Liquid-phase cyclodimerization of 1,3-butadiene in a closed batch system

Article abstract of DOI:10.1246/bcsj.20120333

Dimerization of 1,3-butadiene was investigated in a closed batch system under high-pressure conditions. 4-Vinylcyclohexene was mainly produced without using any solvents or catalysts at temperatures of 150215 °C. The conversion of 1,3-butadiene was signif

Full text of DOI:10.1246/bcsj.20120333

© 2013 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 86, No. 4, 529-533 (2013)
529
Liquid-Phase Cyclodimerization of 1,3-Butadiene
in a Closed Batch System
Daolai Sun, Fumiya Sato, Shin-ichi Yamauchi, Yasuhiro Yamada, and Satoshi Sato*
Graduate School of Engineering, Chiba University, Yayoi, Inage-ku, Chiba 263-8522
Received December 6, 2012; E-mail: satoshi@faculty.chiba-u.jp
Dimerization of 1,3-butadiene was investigated in a closed batch system under high-pressure conditions. 4-Vinyl-
cyclohexene was mainly produced without using any solvents or catalysts at temperatures of 150-215 °C. The conversion
of 1,3-butadiene was significantly dependent on the temperature and pressure. 1,3-Butadiene was converted to 4-vinyl-
cyclohexene at selectivity higher than 90 mol % with by-products of 1,5-cyclooctadiene and 1,2-divinylcyclobutane.
Large charges of reactant are efficient in achieving high conversions of 1,3-butadiene. Use of solvents, which dilute
the reactant and absorb the reaction heat, is not favorable in the present dimerization of 1,3-butadiene under pres-
sured conditions.
Dimerization and polymerization of typical conjugated
dienes, such as 1,3-butadiene, have been investigated for more
than 50 years. 1,3-Butadiene is an important industrial chemical
used as a monomer in the production of synthetic rubber. Many
products, which contain cyclic products, linear chain oligomers,
and polymers, can be produced by the dimerization, trimeriza-
tion, and polymerization of 1,3-butadiene. 4-Vinylcyclohexene
(VCH), which is an intermediate in an industrially important
styrene,1-3 can be produced by Diels-Alder reaction of 1,3-
butadiene. Different reaction conditions always gave different
products. The photochemical cycloaddition of 1,3-butadiene
mainly generates four-membered ring products such as 1,2-di-
vinylcyclobutane (DVCB).4,5 Under very high-pressure condi-
tions, reaction of 1,3-butadiene has been studied at room tem-
perature, with VCH produced from 1,3-butadiene as an only
liquid product at 700 MPa.6 A variety of homogeneous catalysts
have also been investigated in the reaction. Fe catalysts are
favorable for the formation of VCH from 1,3-butadiene.7,8
Nickel catalysts are favorable for the formation of eight-mem-
bered ring products such as cyclooctadienes depending on the
kinds and the amount of the ligands used,9 while palladium cata-
lysts are favorable for the formation of linear chain products.10
It is known that Diels-Alder reactions are accelerated under
pressurized conditions.11-17 Rao et al. investigated the reaction
of 3-methylsulfanylfuran and 3-phenylsulfanylfuran with var-
ious cycloalkenones under pressurized conditions, and almost
all the reactions proceeded at 50 °C under a pressure of 1.1 to
1.5 GPa.14 Intermolecular Diels-Alder reactions of methyl 2-
methyl-5-vinyl-3-furoate with various dienophiles under high
pressure were investigated by Drew et al.15 The yields were
higher than 90% at 1.9 GPa, 25 °C for 1 day when maleic
anhydride or N-methylmaleimide was used as the dienophile
in the reaction. Hetero Diels-Alder reactions, such as the reac-
tion of 2,3-dimethyl-1,3-butadiene with perfluorooctanonitrile,
also proceed at 50 °C and 150 MPa without using solvents
and catalysts.12 However, there are few studies on Diels-Alder
reactions of conjugated dienes themselves under pressure at
high temperature. Recently, we reported solvent-free Diels-
Alder reactions in a closed batch system.18 Typical dienes,
such as 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and iso-
prene, were used in the reactions and high yields of Diels-
Alder products were obtained within short reaction time under
solvent-free conditions. The use of solvent, which dilutes the
reactants and absorbs the reaction heat, was found inefficient
in achieving high conversions. In the reaction of 1,3-butadiene
with methyl vinyl ketone at 125 °C, a small amount of VCH
was generated as a by-product. Thus, at much higher temper-
atures, the possibility that VCH will selectively be produced
under pressured conditions attracted our interests. We prelimi-
narily found that Diels-Alder reaction of conjugated dienes
themselves proceeded under pressure at 200 °C. In this study,
we investigated the reaction behavior of 1,3-butadiene under
pressure at high temperatures and discussed the optimum
reaction conditions for yielding VCH.
