Clay and clay-supported reagents in organic synthesis

Low-power microwaves: a cell-compatible physical treatment to enhance the mechanical properties of self-assembling peptides

Biomaterials designed for tissue engineering applications should, among other requirements, mimic the native extracellular matrix (ECM) of the tissues to be regenerated, both in terms of biomimetic and mechanical properties. Ideally, the scaffold stiffness and stress resistance should be tuned for each specific implantation therapy. Self-assembling peptides (SAPs) are promising synthetic bionanomaterials prone to easy multi-functionalization, bestowing biomimetic properties. However, they usually yield soft and fragile hydrogels unsuited for the regeneration of medium-to-hard tissues. For this purpose, chemical cross-linking of SAPs is an option, but it often requires a moderately toxic and expensive chemical compound and/or the presence of specific residues/reactive sites, posing issues for its feasibility and translational potential. In this work, we introduced, characterized by rheology, atomic force microscopy (AFM), Thioflavin-T assay (ThT), and Fourier transform infrared (FT-IR) tests, and optimized (by tuning the power, temperature and treatment time) a novel fast, green and affordable methodology using mild microwave (MW) irradiation to increase the mechanical properties of diverse classes of SAPs. Low-power MWs increase stiffness, resilience, and β-structuration, while high-power MW treatments partially denature the tested SAPs. Our pure-physical methodology does not alter the SAP biomimetic properties (verified via in vitro tests of viability and differentiation of human neural stem cells), is compatible with already seeded cells, and is also synergic with genipin-based cross-linking of SAPs; therefore, it may become the next standard for SAP preparation in tissue engineering applications at hand of all research labs and in clinics.

A fully quantum-mechanical treatment for kaolinite

Neural network potentials for kaolinite minerals have been fitted to data extracted from density functional theory calculations that were performed using the revPBE + D3 and revPBE + vdW functionals. These potentials have then been used to calculate the static and dynamic properties of the mineral. We show that revPBE + vdW is better at reproducing the static properties. However, revPBE + D3 does a better job of reproducing the experimental IR spectrum. We also consider what happens to these properties when a fully quantum treatment of the nuclei is employed. We find that nuclear quantum effects (NQEs) do not make a substantial difference to the static properties. However, when NQEs are included, the dynamic properties of the material change substantially.

Synthesis of bentonite/Ag nanocomposite by laser ablation in air and its application in remediation

In this research, a simple, green, and efficient approach is described to produce novel bentonite/Ag nanocomposite wherein the preparation of Ag nanoparticles (Ag NPs) deployed the laser ablation method in air; Ag NPs are deposited on the bentonite via the magnetic stirring method. The structural and morphological characterization of the as-prepared bentonite/Ag nanocomposite (denoted as B/Ag30, 30 min being the laser ablation time) is accomplished using different methods. Additionally, the catalytic assessment of the ensued composite exhibited excellent catalytic reduction/degradation activity for common aqueous pollutants namely methyl orange (MO), congo red (CR) and 4-nitrophenol (4-NP) utilizing NaBH₄ as reductant. Furthermore, the recycling tests displayed the high stability/reusability of B/Ag30 nanocomposite for at least 4 runs with retention of catalytic prowess.

Interactions between Nanoclay, CTAB and Linear/Star Shaped Polymers

The influence of star-shaped (PAA-SS) and linear polyacrylic acid (PAA) with different molecular weights (high—PAA-HMW and low—PAA-LMW) on the structure of the adsorption layer, adsorption amount, electrokinetic and stabilizing properties of the PAA/CTAB/nanoclay suspensions was studied. The properties of the systems containing one of these polymers, the cationic surfactant—hexadecyltrimethylammonium bromide (CTAB) and the surface-modified nanoclay (N-SM) were analyzed using the following techniques: BET, CHN, FT-IR, ED-XRF, XRD, HRTEM, UV-Vis, tensiometry and zeta potential measurements. It was proved that PAA could be used as an effective stabilizer of N-SM. Moreover, the addition of CTAB caused a significant increase in the stability of the systems but decreased the adsorption of PAA on the N-SM surface and changed the structure of the adsorption layers. The largest stability was observed in the PAA-HMW/CTAB system. The PAA polymers and PAA/CTAB complexes adsorbed, especially on the clay surface, influenced the primary distribution of the layered sheets but kept the same basal d-spacing. The adsorption of PAA and the PAA/CTAB complexes took place mainly at the plate edges and on the contact space between the sheets. The obtained results will be used for the preparation of the PAA/CTAB/nanoclay composite for water purification.

