dimethyl-2-imidazolidinone
(DMI),
dichloromethane,
chloroform,
cyclohexane. Solubility differences between PE and DPE was observed in several polar
solvents (table 2).
Table 2: PE solubility and DPE solubility in usual solvents
Solvent
Trimethylolpropane
Sulfolane
T (°C)
PE solubility
Very slightly soluble
Soluble
DPE solubility
Insoluble
100
100
Very slightly soluble
Soluble
DMSO
100
Soluble
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7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Water
Methanol
Ethanol
100
65
Soluble
Very slightly soluble
Insoluble
Very slightly soluble
Very slightly soluble
Very slightly soluble
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
78
Insoluble
Acetic acid
100
Insoluble
PE and DPE are insoluble in most of solvents excepted in water, sulfolane and DMSO.
Additional solubility tests were performed in order to determine more precisely solubility
limits of the polyols in those solvents (figures 3 and 4).
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2
200.00
2000.00
800.00
1600.00
400.00
1200.00
1
PE solubility lim
in sulfolane
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
PE solubility lim
in water
1000.00
800.00
600.00
PE limit solubilit
in DMSO
400.00
200.00
0.00
0
25
50
75
100
125
150
175
200
T (°C)
Figure 3: Limit solubility of PE in sulfolane, water and DMSO.
PE presents a relatively good solubility in water (46 g/L at 20 °C, blue curve on figure 3),
in dimethyl sulfoxide (DMSO; 44 g/L at 36 °C, orange curve on figure 3) and in sulfolane
(
37 g/L at 110 °C, green curve on figure 3).
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
00.00
250.00
DPE solubility limit i
sulfolane
200.00
150.00
100.00
50.00
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
DPE solubility limit i
water
DPE limit solubility i
DMSO
0.00
0
25
50
75
100
125
150
175
200
T (°C)
Figure 4: Limit solubility of DPE in sulfolane, water and DMSO.
DPE is slightly soluble in water (15 g/L at 70 °C, blue curve on figure 4), in
dimethylsulfoxyde (DMSO; 15 g/L at 45 °C, orange curve on figure 4) and in sulfolane (20
g/L at 140 °C, green curve on figure 4).
Physicochemical properties of those polyols represented an issue regarding the
dimerization implementation and the quantitative analysis of the reaction medium. A
suitable dosage procedure was developed involving polyols derivatization (scheme 4) and
gas chromatography analyses (dosage from calibration range). Details of the
development and the procedure are available in supporting information.
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O
O
O
O
O
O
HO
HO
HO
OH + HO
HO
O
O
O
O
O
O
O
DMAP (10 mol%)
150°C for 1h30
O
OH
OH
+
O
O
O
+
O
O
OH
OH
O
O
O
O
Excess
O
O
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 4: PE and DPE acetylation with an excess of acetic anhydride catalyzed by
DMAP
Once the analysis method was determined, optimization of PE dimerization parameters
in batch autoclave reactor was carried out.
PE dimerization in batch autoclave reactor study
From literature study, several parameters that could influence the outcome of the
dimerization reaction were highlighted such as the presence of solvent, the acid catalyst,
the reaction temperature and the presence of water throughout the synthesis.
In order to get further information, the influence of the solvent on both PE conversion and
DPE selectivity was first studied in autoclave reactor with mechanical stirring (table 3).
Table 3: Influence of the solvent on DPE selectivity and PE conversion – Dimerization
performed with 0.1 mol% of sulfuric acid for 16 h at 140 °Ca
2
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
OH
OH
OH
H2SO4 (0.1 mol%)
OH
O
HO
HO
+ H2O
HO
HO
OH
OH
PE/Solvent ratio=500g/L
140 °C for 16 h
PE
DPE
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
PE
PE
DPE
DPE
Entry
Solvent
conversion
soluble
yield (%)b selectivity (%)
(
%)b
1
2
Tetralin
CPME
Not
Not
14
0.2
0
1.4
0
15
2-methylbutan-
3
Not
0.4
0.06
15
2ol
4
5
NMP
DMI
Not
Not
11
6
0.2
0
1.8
0
2
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Partiall
6
Sulfolane
47
20
43
y
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
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DMSO
Water
Totally
Totally
19
7
37
2.5
0.1
2.5
a
Reaction conditions: Autoclave reactor (250 mL), PE (0.22 mol, 30 g), solvent (60 mL,
b
PE/Solvent ratio=500 g/L), H SO (0.1 mol%, 11.8 L), 140 °C, 16 hours. Determined by
2
4
GPC following the method detailed in supporting information.