Results
Dimerization of 1,3-Butadiene. Table 1 shows the effect
of reaction temperature in the reaction of 1,3-butadiene, and
Figure 1 shows the main products. Three cyclic dimers were
the main products. Catalysts and solvents were not used dur-
Table 1. Closed Batch Reaction of 1,3-Butadiene at
Different Temperaturesa)
Selectivity/mol %
Temperature Conversion
/°C
/%
VCH COD DVCB Others
215
200
175
150b)
125c)
75.3
64.5
48.0
43.5
36.6
88.8
90.6
82.2
81.5
83.7
7.7
6.5
3.8
2.4
2.1
0
3.6
2.2
9.1
10.7
7.9
0.7
4.9
5.3
6.3
a) The volume of the reaction vessel is 20 cm3. Reaction con-
ditions: 1,3-butadiene charge, 5.5 g; reaction time, 2 h. b) Reac-
tion time, 6 h. c) Reaction time, 40 h.
Published on the web March 20, 2013; doi:10.1246/bcsj.20120333

530
Bull. Chem. Soc. Jpn. Vol. 86, No. 4 (2013)
Liquid-Phase Cyclodimerization of 1,3-Butadiene
Pressure
4-vinyl-1-cyclohexene
(VCH)
1,5-cyclooctadiene
(COD)
1,2-divinylcyclobutane
(DVCB)
1,3-butadiene
Figure 1. Main products derived in the dimerization of 1,3-butadiene.
Table 2. Change in the Reaction of 1,3-Butadiene with
Reaction Timea)
Table 3. Effect of Charge of 1,3-Butadiene at 200 °Ca)
Selectivity/mol %
1,3-Butadiene Conversion
Reaction
time
Selectivity/mol %
/g
/%
VCH COD DVCB Others
Temperature
Conversion
/%
1.1
1.7
3.0
5.5
8.0
21.5
23.2
56.6
64.5
73.3
87.3
90.8
90.6
90.6
90.0
5.4
5.6
5.8
6.5
7.3
1.7
2.5
2.0
0.7
0.1
5.5
1.1
1.6
2.2
2.5
/°C
VCH COD DVCB Others
/h
175
200
2
4
6
48.0
64.3
68.3
82.0 3.8
89.3 4.9
90.2 4.8
4.9
3.2
2.1
9.1
2.6
2.9
2
4
6
64.5
72.9
75.1
90.6 6.5
90.5 6.6
91.2 6.1
0.7
0.0
0.0
2.2
2.8
2.7
a) Reaction conditions: reaction time, 2 h.
a) Reaction conditions: 1,3-butadiene charge, 5.5 g.
Table 4. Effect of Solvents in the Closed Batch Reaction of 1,3-Butadiene at 200 °Ca)
Selectivity/mol %
1,3-Butadiene
/cm3
Solvent
/cm3
Time
/h
Conv.