Research Trends on Pillared Interlayered Clays (PILCs) Used as Catalysts in Environmental and Chemical Processes: Bibliometric Analysis

Over the last four decades, a large number of studies have been published on pillared interlayered clays (PILCs) used as adsorbent materials and catalysts or supports for transition metals in heterogeneous catalysis. Particularly, PILCs have been used for water treatment through advanced oxidation processes (AOPs) to remove organic pollutants. They have also been studied in various chemical and environmental processes. Because of the growing interest in PILCs, this article is focused on analyzing scientific publications such as research/review articles and book chapters from the last four decades (from 1980 to 2019) through a bibliometric analysis (BA) to visualize and describe research trends on PILCs. By narrowing the bibliographic search to titles, keywords, and abstracts of publications related to PILCs, using Scopus and Web of Science (WoS) (the two scientific databases), a total of 3425 documents have been retrieved. The bibliometric dataset was analyzed by VantagePoint^®. The main research trends identified in the last four decades were the use of PILCs in environmental processes (34.4% of total publications) along with chemical processes (petrochemical reactions 17.5%, SCR NOx 10.8%, and decomposition 8.2%). In environmental processes, PILCs have been used in photo-oxidation (32%), CWPO (21.1%), and heterogeneous catalysis (19.4%). Phenols, dyes, and VOCs have been the main pollutants studied using PILCs as catalysts. Fe, Ti, Zr, Cu, and Co are the most supported active phases in PILCs. Other research trends grouped by characterization techniques, countries, research areas, institutes, scientific journals that have published the most on this topic, number of publications per 5-year period, and most frequently used keywords through the last four decades have been identified. It was determined that the number of publications on PILCs has increased since 1980 and the countries with the highest number of publications are China, Spain, and The United States of America.

Solid Acid Catalysts for the Hock Cleavage of Hydroperoxides

The oxidation of cumene and following cleavage of cumene hydroperoxide (CHP) with sulfuric acid (Hock rearrangement) is still, by far, the dominant synthetic route to produce phenol. In 2020, the global phenol market reached a value of 23.3 billion US$ with a projected compound annual growth rate of 3.4% for 2020–2025. From ecological and economical viewpoints, the key step of this process is the cleavage of CHP. One sought-after way to likewise reduce energy consumption and waste production of the process is to substitute sulfuric acid with heterogeneous catalysts. Different types of zeolites, silicon-based clays, heteropoly acids, and ion exchange resins have been investigated and tested in various studies. For every type of these solid acid catalysts, several materials were found that show high yield and selectivity to phenol. In this mini-review, first a brief introduction and overview on the Hock process is given. Next, the mechanism, kinetics, and safety aspects are summarized and discussed. Following, the different types of heterogeneous catalysts and their performance as catalyst in the Hock process are illustrated. Finally, the different approaches to substitute sulfuric acid in the synthetic route to produce phenol are briefly concluded and a short outlook is given.

Activation and Characterization of Algerian Kaolinite, New and Green Catalyst for Synthesis of Polystyrene and Poly(1,3-dioxolane)

In the present work we have explored a new catalyst prepared with Algerian clay and a new method to synthesise polystyrene and poly(1,3-dioxolane). This technique consists of using Algerian modified clay (Kaolinite-H+) as a green catalyst. Kaolinite-H+ is a proton exchanged clay which is prepared through a simple exchange process. Synthesis experiments are performed in bulk. The polymerization of styrene in bulk leads to the yield of 83 % at room temperature with the reaction time of 3 h. Molecular weight of the obtained polystyrene is calculated by 1H NMR and is about 2196 g/mol. Polymerization of (1,3-dioxolane) is carried out at room temperature with the reaction time of 3 h and polymerization yield of 91 %. The calculated molecular weight of the obtained poly(1,3-dioxolane) is about 573 g/mol. The structure of the obtained polymers is confirmed by FT-IR and 1H NMR. The modified clay (Kaolinite-H+) is characterized by FT-IR, XRD and SEM analysis.

