Advancements in green chemistry approaches to chemical synthesis
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[EMBARGOED UNTIL 12/01/2025] Green chemistry approaches in chemical synthesis aim to reduce environmental impact while improving the efficiency and sustainability of chemical processes. In this work, we present two significant advancements in this field. First, the introduction and development of a non-pyrophoric version of Raney-nickel (Ra- Ni) by modifying the catalyst's surface. Raney nickel is renowned for its high catalytic activity in a variety of transformations. Predominantly, it is used to reduce unsaturated hydrocarbons and various functional groups. However, in anhydrous form, it is highly flammable when exposed to air, which makes it unsafe to use. To mitigate this issue, we have developed a non-pyrophoric version of Ra-Ni that is easier to handle in powder form. It can be weighed easily and requires no pre-activation procedures. The modified version of Ra-Ni is recyclable and catalytically active under mild conditions in water. The catalyst structure was characterized by scanning transmission electron microscopy (STEM), high- resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). Its activity was tested on various transformations, such as the hydrogenation of quinolines, chalcones, and substituted 1,10-phenanthroline. The catalytic process is safe and sustainable as we have mitigated its flammability hazard, making it more suitable for potential large-scale industrial applications. The second advancement was modifying the PS-750-M amphiphile by replacing its mPEG part with a sugar molecule to enable chemistry in water. Water is regarded as an eco- friendly, sustainable, and cost-effective solvent for organic synthesis. However, conducting organic reactions in water presents significant challenges, primarily due to the poor solubility of substrates and catalysts. To solve this issue, as of now numerous non-ionic designer surfactants are developed for efficient organic transformations in water. Notably, most of surfactant molecules contain polyethylene glycol as its hydrophilic part. For instance, in vitamin E derived TPGS-750-M by Lipshutz's group and L-proline based PS- 750-M from Handa's group, polyethylene glycol moiety as a hydrophilic part may not be biodegradable. Therefore, a second-generation PS-750-M (2nd Gen-PS) is developed as an alternative of polyethylene glycol (PEG)-based surfactant. The synthetic protocol for this newer version is simple, scalable, and derived from economical sources such as L-proline, lauroyl chloride, and N-methyl glucamine. This surfactant is compatible with various organic transformations in water and has been characterized by NMR spectroscopy and dynamic light scattering. By incorporating another sustainability feature to micellar catalysis, we contribute to sustainable and eco-friendly chemical processes as well as reducing reliance on toxic solvents by their usage.
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M.S.