Cyclic carbonates transesterification

In our previous works[8,9] on the synthesis of various 5-membered cyclic carbonate, quaternary ammonium salts such as tetrabutylammonium halides showed excellent catalytic activities in relatively mild reaction conditions, under atmospheric pressure and below 140 U. hi this work, several kinds of quaternary ammonium salts have been used for the transesterification reactions of the ethylaie carbonate with methanol to DMC and ethylene glycol. 

Cyclic carbonate esters are easily prepared from 1,2- and 1,3-diols. These are commonly prepared by reaction with A.A -carbonyldiimidazole214 or by transesterification with diethyl carbonate. 

Aromatic polycarbonates are currently manufactured either by the interfacial polycondensation of the sodium salt of diphenols such as bisphenol A with phosgene (Reaction 1, Scheme 22) or by transesterification of diphenyl carbonate (DPC) with diphenols in the presence of homogeneous catalysts (Reaction 2, Scheme 22). DPC is made by the oxidative carbonylation of dimethyl carbonate. If DPC can be made from cyclic carbonates by transesterification with solid catalysts, then an environmentally friendlier route to polycarbonates using C02 (instead of COCl2/CO) can be established. Transesterifications are catalyzed by a variety of materials K2C03, KOH, Mg-containing smectites, and oxides supported on silica (250). Recently, Ma et al. (251) reported the transesterification of dimethyl oxalate with phenol catalyzed by Sn-TS-1 samples calcined at various temperatures. The activity was related to the weak Lewis acidity of Sn-TS-1 (251). 

The transesterifications of chloropropene carbonate and propene carbonate with methanol and phenol catalyzed by TS-1, Ti-MCM-41, and Ti02 (Table XLI) have been reported (248). Neither Ti02 nor TS-1 showed any activity in the transesterification reactions. Ti-MCM-41 catalyzed the reaction with a high selectivity for DMC (86%). Ti-MCM-41 also catalyzes the transesterification of cyclic carbonates with phenols (Table XLI). 

Transesterification of cyclic carbonates with CH3OH and phenol catalyzed by Ti-MCM-41... 

Komura, H., Yoshino, T. and Ishido, Y., Synthetic studies by the use of carbonates. II. Easy method of preparing cyclic carbonates of polyhydroxy compounds by transesterification with ethylene carbonate. Bull. Chem. Soc., 1973, 46, 550-553. 

Cyclic carbonates result from polyols by transesterification using organic carbonates (115). Thus sorbitol and diphenylcarbonate in the presence of dibutyl tin oxide at 140—150°C form sorbitol tricarbonate in quantitative yield (116). 

Glycols may undergo intramolecular cydization or cyclically condense with other molecules to form a number of ring structures. Transesterification of carbonates with ethylene glycol produces ethylene carbonate [96 49-1] (eq. 4). Numerous materials catalyze carbonate transesterifications. 

Cyclic carbonates are prepared in satisfactory quality for anionic polymerization by catalyzed transesterification of neopentyl glycol with diaryl carbonates, followed by tempering and depolymerization. Neopentyl carbonate (5,5-dimethyl-l,3-dioxan-2-one) (6) prepared in this manner has high purity (99.5%) and can be anionically polymerized to polycarbonates with mol wt of 35,000 (39). 

R,R-diphenyl ethylene carbonate CR,R-DPEC)) with a racemic zirconaaziridine. (C2-symmetric, cyclic carbonates are attractive as optically active synthons for C02 because optically active diols are readily available through Sharpless asymmetric dihydroxylations [67].) Reaction through diastereomeric transition states affords the two diastereomers of the spirocyclic insertion product protonolysis and Zr-mediated transesterification in methanol yield a-amino acid esters. As above, the stereochemistry of the new chiral center is determined by the competition between the rate of interconversion of the zirconaaziridine enantiomers and the rate of insertion of the carbonate. As the ratio of zirconaaziridine enantiomers (S)-2/(R)-2 is initially 1 1, a kinetic quench of their equilibrium will result in no selectivity (see Eq. 32). Maximum diastereoselec-tivity (and, therefore, maximum enantioselectivity for the preparation of the... 

Figure 2.27 Sequential coupling ofthe transesterification of cyclic carbonates with the selective N-methylation of anilines catalyzed by faujasites [220],...

An interesting feature that made the commercialization of the synthesis of linear carbonates possible is that both linear and cyclic carbonates easily undergo transesterification with alcohols (Scheme 6.9). This process is used industrially for the synthesis of diphenylcarbonate from DMC.72 The coproduct methanol is recycled to DMC. Nevertheless, once a highly efficient direct C02 process for an organic carbonate is found, transesterification makes possible the production of any other carbonates. 

Polycarbonates (. Polycarbonates may be prepared by a variety of synthetic methods. Procedures most commonly used include reaction of diols with phosgene (Reaction 2A), transesterification of diesters of carbonic acid with dihydroxy compounds (Reaction 25), and polymerization of cyclic carbonates (Reaction 26). 

Cyclic carbonate esters are easily prepared from uic-diols and can be used in a complementary fashion to the cyclic acetals previously described. These esters are commonly prepared from N,N -carbonyldiimidazole or by transesterification using diethyl carbonate. These reagents are preferable to phosgene both in efficiency and convenience. 

