A new synthetic approach to dialkyl carbonates and their use as green solvents for the preparation of PVDF membranes

Dialkyl carbonates (DACs) are well-known green solvents and reagents that have been extensively investigated as safe alternatives to chlorine-based compounds. In fact, they can replace alkyl halides and dimethyl sulfate in alkylation and carbonylation reactions as well as phosgene and its derivatives in alkoxycarbonylation ones [1]. Recently we have developed a high yielding scale-up synthesis of non-commercially available or expensive DACs via transcarbonylation reactions of an alcohol with dimethyl carbonate (DMC) promoted by the nitrogen-ased organocatalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD [2]. Compared to previously published works, [3] the proposed procedure has been customized for DACs large scale production (up to 100 mL of product obtained). Purification of these compounds has been achieved by fractional distillation and the exceeding reagents have been recovered and recycled. Selected DACs for this study include both symmetrical and nsymmetrical compounds, incorporating several alkyl, alkoxyalkyl, alkylamino and alkylthio functional groups. Chemical-physical properties of the new DACs have been also evaluated, as well as their water solubility. Furthermore, biodegradability and cytotoxicity tests have been carried out to investigate the effects of the different substituents on the greenness of these potential solvents and reagents. DACs application as green solvents for membrane preparation was next investigated, using non-solvent induced phase separation (NIPS) and vapor induced phase separation (VIPS) techniques, achieving both porous and plain membranes [4]. Morphology, additives effect, physical-chemical and mechanical proprieties as well as their performances in terms of water permeability and rejection were evaluated and compared to membranes obtained using commercially available cyclic carbonates (namely ethylene carbonate – EC and propylene carbonate – PC).