CO₂ promoted synthesis of unsymmetrical organic carbonate using switchable agents based on DBU and alcohols

Abstract

Transesterification can be accelerated under pressurized CO2 and satisfactory activity and selectivity to unsymmetrical organic carbonate can be obtained.

Solid acid catalyzed carboxymethylation of bio-derived alcohols: an efficient process for the synthesis of alkyl methyl carbonates

“…DMC undergoes carboxymethylation/carbonate interchange reaction (CIR) with various alcohols to yield alkyl methyl carbonates or dialkyl carbonates without generating inorganic salts as the byproduct (Scheme 1 ). These organic carbonates have got numerous applications such as nonprotic solvents, lubricating oils, fuel additives and key intermediates to synthesize polycarbonates, plasticizers, monomers for organic glasses, atomoxetine, roccellaric acid, herbicides, fungicides, pesticides and nephrosteranic acid 23 , 24 , 27 – 32 . The reduced environmental footprints and replacement of various hazardous chemicals by organic carbonates make them one of the strong contenders to meet guidelines of green chemistry.…”

One‐Pot Synthesis of Organic Carbonate from Alcohol and Alkyl Bromide under Low CO2 Pressure

“…However, as CO 2 pressure was higher than 0.25 MPa, more CO 2 would capture most of DBU to form the DBU-CO 2 adduct, resulting in a more difficult dissociation into the active species. [29] This might be also related to a dilution effect whereby the excess CO 2 reduced the concentration of 1-bromobutane in the vicinity of the DBU. [39] Hence, 0.25 MPa was chosen as the optimal initial pressure for the one-pot synthesis of BMC.…”

“…The increase in BMC yield under the CO 2 pressure less than 0.25 MPa could be explained that the introduction of CO 2 could result in the consumption of methanol to form [DBUH][O(CO)OCH 3 ], which could facilitate the formation of BMC. However, as CO 2 pressure was higher than 0.25 MPa, more CO 2 would capture most of DBU to form the DBU‐CO 2 adduct, resulting in a more difficult dissociation into the active species [29] . This might be also related to a dilution effect whereby the excess CO 2 reduced the concentration of 1‐bromobutane in the vicinity of the DBU [39] .…”

“…DBU can produce an unstable amidinium alkyl carbonate intermediate I [DBUH] + [R 1 OCOO] À by reacting with CO 2 and alcohol. [29,[41][42][43] A substitution reaction takes place between the intermediate I and an alkyl halide R 2 Br, and the target products (the symmetrical and unsymmetrical organic carbonates) are generated with the protonated base DBUHBr. DBU is proved to be recyclable after having been treated with KOH in ethanol.…”

“…Besides, transesterification of DMC with ethanol or DMC with diethyl carbonate (DEC) is considered a promising method for the synthesis of EMC. Therein, various homogeneous and heterogeneous catalysts have been developed, including ionic liquid, [24] TiO 2 nanofibers, [25] metal complex Co 2 (CO) 8 /W(CO) 6 , [26] KF/Al 2 O 3 , [27] carbonate phosphonium salts, [28] DBU, [29] MgO/HZSM‐5, [30] Ti(OBu) 4 , Ti(OPh) 4 , Bu 2 SnO and BuSnCl 3 , [31] Zn−Co@N‐doped carbon materials, [32] amorphous mesoporous aluminophosphate, [33] nitrogen‐doped carbon/ZnO [34] etc . However, these methods usually encounter with high reaction temperature, long reaction time, low production efficiency, poor atom economy, and challenge in the separation of products.…”