Batch and Flow Green Microwave-Assisted Catalytic Conversion Of Levulinic Acid to Pyrrolidones.

This paper reports a new sustainable protocol for the microwave-assisted catalytic conversion of levulinic acid into N-substituted pyrrolidones over tailor-made mono (Pd, Au) or bimetallic (PdAu) catalysts supported on either highly mesoporous silica (HMS) or titania-doped HMS, exploiting the advantages of dielectric heating. MW-assisted reductive aminations of levulinic acid with several amines were first optimized in batch mode under hydrogen pressure (5 bar) in solvent-free conditions. Good-to-excellent yields were recorded at 150 °C in 90 min over the PdTiHMS and PdAuTiHMS, that proved recyclable and almost completely stable after six reaction cycles. Aiming to scale-up this protocol, a MW-assisted flow reactor was used in combination with different green solvents. Cyclopentyl methyl ether (CPME) provided a 99 % yield of N-(4-methoxyphenyl) pyrrolidin-2-one at 150 °C over PdTiHMS. The described MW-assisted flow synthesis proves to be a safe procedure suitable for further industrial applications, while averting the use of toxic organic solvents.

Leading Edge Technologies and Perspectives in Industrial Oilseed Extraction.

With the increase in the world's population and per capita wealth, oil producers must not only increase edible oil production but also meet the demand for a higher quality and variety of products. Recently, the focus has shifted from single processing steps to the entire vegetable oil production process, with an emphasis on introducing innovative technologies to improve quality and production efficiency. In this review, conventional methods of oilseed storage, processing and extraction are presented, as well as innovative processing and extraction techniques. Furthermore, the parameters most affecting the products' yields and quality at the industrial level are critically described. The extensive use of hexane for the extraction of most vegetable oils is undoubtedly the main concern of the whole production process in terms of health, safety and environmental issues. Therefore, special attention is paid to environmentally friendly solvents such as ethanol, supercritical CO2, 2-methyloxolane, water enzymatic extraction, etc. The state of the art in the use of green solvents is described and an objective assessment of their potential for more sustainable industrial processes is proposed.

Food-Waste Valorisation: Synergistic Effects of Enabling Technologies and Eutectic Solvents on the Recovery of Bioactives from Violet Potato Peels.

The recovery of valuable bioactive compounds from the main underutilised by-products of the food industry is one of the greatest challenges to be addressed in circular economy. Potato peels are the largest waste generated during potato processing. However, they could be a potential source of valuable bioactive compounds, such as polyphenols, that can be reused as natural antioxidants. Currently, environmentally benign enabling technologies and new types of non-toxic organic solvents for the extraction of bioactive compounds may dramatically improve the sustainability of these processes. This paper focuses on the potential inherent in the valorisation of violet potato peels (VPPs) by recovering antioxidants using natural deep eutectic solvents (NaDES) under ultrasound (US)- and microwave (MW)-assisted extraction. Both the enabling technologies provided performances that were superior to those of conventional extractions in terms of antioxidant activity determined by the DPPH· (2,2-diphenyl-1-picrylhydrazyl) assay. In particular, the most promising approach using NaDES is proven to be the acoustic cavitation with a Trolox eq. of 1874.0 mmolTE/gExtr (40 °C, 500 W, 30 min), vs. the 510.1 mmolTE/gExtr of hydroalcoholic extraction (80 °C, 4 h). The shelf-life of both hydroalcoholic and NaDES-VPPs extracts have been assessed over a period of 24 months, and found that NaDES granted a 5.6-fold shelf-life extension. Finally, the antiproliferative activity of both hydroalcoholic and NaDES-VPPs extracts was evaluated in vitro using the MTS assay on human tumour Caco-2 cells and normal human keratinocyte cells (HaCaT). In particular, NaDES-VPPs extracts exhibited a significantly more pronounced antiproliferative activity compared to the ethanolic extracts without a noteworthy difference between effects on the two cell lines.

Towards Substitution of Hexane as Extraction Solvent of Food Products and Ingredients with No Regrets.