/%
VCH
COD
DVCB
Others
4.7 (3.0 g)
4.7 (3.0 g)
8.6 (5.5 g)
4.7 (3.0 g)
4.7 (3.0 g)
4.7 (3.0 g)
12.5 (8.0 g)
4.7 (3.0 g)
0
1
1
2
2
2
2
2
2
26.4
19.8
64.5
56.6
54.1
54.9
73.3
52.9
90.3
90.5
90.6
90.6
93.0
92.0
90.0
91.3
4.7
5.1
6.5
5.8
5.2
5.6
7.3
5.7
4.0
3.2
0.7
2.0
1.3
1.3
0.1
1.3
1.0
1.3
2.2
1.6
0.6
1.1
2.5
1.7
3.9 (THF)
0
0
3.9 (THF)
3.9 (cyclohexane)
0
7.8 (THF)
a) The volume of the reaction vessel is 20 cm3.
ing the reaction. Since the vessel made of poly(tetrafluoro-
ethylene) begins to deteriorate at about 230 °C, the reaction was
conducted at temperatures up to 215 °C. The conversion of 1,3-
butadiene increased with increasing temperature. The selec-
tivity to VCH, which was the only product generated through
Diels-Alder reaction, was high and even exceeded 90% at
200 °C. The reaction proceeded with difficulty at temperatures
lower than 150 °C: the conversion was 36.6% at 125 °C for
40 h. The selectivity to 1,5-cyclooctadiene (COD) increased
with increasing temperature while the selectivity to 1,2-di-
vinylcyclobutane (DVCB) decreased. DVCB was not detected
in the reaction at 215 °C for 2 h. A small amount, lower than
0.03 g per 5.5 g of reactant, of polymer was observed at tem-
peratures higher than 200 °C.
Table 2 shows the effect of reaction time at 175 and 200 °C.
The conversion of 1,3-butadiene increased with increasing
the reaction time. Selectivity to VCH was almost constant
irrespective of the reaction time, while the selectivity to COD
tended to increase with increasing reaction time, and the
selectivity to DVCB tended to decrease.
steeply increased with increasing the charge of 1,3-butadiene to
more than 3.0 g. The conversion increased to 73.3% at a charge
of 8 g. The selectivity to VCH was nearly unchanged while
the selectivity to COD increased with increasing the charge of
1,3-butadiene and the selectivity to DVCB decreased.
Table 4 shows the effect of solvents in the closed batch
reaction of 1,3-butadiene at 200 °C. THF and cyclohexane were
used as polar and nonpolar solvents, respectively. For 4.7 cm3 of
1,3-butadiene without using solvent, the conversion was 26.4%
for 1 h, which was higher than that of 19.8% with THF solvent.
However, the conversion without using solvent was 56.6% for
2 h, which was slightly higher than those with THF and cyclo-
hexane solvents. When 3.9 cm3 of THF and cyclohexane was
added to 4.7 cm3 of 1,3-butadiene at 200 °C for 2 h, the con-
version was 54.1% and 54.9%, respectively. In contrast, the
solvent-free reaction showed a higher conversion of 64.5% at
the 1,3-butadiene charge volume of 8.6 cm3 (Entry 3). In
the same void space of the reactor, this clearly indicates that
solvents decrease the reaction rate. The conversion was 73.3% at
a charge of 12.5 cm3 1,3-butadiene at 200 °C (Entry 7), which
was much higher than that of 52.9% in THF at the same reactant
volume. Namely, small void space in the reactor increases the
conversion.
Table 3 shows the effect of the charge of 1,3-butadiene at
200 °C. The conversion of 1,3-butadiene was low at amounts
less than 1.7 g in a vessel with a volume of 20 cm3, while it

D. Sun et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 4 (2013)
531
6
5
4
3
2
1
5
4
3
2
1
0
d
c
c
b
a
b
a
0
0
100
200
300
400
0
100
200
300
400
Reaction time / min
Reaction time / min
Figure 2. Changes of pressure with reaction time at differ-
ent temperatures in the reaction of 1,3-butadiene. 1,3-
Butadiene charge, 5.5 g; reaction temperature: (a) 125, (b)
150, (c) 175, and (d) 200 °C.
