C O M M U N I C A T I O N S
Table 2. Stoichiometric Reactiona of HAuCl4 with CO and MeOH
amount of products/µmol
entry
DMC 1
DMO 2
DMM+MF
CO
2
1
2
3
4
5
HAuCl4,CO, CH3OH
HAuCl4, He, CH3OH
HAuCl4, CO, H2O
15.3
0
0
0
3.4
0
0
0
0
0
trace
0
0
trace
trace
4.2
0
43.5
0
Au/AC, CO, CH3OH
HAuCl4,CO, CH3OH b
trace
a T ) 298 K, reaction time ) 60 min, Au compounds 30 µmol, CO 101
kPa, NaClO4 (0.1 mol 1-1)/MeOH (30 mL). b Without NaClO4.
with the Au0/AC (entry 4). It is to be noted that the yields of 1 and
CO2 remarkably decreased (entry 5) when NaClO4 was removed
from the reaction conditions of entry 1. This result proposed that
NaClO4 in methanol should enhance the carbonylation.
Figure 2. Cyclic voltammograms over the Au electrode. Scan rate 50 mV/
s, NaClO4 electrolyte 0.1 mol l-1, (a) He, CH3OH, (b) CO, CH3OH.
V and Ox(3) at +1.4 V, were observed in CV(b). When the potential
was returned and swept to the negative side, there were no reduction
peaks corresponding to the Ox(2) and Ox(3), but an oxidation peak,
Ox(4), was observed. No redox couple in CV(b) proposed that the
Ox(2), Ox(3), and Ox(4) peaks were electrochemically irreversible
reactions. The Ox(2) peak potential was more negative than that
of Au0/Au3+. Therefore, the oxidation current in the Ox(2) should
be due to oxidation of CO or the carbonylation over Au0. The Ox(3)
peak potential overlapped that of the Au0/Au3+, Ox(1), which
proposed that the large oxidation current was due to the CO
oxidation or the carbonylation over Au3+. The Ox(4) peak may
correspond to that of the Ox(3). On the basis of potentiostatic
electrolysis results (Figure 1), the Ox(2) over Au-wire anode may
be corresponding to the formation of 2, and the Ox(3) and the Ox(4)
may be corresponding to the formation of 1.
To identify a correlation between oxidation currents of Ox(2),
Ox(3), Ox(4), and product formations, quantitative analysis of
product yields during the CV cycle were examined by repeating
CV cycles more than 200 times. A very good reproducibility of
CV spectra was observed. Yields of 2 and 1 normalized at 100
cycles between +0.5 and +1.2 V were 0.5 µmol (26% CE) and
0.4 µmol (24% CE), respectively. Significant yields of 2 and 1
were obtained, which proved that the electrochemical carbonylation
of methanol was completed during the CV cycle. When the CV
scan extended from +0.5 to +1.6 V, the 2 and 1 yields (100 CV)
were 0.8 µmol (13% CE) and 2.1 µmol (33% CE), respectively. A
large increase in the 1 yield was observed by the extension of the
potential from +1.2 to +1.6 V but a little increase in the 2 yield.
These results strongly proposed that the oxidation current of the
Ox(3) and Ox(4) was corresponding to the formation of 1. On the
other hand, the oxidation current of Ox(2) was mainly corresponding
to the formation of 2.
2MeOH + CO + 2/3Au3+ f DMC (1) + 2H+ + 2/3Au0
(1)
CO + H2O + 2/3Au3+ f CO2 + 2H+ + 2/3Au0 (2)
In conclusion, 1 was produced through the indirect electrochemi-
cal carbonylation of MeOH and CO, mediated by Au3+/Au0 (or
Au+) redox reaction. On the other hand, 2 was produced by the
direct electrochemical carbonylation of methanol with CO over Au0,
because the oxidation current of Ox(2) was corresponding to the
formation of 2 and 2 was not formed in the stoichiometric reactions
(Table 2). Detailed reaction mechanisms for the formation of 2 over
Au0 and for 1 over Au3+ have not yet been clarified. The
carbonylation selectivities to 2 and 1 over the [Au0/AC + VGCF]
anode could be controlled by changing the oxidation state of gold
with anode potentials. This unique function of Au electrocatalysis
should be the first report.8
References
(1) Tundo, P.; Selva, M. Acc. Chem. Res. 2002, 35, 706-716. Delledonne,
D.; Rivetti, F.; Romano, U. Appl. Catal., A 2001, 221, 241-251. Ono,
Y. Appl. Catal., A 1997, 155, 133-166. Rivetti, F., Romano, U. In Green
Chemistry: Designing Chemistry for the EnVironment; Anastas, P.,
Williamson, T. C., Eds.; ASC Symposium Series 626, American Chemical
Society, Washington, DC, 1996; pp 70-80.