Variation of Used Vegetable Oils’ Composition upon Treatment with Algerian Clays

The treatment of used vegetable oils (UVOs) with clays represents a pivotal step in their industrial recycling process as well as one of the most challenging topics for researchers. In particular, cheap, effective, and sustainable powders need to be explored in order to develop new processes which produce beneficial results in relation to economic and environmental aspects. In this context, five samples within commercial and waste vegetable oils were treated with two sodium- and calcium-based bentonites employing a low oil/bentonite ratio (0.15 wt%). The outcomes of the processes were monitored by FT-IR spectroscopy and compared with the data relative to the parent commercial edible oil. In particular, treatment of FT-IR data by multivariate statistical analysis allowed us to determine a chemical fingerprint characteristic of each sample. Important relationships between the overall chemical composition and the specific clay employed and the treatment time (2 or 4 h) were highlighted. Finally, N2 physisorption, TEM microscopy, and FT-IR analyses of the more efficient Na bentonite allowed us to characterize the material and thus to furnish all the information needed to set-up a general protocol for the partial regeneration of waste vegetable oil destined for further processing.

Synthesis of Organic Matter in Aqueous Environments Simulating Small Bodies in the Solar System and the Effects of Minerals on Amino Acid Formation

The extraterrestrial delivery of organics to primitive Earth has been supported by many laboratory and space experiments. Minerals played an important role in the evolution of meteoritic organic matter. In this study, we simulated aqueous alteration in small bodies by using a solution mixture of H₂CO and NH₃ in the presence of water at 150 °C under different heating durations, which produced amino acids after acid hydrolysis. Moreover, minerals were added to the previous mixture to examine their catalyzing/inhibiting impact on amino acid formation. Without minerals, glycine was the dominant amino acid obtained at 1 d of the heating experiment, while alanine and β-alanine increased significantly and became dominant after 3 to 7 d. Minerals enhanced the yield of amino acids at short heating duration (1 d); however, they induced their decomposition at longer heating duration (7 d). Additionally, montmorillonite enhanced amino acid production at 1 d, while olivine and serpentine enhanced production at 3 d. Molecular weight distribution in the whole of the products obtained by gel chromatography showed that minerals enhanced both decomposition and combination of molecules. Our results indicate that minerals affected the formation of amino acids in aqueous environments in small Solar System bodies and that the amino acids could have different response behaviors according to different minerals.

Catalytic Applications of Clay Minerals and Hydrotalcites

Clay minerals are the most abundant minerals on the surface of Earth [...]

Facile synthesis of 2-deoxy-2-[18 F]fluorosorbitol using sodium borohydride on aluminum oxide

2-Deoxy-2-[18 F]fluorosorbitol (18 F-FDS) has become increasingly useful in functional renal imaging. FDS is synthesized by the one-step reduction of 2-deoxy-2-[18 F]fluoroglucose (18 F-FDG). To develop a more simple and rapid procedure for 18 F-FDS synthesis, we examined reduction reactions with solid-supported NaBH4 . Synthetic yields using BH4 -IRA400 (polymer-based matrix) and NaBH4 -Al2 O3 (clay-based matrix) as solid-supported reagents were compared. NaBH4 -Al2 O3 was found to be far superior to BH4 -IRA400 in the FDG reduction reaction. IRA 400 was not suitable for this reaction because it adsorbs FDG, in addition to glucose, with no FDS synthesized when using BH4 -IRA400. By contrast, NaBH4 -Al2 O3 only required a filtration as workup, affording FDS in 90% yield after a total of 10 min. NaBH4 on alumina was readily consumed in the reaction within 1 min, regardless of the amount used, by simply stirring with a vortex mixer. Complicated procedures, such as microwave irradiation, were not necessary. This simple operation will allow kit formulation and is suitable for radiosynthesis. In conclusion, clay-supported reagents showed low absorption and were time saving, which are highly compatible with 18 F-FDS synthesis.

Preparation and catalytic properties of poly(methyl methacrylate)-supported Pd0 obtained from room-temperature, dark reduction of ionic aggregates of the unstable Pd2+ solution ionomer

