## 2 Applications in Chemistry
### Hydrogenation Reaction
Six examples of glycols **12** were prepared with 64-98% yields by using 1-6 wt% zwitterionic 1,3-dimethylimidazolium-2-carboxylate (DMImC), cyclic carbonate **1**/H\({}_{2}\)O = 1:1.5 (molar ratio), at 140 \({}^{\circ}\)C and under 0.4 MPa for 30 min to 6 h (Scheme 8). A reaction time of 24 h was required to convert 4-phenyl-1,3-dioxolan-2-one **1b** into the corresponding vicinal diol **12a** with 90% yield. The catalyst DMImC was recovered and re-used six times at 140 \({}^{\circ}\)C, 0.4 MPa for 30 min, keeping good selectivity and high yield. Based on the experimental results, NMR spectroscopy, and theoretical calculations, a possible catalytic cycle was suggested (Scheme 9). Generated by formation of the conjugated acid DMImCH, the hydroxide ion promotes opening of the cyclic carbonate **1b**, forming the intermediate **I**, which is converted to **II** by intramolecular hydrogen transfer. Then, **II** is converted into a possible imidazolium alkylcarbonate salt **III** or **IV** by reaction with DMImCH. Subsequent elimination of DMImC and production of **II** occurs. The reaction of **II** with OH-i affords **V** with CO\({}_{2}\) and H\({}_{2}\)O release to the reaction medium. Finally, a proton from DMImCH is captured by **V**, producing the desired glycol **12a** while regenerating the catalyst for a new cycle. The indirect hydrogenation of CO\({}_{2}\) via the ethylene carbonate intermediate **1c** to produce ethylene glycol **12b** and methanol was proposed by using mesoporous silica (KIT-6, MCM-41, and SBA-15) as the support for copper-based catalysts (Scheme 10, condition a) [41]. This attractive approach showed 100% conversion of carbonate **1c**, yielding 94.7% of diol **12b** and 62.3% of CH\({}_{3}\)OH **7a** in only 4 h reaction time over Cu/SBA-15 under the optimal conditions. This copper-based catalyst exhibited superior catalytic activity with turnover numbers of 22.0 and 11.4 (mol mol\({}^{-1}\)) towards diol and methanol, respectively. It is noteworthy that the higher catalytic performance was due to the synaptic effect between the Cu\({}^{0}\) and Cu\({}^{+}\) species that co-exist on the surface of the catalysts and also to a larger metallic surface area on SBA-15 when compared with KIT-6 and MCM-41. Additionally, the thermodynamic calculation showed the ethylene glycol hydrogenation to be exothermic (\(\Delta_{\rm r}H^{\Theta}{}_{m}=-71.59\) kJ mol\({}^{-1}\)) and thermodynamically favorable (\(\Delta_{\rm r}G^{\Theta}{}_{m}=-25.62\) kJ mol\({}^{-1}\)). In another study, the same authors reported the selective hydrogenation of ethylene carbonate **1c** with 100% of conversion over Cu/SiO\({}_{2}\) catalysts, prepared using the ammonia evaporation method, with silica sol as the silica source (Scheme 10, condition b) [42]. The 10%Cu/SiO\({}_{2}\)-AE catalyst with moderate copper loading exhibited better catalytic activity to co-produce methanol **7a** with 70.8% yield and EG **12c** at 98.0% yield. After catalyst characterization, the authors disclosed the synergic effects of Cu\({}^{0}\) and Cu\({}^{+}\) species in this reaction; while Cu\({}^{0}\) species promoted H\({}_{2}\) dissociation, Cu\({}^{+}\) species were adsorbed on the  
Figure 9: Glycols synthesis through hydrolysis of cyclic carbonates. carbonyl group of EC. Moreover, in catalyst reusability experiments, the 10%Cu/SiO\({}_{2}\)-AE catalyst showed agglomeration of Cu and Cu\({}_{2}\)O particles, which were responsible for the gradually decreasing activity after consecutive recycling runs. Similarly, nanoarray Cu/SiO\({}_{2}\) catalysts embedded in monolithic channels (CuSi-NAM) were applied in hydrogenation reactions (Scheme 10, condition c) [43]. Monolithic Cu-based catalysts exhibited high activity in the conversion of ethylene carbonate **1c** (99%) into EG **12c** and methanol **7a** selectivity, with yields of 97% and 50%, respectively. The most frequently used methods to produce diols are described above, which involve catalytic hydrogenation or hydrolysis of cyclic carbonates using organic solvents.