Figure 3. Changes of pressure with reaction time at differ-
ent charges in the reaction of 1,3-butadiene. Reaction tem-
perature, 175 °C. 1,3-Butadiene charge was 5.5 (a), 8.0 (b),
and 5.5 g (c); 3.9 cm3 of THF was used as solvent in (a).
The pressures were measured in the reaction of 1,3-buta-
diene at different temperatures. Figure 2 shows the changes of
the pressures with the reaction time. The maximum pressure
of 2.20 MPa was observed after 80 min from the start of the
reaction and remained almost unchanged with the reaction time
at 125 °C. It required 80, 70, and 50 min to reach the maximum
pressures at 150, 175, and 200 °C, respectively, and after that
the pressure decreased with the reaction time. The maximum
observed pressure was 4.78, 4.16, 3.35, and 2.20 MPa at 200,
175, 150, and 125 °C, respectively. The pressure at 6 h was
2.32, 1.40, and 1.98 MPa at 150, 175, and 200 °C, correspond-
ing with the conversion of 1,3-butadiene at 43.5, 68.3, and
75.1%, respectively.
The pressure during the reaction time at different charges
of 1,3-butadiene was measured at 175 °C (Figure 3). The
maximum pressure of 4.16 MPa was observed at ca. 70 min
at a charge of 5.5 g (Figure 3c). The maximum pressure of
4.20 MPa was observed at ca. 55 min at a charge of 8.0 g
(Figure 3b), and the decrease of pressure was faster than that at
a charge of 5.5 g. For the reaction in THF solvent (Figure 3a),
the maximum pressure was 2.78 MPa at ca. 70 min, and the
decrease of pressure was slower than that without solvent.
It is known that the dimerization of 1,3-butadeiene to VCH
is through Diels-Alder reaction. Many Diels-Alder reactions
proceed in both thermal and high-pressure conditions,19-25
which indicate that high temperature and pressure are efficient
for Diels-Alder reaction. Minuti et al. investigated the Diels-
Alder reactions of 5-nitro[2.2]paracyclophanepyran-6-one with
1,2-dihydro-3-vinylnaphthalene under both thermal and high-
pressure conditions, and the yields were 70 and 75% at 50 °C,
800 MPa for 24 h and at 110 °C, 0.1 MPa for 40 h, respective-
ly.23 In the reaction of 2-vinyl-2-benzo[b]furan with 2-inden-1-
one, the Diels-Alder yield was 80% at 50 °C and 1000 MPa for
3 days, while it was 68% at 76.8 °C and 0.1 MPa for 3 days.20
In our reaction conditions, high pressure was also obtained at
high temperatures, and it is reasonable that the high temper-
ature and pressure result in the high conversions of dienes.
The temperature also affects the selectivity of dimers pro-
duced from dienes. The favorable temperature for yielding
VCH is 200 °C. It is interesting that the changes in the
selectivities to COD and DVCB are always opposite in the
reaction of 1,3-butadiene. Since COD can be produced by
cis-DVCB (cis-1,2-divinylcyclobutane) under thermal condi-
tions,4,5 cis-DVCB generated is possibly converted to COD at
high temperatures.
Discussion
The mechanism of Diels-Alder dimerization of 1,3-buta-
diene had been studied by several groups. Benson estimated the
heats of formation for the transition state and concluded that
the reaction is not a concerted process but a two-step process.26
However, Doering et al. by a careful thermochemical analy-
sis showed that the mechanism of the reaction is likely to be
concerted, but not two-step.27 Li et al. also investigated the
mechanism of 1,3-butadiene dimerization by MCSCF calcu-
lations.28 Since the formation of trans-trans divinyltetrameth-
ylene biradicals, which lead to DVCB, was the most favorable
process, the stepwise biradical pathway was found slightly
more favorable than the concerted pathway, which is explained
to be simultaneous ·-bond formation. In our conditions, DVCB
is generated by a small amount, which does not agree with the
calculation results of Li and supports the concerted pathway.