Syntheses achieved in solvents in which PE is not soluble such as tetralin, cyclopentyl
methyl ether (CPME), 2-methylbutan-2ol, N-methyl-2-pyrrolidone (NMP) and 1,3-
dimethyl-2-imidazolidinone (DMI), converted a small amount of pentaerythritol (from 0.4
to 15%) in favour of side-products since no DPE was observed (table 3, entries 1 to 5).
Dimerization reaction in sulfolane converted 47% of pentaerythritol for 43% DPE
selectivity (table 3, entry 6). At this temperature, PE is in suspension in sulfolane, PE limit
solubility in sulfolane at 140 °C is 250 g/L (green curve on figure 3). Thus, PE in
suspension could be considered as a PE reservoir which could continuously feed the
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system during the dimerization. Conversely, using a solvent in which PE is totally soluble
seems inappropriate since the reaction performed in DMSO converted 19% of PE for 37%
DPE selectivity (table 3, entry 7) and in water converted only 2.5% of PE in favour of 0.1%
of DPE (table 3, entry 8).
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Using a solvent in which PE is partially soluble demonstrated its beneficial impact on DPE
selectivity. Sulfolane have therefore been preferred as solvent for dimerization reaction
from PE. Solubility of PE in the solvent should be an important parameter throughout PE
dimerization in acid conditions. Hence, impact of PE/Sulfolane ratio was next investigated
(figure 5).
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32
31
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30
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PE conversion
DPE yield
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0
1
8
1
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17
16
2
0
0
0
1
2
1
4
DPE selectivity
5
0
250
500
600
700
835
PE/Sulfolane ratio (g/L)
Figure 5: PE conversion and DPE selectivity Versus PE loading. Reaction conditions:
Autoclave reactor, PE, Sulfolane (60 mL), H SO , (0.1 mol%), 140 °C, 16 hours. The
2
4
conversion of PE and yield of DPE were determined by gas chromatography following the
method detailed in supporting information.
In a concentrated medium with PE fully soluble, which corresponds to PE/Sulfolane ratio
at 250 g/L (limit solubility at 140 °C, green curve on figure 3), DPE selectivity reached
2
6% for 46% conversion of PE (figure 5). At iso-conversion of PE, DPE selectivity
increased when PE/Sulfolane ratio increased from 250 to 500 g/L (figure 5), thus
confirming the importance of the presence of PE suspensions at the beginning of the
synthesis. Indeed, at this temperature and for this concentration, PE exceeds the limit of
solubility (green curve on figure 3). The selectivity dropped at 32% when increasing this
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ratio at 600 g/L (figure 5). A maximum value at 31-32% DPE selectivity is obtained for
PE/Sulfolane ratios from 600 to 835 g/L (figure 5). Experiment with 600 to 835 g/L needed
a high amount of PE which means that a high amount of acid catalyst was used in order
to study the influence of PE loading at 0.1 mol% of sulfuric acid. Throughout the study,
the volume of sulfolane was kept constant. Solutions which used PE/Sulfolane ratios from
0
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600 to 835 g/L were more concentrated in sulfuric acid. This could explain the fact that
side-reactions, such as oligomerization from the dimer, were accelerated thereby
decreasing DPE selectivity. Dimerization reaction from PE in suspensions were preferred,
PE potentially acting as a reservoir throughout DPE synthesis. During PE loading study,
side-reactions appeared to significantly affect DPE selectivity.
Nevertheless, the results obtained in autoclave reactor were difficult to compare due to
some variances with this system. After addition of all the compounds, the reactor was
sealed. A strip heater then ensured heating. This method induced time variations during
the temperature rise (from 15 min to 2 h) and the cooling (from 3 to 4 h), depending of
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the targeted temperature. Moreover, the maximum temperature provided by this system
was 160 °C. Changing the equipment was proposed in order to use one in which the
addition of acid catalyst could be realized when system is stabilized at the target
temperature. Thus, optimization of the parameters was pursued in a glass reactor.
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0
Transposition from autoclave reactor to glass reactor
Transposition process was investigated in order to both scale-up (realize a 140 grams
scale process) and to avoid variances from synthesis performed in autoclave reactor
which could influence the results. Hence, the optimal conditions previously determined in
autoclave reactors were directly transposed into glass reactor (figure 6).
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