Published on the web August 1, 2012
831
Stable Vapor-phase Catalytic Conversion of Pinacolone into 2,3-Dimethyl-1,3-butadiene
Satoshi Sato,* Natsumi Sato, and Yasuhiro Yamada
Graduate School of Engineering, Chiba University, Yayoi, Inage-ku, Chiba 263-8522
(Received May 18, 2012; CL-120433; E-mail: satoshi@faculty.chiba-u.jp)
In the vapor-phase synthesis of 2,3-dimethyl-1,3-butadiene
from pinacolone over modified alumina catalysts, it was found
that alumina modified with transition metals such as Co
stabilized the conversion of pinacolone and produced 2,3-
dimethyl-1,3-butadiene selectively under hydrogen flow con-
ditions, whereas the catalytic activity of pure alumina was
seriously deteriorated irrespective of its high initial activity.
were prepared by impregnating metal nitrate solution to a
support, and water was evaporated at ambient pressure and
ca. 70 °C by illuminating with a 350-W electric light bulb. The
obtained solid was calcined at 500 °C for 3 h.
The catalytic reaction was performed in a fixed-bed down-
flow glass tube reactor at atmospheric pressure in H2 or N2 flow
of 30 cm3 min¹1. Prior to the reaction, a catalyst was preheated in
¹1
the carrier gas at a flow rate of 30 cm3 min at 500 °C for 1 h.
The effluent was collected in a liquid nitrogen trap at ¹196 °C
every 1 h, and analyzed by FID-GC (GC-14A, Shimadzu) using
a 30-m capillary column of TC-5 (GL Science, Japan). A GC-
MS (QP5050A, Shimadzu) was used for identification of
products in the effluent. A typical reaction was carried out
under the conditions at 425 °C and W/F = 0.265 g h cm¹3 where
W and F are catalyst weight and reactant feed rate, respectively.
In our preliminary screening of catalyst, Al2O3 was found to
be selective for the formation of DMB: pure Al2O3 catalyst
showed an excellent selectivity to DMB of 96.2% (Table 1). But
the catalytic activity of Al2O3 steeply decreased with time on
stream (Figure 2) irrespective of carrier gas, either N2 or H2.
After reaction the alumina catalyst turns black because of being
covered by coke. Other catalysts such as SiO2-Al2O3 and TiO2
as well as Al2O3 showed deactivation, as shown in detail in the
Supporting Information (Figure S111). However, ZrO2 showed
an induction period in the initial stage of reaction.
2,3-Dimethyl-1,3-butadiene, abbreviated as DMB, is a
useful chemical such as a synthetic rubber and a diene in
Diels-Alder reactions. It is well known that ketones are
synthesized in the pinacol rearrangement of vicinal diols:
for example, 2,3-dimethyl-2,3-butanediol, so-called pinacol, is
converted into 3,3-dimethyl-2-butanone, pinacolone, through
1
dehydration. Homogeneous acids such as SbCl5-AgSbF6 and
2
BF3 catalyze the rearrangement. It is reported that the
rearrangement proceeds under supercritical conditions without
catalyst.3 It is also reported that solid acids such as aluminum
phosphate,4,5 sulfated zirconia,6 and zeolite7 catalyze the
rearrangement in the vapor phase. In the vapor-phase catalytic
rearrangement, however, DMB can be produced as a by-product,
into which pinacolone is transformed and dehydrated.4,5
It is reported that DMB is produced from pinacolone
through migration of a methyl group of pinacolone and the
following dehydration over alumina.8-10 The selectivity to
pinacolone is at most 77 mol %.8 But it has some problems
such as degradation of catalyst and the resulting low yield of
DMB for a long operation. The catalyst deactivation prevents
industrialization of the process. In acid-catalyzed reactions, the
catalytic activity is often deactivated due to coke formation.
Supported noble metals such as Pt often affect stabilization of
catalytic activity in the acid-catalyzed reactions. In this paper,
we developed an effective catalytic system for the conversion of
pinacolone into DMB (Figure 1) using acid catalysts modified
with transition metals, such as Co, Ni, Cu, Ag, and Rh.
Pinacolone, metal nitrates, and Rh/Al2O3 catalyst were
purchased from Wako Pure Chemical Industries Ltd. ZrO2
(RSC-HP) and TiO2 (CS-750-24) were supplied by Daiichi
Kigenso Kagaku Kogyo Co., Ltd. and Sakai Chemical Industry
Co., respectively. SiO2-Al2O3 (N632HN) was purchased from
Nikki Chemical Co. Al2O3 (DC2282, specific surface area
of 200 m2 g¹1; other basic data are cited in the Supporting
Information11) was supplied by Dia Catalyst. Supported catalysts
Among the tested catalysts, Al2O3 was the most selective, so
we modified Al2O3 with transition metals. Table 1 also shows
the catalytic performance of several Al2O3 modified with
Table 1. Conversion of pinacolone over metal oxide supported
on alumina and pure oxide catalystsa
Selectivity/mol %b
Catalyst
(oxide content/wt %)
Conversionb
/mol %
DMB DMBns 33DM1
Al2O3
SiO2-Al2O3 (0)
ZrO2
TiO2
(0)
65.3
55.7
67.8
41.3
96.2
66.7
80.0
86.6
3.2
10.3
6.7
0.2
2.1
0.5
0.6
(0)
(0)
8.5
MnO2/Al2O3 (2.5)
Fe2O3/Al2O3 (2.5)
Co3O4/Al2O3 (2.5)
54.9
77.3
87.7
81.2
91.8
83.8
96.6
98.4
97.7
96.6
91.9
85.8
86.9
86.5
0.8
2.1
3.3
7.1
11.9
8.1
0
0.2
0
0.4
0.9
0.9
0.5
NiO/Al2O3
(2.5)
CuO/Al2O3 (2.5)
Ag2O/Al2O3 (2.5)
Rh/Al2O3
(0.5c)
11.0
O
aCarrier gas, H2; reaction temperature, 425 °C. bAverage
conversion in the initial 5 h; DMBns, average selectivity to
the sum of 2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene,
H2O
c
and 2,3-dimethylbutane; 33DM1, 3,3-dimethyl-1-butene. Rh
metal content.
Figure 1. Conversion of pinacolone to DMB.
Chem. Lett. 2012, 41, 831-833
© 2012 The Chemical Society of Japan