Hexane is a solvent used extensively in the food industry for the extraction of various products such as vegetable oils, fats, flavours, fragrances, colour additives or other bioactive ingredients. As it is classified as a "processing aid", it does not have to be declared on the label under current legislation. Therefore, although traces of hexane may be found in final products, especially in processed products, its presence is not known to consumers. However, hexane, and in particular the n-hexane isomer, has been shown to be neurotoxic to humans and has even been listed as a cause of occupational diseases in several European countries since the 1970s. In order to support the European strategy for a toxic-free environment (and toxic-free food), it seemed important to collect scientific information on this substance by reviewing the available literature. This review contains valuable information on the nature and origin of the solvent hexane, its applications in the food industry, its toxicological evaluation and possible alternatives for the extraction of natural products. Numerous publications have investigated the toxicity of hexane, and several studies have demonstrated the presence of its toxic metabolite 2,5-hexanedione (2,5-HD) in the urine of the general, non-occupationally exposed population. Surprisingly, a tolerable daily intake (TDI) has apparently never been established by any food safety authority. Since hexane residues are undoubtedly found in various foods, it seems more than necessary to clearly assess the risks associated with this hidden exposure. A clear indication on food packaging and better information on the toxicity of hexane could encourage the industry to switch towards one of the numerous other alternative extraction methods already developed.

Lignin as a Natural Carrier for the Efficient Delivery of Bioactive Compounds: From Waste to Health.

Lignin is a fascinating aromatic biopolymer with high valorization potentiality. Besides its extensive value in the biorefinery context, as a renewable source of aromatics lignin is currently under evaluation for its huge potential in biomedical applications. Besides the specific antioxidant and antimicrobial activities of lignin, that depend on its source and isolation procedure, remarkable progress has been made, over the last five years, in the isolation, functionalization and modification of lignin and lignin-derived compounds to use as carriers for biologically active substances. The aim of this review is to summarize the current state of the art in the field of lignin-based carrier systems, highlighting the most important results. Furthermore, the possibilities and constraints related to the physico-chemical properties of the lignin source will be reviewed herein as well as the modifications and processing required to make lignin suitable for the loading and release of active compounds.

Higher Yield and Polyphenol Content in Olive Pomace Extracts Using 2-Methyloxolane as Bio-Based Solvent.

Despite its severe toxicity and negative environmental impact, hexane remain the solvent of choice for the extraction of vegetable oils. This is in contrast with the constantly growing demand for sustainable and green extraction processes. In recent years a variety of alternatives to hexane have been reported, among them 2-methyloxolane (2-MeOx), which has emerged as a promising bio-based alternative. This study evaluates the possibility of replacing hexane, in the extraction of olive pomace (OP), with 2-MeOx, both dry and saturated with water (4.5%), the latter of which is called 2-MeOx 95.5%. The three solvents have been compared in terms of extraction yield and quality, as well as the lipid and polyphenol profiles of the extracts. The work concluded that both dry 2-MeOx and 2-MeOx 95.5% can replace hexane in OP extraction, resulting in higher yields and extracts richer in phenolic compounds. This study should open the road to further semi-industrial scale investigations toward more sustainable production processes.

Mechanochemical Applications of Reactive Extrusion from Organic Synthesis to Catalytic and Active Materials.

In the past, the use of mechanochemical methods in organic synthesis was reported as somewhat of a curiosity. However, perceptions have changed over the last two decades, and this technology is now being appreciated as a greener and more efficient synthetic method. The qualified "offer" of ball mills that make use of different set-ups, materials, and dimensions has allowed this technology to mature. Nevertheless, the intrinsic batch nature of mechanochemical methods hinders industrial scale-ups. New studies have found, in reactive extrusion, a powerful technique with which to activate chemical reactions with mechanical forces in a continuous flow. This new environmentally friendly mechanochemical synthetic method may be able to miniaturize production plants with outstanding process intensifications by removing organic solvents and working in a flow mode. Compared to conventional processes, reactive extrusions display high simplicity, safety, and cleanliness, which can be exploited in a variety of applications. This paper presents perspective examples in the better-known areas of reactive extrusions, including oxidation reactions, polymer processing, and biomass conversion. This work should stimulate further developments, as it highlights the versatility of reactive extrusion and the huge potential of solid-phase flow chemistry.