Effect of Reaction Temperature and Pressure. Since the
dienes have vapor pressures higher than those of the dimers
produced at the same temperature, the pressure decreases as
the reaction proceeds. The changes in pressures measured in the
reaction of 1,3-butadiene at different temperatures are shown in
Figure 2. For the reaction at 125 °C, it took ca. 80 min to reach
the maximum pressure, which indicates that the reaction of 1,3-
butadiene hardly proceeds at 125 °C and ca. 80 min are required
for the reactant to reach 125 °C. After 80 min, the pressure
starts to plateau, which must contribute to the low conversion
(Table 1). It took less time to reach maximum pressures at high
temperatures than those at low temperatures, which is possibly
contributed to that the reaction has proceeded before reaching
the set temperature at high temperatures.

532
Bull. Chem. Soc. Jpn. Vol. 86, No. 4 (2013)
Liquid-Phase Cyclodimerization of 1,3-Butadiene
Effect of Charge of Dienes. The high conversion achieved
by using high charges attracted our interest. To understand the
effect of charge, the pressure during the reaction was measured.
As shown in Figure 3, the changes of pressure are different at
different charges. It took less time to reach to the maximum
pressure at a charge of 8.0 g of 1,3-butadiene than at a charge
of 5.5 g. In our recent paper, the temperature during the reaction
was measured in the solvent-free Diels-Alder reaction of 1,3-
butadiene with methyl vinyl ketone.18 The maximum tem-
perature was found to be 15 °C higher than the set temperature
of 125 °C, which contributed to the accumulation of reaction
heat, the increased temperature was found to accelerate the
reaction. The change in temperature was not measured in this
work since the equipment for measuring temperature could
not be used higher than 150 °C. However, the enthalpy change
of the dimerization of 1,3-butadiene to VCH was calculated
using B3LYP/6-31g(d) of Gaussian 03. The enthalpy change
sure, which resulted in low conversion. Moreover, use of
solvents dilutes the reactant, which is another reason for low
conversions.
As we have demonstrated in Table 4, large void space in
the reactor decreases conversion. Although the use of solvent
and solvent-free conditions seem to give similar conversions
(Entries 4-6 in Table 4), the time profiles of the pressures are
much different (Figure 3). The initial pressure was different
between the solvent-used and solvent-free reactions (Figures 3a
and 3c), while the conversion for 1 h (Entries 1 and 2 in
Table 4) is correlated with vapor pressure. It is, however,
difficult to discuss the relation between changes in the reaction
rate and the pressure with reaction time. It can be claimed that
small void space leads to a high conversion because of small
volume for 1,3-butadiene vapor in the reactor.
Conclusion
¹1
was ¹41.6 kcal mol at 200 °C, 4 MPa, which is close to that
Dimerization of 1,3-buadiene was studied in a closed batch
system under pressure at high temperature. VCH was obtained
at a high yield from 1,3-butadiene without using solvents or
catalysts. High temperature and pressure are necessary for the
dimerization of 1,3-butadiene. Large charges of substrate leads
to high percentage of liquid 1,3-butadiene, which is efficient
for the reaction. The reaction without solvent proceeds more
rapidly than the solvent-used reaction, since the solvent
decreases the concentration of reactant. In addition, it is
convenient that pressure is controlled only by changing the
substrate charge and the temperature. Furthermore, the solvent-
free system has a significant advantage that there is no need to
separate solvents from the products, which has less impact on
the environment.
of ¹35.4 kcal mol¹1 at 25 °C, and 0.1 MPa calculated by Janz.29
The enthalpy change of dimerization of 1,3-butadiene to VCH
was lower than those in the Diels-Alder reaction of 1,3-
butadiene with methyl vinyl ketone and methyl acrylate, which
was ¹150.1 and ¹163.4 kcal mol¹1, respectively, calculated at
125 °C, 0.1 MPa.18 It can be also understood that 1,3-butadiene,
as a dienophile, is less reactive than methyl vinyl ketone and
methyl acrylate, since 1,3-butadiene is not substituted with
electron-withdrawing group(s).24 However, it is also reasonable
that the reaction heat increases the temperature and affects
the rate.