A poly(methyl methacrylate)-supported Pd⁰ nanocatalyst was successfully prepared from solution reaction of Pd(CH₃COO)₂ with a copolymer acid, poly(methyl methacrylate-ran-methacrylic acid) (MMA–MAA). The reaction was carried out in a benzene/methanol mixed solvent in the dark at room temperature (∼25 °C) in the absence of a typical chemical reductant. There was coordination between the Pd⁰ nanoclusters and MMA–MAA, resulting in Pd⁰ nanoclusters being stably and uniformly dispersed in the MMA–MAA matrix, with an average particle size of ∼2.5 ± 0.5 nm. Mechanistically, it can tentatively be proposed that PMMA-ionomerization of the Pd²⁺ ions produces intramolecular –2COO⁻–Pd²⁺ aggregate cross-links in the solution. On swelling of the chain-segments that are covalently bound via multiple C–C bonds, the resultant elastic forces cause instantaneous dissociation at the O–Pd coordination bonds to give transient bare (i.e., uncoordinated), highly-oxidative Pd²⁺ ions and H⁺-associative carboxylate groups, both of which rapidly scavenge electrons and protons, respectively, of the active α-H atoms abstracted from the methanol molecules of the solvent to make Pd⁰ nanoclusters supported by the re-formed MMA–MAA. The MMA–MAA acid copolymer, without itself undergoing any permanent chemical change, serves as a mechanical activator or catalyst for the mechanochemical reduction of Pd(CH₃COO)₂ under mild conditions. Compared with traditional Pd/C catalysts, this Pd⁰ nanocatalyst exhibited more excellent catalytic efficiency and reusability in the Heck reaction between iodobenzene and styrene, and it could be easily separated. The supported Pd⁰ nanocatalyst prepared using this novel and simple preparation method may display high-efficiency catalytic properties for other cross coupling reactions.

A polymer-supported Pd⁰ nanocatalyst is prepared by using mechanochemical reduction as the driving force for the reaction.

An Overview on Steroids and Microwave Energy in Multi-Component Reactions towards the Synthesis of Novel Hybrid Molecules

In recent years, hybrid systems are gaining considerable attention owing to their various biological applications in drug development. Generally, hybrid molecules are constructed from different molecular entities to generate a new functional molecule with improved biological activities. There already exist a large number of naturally occurring hybrid molecules based on both non-steroid and steroid frameworks synthesized by nature through mixed biosynthetic pathways such as, a) integration of the different biosynthetic pathways or b) Carbon- Carbon bond formation between different components derived through different biosynthetic pathways. Multicomponent reactions are a great way to generate efficient libraries of hybrid compounds with high diversity. Throughout the scientific history, the most common factors developing technologies are less energy consumption and avoiding the use of hazardous reagents. In this case, microwave energy plays a vital role in chemical transformations since it involves two very essential criteria of synthesis, minimizing energy consumption required for heating and time required for the reaction. This review summarizes the use of microwave energy in the synthesis of steroidal and non-steroidal hybrid molecules and the use of multicomponent reactions.

Greener and sustainable production of bioethylene from bioethanol: current status, opportunities and perspectives

The economic value of bioethylene produced from bioethanol dehydration is remarkable due to its extensive usage in the petrochemical industry. Bioethylene is produced through several routes, such as steam cracking of hydrocarbons from fossil fuel and dehydration of bioethanol, which can be produced through fermentation processes using renewable substrates such as glucose and starch. The rise in oil prices, environmental issues due to toxic emissions caused by the combustion of fossil fuel and depletion of fossil fuel resources have led a demand for an alternative pathway to produce green ethylene. One of the abundant alternative renewable sources for bioethanol production is biomass. Bioethanol produced from biomass is alleged to be a competitive alternative to bioethylene production as it is environmentally friendly and economical. In recent years, many studies have investigated catalysts and new reaction engineering pathways to enhance the bioethylene yield and to lower reaction temperature to drive the technology toward economic feasibility and practicality. This paper critically reviews bioethylene production from bioethanol in the presence of different catalysts, reaction conditions and reactor technologies to achieve a higher yield and selectivity of ethylene. Techno-economic and environmental assessments are performed to further development and commercialization. Finally, key issues and perspectives that require utmost attention to facilitate global penetration of technology are highlighted.

Effect of Irrigation Systems and Soil Conditioners on the Growth and Essential Oil Composition of Rosmarinus officinalis L. Cultivated in Egypt

A relevant improvement of the cultivar conditions of Rosmarinus officinalis L. in desert areas was achieved by a specific combination between an irrigation system and soil conditioner. A drastic reduction in water employment was obtained without affecting the quality of the plants, which was determined by monitoring the growth parameters and essential oil characteristics. In particular, the effect of surface and subsurface drip irrigation systems and different soil conditioners on the growth parameters, yield, and essential oil constituents of rosemary plants was assessed. Field experiments at the Agricultural Research Station (Al-Adlya farm), SEKEM Group Company, El-Sharkiya Governorate, Egypt, conducted over the two seasons, revealed the effectiveness of subsurface irrigation systems in obtaining better performances, especially in terms of saving water. The combination of subsurface irrigation and the conditioner HUNDZ soil with bentonite showed the maximum mean values of growth characteristics compared with other soil amendments during both seasons. The possibility to employ a water-saving irrigation system at the subsurface level without any drawback in the resulting plants was also explored in terms of molecular composition. Gas chromatography-mass (GC-MS) analysis of the essential oils extracted from plants grown under different irrigation conditions revealed a comparable composition in both cases. The quality of the system that showed the best performance was also confirmed by the comparable yield of the essential oil.