Green Deep Eutectic Solvents for Microwave-Assisted Biomass Delignification and Valorisation.

Aiming to fulfil the sustainability criteria of future biorefineries, a novel biomass pretreatment combining natural deep eutectic solvents (NaDESs) and microwave (MW) technology was developed. Results showed that NaDESs have a high potential as green solvents for lignin fractionation/recovery and sugar release in the following enzymatic hydrolysis. A new class of lignin derived NaDESs (LigDESs) was also investigated, showing promising effects in wheat straw delignification. MW irradiation enabled a fast pretreatment under mild condition (120 °C, 30 min). To better understand the interaction of MW with these green solvents, the dielectric properties of NaDESs were investigated. Furthermore, a NaDES using the lignin recovered from biomass pretreatment as hydrogen bond donor was prepared, thus paving the way for a "closed-loop" biorefinery process.

Sono- and mechanochemical technologies in the catalytic conversion of biomass.

This tutorial review focuses on the valorisation of biomass by sonochemical and mechanochemical activation. Although several of the examples reported herein rely on the use of model compounds rather than native feedstocks, the conversion of lignocellulosic fractions into valuable compounds is a great opportunity with which to more sustainably exploit natural resources, from environmental, economic and social points of view. The use of non-conventional technologies that generate high-energy microenvironments can improve biomass deconstruction and the accessibility of catalysts, granting higher conversion and selectivity. The critical parameters in sonochemical and mechanochemical conversions have been analysed together with the most common devices and reactors, and the potential of sonocatalysis and mechanocatalysis as emerging tools for both catalytic and biocatalytic biomass conversion will be discussed. A SWOT (strengths, weaknesses, opportunities and threats) analysis will provide an overview of the effective feasibility of these approaches in a biorefinery context. Although these technologies offer indisputable advantages (mild reaction conditions, enhanced reaction rates and mass transfer), their mechanisms and the systematic adjustment of parameters to give optimal outcomes still require further investigation, which will pave the way for reproducible and scalable experiments. Indeed, process scale-up can be accomplished both in batch and flow mode. However, results are not particularly predictable, despite the accurate control of instrumental variables, because of the variability found in biomass sources and the complexity inherent in structures.

Emerging Processing Technologies for the Recovery of Valuable Bioactive Compounds from Potato Peels.

Potato peel (PP) is the major underutilised by-product in the potato-processing industry and a potential source of valuable bioactive molecules. Among them, glycoalkaloids and polyphenols are important precursors for steroid hormones and natural antioxidants, respectively. Moreover, the huge quantities of industrial potato-peel waste that are produced are a rich source of primary metabolites, which principally include starch as well as non-starch polysaccharides, proteins, lipids, lignin and cellulose. All carbohydrates are prone to undergo fermentation to produce ethanol, lactic and acetic acid. Finally, the main portion of PP is made up of alcohol-insoluble matter with a dietary fibre content of approximatively 40%. The present review summarises the recent advances and emerging technologies in potato-peel extraction and further valorisation processing in the food industry.

Microwave-Assisted Protocol for Green Functionalization of Thiophenes With a Pd/ß-Cyclodextrin Cross-Linked Nanocatalyst.

Microwaves (MW) are often the most efficient, in terms of heat exchange and conversion rate, of all the energy sources used to promote chemical reactions thanks to fast volumetric dielectric heating, and metal-catalyzed synthetic reactions under heterogeneous conditions are an eloquent example. We herein report a MW-assisted green protocol for the C-H arylation of thiophenes with substituted aryl halides. This sustainable protocol carried out in γ-valerolactone (GVL) is catalyzed by Pd nanoparticles embedded in cross-linked ß-cyclodextrin. In view of the excellent results achieved with activated substrates, the one-pot synthesis of a 4(3H)-quinazolinone derivative has been accomplished. A pressure-resistant MW reactor, equipped with multiple gas inlets, was used for sequential (i) C-H arylation, (ii) reduction, and (iii) carbonylation in the presence of the same catalyst, but under different gas atmospheres. The robust heterogeneous Pd catalyst showed limited metal leaching in GVL, making this an efficient MW-assisted process with high atom economy.

