Cyclic carbonate production

Polymer Chain Growth Versus Cyclic Carbonate Production. 5... 

Most often, the extent of completely alternating copolymer formation, expressed as 100% C02 linkages or 50% C02 content, is very high. With regards to the selectivity of the coupling reaction for copolymer versus cyclic carbonate production, two observations are consistently found, regardless of the catalyst. First, aliphatic epoxides are more prone to cyclic carbonate formation than alicyclic epoxides for example, PO affords propylene carbonate more readily than CHO provides cyclohexene carbonate. Second, in either instance, since it has been shown that the activation barriers for cyclic carbonate production are higher... 

Following these results, Darensbourg et al. have continued the research and used other bifunctional Cr(salen) complexes as catalysts for polycarbonate synthesis. They observed that when a monofunctional Cr(salen) complex (5) was used to catalyze the reaction between epoxide and CO2, the product formed was cyclic carbonate. However, when a bifunctional Cr(salen) catalyst (6) was used, 79% selectivity towards the polycarbonate was obtained at 70 °C. The reason for this difference lies in the structure of the bifunctional catalyst, which provides steric hindrance in the epoxide ring-opening process to form the cyclic carbonate. Therefore, it can be inferred that spatial requirements in the active site of the metal catalyst determine the selectivity for the kinetic polymer product over the thermodynamically more stable cyclic carbonate product. 

Darensbourg DJ, Yarbrough JC, Ortiz C, Fang CC (2003) Comparative kinetic studies of the copolymerization of cyclohexene oxide and propylene oxide with carbon dioxide in the presence of chromium salen derivatives. In situ FTIR measurements of copolymer vs cyclic carbonate production. J Am Chem Soc 125 7586-7591... 

It is clear from the numerous accounts in literature that DMCs can efficiently catalyze the copolymerization of CO2 and epoxides. DMCs can however also be used to develop systems that selectively catalyze the CO2 cycloaddition rather than the copolymerization (Scheme 1.4) as is illustrated by the work of Dharman et al. [20]. By itself, a Zn-Co-DMC is an efficient catalyst for the copolymerization reaction. However, the addition of a quaternary ammonium salt to the reaction mixture switches the selectivity of the catalytic system toward the exclusive formation of the cyclic carbonate. The quaternary ammonium ion plays two important roles in the catalytic system it accelerates the diffusion of CO2 into the reaction mixture and it favors a backbiting mechanism. As such, it hinders the growth of the polymer chain and it enables the selective cyclic carbonate production. Although most zinc-containing catalysts for this reaction are very sensitive toward water, Wei et al. have shown that, for example, the combination of Zn-Co-DMC with CTAB (cetyltrimethylammonium bromide) could even use water-contaminated epoxides as an epoxide feed [21]. 

The next phase of the synthesis was construction of the C-ring. An aldol addition was used to introduce a 3-butenyl group at C(8) and the product was trapped as a carbonate ester. The Davis oxaziridine was then used to introduce an oxygen at C(2). After reduction of the C(3) oxygen, a cyclic carbonate was formed, and C(2) was converted... 

Cyclic carbonic esters can be readily obtained from 1,2-diols and CDI.[242H254] Apart from the observed high yields, the procedure is so straightforward that it undoubtedly constitutes the method of choice for compounds of this type. The procedure offers the advantages of mildness, simplicity, and absence of by-products other than imidazole,... 

The five-membered 1,2-cyclic carbonate was isolated as the only product (regio-selective protection of the vicinal diol system).[255J Analogous formation of a cyclic carbonate containing a secondary hydroxy group is described in reference [256]. 

Products in several isomeric forms can occur in systems with fewer atoms than considered above the association reaction between C3H+ and H2 to produce both cyclic and noncyclic C3H3 is a case in point, although the branching ratio in this instance seems to be noncontroversial.30 The problem of whether product hydrocarbon ions are cyclic or noncyclic extends to other classes of ion-molecule reactions such as condensation and carbon insertion reactions, where studies of product reactivity have only been undertaken in a few instances. In general, cyclic ion products are less reactive than their noncyclic counterparts. For systems with a... 

Lactone product 104 is now susceptible to reductive C-3 hydroxyl removal, providing an enol product 105 that can be converted to the ketone 106 upon silica gel treatment. C-l a-hydroxylation of compound 106 provides compound 107. Compound 108 is then produced via Red-Al reduction of 107 and subsequent formation of the cyclic carbonate upon phosgene treatment (Scheme 7-33). 

