a
Table 1 Methanol carbonylation with SILP [BMIM][Rh(CO)
2
2
I ]–[BMIM]I–SiO
2
catalyst
c 21 21
TOF /mol mol h
d
Production rate /mol L
21 21
h
Product selectivity (%)
b
Conv. (%)
Entry
P
r
/bar
AcOR
DME
AcOR
DME
AcOH
AcOMe
DME
1
2
3
20
10
10
99
45
20
76.5
69.7
32.1
3.4
1.5
3.3
21.0
19.1
8.8
0.9
0.4
0.9
21
21.4
4.7
14.1
74.4
93.1
76.7
4.2
2.2
9.2
21
e
a
3
Reaction conditions: T
r
= 180 uC, reaction time = 1.5 h, FCO = 50 ncm min , Fliq (MeOH : MeI = 75 : 25 wt%) = 0.69 g h
.
b
c
Determined within 1–5%. Catalyst activities are determined as turn-over frequencies (TOFs) at steady-state conversions and reported in mol
d
21
product per mol rhodium per hour with TOFAcOR = TOFAcOH + TOFAcOMe
the volume of the supported ionic liquid catalyst solution is the same as the initial ionic liquid volume.
. Production rates calculated as TOF 6 nRh 6 VIL , assuming that
e 3 21 21
FCO = 100 ncm min , Fliq = 1.38 g h
.
(
monomodal): 13.2 nm) was added, whereafter the suspension was left with
to 96% acetic acid), most likely as a result of a relatively longer
residence time of the reactant gas in the SILP system.
Accordingly, reaction at low space velocity at a pressure of 10
bar (Table 1, entry 3) resulted in increased formation of acetic
acid (and DME, 9%) relatively to ester (ester/acid ratio of 5.4)
than found at twice the gas space velocity (entry 2, ester/acid
ratio = 19.8). Moreover, the formation of DME proved to be
reduced to about 2% by applying a combination of low reaction
pressure and long contact time of the gas with the supported
ionic liquid catalyst phase (i.e. low gas space velocity), thus
providing a mixed acetyl reaction product with high purity
slow stirring for an additional 4 h before the volatile solvent was removed
under reduced pressure at room temperature. The residue consisting of fine
red–brown SILP catalyst particles was finally dried in vacuo overnight
(0.1 mbar, 60 uC) and further kept under CO atmosphere at ambient
pressure prior to use.
§
Gas-phase methanol carbonylation. In catalyst tests 1.00 g of SILP catalyst
containing 0.0437 mmol Rh) was placed as fixed catalyst bed in the
tubular reactor, pressurized with CO gas at a constant flow (FCO) to a
constant reaction pressure (P ) while heated to a constant reaction
temperature (T ) of 180 uC (the rest of the test system was heated to ca.
60 uC). Then, at the preset reaction pressure and temperatures the reactor
was bypassed, and the vaporized liquid methanol–methyl iodide feed (75 :
25 wt%) introduced into the bypassed reactant gas at a constant flow (Fliq
(
r
r
1
)
resulting in a CO/methanol ratio of approximately 8. When the reactant
gas mixture composition became constant (determined by FID-GC
analysis) the reaction was initiated by passing the reactant gas stream
through the SILP catalyst bed.
(
about 98%) which can be further hydrolyzed into acetic acid if
required.
In conclusion, the introduced SILP Monsanto catalysts are
different from present catalytic alcohol carbonylation technol-
ogies by using an ionic liquid as reaction medium, and by
offering a highly efficient use of the ionic liquid catalyst phase
containing the precious metal catalyst, having it dispersed on a
robust, inert, porous high-area support material as a liquid film
the size of a diffusion layer. Moreover, the fixed-bed SILP
process design requires a smaller reactor size than existing
technology in order to obtain the same productivity, which
makes the SILP carbonylation concept potentially interesting
for technical applications. The shift in CO stretching frequencies
in the FT-IR spectra of the SILP catalyst indicated bonding
interaction between protons in the imidazolium cation and the
1 K. Weissermel and H.-J. Arpe, in Industrial Organic Chemistry, Wiley-
VCH, Weinheim, 2003, ch. 7, pp. 145–192.
2
N. Yoneda, S. Kusano, M. Yasui, P. Pujado and S. Wilcher, Appl.
Catal. A, 2001, 221, 253–265 and references therein.
3 (a) J. H. Jones, Platinum Met. Rev., 2000, 44, 94–105; (b) G. J. Sunley
and D. J. Watson, Catal. Today, 2000, 58, 293–307.
4
P. M. Maitlis, A. Haynes, G. J. Sunley and M. J. Howard, J. Chem.
Soc., Dalton Trans., 1996, 2187–2196.