Cross-Linked Cyclodextrins Bimetallic Nanocatalysts: Applications in Microwave-Assisted Reductive Aminations.

The optimization of sustainable protocols for reductive amination has been a lingering challenge in green synthesis. In this context, a comparative study of different metal-loaded cross-linked cyclodextrins (CDs) were examined for the microwave (MW)-assisted reductive amination of aldehydes and ketones using either H2 or formic acid as a hydrogen source. The Pd/Cu heterogeneous nanocatalyst based on Pd (II) and Cu (I) salts embedded in a ß-CD network was the most efficient in terms of yield and selectivity attained. In addition, the polymeric cross-linking avoided metal leaching, thus enhancing the process sustainability; good yields were realized using benzylamine under H2. These interesting findings were then applied to the MW-assisted one-pot synthesis of secondary amines via a tandem reductive amination of benzaldehyde with nitroaromatics under H2 pressure. The formation of a CuxPdy alloy under reaction conditions was discerned, and a synergic effect due to the cooperation between Cu and Pd has been hypothesized. During the reaction, the system worked as a bifunctional nanocatalyst wherein the Pd sites facilitate the reduction of nitro compounds, while the Cu species promote the subsequent imine hydrogenation affording structurally diverse secondary amines with high yields.

A smart use of biomass derivatives to template an ad hoc hierarchical SAPO-5 acid catalyst.

A smart design of hierarchical SAPO-5 acid catalyst using biomass derived monosaccharides as sustainable and low-cost mesoporogens has been developed. The hierarchical SAPO-5 was characterized by several physico-chemical techniques to elucidate structure-properties relationships and was tested as a catalyst in the MW-assisted glucose transformation in 5-HMF using γ-valerolactone (GVL) as green solvent.

Microwave-Assisted Dehydrogenative Cross Coupling Reactions in γ-valerolactone with a Reusable Pd/ß-cyclodextrin Crosslinked Catalyst.

Transition-metal mediated C⁻H bond activation and functionalization is one of the most straightforward and powerful tools in modern organic synthetic chemistry. Oxidative C⁻H/C⁻H coupling reactions between two (hetero)arenes under heterogeneous catalysis may be a valuable means for the production of a plethora of bi(hetero)aryls, and one that adheres to the increasing demand for atom-economic and sustainable chemistry. We have therefore developed a reusable heterogeneous catalytic system, which is based on Pd cross-linked ß-cyclodextrin, to perform an efficient microwave-assisted oxidative C⁻H/C⁻H cross coupling process between benzothiazoles and methyl thiophene in the presence of green solvents.

Reactive Hypersaline Route: One-Pot Synthesis of Porous Photoactive Nanocomposites.

Herein, porous photoactive nanocomposites are prepared by a simple one-pot synthesis approach using a salt and aqueous media. Within this reactive hypersaline route, the salt not only serves in the structuring of the composite but also becomes an integral active part of it. Here, the addition of sodium thiocyanate to a titania precursor guides, on the one hand, the formation of needle-shaped nanoparticles and, on the other hand, forms yellow compound isoperthiocyanic acid, which is homogeneously incorporated into the porous nanocomposite. Compared to a pure titania reference, this material reveals a 7-fold-increased photodegradation rate of Rhodamine B as a model compound. This reveals the reactive hypersaline route to be a promising and facile synthesis route toward photoactive porous materials.

Bioherbicidal activity of a germacranolide sesquiterpene dilactone from Ambrosia artemisiifolia L.