Phosphorous-Doped Graphitic Material as a Solid Acid Catalyst for Microwave-Assisted Synthesis of β-Ketoenamines and Baeyer-Villiger Oxidation

Synthesis of phosphorous-doped graphitic materials (P-Gc) using phytic acid as a precursor was done in a microwave oven in a cost- and time-effective green way. The material was used as a solid acid catalyst for microwave (MW)-assisted synthesis of β-ketoenamines and Baeyer-Villiger (BV) oxidation. In the case of BV oxidation, hydrogen peroxide (H2O2) was used as a green oxidant. For β-ketoenamines, in most cases, 100% conversion with an ∼95% yield was achieved in ethyl acetate medium. In solvent-free conditions, the yield of β-ketoenamines was ∼75%. A kinetic study suggested that the resonance stabilization of the positive reaction center happens in the transition state for β-ketoenamine synthesis. In BV oxidation, cyclic ketones were converted to their corresponding cyclic esters in good to high yields (∼80% yield) in a shorter reaction time (6-20 min). As per our knowledge, this is the first report of BV oxidation catalyzed by a heteroatom-doped graphitic material. For BV oxidation, the phosphoric acid functional groups present in P-Gc might increase the electrophilicity of the carbonyl group of the ketones to compensate for the weakness of H2O2 as a nucleophile and a spiro-bisperoxide intermediate has been identified in high-resolution mass spectrometry.

Novel Brönsted Acidic Ionic Liquids Confined in UiO-66 Nanocages for the Synthesis of Dihydropyrido[2,3-d]Pyrimidine Derivatives under Solvent-Free Conditions

The effective and simple one-pot, three-component protocol for the synthesis of dihydropyrido[2,3-d]pyrimidine derivatives is presented using a triethylenediamine or imidazole Brönsted acidic, ionic-liquid-supported Zr metal-organic framework (TEDA/IMIZ-BAIL@UiO-66) as a green, novel, and retrievable heterogeneous catalyst under mild conditions. The multicomponent reactions of 6-amino-1,3-dimethyl uracil, various aromatic aldehydes, and acetyl acetone were conducted under solvent-free conditions so that dihydropyrido[2,3-d]pyrimidine derivatives can be obtained. It is possible to separate and purify the respective products easily using crystallization. We can recycle the catalysts six times without losing any major activity. Also, the characterization of the catalyst was done by energy-dispersive X-ray, field emission scanning electron microscopy, Fourier transform infrared, Brunauer-Emmett-Teller, X-ray diffraction, and thermogravimetric analysis analyses.

Synthesis of 1,2,4-triazolo[4,3-a][1,8]Naphthyridines using Chloranil under Microwave Irradiation

A simple and highly efficient procedure has been described for the synthesis of 1-aryl-4-[p-bromophenyl)-1,2, 4-triazolo[4,3-a][1,8]naphthyridines (8) by the oxidation of the corresponding aryl aldehyde 3-(p-bromophenyl)-1, 8-naphthyridin-2-ylhydrazones (7) with chloranil under microwave irradiation. The products are obtained in good yields and in a state of high purity.

Silica Gel Supported Sodium Hydrogen Sulfate as an Efficient and Reusable Heterogeneous Catalyst for the Synthesis of Imines in Solvent-free Conditions under Microwave Irradiation

This synthesis of imines has been carried out efficiently by the condensation of carbonyl compounds with amines in the presence of silica gel supported sodium hydrogen sulfate (NaHSO4.SiO2) as a heterogeneous catalyst under microwave irradiation in solvent-free conditions. NaHSO4.SiO2 can be recovered and re-used up to ten times by simple washing with diethyl ether after each use and activated in an oven at 120 °C for 1 h, thus rendering the process more economical.

