Hydrodeoxygenation of Oxygen-Containing Aromatic Plastic Wastes to Liquid Organic Hydrogen Carriers.

To address the global plastic pollution issues and the challenges of hydrogen storage and transportation, we report a system, based on the hydrodeoxygenation (HDO) of oxygen-containing aromatic plastic wastes, from which organic hydrogen carriers (LOHCs) can be derived. We developed a catalytic system comprised of Ru-ReOx /SiO2 +HZSM-5 for direct HDO of polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyphenylene oxide (PPO), and their mixtures, to cycloalkanes as LOHCs, with high yields up to 99 %, under mild reaction conditions. The theoretical hydrogen storage capacity reaches ca. 5.74 wt%. The reaction pathway involves depolymerization of PC into C15 aromatics and C15 monophenols by direct hydrogenolysis of the C-O bond between the benzene ring and ester group, and subsequent parallel hydrogenation of C15 aromatics and HDO of C15 monophenols. HDO of cyclic alcohol is the rate-determining step. The active site is Ru metallic nanoparticles with partially covered ReOx species. The excellent performance is attributed to the synergetic effect of oxophilic ReOx species and Ru metallic sites for C-O hydrogenolysis and hydrogenation, and the promotion effect of HZSM-5 for dehydration of cyclic alcohol. The highly efficient and stable dehydrogenation of cycloalkanes over Pt/γ-Al2 O3 confirms that HDO products can act as LOHCs.

Converting Waste Plastic to Liquid Organic Hydrogen Carriers.

The accumulation of waste plastics in landfills and the environment, as well as the contribution of plastics manufacturing to global warming, call for the development of new technologies that would enable circularity for synthetic polymers. Thus far, emerging approaches for chemical recycling of plastics have largely focused on producing fuels, lubricants, and/or monomers. In a recent study, Junde Wei and colleagues demonstrated a new catalytic system capable of converting oxygen-containing aromatic plastic waste into liquid organic hydrogen carriers (LOHCs), which can be used for hydrogen storage. The authors utilized Ru-ReOx /SiO2 materials with zeolite HZSM-5 as a co-catalyst for the direct hydrodeoxygenation (HDO) of oxygen-containing aromatic plastic wastes that yield cycloalkanes as LOHCs with a theoretical hydrogen capacity of ≈5.74 wt % under mild reaction conditions. Subsequent efficiency and stability tests of cycloalkane dehydrogenation over Pt/Al2 O3 validated that the HDO products can serve as LOHCs to generate H2 gas. Overall, their approach not only opens doors to alleviating the severe burden of plastic waste globally, but also offers a way to generate clean energy and ease the challenges associated with hydrogen storage and transportation.

Effect of gem-Difluorination on the Key Physicochemical Properties Relevant to Medicinal Chemistry: The Case of Functionalized Cycloalkanes.

Physico-chemical properties important to drug discovery (pKa , LogP, and aqueous solubility), as well as metabolic stability, were studied for a series of functionalized gem-difluorinated cycloalkanes and compared to those of non-fluorinated and acyclic counterparts to evaluate the impact of the fluorination. It was found that the influence of the CF2 moiety on the acidity/basicity of the corresponding carboxylic acids and amines was defined by inductive the effect of the fluorine atoms and was nearly the same for acyclic and cyclic aliphatic compounds. Lipophilicity and aqueous solubility followed more complex trends and were affected by the position of the fluorine atoms, ring size, and even the nature of the functional group present; also, significant differences were found for the acyclic and cyclic series. Also, gem-difluorination either did not affect or slightly improved the metabolic stability of the corresponding model derivatives. The presented results can be used as a guide for rational drug design employing fluorine and establish the first chapter in a catalog of the key in vitro properties of fluorinated cycloalkanes.

A-X⋯σ Interactions-Halogen Bonds with σ-Electrons as the Lewis Base Centre.

CCSD(T)/aug-cc-pVTZ//ωB97XD/aug-cc-pVTZ calculations were performed for halogen-bonded complexes. Here, the molecular hydrogen, cyclopropane, cyclobutane and cyclopentane act as Lewis base units that interact through the electrons of the H-H or C-C σ-bond. The FCCH, ClCCH, BrCCH and ICCH species, as well as the F2, Cl2, Br2 and I2 molecular halogens, act as Lewis acid units in these complexes, interacting through the σ-hole localised at the halogen centre. The Quantum Theory of Atoms in Molecules (QTAIM), the Natural Bond Orbital (NBO) and the Energy Decomposition Analysis (EDA) approaches were applied to analyse these aforementioned complexes. These complexes may be classified as linked by A-X···σ halogen bonds, where A = C, X (halogen). However, distinct properties of these halogen bonds are observed that depend partly on the kind of electron donor: dihydrogen, cyclopropane, or another cycloalkane. Examples of similar interactions that occur in crystals are presented; Cambridge Structural Database (CSD) searches were carried out to find species linked by the A-X···σ halogen bonds.