Ambrosia artemisiifolia L. (common ragweed) is an invasive plant whose allelopathic properties have been suggested by its field behaviour and demonstrated through phytotoxicity bioassays. However, the nature of the molecules responsible for the allelopathic activity of common ragweed has not been explored. The main objective of this study was to identify the phytotoxic molecules produced by A. artemisiifolia. A preliminary investigation has indicated that a methanol extract of A. artemisiifolia completely inhibited the germination of cress and radish. Semi-preparative fractionation of the methanol extract allowed separating of phytotoxic fraction which contained a single compound. The structure of this compound was elucidated by liquid chromatography-mass spectrometry (LC-MS)/MS, high-resolution mass spectral, nuclear magnetic resonance, and Fourier transform infrared spectra as sesquiterpene lactone isabelin (C15H16O4). The effect of pure isabelin was tested on four different weed species, confirming the inhibitory activity of molecule. The results indicate directions for the future studies about herbicidal specific activity of isabelin, as pure molecule or in the crude extract, as a potential candidate for biological weed control.

Microwave-Assisted γ-Valerolactone Production for Biomass Lignin Extraction: A Cascade Protocol.

The general need to slow the depletion of fossil resources and reduce carbon footprints has led to tremendous effort being invested in creating "greener" industrial processes and developing alternative means to produce fuels and synthesize platform chemicals. This work aims to design a microwave-assisted cascade process for a full biomass valorisation cycle. GVL (γ-valerolactone), a renewable green solvent, has been used in aqueous acidic solution to achieve complete biomass lignin extraction. After lignin precipitation, the levulinic acid (LA)-rich organic fraction was hydrogenated, which regenerated the starting solvent for further biomass delignification. This process does not requires a purification step because GVL plays the dual role of solvent and product, while the reagent (LA) is a product of biomass delignification. In summary, this bio-refinery approach to lignin extraction is a cascade protocol in which the solvent loss is integrated into the conversion cycle, leading to simplified methods for biomass valorisation.

Chemical modeling of acid-base properties of soluble biopolymers derived from municipal waste treatment materials.

This work reports a study of the proton-binding capacity of biopolymers obtained from different materials supplied by a municipal biowaste treatment plant located in Northern Italy. One material was the anaerobic fermentation digestate of the urban wastes organic humid fraction. The others were the compost of home and public gardening residues and the compost of the mix of the above residues, digestate and sewage sludge. These materials were hydrolyzed under alkaline conditions to yield the biopolymers by saponification. The biopolymers were characterized by 13C NMR spectroscopy, elemental analysis and potentiometric titration. The titration data were elaborated to attain chemical models for interpretation of the proton-binding capacity of the biopolymers obtaining the acidic sites concentrations and their protonation constants. The results obtained with the models and by NMR spectroscopy were elaborated together in order to better characterize the nature of the macromolecules. The chemical nature of the biopolymers was found dependent upon the nature of the sourcing materials.

From lignocellulosic biomass to lactic- and glycolic-acid oligomers: a gram-scale microwave-assisted protocol.

The conversion of lignocellulosic biomass into platform chemicals is the key step in the valorization of agricultural waste. Of the biomass-derived platform chemicals currently produced, lactic acid plays a particularly pivotal role in modern biorefineries as it is a versatile commodity chemical and building block for the synthesis of biodegradable polymers. Microwave-assisted processes that furnish lactic acid avoid harsh depolymerization conditions while cutting down reaction time and energy consumption. We herein report a flash catalytic conversion (2 min) of lignocellulosic biomass into lactic and glycolic acids under microwave irradiation. The batch procedure was successfully adapted to a microwave-assisted flow process (35 mL min(-1) ), with the aim of designing a scalable process with higher productivity. The C2 and C4 units recovered from the depolymerization were directly used as the starting material for a solvent and catalyst-free microwave-assisted polycondensation that afforded oligomers in good yields.

Enabling technologies built on a sonochemical platform: challenges and opportunities.

Scientific and technological progress now occurs at the interface between two or more scientific and technical disciplines while chemistry is intertwined with almost all scientific domains. Complementary and synergistic effects have been found in the overlay between sonochemistry and other enabling technologies such as mechanochemistry, microwave chemistry and flow-chemistry. Although their nature and effects are intrinsically different, these techniques share the ability to significantly activate most chemical processes and peculiar phenomena. These studies offer a comprehensive overview of sonochemistry, provide a better understanding of correlated phenomena (mechanochemical effects, hot spots, etc.), and pave the way for emerging applications which unite hybrid reactors.