Synthesis from cyclic carbonates

Ni(cyclam)]2+ was shown to be an efficient electrocatalyst for the intramolecular cyclization-carboxylation of allyl or propargyl-2-haloaryl ethers,200 and for the synthesis of cyclic carbonates from epoxides and carbon dioxide.201... 

Silica gel-based catalytic systems have been described as efficient promoters for a number of organic reactions.28 Illustrative examples include the oxidative cleavage of double bonds catalyzed by silica-supported KM11O4,29 reaction of epoxides with lithium halides to give /i-halohydrins performed on silica gel,30 selective deprotection of terf-butyldimethylsilyl ethers catalyzed by silica gel-supported phosphomolybdic acid (PMA),31 and synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts.32... 

J.-Q. Wang, D.-L. Kong, J.-Y. Chen, F. Cai, and L.-N. He, Synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts under supercritical conditions, /. Mol. Cat. A Chem., 249 (2006) 143-148. 

Synthesis of cyclic carbonates from alkenes epoxidation-cum-cycloaddition... 

Scheme 4.49 Asymmetric synthesis of allenic alcohols from cyclic carbonates or sulfites...

The synthesis of cyclic carbonates, starting from olefins, can be also carried out via a multistep method based on two separate reactions. To this end, C02 and the carboxylation catalyst have been added to the same reactor in which a preliminary epoxidation process had been carried out. 

Synthesis of Cyclic Carbonates from Propargylic Alcohols... 

Dunach, Inesi and others also investigated the electrochemical synthesis of cyclic carbonates from C02 with epoxides, alcohols and glycols [66]. In this regard, Yang et al. [67] reported the use of pure room temperature ionic liquids (ILs) as reaction media in the electrochemical activation of C02 for the synthesis of cyclic carbonate from epoxide, under mild conditions. C02-saturated IL (BMIMBF4) solutions were also used for the electrochemical carboxylation of activated olefins [68]. Monocarboxylic acids were obtained in moderate yield (35-55%), and the IL was recycled five times. 

Guanidinium salt has special properties of high thermal and chemical stability, tunable groups attached on the three N atoms in the molecular structure, and excellent catalytic activity for cycloaddition of C02 and epoxides to produce cyclic carbonate [11, 12]. A functionalized-PEG, hexaalkylguanidinium bromide (Scheme 5.3) being covalently tethered to PEG (MW = 6000) is utilized as an active homogeneous catalyst, which includes the benefits of recyclability and high catalytic activity, for the synthesis of cyclic carbonates from C02 and epoxides with almost quantitative yield and excellent selectivity [13]. 

Scheme 5.5 Structures of PEG-functionalized ionic liquids for the synthesis of cyclic carbonates. Reproduced from Ref. [15] by permission of The Royal Society of Chemistry...

Scheme 5.9 Synthesis of cyclic carbonates from halohydrin with C02 catalyzed by PEG/K2C03 system. Reprinted with the permission from Ref. [42].

Dou X, Wang J, Du Y et al (2007) Guanidinium salt functionalized PEG an effective and recyclable homo-geneous catalyst for the synthesis of cyclic carbonates from C02 and epoxides under solvent-free conditions. Synlett 18(19) 3058—3062... 

Wang JL, He LN, Dou XY et al (2009) Poly (ethylene glycol) an alternative solvent for the synthesis of cyclic carbonate from vicinal halohydrin and carbon dioxide. Aust J Chem 62(8) 917-920... 

The synthesis of cyclic carbonates, which start from COj and epoxides, is possible even with nonmetal catalysts and examples of the catalysts which have been used are ammonium salts [193 196], amines [197-199], halides... 

Figure 8.8 Functionalized PEG in solventless catalytic synthesis of cyclic carbonates from carbon dioxide and epoxides.

Figure 2.45 Acid-base bifunctional reaction mechanism in the synthesis of cyclic carbonates over mixed oxides obtained from a Mg-Al hydrotalcite. Source Kaneda et al. [28].

Scheme 16.16 Electrochemically activated carbon dioxide in the synthesis of cyclic carbonates and unsymmetiical carbonates and carbamates (Reprinted from Ref. [132] and [133] with kind permission of Elsevier)...

North, M. Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide Using Bimetallic Aluminium (Salen) Complexes, ARKTVOC, no. i (2012) 610-628. 

Li, R., Tong, X., Li, X., and Hu, C. Chlorine-Free Catalysts for Green Synthesis of Cyclic Carbonates from Carbon Dioxide, Pure Appl. Chem. 84, no. 3 (2012) 621-636. 

Titanium complexes have been shown to be active for the synthesis of cyclic carbonates or either di- or trithiocarbonates from epoxides and either carbon dioxide or carbon disulfide (Scheme 5.6). Titanium-catalysed synthesis of cyclic carbonates has been recently reviewed by North and coworkers. Titanium-salen complexes find application as catalysts, in combination with tetrabutylammonium bromide or tributylamine, for the synthesis of di- or trithiocarbonates from epoxides and carbon disulfide. It is worth highlighting that the catalyst loading can be reduced to 0.5 mol%, although 1 mol% of catalyst was required in order to achieve quantitative yields. The catalyst system showed a preference for dithiocarbonate formation for most of the epoxides studied. 

Most importantly, layered materials are currently of particular interest as supports for the immobihzation and/or intercalation of various ILs in order to prepare polymer nanocomposites [83, 84] with improved thermal and mechanical properties, nanohybrid materials for electrochemical sensors [85, 86], and efficient catalysts for the synthesis of cyclic carbonate by the cycloaddition of CO2 to allyl glycidyl ether [87] and propylene glycol methyl ether (PGME) from propylene oxide and methanol [88]. A detailed list of applications involving layered materials and ILs can be found in a recent review [16]. 

A siUca-SIL [BMIM]BF4 material was synthesized [80]. The catalyst proved to be an efHdent heterogeneous catalyst for solventless synthesis of cyclic carbonates from epoxides and CO2 under supercritical conditions, which required no additional organic solvents either for the reaction or for the separation of product. High yields with excellent selectivity were obtained. Moreover, the catalyst could be easily... 

The immobilized IL-zinc chloride catalyst system was also reported [81], which was very efficient in chemical fixation of CO2 to form cyclic carbonates under mild condihons in high TOP. The synthesis of five-membered cychc carbonate from aUyl glycidyl ether (AGE) and CO2 was reported using immobilized imidazolium IL on silica, which was also proved to be an effective heterogeneous catalyst for the solventless synthesis of cyclic carbonate [82]. Then, MCM-41 was used as the support to immobihze ILs and the resulting material showed excellent activities for CO2 insertion reactions [83]. 

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