5
(a) M. J. Howard, M. D. Jones, M. S. Roberts and S. A. Taylor, Catal.
Today, 1993, 18, 325–354 and references therein; (b) N. De Blasio,
M. R. Wright, E. Tempesti, C. Mazzocchia and D. J. Cole-Hamilton,
J. Organomet. Chem., 1998, 551, 229–234; (c) N. De Blasio, E. Tempesti,
A. Kaddouri, C. Mazzocchia and D. J. Cole-Hamilton, J. Catal., 1998,
176, 253–259; (d) C. M. Thomas and G. S u¨ ss-Fink, Coord. Chem. Rev.,
2003, 243, 125–142 and references therein.
2
rhodium metal center in the [Rh(CO) I ] anion, thereby
2
2
6
7
8
9
R. S. Drago, E. D. Nyberg, A. El A’mma and A. Zombeck, Inorg.
Chem., 1981, 20, 641–644.
A. Haynes, P. M. Maitlis, R. Quyoum, C. Pulling, H. Adams, S. E. Spey
and R. W. Strange, J. Chem. Soc., Dalton Trans., 2002, 2565–2572.
(a) D. Zhao, M. Wu, Y. Kou and E. Min, Catal. Today, 2002, 74,
157–189; (b) T. Welton, Coord. Chem. Rev., 2004, 248, 2459–2477.
Ionic Liquids in Synthesis, ed. P. Wasserscheid and T. Welton, Wiley-
VCH, Weinheim, 2003.
lowering the nucleophilicity of the metal. Hence, assuming the
rate determining step in the carbonylation reaction to be the
oxidative addition of methyl iodide to the metal center, as
4
normally found, an even higher catalyst activity may be
realized by employing ionic liquids containing cations with
lower ability for hydrogen bonding (i.e. with lower Kamlet–Taft
1
9
a parameter) like, e.g. 1,2,3-trialkylimidazolium cations. This
proposition will be examined in future work.
10 US Pat. Appl., 0059153A1, 2004 (IFP).
1 US Pat. Appl., 0212295A1, 2003 (Eastman).
2 (a) C. P. Mehnert, Chem.–Eur. J., 2005, 11, 50–56 and references
1
1
The work was supported by the Danish Research Council for
Technology and Production (project no. 21-04-0068 and 26-04-
therein; (b) A. Riisager, R. Fehrmann, M. Haumann and
P. Wasserscheid, Eur. J. Inorg. Chem., in press.
0
139) and by the Villum Kann Rasmussen Foundation via a
13 (a) A. Riisager, R. Fehrmann, S. Flicker, R. van Hal, M. Haumann and
P. Wasserscheid, Angew. Chem., Int. Ed., 2005, 44, 815–819; (b)
A. Riisager, R. Fehrmann, M. Haumann, B. S. K. Gorle and
P. Wasserscheid, Ind. Eng. Chem. Res., 2005, 44, 9853–9859.
postdoctoral grant (A. Riisager).
1
4 Dan. Pat. Appl., 00735, 2005 (Technical University of Denmark).
Notes and references
15 P. J. Dyson, J. S. McIndoe and D. Zhao, Chem. Commun., 2003,
508–509.
{ Catalyst preparation. The Monsanto-type SILP catalyst was initially
prepared as earlier described, whereas the [BMIM][Rh(CO)
liquid was synthesized by stirring a dry, degassed methanolic solution (8 ml)
1
5
2
I
2
] ionic
16 S. Burger, B. Therrien and G. S u¨ ss-Fink, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2003, 59, i53–i54.
17 A. Fulford, C. E. Hickey and P. M. Maitlis, J. Organomet. Chem., 1990,
398, 311–323.
18 J. Dupont and J. Spencer, Angew. Chem., Int. Ed., 2004, 43, 5296–5297.
19 L. Crowhurst, P. R. Mawdsley, J. M. Perez-Arlandis, P. A. Salter and
T. Welton, Phys. Chem. Chem. Phys., 2003, 5, 2790–2794.
1
2
7
containing 16.5 mg [Rh(CO)
2
I]
(0.029 mmol) metal precursor and
02.5 mg ionic liquid [BMIM]I (1.137 mmol) (i.e. with excess of ionic
3
liquid) under argon atmosphere for 24 h. Subsequently, 0.600 g thermally
pretreated (500 uC, 15 h, in air) silica support (silica gel 100, Merck; BET
surface area: 304 m g ; pore volume: 1.01 cm g ; mean pore diameter
2
21
3 21
9
96 | Chem. Commun., 2006, 994–996
This journal is ß The Royal Society of Chemistry 2006