The coupling product 177 is subjected to epoxidation to give epoxide compound 178 on which the C-l hydroxyl group will be generated via catalytic hydrogenation. After the dihydroxyl groups of the hydrogenation product 179 have been protected with cyclic carbonate, the C=C double bond between C-l2... 

Not least for the syntheses of natural products, alkoxycarbonylations with formation of allenic esters, often starting from mesylates or carbonates of type 89, are of great importance [35, 137]. In the case of carbonates, the formation of the products 96 occurs by decarboxylation of 94 to give the intermediates 95 (Scheme 7.14). The mesylates 97 are preferred to the analogous carbonates for the alkoxycarbonylation of optically active propargylic compounds in order to decrease the loss of optical purity in the products 98 [15]. In addition to the simple propargylic compounds of type 89, cyclic carbonates or epoxides such as 99 can also be used [138]. The obtained products 100 contain an additional hydroxy function. 

Cyclic alkynyl carbonates undergo carbonylation in the presence of a palladium catalyst and carbon monoxide (5 MPa) in MeOH to give allenic carboxylates (Eq. 9.118) [92], Bu3P proved superior to Ph3P as the catalyst ligand. An enynyl cyclic carbonate underwent double vicinal carbonylation at 80 °C to produce a five-membered lactone product in 52% yield (Eq. 9.119). When the reaction was performed at 50 °C, the bicyclic enone lactone was produced in 75% yield along with 10% of the y-lactone. 

It seems reasonable that polyester cyclics could be prepared by an extension of the /wendo-high-dilution [17] chemistry used for the preparation of cyclic carbonate oligomers [18, 19] however, such proved not to be the case. Brunelle et al. showed that the reaction of terephthaloyl chloride (TPC) with diols such as 1,4-butanediol did not occur quickly enough to prevent concentration of acid chlorides from building up during condensation [14]. Even slow addition of equimolar amounts of TPC and butanediol to an amine base (triethylamine, pyridine or dimethylaminopyridine) under anhydrous conditions did not form cyclic oligomers. (The products were identified by comparison to authentic materials isolated from commercial PBT by the method of Wick and Zeitler [9].)... 

Using mild reaction conditions (10 bar, 125 °C), a high conversion of trans-4-octene and a high selectivity to n-nonanal can be obtained with toluene as the solvent. Cyclic carbonates like propylene carbonate (PC) are also suitable solvents for the isomerizing hydroformylation of trans-4-octene. Furthermore, the selectivity to -nonanal is increased up to 95% when PC is used in a single phase. The product n-nonanal can be extracted with n-dodecane or with a mixture of dodecane isomers. 

Both the cyclic carbonates and NOP are able to dissolve the catalyst. It was observed that at separation temperature NOP can be found in the product phase as well as in the catalyst phase. This causes again imdesired catalyst leaching (Table 8) albeit at levels that could be reduced already down to 1% with BC as the polar phase. Thus, it was necessary to identify a mediator with a similar property like NOP that exclusively can be found in the catalyst phase. 

As stated previously the main criteria in solvent selection for extraction purposes is the polarity. To prevent miscibihty of the mediator with the product phase at separation temperature the mediator s polarity has to be preferably in the range of the cyclic carbonate. Table 9 shows that with decreasing chain length of the N substituent of a pyrrohdone cycle, the solubil-... 

In general, more NMP than NOP is needed to close the miscibility gap between the cyclic carbonate and the extraction agent. In addition, a higher temperature dependency of the mixing behaviour can be recognized upon use of NMP at room temperature the NMP-TMS systems pass from closed to open systems. This effect results in an almost complete immiscibihty of the mediator and the cycHc carbonate with the extraction agent at separation temperature. In this way the catalyst leaching into the product phase can be suppressed. 

Aurbach and co-workers performed a series of ex situ as well as in situ spectroscopic analyses on the surface of the working electrode upon which the cyclic voltammetry of electrolytes was carried out. On the basis of the functionalities detected in FT-IR, X-ray microanalysis, and nuclear magnetic resonance (NMR) studies, they were able to investigate the mechanisms involved in the reduction process of carbonate solvents and proposed that, upon reduction, these solvents mainly form lithium alkyl carbonates (RCOsLi), which are sensitive to various contaminants in the electrolyte system. For example, the presence of CO2 or trace moisture would cause the formation of Li2COs. This peculiar reduction product has been observed on all occasions when cyclic carbonates are present, and it seems to be independent of the nature of the working electrodes. A single electron mechanism has been shown for PC reduction in Scheme 1, while those of EC and linear carbonates are shown in Scheme 7. ... 

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