Sodium hydrogen carbonate Cyclic carbonic acid esters by transesterification... 

Pure and mixed metal oxides have been widely investigated as Lewis acid and/or Lewis base for the reaction epoxides with CO to form the corresponding cyclic carbonates. Bhanage et al. [31] investigated several kinds of basic metal oxides (MgO, CaO, ZnO, ZrO, La Oj, CeO, Al Oj and K CO ) for the reactions of EO and PO with CO to the corresponding cyclic carbonates and for the transesterification reactions of the cyclic carbonates with methanol to DMC and the corresponding glycols. The catalytic performance of the various metal oxides for the synthesis of PC (express in Yp ) was (54.1%) >MgO (32.1%) > ZrO (10.9%) > K CO (8.7%) =... 

Pyo, S.H., Hatti-Kaul, R., 2012. Selective, green synthesis of six-membered cyclic carbonates by Upase-catalyzed chemospecific transesterification of diols with dimethyl carbonate. Advanced Synthesis Catalysis 354, 797—802. 

Several decades later, in the early 1930s, work (and interest) once more revived on aliphatic polycarbonates when Carothers and van Natta were able to produce low-melting, low-molecular-weight, microcrystalline aliphatic polycarbonates via two different synthetic pathways [27]. The first method was the transesterification of aliphatic dihydroxylic compounds with diethyl carbonate. The second approach was via ring-opening polymerization of cyclic carbonates of aliphatic dihydroxylic... 

Scheme 24 Synthesis of DMC (A) from CO2 and methanol, and (B) by the transesterification of cyclic carbonate with methanol.

The above mentioned direct synthesis of DMC requires organic or inorganic dehydration reagents to get high DMC yields because of the reaction equilibrium. On the other hand, the transesterification of cyclic carbonate with methanol relatively easily gives high DMC yields. ILs can also be used as the catalysts for this reaction. Scheme 26 illustrates the generally accepted reaction mechanism for the base catalyzed transesterification of... 

Without additional reagents Cyclic ethers via cyclic carbonic acid esters Transesterification s. 72, 350 Thermal cleavage of dicyclopentadienes... 

The alkylene carbonates are easily available through transesterification of dialkyl carbonates (usually dimethyl or diethyl carbonate) or diphenyl carbonate with appropriate 1,2-diols in the presence of alkaline catalysts.This approach for the preparation of five-membered cyclic carbonates also was described in the 1950s by Ludwig and Piech ° and Sarel et al ... 

Thus, when 2,2-dimethyl-, 2-methyl-2-n-propyl- and 2-methyl-2-iso-amylpropane-l,3-diol were treated with diethyl carbonate in the presence of catalytic amounts of sodium methoxide, only PCs were produced in high yield. On the other hand, six-membered cyclic carbonates are exclusively produced when 2,2-diethyl-, 2-ethyl-2-phenylpropane-1,3-diol, pentane-2,4-diol, 2-methylpentane-2,4-diol, and butane-1,3-diol were subjected to the transesterification reaction (Scheme 10). 

The synthesis of six-membered cyclic carbonates by transesterification of propane-1,3-diols (PPDs) with diethyl carbonate catalyzed with sodium ethanolate described by Carothers and Van Natta gives a yield of 40%. Also Pohoryles and... 

Seven-membered and larger ring size cyclic carbonates can be synthesized according to the same transesterification reaction pathways as those leading to five- and six-membered rings or in the reaction of appropriate diol with phosgene (or its derivative) in the presence of antipyrine. ... 

The smallest possible five-membered aromatic cyclic carbonate is a derivative of catechol benzo-l,3-dioxolan-2-one (o-phenylene carbonate) (1, Scheme 13). It was synthesized using three different methods the reaction of catechol with phosgene (or its dimer or trimer), ° the reaction of catechol with chloroformate, ° or by transesterification of catechol with diphenyl carbonate. ... 

Vinyl-functional alkylene carbonates, useful in the preparation of polymers that contain alkylene carbonate pendant groups, can also be prepared from GC. Two examples are the reaction of GC with maleic anhydride and acryloyl chloride to produce the acrylate-functional cyclic carbonates (3 and 4, respectively. Scheme 24). Although the transesterification of alkyl esters such as dimethyl maleate or methyl acrylate by reaction with GC represents an obvious means of obtaining the above materials, the temperatures required of such processes (>100°C) result in unwanted polymerization of both the reactant and product species, even in the presence of well-known radical inhibitors such as 2,6-di-tert-butyl-p-cresol or phenothiazine. In addition, the synthesis of vinyl-functional alkylene carbonates is greatly complicated by the fact that such materials cannot be purified by distillation and must be stored at temperatures < 0 ° C in the presence of a... 

The ROP of six-membered cyclic carbonates with nucleophilic initiators is a chain reaction in which, besides initiation and propagation reactions, transesterification reactions can also take place (Scheme 32).Intramolecular nucleophile (e.g., alkoxide) attacks on carbonyl carbon atom (backbiting) lead to cyclic oligomers, while intermolecular transesterifica-tion leads to a change of the macromolecule length with the consequence that, at equilibrium, the most probable distribution of the molecular weight is obtained (Scheme 32). 

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