Tetrahedron Green Chem最新文献

The rapid development of flow chemistry and its related microfluid technology has accelerated the innovation in material science and the research into alternative, environmentally, and cost-effective microfabrication procedures. This article reviews the latest advances in bamboo-based microfluidic devices, highlighting the heterogeneous catalysis in flow mode through the three-dimensional (3D) structures of the plant's vascular bundles. Different strategies for immobilizing catalysts (metal and enzymes) and the design of the lignocellulosic-based flow reactor are presented.

Typically, nano-emulsions are prepared in batch high-speed homogenization or ultrasound processes and polymerized afterwards in batch reactors. However, fully continuous processes have the potential to decrease production costs and energy consumption compared to batch processes. This research thus focuses on implementing ultrasound into a fully continuous emulsification and nano-emulsion polymerization process to obtain latex nano-particles from butylmethacrylate and ethylene glycol dimethacrylate. The goal of this research is to produce nano-emulsions and nano-particles with the smallest obtainable size and polydispersity in a fully continuous two-stage process. In the first stage or emulsification stage, parameters like flowrate, residence time and acoustic power are varied to influence and determine the optimal energy density. In second stage or reaction stage, residence time and reaction temperature are studied to obtain particles of monodisperse sizes. Samples produced in both stages are analysed with Dynamic Light Scattering to measure the average size and polydispersity (PdI) of the emulsion droplets and particles. Emulsification results indicate that droplet size and PdI decreases at increasing energy densities (J/ml) until 60 J/ml after which a constant droplet size of 150 nm and PdI of 0.230 are reached. Furthermore, a particle size of 50 nm and PdI of 0.080 were achieved in both batch and continuous polymerization reactors after 5 min at 85 °C. By implementing the most optimal process parameters, small emulsion droplets and particles were obtained more energy efficient in a shorter emulsification and reaction time compared to literature ultrasound assisted nano-emulsion polymerization processes.

In this study, a gold nanoparticles (GNPs) have been successfully fabricated by the bio reduction route using soil extract Aspergillus trinidadensis (VM ST01’ OL587588) fungi as a reducing and capping agent without any solvent interference. The GNPs were grown and stabilized by a two-step one-pot method, without any influence of chemical reactants. Characteristics of prepared GNPs were investigated using various microscopic and spectroscopic techniques. GNPs were roughly spherical in shape. Water dispersion study of GNPs has shown a stable dispersion in a broad range of 2–12 pH. The stirring and precursor salt concentration has influenced the kinetics involved in the fabrication process. Stoichiometric data has shown 3.5 × 10²⁰ gold atoms per gram of biomass with diameters of around 35 nm, as determined with High-Resolution Transmission Electron Microscopy (HR-TEM). Zeta potential and Powder X-Ray Diffraction (P-XRD) studies have elucidated the crystalline nature of GNPs. Presence of participating functional groups were examined with Fourier Transform Infra-Red Spectroscopy (FT-IR). Synthesized GNPs were analyzed for surface morphology by Scanning Electron Microscope (SEM). The thermal stability of the lyophilized GNPs sample and capping of the particle were evaluated with Thermo-Gravimetric Analysis (TGA) and had a residual mass of 25% at 306 °C. The Aspergillus trinidadensis capped GNPs have been demonstrated as an efficient heterogeneous catalyst (AtGNHC) for the reduction of 4-Nitrophenol as a model substrate in water. An isolated yield (>95%) of the reduced product in 4 h has shown the effectiveness of the prepared catalyst.

Mn-catalysed C–H activation has emerged as a useful sustainable methodology for the formation of new C–C bonds. To date most of the protocols are described in organic solvents. Water as solvent, on the other hand, would be highly advantageous, but is often incompatible with organometallic chemistry. Herein, we describe the C–H activation of indoles using an unmodified, commercially available manganese catalyst in water. Two types of valuable allyl groups can be added and a good substrate scope is described. Substitution at the C-3 group is tolerated, allowing access to medicinally important frameworks, and the reaction works on a gram scale. Finally, harnessing the tolerance of water as the reaction medium, D₂O can be used as an inexpensive source of deuterium for the C-2 labelling of indoles.

