Chemistry Letters Vol.33, No.8 (2004)
959
for a pure CuCl2 catalyst, also in sharp contrast to the case of the
CuCl2–NaOAc system. In addition, the selectivity based on O2
consumption is also slightly improved. However, a further in-
crease in the amount of NaOAc to 5 wt % results in a sharp de-
crease of the TOF value for methanol conversion, suggesting the
detrimental effect of the excess amount of alkali addition on the
performance of the PVP–CuCl2 catalyst.
The catalytic performance of the PVP–CuCl2 catalyst in the
presence of 2 wt % NaOAc in the reaction system as a function
of time is plotted in Figure 1. As a direct comparison, the cata-
lytic data obtained over the polymer-complexed catalyst in the
absence of the base are also illustrated. It is seen that the meth-
anol oxidative carbonylation reaction proceeds in a moderate
rate over the catalyst in the absence of the alkali, whereas the
methanol conversion approaches the maximum value only after
the reaction is carried out for a time of 5 h. In sharp contrast, the
conversion value of methanol increases much more steeply up to
Cu2(OH)3Cl intermediate species in CuCl2/NaOH/AC catalysts
1
4
as a consequence of alkali addition. Figure 2 shows that the
symmetric carbonyl band due to the amide carbonyl group of
ꢂ1
pure PVP appears at 1662 cm . In comparison, a drastic red-
ꢂ1
shift of the carbonyl band to 1618 cm with a well-resolved
ꢂ1
shoulder at 1640 cm in the PVP–CuCl2 complex is observed,
demonstrating a strong ligand interaction between Cu(II) species
9
and the polymeric ligands. However, a great attenuation of the
ꢂ1
carbonyl peaks at 1618 and 1640 cm is identified for the PVP–
CuCl2 complex in the presence of NaOAc, accompanied by the
ꢂ1
appearance of an additional intense peak at 1652 cm . Thus, the
promotional effect of the alkali in the present reaction system is
possibly due to a further modification of the ligand interaction
between the Cu(II) species and the amide moieties in the PVP
chains by facilitating the intrinsic Cu(II)/Cu(I) redox processes
9
,15
involved in the DMC synthesis reaction.
In summary, we have shown that the use of the simple and
inexpensive alkali additive strongly modified the course of the
PVP–CuCl2–catalyzed oxidative carbonylation of methanol.
Under these novel conditions, methanol could be transformed
more efficiently into DMC with a higher formation rate. Al-
though the mechanism of the improvement of the PVP–CuCl2
catalyst system with alkali addition needs to be further clarified,
this work presents a highly efficient protocol for improving the
synthesis of DMC under homogeneous conditions.
2
1% in a reaction time of 2 h accompanied by a slight decrease in
the overall selectivity based on methanol consumption. It is re-
markable that maximum DMC concentration of ca.
5.3 wt % can be attained after a reaction time of 2 h, demon-
a
2
strating the superior performance of the alkali-modified PVP–
CuCl2 catalyst for DMC synthesis.
The promotional effect of alkali addition has also been re-
ported for a heterogeneous catalyst system in vapor phase
DMC synthesis, where the beneficial effect of alkali addition
has been ascribed to the formation of catalytically active
This work was supported by the National Natural Science
Foundation of China (Grant No. 20203003), the National Major
Basic Research Program of China (Grant No. 2003CB615807),
and the Committee of Shanghai Science and Technology (Grant
No. 02QA14006).
40
35
30
25
20
15
10
5
0
1
9
9
8
00
5
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PVP-CuCl -2wt% NaOAc
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Published on the web (Advance View) June 28, 2004; DOI 10.1246/cl.2004.958