(2) Romano, U.; Mauri, M. M.; Rivetti, F. Ing. Chim. Ital. 1985, 21, 6-12.
Romano, U.; Tessei, R.; Mauri, M. M.; Rebora P. Ind. Eng. Chem. Prod.
Res. DeV. 1980, 19, 396-403.
(3) Tsuji, J. Palladium Reagents and Catalysts; Wiley: Chichester, 1995.
Heck, R. F. Palladium Reagents in Organic Synthesis; Academic Press:
Orlando, 1985.
(4) Nakamura, A.; Matsuzaki, T. Res. Chem. Intermed. 1998, 24, 213-225.
Matsuzaki, T.; Nakamura, A. Catal. SurV. Jpn. 1997, 1, 77-88. Nishimura,
K.; Uchiumi, S.; Fujii, Nishihira, K.; Yamashita, M.; Itatani, H.; Matsuda,
M. (UBE Industries Ltd.). U.S. Patents 4,229,589 and 4,229,591; Chem.
Abstr. 1979, 91, 4968.
(5) Uchiumi, S.; Ataka, K.; Matsuzaki, T. J. Organomet. Chem. 1999, 576,
279-289. Waller, F. J. J. Mol. Catal. 1985, 31, 123-136.
(6) Yamanaka, I.; Funakawa, A.; Otsuka, K. J. Catal. 2004, 221, 110-118.
Yamanaka, I.; Funakawa, A.; Otsuka, K. Chem. Lett. 2002, 448-449.
Otsuka, K.; Yagi, T.; Yamanaka, I. Electrochim. Acta 1994, 14, 2109-
2115.
(7) Filardo, G.; Galia, A.; Rivetti, F.; Scialdone, O.; Silvestri, G. Electrochem.
Acta 1997, 42, 1961-1965. Galia, A.; Filardo, G.; Gambino, S.;
Mascolino, R.; Rivetti, F.; Silvestri, G. Electrochem. Acta 1996, 41, 2893-
2896.
(8) Dyker, G. Angew. Chem., Int. Ed. 2000, 39, 4237-4239. Burke, L. D.;
Buckley, D. T.; Morrissey, J. A. Analyst 1994, 119, 841-845. Xu, Q.;
Imamura, Y.; Souma, Y. J. Org. Chem. 1997, 62, 1594-1598. Haruta,
M. Stud. Surf. Sci. Catal. 2003, 145, 31-38. Bond, G. C.; Thompson, D.
T. Catal. ReV. Sci. Eng. 1999, 41, 319-388.
If the Ox(3) and Ox(4) were strongly involved in the formation
of 1, Au3+ would promote the formation of 1. Therefore, stoichio-
metric reactions of Au3+, MeOH, and/or CO in the presence of
NaClO4 were studied (Table 2). Entry 1 shows the stoichiometric
reaction among HAuCl4, MeOH, and CO. 1 and CO2 were pro-
duced, but there were no formations of 2, DMM, and MF (eq 1).
When CO was absent (entry 2), no products were observed. On
the other hand, when MeOH was replaced by H2O (entry 3), almost
perfect stoichiometric oxidation of CO to CO2 with H2O by Au3+
proceeded (eq 2). Purple-black powder (Au0) was deposited after
the experiments of entries 1 and 3. Of course, no products formed
JA0395700
9
J. AM. CHEM. SOC. VOL. 126, NO. 17, 2004 5347