A Facile Clay-Mediated Synthesis of 3,3-diindolyl-2-indolinones from Isatins

Dry reaction of isatins (3a, 3b) with indoles (4a–e) on montmorillonite K10 clay at room temperature furnished within minutes 3,3-bis(3′-indolyl)-2-indolinones (1a–f) in high yields. 5-Nitroisatin (3c) furnished, in addition to the expected indolinone 1h, 3-hydroxy-3-(3′-indolyl)-5-nitro-2-indolinone (6), a likely intermediate to 1h.

Copper nitrate: a privileged reagent for organic synthesis

Copper has been explored as an ideal candidate for replacing noble metals in organic synthesis, especially for practical large scale preparation. Recent decades have witnessed the renaissance and improvement of copper-catalyzed and copper-mediated organic reactions. Copper nitrate is a common inorganic copper salt which has been proved to be a ubiquitous reactant in organic synthesis due to its commercial availability, stability, inexpensiveness and environmentally benign nature. Copper nitrate could be used as a nitration reagent, oxidant, catalyst or promoter, and Lewis acid as well. Remarkably, great attention has been devoted to the efficient transformation of copper nitrate into functionalized or complicated compounds through various reaction types including cyclization, C-H activation, difunctionalization, nitration, rearrangement and asymmetric synthesis with chiral ligands. Further modification of copper nitrate, such as solid-supported copper nitrate or copper nitrate complexes, extends its applications in organic synthesis. The present review highlights recent advances of copper nitrate in organic synthesis, along with the mechanisms.

A Low-Cost, Well-Designed Catalytic System Derived from Household Waste "Egg Shell": Applications in Organic Transformations

A waste feedstock-derived economical basic alternative catalyst is described in this review. Eggshell is one of the household wastes created in tons of weight daily. Therefore, in order to reduce the environmental pollution-related problems, its use in heterogeneous catalysis can be attributed as a great contribution for the chemical and material science society to carry out several known reactions and for the much-needed energy alternative biodiesel production as low-cost catalytic system. Keeping green chemistry in mind, industrial use of these catalysts may also reduce the use of other traditionally used high-cost chemical catalytic systems.

Nanoscale infrared imaging analysis of carbonaceous chondrites to understand organic-mineral interactions during aqueous alteration

Organic matter in carbonaceous chondrites is distributed in fine-grained matrix. To understand pre- and postaccretion history of organic matter and its association with surrounding minerals, microscopic techniques are mandatory. Infrared (IR) spectroscopy is a useful technique, but the spatial resolution of IR is limited to a few micrometers, due to the diffraction limit. In this study, we applied the high spatial resolution IR imaging method to CM2 carbonaceous chondrites Murchison and Bells, which is based on an atomic force microscopy (AFM) with its tip detecting thermal expansion of a sample resulting from absorption of infrared radiation. We confirmed that this technique permits ∼30 nm spatial resolution organic analysis for the meteorite samples. The IR imaging results are consistent with the previously reported association of organic matter and phyllosilicates, but our results are at much higher spatial resolution. This observation of heterogeneous distributions of the functional groups of organic matter revealed its association with minerals at ∼30 nm spatial resolution in meteorite samples by IR spectroscopy.

Fluorescence enhancement novel green analytical method for paraquat herbicide quantification based on immobilization on clay

Fluorescence emission enhancement by adsorption as a promising tool for the development of future green sensors.

Bentonite as a Refining Agent in Waste Cooking Oils Recycling: Flash Point, Density and Color Evaluation

Clarification of waste recycled cooking oil (WCO) is very important in order to refine the intermediate regenerated base resulting from the previous steps. Bentonite has been historically employed as a filling material for oil refining filters due to its easy availability and its cheap price. In the present communication our early results from the filtration of degummed WCO through a pad of bentonite are presented. In particular, the variation of density, flash point and color have been monitored prior and after the filtration process and compared with samples of non-filtered WCO. An early classification of the bentonite employed has been conducted on the basis of FT-IR and XRD measurements.

From Conventional Lewis Acids to Heterogeneous Montmorillonite K10: Eco-Friendly Plant-Based Catalysts Used as Green Lewis Acids

The concept of green chemistry began in the USA in the 1990s. Since the publication of the 12 principles of this concept, many reactions in organic chemistry have been developed, and chemical products have been synthesized under environmentally friendly conditions. Lewis acid mediated synthetic transformations are by far the most numerous and best studied. However, the use of certain Lewis acids may cause risks to environmental and human health. This Review discusses the evolution of Lewis acid catalyzed reactions from a homogeneous liquid phase to the solid phase to yield the expected organic molecules under green, safe conditions. In particular, recent developments and applications of biosourced catalysts from plants are highlighted.