Table 2 Optimization of the reaction conditions.
Entry | Catalyst/amount (mol%) | Solvent | Temp. (°C) | Time (min) | Yield (%) | |
|---|---|---|---|---|---|---|
1 | – | H2O | Reflux | 70 | 20 | |
2 | Silica sulfuric acid | H2O | Reflux | 50 | 80 | |
3 | p-Toluenesulfonic acid | H2O | Reflux | 45 | 82 | |
4 | H3PW12O40 | H2O | Reflux | 40 | 88 | |
5 | Lanthanum nitrate | H2O | Reflux | 25 | 91 | |
6 | K9[BW11O39]·13H2O | H2O | Reflux | 20 | 90 | |
7 | ZnO | H2O | Reflux | 30 | 91 | |
8 | Nd-B2W22/10 | H2O | Reflux | 20 | 90 | |
9 | Sm-B2W22/10 | H2O | Reflux | 15 | 95 | |
10 | Er-B2W22/10 | H2O | Reflux | 15 | 94 | |
11 | Ce-B2W22/10 | H2O | Reflux | 25 | 92 | |
12 | La-B2W22/10 | H2O | Reflux | 25 | 90 | |
13 | Gd-B2W22/10 | H2O | Reflux | 12 | 96 | |
14 | Gd-B2W22/15 | H2O | Reflux | 12 | 95 | |
15 | Gd-B2W22/10 | H2O | r.t | 25 | 80 | |
16 | Gd-B2W22/10 | H2O | 50 °C | 20 | 91 | |
17 | Gd-B2W22/10 | H2O/EtOH | Reflux | 15 | 90 | |
18 | Gd-B2W22/10 | EtOH | Reflux | 20 | 92 | |
19 | Gd-B2W22/10 | CH2Cl2 | Reflux | 25 | 90 | |
20 | Gd-B2W22/10 | CH3CN | Reflux | 25 | 85 | |
21 | Gd-B2W22/10 | Tuloene | Reflux | 30 | 85 | |