It was found that the increase of pressure at a charge of
8.0 g (Figure 3b) was faster than that of 5.5 g (Figure 3c),
which indicated that more reaction heat was generated at higher
charge and the increase in temperature and pressure was
accelerated. Moreover, the temperature and pressure increased
quickly as the reaction proceeded, and resulted in the quick
decrease of the pressure at high charge. High charge also
leads to high percentage of liquid-phase 1,3-butadiene, which
is more reactive than gas-phase 1,3-butadiene because of high
concentration. Thus, the high charge of reactant 1,3-butadiene
is efficient for achieving high conversions.
Experimental
1,3-Butadiene was purchased from Tokyo Chemical Indus-
tries Co., Ltd. THF and cyclohexane were purchased from
Wako Pure Chemical Industries Ltd. The dimerization of 1,3-
butadiene was performed in a pressure vessel made of poly-
(tetrafluoroethylene) with a volume of 20 cm3. A prescribed
amount of reactant diene was poured into the vessel. Residual
space in the vessel contained ambient air. The vessel with
reactant diene was set in a stainless steel jacket and placed in
an oven controlled at 200 °C. After 2 h, the vessel was cooled
at 0 °C in ice bath. The recovered reaction mixture was diluted
with n-decane and analyzed on a gas chromatograph (FID-GC,
Shimadzu GC-14A) using a 60-m capillary column (Inertcap-1,
GL Science, Japan). The temperature program for analyzing the
products of 1,3-butadiene was 60 to 250 °C at a heating rate
of 10 °C min¹1. A gas chromatograph with a mass spectrometer
(GCMS-QP-5050A, Shimadzu, Japan) and a 30-m capillary
column (DB-WAX, Agilent Technologies, USA) was used
for identification of recovered compounds. The pressure was
independently measured by using another vessel with a volume
of 22.7 cm3 and with a pressure gauge ranging from 0.1 MPa to
6.1 MPa. The volume of 1,3-butadiene was calculated from
weight of liquid 1,3-butadiene poured into the vessel divided
Effect of Solvents. Under pressure, the use of solvents
resulted in lower conversions than without solvents at the same
reactant volume. It can be shown that use of solvents affects
the pressure of a reaction system through Raoult’s law:
X
Ptotal
¼
PiꢀXi
ð1Þ
i
where Pi* is the partial pressure of the component i in the
solution, and Xi is the mole fraction of the component i in
the solution. Since the solvents used in this work have vapor
pressures lower than 1,3-butadiene, the pressure of the mix-
ture would be lower than that without solvents at the same
temperature.
The pressure was measured in the reaction of 1,3-butadiene
using THF as a solvent (Figure 3a). The maximum pressure
was much lower than that without solvents, as expected from
Raoult’s law. It should be noted that the solvent also absorbs
the reaction heat, which decreases the temperature. The use
of solvent caused the decrease of both temperature and pres-
¹3
by the density of 0.64 g cm at ¹6 °C.
Enthalpy change of reaction was calculated using B3LYP30/
6-31g(d) of Gaussian 03,31 which is based on density func-
tional theory. The calculation was done without consideration

D. Sun et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 4 (2013)
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533
of scaling factor. Depending on the experimental reaction
conditions, temperature was set at 200 °C and a pressure of
4 MPa.
21 K. Kranjc, M. Kočevar, New J. Chem. 2005, 29, 1027.
22 M. Kosior, P. Kwiatkowski, M. Asztemborska, J. Jurczak,
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