Biomass, a renewable and carbon neutral energy source, is highly promising within the upcoming decades for addressing several consumer goods and fuel requirements of humankind. Using catalysts in the biomass valorization industry increases the recyclability of feedstock, offers higher selectivity in products, reduces environmental impact, and controls the reactivity of the procedures. In this review, we have scrutinized the status of the development of multifunctional metal-based catalysts that can help convert various biomass into high-value fine goods. The catalytic systems have been divided into subgroups to deeply study their structural characteristics and active sites towards intrinsic reactivity and selectivity in the transformation of biomass intermediates, which mostly occurs via hydrolysis, dehydration, hydrodeoxygenation, and oxidation pathways In this review, we mainly focus on the role and significance of metal oxide-based catalysts, metal-oxide supported catalysts, heteropoly acids, aluminosilicates, and mesoporous catalysts in biomass valorization. Recent developments in photocatalytic materials for the oxidation of small molecules produced from biomass (such sugars, alcohols, and carboxylic acids) and lignin model compounds are described, as well as the function of various heteroatoms in enhancing photo-electronic characteristics. Bimetallic catalytic systems' acid-base supports and metal nanoparticulate sites work together synergistically to enable one-pot multistep cascade reactions.

The problems associated with the use of molecular hydrogen (transportation, storage and high cost) have pushed scientists to the pursuit of efficient hydrogen donors, able to reduce chemical bonds in the presence of catalysts through catalytic transfer hydrogenation (CTH) reactions. In this sense, formic acid stands up as one of the most important and safest chemical molecules for H₂ generation under mild conditions. It can be obtained from biomass through different catalytic transformations and used as well to upgrade biomass to platform chemicals. This review summarizes the recently published studies dealing with formic acid production from biomass (using glucose as representing molecule) along with its use in hydrogen involved reactions of different groups of platform chemicals upgrading.

The advent of flow chemistry and flow microreactor technology in organic synthesis has added a series of options to the toolbox of synthetic chemists by enabling access to chemical reactions, which had hitherto been little explored or impossible in classical batch methods. In this review article, we provide an update on recent reports (published since 2020) showcasing examples of flow technology enabling the genesis and use of highly reactive organometallic intermediates for the synthesis of key building blocks and active pharmaceutical ingredients. In addition to showcasing the known advantages of flow technology (e.g., safety, scalability and productivity) we also highlight its positive impact on the greenness of organic reactions.

The hydrogenation of the monoterpene β-myrcene, the sesquiterpene farnesene and the triterpene squalene was studied in a custom-built continuous flow reactor using 3D printed stainless steel static mixers coated with Palladium catalyst. Full hydrogenation was achieved in a facile and cost-effective fashion using Catalytic Static Mixer (CSM) technology. Wash coated Pd/Al₂O₃ CSMs for the hydrogenation of β-myrcene in ethyl acetate and electroplated Pd CSMs proved to be efficient for the hydrogenation of farnesene and squalene in solvent-free reactions to produce the fully hydrogenated terpenes 2,6-dimethyloctane, farnesane and squalane.

Efficacious waste valorisation is a promising strategy towards sustainability. Marine waste which was undervalued and underutilized for a long time has attracted attention recently to realize its economic value to meet the sustainable development requirements. Chitin, a naturally occurring nitrogen-rich marine biopolymer has tremendous potential for material synthesis and chemical production. The current review is focussed on highlighting the effectiveness of chitin from a catalytic perspective. Unlike chitosan, the usage of chitin for constructing catalyst has not been demonstrated thoroughly. Thus, the present study exhibits strategical chemical modification of chitin, its conversion to N-doped carbon materials as efficient catalyst for various transformation. Advancements on deriving organo-nitrogen chemicals catalytically from chitin has also been discussed. Through these two aspects the potency of chitin as a sustainable candidate for catalysis is projected. Finally, challenges and prospects are accessed to enhance the production of valuable chemicals/materials from chitin biomass via greener protocols.

Chromenes, biologically-active scaffolds, and their variants have been often synthesized by the combination of salicylaldehyde, malononitrile, and nucleophilic species (indoles, naphthols, nitro compounds, thiols). Whereas this combination furnishes specifically 2-amino-4H-chromenes, other related compounds such as chromeno[2,3-b]pyridines and chromeno[2,3-d]pyrimidines may be also attained using similar readily available reactants: salicylaldehyde, two equivalents of malononitrile and a thiol for the former and malononitrile, two salicylaldehyde equivalents and an amine for the latter. To the best of our knowledge, there are no reported studies which have attempted to synthesize these products using the same catalyst. Hence, the aim of the below study was to find a cheap and recyclable catalyst that would be able to drive the synthesis of all three products. Positively, piperazine supported on the polymeric sulfonic acid resin Amberlyst® 15 was found to be an inexpensive and easily-prepared novel catalyst that could be used to synthesize all three derivatives (33 examples, 18–82%) in fairly good yields whilst also being recyclable and reusable (for up to four or five runs).