POLITAG-M-F as Heterogeneous Organocatalyst for the Waste-Minimized Synthesis of β-Azido Carbonyl Compounds in Batch and under Flow Conditions

We herein report a waste minimization protocol for the β-azidation of α,β-unsaturated carbonyl compounds using TMSN₃. The selection of the appropriate catalyst (POLITAG-M-F), in combination with the reaction medium, resulted in enhanced catalytic efficiency and a low environmental footprint. The thermal and mechanical stability of the polymeric support allowed us to recover the POLITAG-M-F catalyst for up to 10 consecutive runs. The CH₃CN:H₂O azeotrope has a 2-fold positive effect on the process, increasing the efficiency of the protocol and minimizing waste generation. Indeed, the azeotropic mixture, used as a reaction medium and for the workup procedure, was recovered by distillation, leading to an easy and environmentally friendly procedure for product isolation in high yield and with a low E-factor. A comprehensive evaluation of the environmental profile was performed by the calculation of different green metrics (AE, RME, MRP, 1/SF) and a comparison with other literature available protocols. A flow protocol was defined to scale-up the process, and up to 65 mmol of substrates were efficiently converted with a productivity of 0.3 mmol/min.

A Waste-Minimized Approach to Cassar-Heck Reaction Based on POLITAG-Pd0 Heterogeneous Catalyst and Recoverable Acetonitrile Azeotrope

Three different Pd0 -based heterogeneous catalysts were developed and tested in the Cassar-Heck reaction (i. e., copper-free Sonogashira reaction) aiming at the definition of a waste minimized protocol. The cross-linked polymeric supports used in this investigation were designed to be adequate for different reaction media and were decorated with different pincer-type ionic ligands having the role of stabilizing the formation and dimension of palladium nanoparticles. Among the ionic tags tested, bis-imidazolium showed the best performances in terms of efficiency and durability of the metal catalytic system. Eventually, aqueous acetonitrile azeotrope was selected as the reaction medium as it allowed the best catalytic efficiency combined with easy recovery and reuse. Finally, the synergy between the selected catalyst and reaction medium allowed to obtain highly satisfactory isolated yields of a variety of substrates while using a low amount of metal catalyst. The high performance of the designed POLymeric Ionic TAG (POLITAG)-Pd0 , along with its good selectivity achieved in a copper-free process, also led to a simplified purification procedure allowing the minimization of the waste generated as also proven by the very low E-factor values (1.4-5) associated.

Azeotropes as Powerful Tool for Waste Minimization in Industry and Chemical Processes

Aiming for more sustainable chemical production requires an urgent shift towards synthetic approaches designed for waste minimization. In this context the use of azeotropes can be an effective tool for “recycling” and minimizing the large volumes of solvents, especially in aqueous mixtures, used. This review discusses the implementation of different kinds of azeotropic mixtures in relation to the environmental and economic benefits linked to their recovery and re-use. Examples of the use of azeotropes playing a role in the process performance and in the purification steps maximizing yields while minimizing waste. Where possible, the advantages reported have been highlighted by using E-factor calculations. Lastly azeotrope potentiality in waste valorization to afford value-added materials is given.

Effect of Temperature and Branched Crosslinkers on Supported Graphene Oxide Pervaporation Membranes for Ethanol Dehydration

We describe the performance of graphene oxide (GO) membranes stabilized by crosslinkers and supported on polyethersulfone films in the dehydration of ethanol in a continuous cross-flow pervaporation set-up. We used two crosslinker species with branched structures (humic acid-like substances derived from urban waste and a synthetic hyperbranched polyol). The supported crosslinked GO films were prepared by rod coating on a polyethersulfone ultrafiltration membrane. Pervaporation experiments were carried out at temperatures of 40, 50, 60 and 70 °C. When the feed comprised pure water and ethanol, a much higher flux of water than ethanol was observed at all temperatures through GO films stabilized by the two crosslinkers (humic acid, GO-HAL, and the synthetic hyperbranched polyol, GO-HBPO), indicating the separation ability of these crosslinked membranes. For feed mixtures of water and ethanol, the GO-HAL and GO-HBPO membranes showed good separation performances by producing permeates with a significantly higher water content than the feed at all temperatures.

Nanoparticle-Mediated, Light-Induced Phase Separations

Nanoparticles that both absorb and scatter light, when dispersed in a liquid, absorb optical energy and heat a reduced fluid volume due to the combination of multiple scattering and optical absorption. This can induce a localized liquid-vapor phase change within the reduced volume without the requirement of heating the entire fluid. For binary liquid mixtures, this process results in vaporization of the more volatile component of the mixture. When subsequently condensed, these two steps of vaporization and condensation constitute a distillation process mediated by nanoparticles and driven by optical illumination. Because it does not require the heating of a large volume of fluid, this process requires substantially less energy than traditional distillation using thermal sources. We investigated nanoparticle-mediated, light-induced distillation of ethanol-H2O and 1-propanol-H2O mixtures, using Au-SiO2 nanoshells as the absorber-scatterer nanoparticle and nanoparticle-resonant laser irradiation to drive the process. For ethanol-H2O mixtures, the mole fraction of ethanol obtained in the light-induced process is substantially higher than that obtained by conventional thermal distillation, essentially removing the ethanol-H2O azeotrope that limits conventional distillation. In contrast, for 1-propanol-H2O mixtures the distillate properties resulting from light-induced distillation were very similar to those obtained by thermal distillation. In the 1-propanol-H2O system, a nanoparticle-mediated, light-induced liquid-liquid phase separation was also observed.