Organic Carbonates as Solvents in Synthesis and Catalysis

Since the 1960s applications of organic carbonates as solvents have spread to nearly every field of chemistry. In particular, the use in lithium batteries and other electrochemical applications like the electropolymerization are well established. The high solubility of ions, dielectric constants, and dipole moments are basic properties for the success of organic carbonates in these research areas. Furthermore, the low toxicities and environmentally benign properties make them acceptable alternatives for standard organic solvents and valuable candidates to substitute NMP, DMF, and other polar, aprotic solvents. Not mentioned in this review is the extensive use of organic carbonates as environmentally friendly building blocks for classical organic transformations, where they can be used as methylation agents or in methoxycarbonylations.356-358 Furthermore, it has to be noted that synthesis and application of organic carbonates is often connected with the synthesis of polycarbonates.359 These processes are already highlighted in separate reviews with regard to the special properties of various polycarbonates.360,40 The synthesis of organic carbonates is still the bottleneck in their use as real "green" solvents. Today numerous applications have been published with these polar solvents especially in research of homogeneous catalysis. However, due to the high boiling point, from an ecological point of view an advantage, product separation will be the major challenge for the future. An alternative for this could be the use of noncyclic carbonates, which can be evaporated more easily. The results of carbonylations, metathesis reactions, and hydrogenations show clearly that organic carbonates are not magic solvents which are able to replace every other solvent. However, their use should always be taken into consideration in a solvent screen for new reactions and catalysts. In particular, the weak interactions between catalysts and the organic carbonates could be of interest to stabilize nanocluster or even homogeneous catalysts in order to develop more efficient recycling processes. The numerous publications on the synthesis and use of organic carbonates each year reveal that this field is of major interest to the chemical community, and the authors hope that this review will stimulate further work. © 2010 American Chemical Society.