Green Chemistry最新文献

Chemical recycling of polymers to monomers and chemicals is a promising pathway to valorize plastic waste that cannot be mechanically recycled, thus potentially minimizing resource consumption and the overall CO₂ impact of the polymer industry. Among chemical recycling technologies, solvolytic depolymerization of poly(ethylene terephthalate) stands out as a selective process that maximizes monomer recovery. However, many challenges still remain regarding the optimization of these recycling technologies. Addressing these challenges could lead to these technologies becoming truly environmentally advantageous compared to alternative waste management solutions. Subcritical water has proven to be an outstanding media for a broad variety of reactions and its potential as a green solvent for PET depolymerization is reassessed based on a new nuclear magnetic resonance quantification method allowing for product characterization to a degree never reported before. In order to study the intrinsic product composition at every reaction condition (280 to 340 °C and 0 to 45 min reaction time), depolymerization experiments were performed in agitated micro-batch reactors, and NMR analysis was conducted prior to any alkaline-based purification. The highest recovery of terephthalic acid was achieved after 45 min at 340 °C, however, under these conditions ethylene glycol experiences a high degree of degradation. Collected data was then used to compare the environmental performance of different case scenarios leading to the preferable conditions to be 5 min at 310 °C, where the recovery of terephthalic acid, ethylene glycol, mono(2-hydroxyethyl) terephthalate and bis(2-hydroxyethyl) terephthalate is as high as 0.9 g g^?1 PET.

One approach to recycle homogeneous catalysts is through multiphase catalysis. Multiphase catalysis is not only limited to liquid–liquid multiphase systems but also includes for example solid and liquid phases. In this work, we present a catalyst recycling system based on the crystallization of the entire catalyst phase after the reaction at ambient temperature. Using the green and polar solvent ethylene carbonate, the polar Rh/sulfoXantphos catalyst is trapped in the crystallized ethylene carbonate phase. The product can be decanted under air as the catalyst is stabilized in the solid phase and the entire solid phase including the solvent is recycled. Several reactions such as the hydroformylation of hexene, octene and decene, and the hydrogenation of C₁₄ aldol products were conducted with this system. A TTON of 8627 could be achieved in the hydroformylation of 1-octene with initial turnover frequencies up to 1460 h^?1. In addition, the catalyst “pill” was switched between different reactions to show the flexibility of the system.

The development of atom- and step-economical methods for converting hazardous CS₂ into harmless chemicals is a challenging endeavor. Herein, we disclose a feasible strategy for the electrochemical dehydrogenative coupling of CS₂ and amines with β-ketoesters, which leads to dithiocarbamate intermediates in the presence of bases. In addition, inexpensive starting materials, broad substrate scope, and compatibility with natural product moieties make this efficient and sustainable reaction practical.

A solvent-free, rapid and operationally simple method for the chlorination of pyrazoles with trichloroisocyanuric acid to access 4-chloropyrazole derivatives is described. This high-yielding protocol avoids tedious column chromatography and reduces solvent consumption. Mechanistic studies suggested an electrophilic aromatic substitution mechanism. This system also gives good green chemistry metrics.

The efficient and selective cleavage of the β-O-4 linkage under mild conditions represents a promising strategy to convert lignocellulose to value-added aromatic chemicals. In this work, a recoverable polyoxometalate-ionic liquid (POM-IL) catalyst has been successfully constructed by reacting H₅PMo₁₀V₂O₄₀ (HPMoV) polyoxoacids with 1-methyl-3-(4-sulfobutyl)-1H-imidazolium (BMIM-SO₃) zwitterions. Such a POM-IL catalyst can selectively and effectively convert various β-O-4 lignin models into aromatic acids and phenols under mild homogeneous conditions. Addition of ethyl acetate to the homogeneous post-reaction solution allows the easy recovery of the POM-IL catalyst for successive five recycling tests with high robustness. The dominant catalytic pathway was elucidated by a series of mechanistic studies.

Direct C–H functionalisation methodologies represent an opportunity to improve the overall ‘green’ credentials of organic coupling reactions, improving atom economy and reducing overall step count. Despite this, these reactions frequently run under reaction conditions that leave room for improved sustainability. Herein, we describe a recent advance in our ruthenium-catalysed C–H arylation methodology that aims to address some of the environmental impacts associated with this procedure, including solvent choice, reaction temperature, reaction time, and loading of the ruthenium catalyst. We believe that our findings demonstrate a reaction with improved environmental credentials and showcase it on a multi-gram scale within an industrial setting.

Facile reductions of carboxylic acids to aldehydes or alcohols can be effected under mild conditions upon initial conversion to their corresponding S-2-pyridyl thioesters. Upon treatment with a commercially available and air-stable nickel pre-catalyst and silane as a stoichiometric reductant, aldehydes are formed in moderate to good yields. Alternatively, the 1-pot conversion of acids to their thioester derivatives can be followed by reduction to the alcohol upon treatment with sodium borohydride. A variety of starting materials ranging from highly functionalized acids to educts from the Merck informer library can be transformed using these green reaction media.

The emergence of accelerated aging reaction provided a safer, cleaner, and more sustainable technology for material manufacturing and biomass treatment but still underexploited in organic synthesis and medicinal chemistry. We report the first mechanochemical accelerated aging strategy for solvent-minimal (cascade) cross dehydrogenative coupling (CDC) reactions between glycine esters/amides and a range of nucleophiles, which features clean and convenient setup, ambient temperature, atmospheric oxidation, and feasibility, for multigram-scale synthesis. By virtue of these facts, the present method provided an expedient and sustainable alternative to synthesize biologically important α-glycine derivatives and functionalized 1,4-dihydropyridines including the precursor of the antioxidant AV-154 and calcium channel blocker analogs. Mechanistically, a pre-grinding of the reactants and silica gel/NaCl facilitated spontaneous oxidation of glycine esters/amides under open air without continuous energy input followed by a coupling reaction (and sequential transformations). Multiform green metrics calculation demonstrates that the current accelerated aging protocol meets many of the principles of green chemistry such as waste prevention, high atom economy, unnecessary solvent, and good energy efficiency.