Diversity and degradative capabilities of bacteria and fungi isolated from oil-contaminated and hydrocarbon-polluted soils in Kazakhstan.

Bacteria and fungi were isolated from eight different soil samples from different regions in Kazakhstan contaminated with oil or salt or aromatic compounds. For the isolation of the organisms, we used, on the one hand, typical hydrocarbons such as the well utilizable aliphatic alkane tetradecane, the hardly degradable multiple-branched alkane pristane, and the biaromatic compound biphenyl as enrichment substrates. On the other hand, we also used oxygenated derivatives of alicyclic and monoaromatic hydrocarbons, such as cyclohexanone and p-tert-amylphenol, which are known as problematic pollutants. Seventy-nine bacterial and fungal strains were isolated, and 32 of them that were clearly able to metabolize some of these substrates, as tested by HPLC-UV/Vis and GC-MS analyses, were characterized taxonomically by DNA sequencing. Sixty-two percent of the 32 isolated strains from 14 different genera belong to well-described hydrocarbon degraders like some Rhodococci as well as Acinetobacter, Pseudomonas, Fusarium, Candida, and Yarrowia species. However, species of the bacterial genus Curtobacterium, the yeast genera Lodderomyces and Pseudozyma, as well as the filamentous fungal genera Purpureocillium and Sarocladium, which have rarely been described as hydrocarbon degrading, were isolated and shown to be efficient tetradecane degraders, mostly via monoterminal oxidation. Pristane was exclusively degraded by Rhodococcus isolates. Candida parapsilosis, Fusarium oxysporum, Fusarium solani, and Rhodotorula mucilaginosa degraded cyclohexanone, and in doing so accumulate ε-caprolactone or hexanedioic acid as metabolites. Biphenyl was transformed by Pseudomonas/Stenotrophomonas isolates. When p-tert-amylphenol was used as growth substrate, none of the isolated strains were able to use it.

Selective Arene Hydrogenation for Direct Access to Saturated Carbo- and Heterocycles.

Arene hydrogenation provides direct access to saturated carbo- and heterocycles and thus its strategic application may be used to shorten synthetic routes. This powerful transformation is widely applied in industry and is expected to facilitate major breakthroughs in the applied sciences. The ability to overcome aromaticity while controlling diastereo-, enantio-, and chemoselectivity is central to the use of hydrogenation in the preparation of complex molecules. In general, the hydrogenation of multisubstituted arenes yields predominantly the cis isomer. Enantiocontrol is imparted by chiral auxiliaries, Brønsted acids, or transition-metal catalysts. Recent studies have demonstrated that highly chemoselective transformations are possible. Such methods and the underlying strategies are reviewed herein, with an emphasis on synthetically useful examples that employ readily available catalysts.

Hydrogenation of Borylated Arenes.

A cis-selective hydrogenation of abundant aryl boronic acids and their derivatives catalyzed by rhodium cyclic (alkyl)(amino)carbene (Rh-CAAC) is reported. The reaction tolerates a variety of boron-protecting groups and provides direct access to a broad scope of saturated, borylated carbo- and heterocycles with various functional groups. The transformation is strategically important because the versatile saturated boronate products are difficult to prepare by other methods. The utility of the saturated cyclic building blocks was demonstrated by post-functionalization of the boron group.

Biocatalytic conversion of cycloalkanes to lactones using an in-vivo cascade in Pseudomonas taiwanensis VLB120.

Chemical synthesis of lactones from cycloalkanes is a multi-step process challenged by limitations in reaction efficiency (conversion and yield), atom economy (by-products) and environmental performance. A heterologous pathway comprising novel enzymes with compatible kinetics was designed in Pseudomonas taiwanensis VLB120 enabling in-vivo cascade for synthesizing lactones from cycloalkanes. The respective pathway included cytochrome P450 monooxygenase (CHX), cyclohexanol dehydrogenase (CDH), and cyclohexanone monooxygenase (CHXON) from Acidovorax sp. CHX100. Resting (non-growing) cells of the recombinant host P. taiwanensis VLB120 converted cyclohexane, cyclohexanol, and cyclohexanone to ϵ-caprolactone at 22, 80-100, and 170 U gCDW-1 , respectively. Cyclohexane (5 mM) was completely converted with a selectivity of 65% for ϵ-caprolactone formation in 2 hr without accumulation of intermediate products. Promiscuity of the whole-cell biocatalyst gave access to analogous lactones from cyclooctane and cyclodecane. A total product concentration of 2.3 g L-1 and a total turnover number of 36,720 was achieved over 5 hr with a biocatalyst concentration of 6.8 gCDW L-1 .

The sub-chronic toxicity of a naphthenic hydrocarbon solvent in rats.

Cycloalkanes/naphthenes are constituents of complex hydrocarbon solvents, and hence an understanding of their toxicological profile is critical to establish safe limits for occupational exposures to these solvents. Although naphthenes are structurally related to and share a common metabolic fate with the straight and branched chain analogues, some toxicokinetic differences have been noted. The acute central nervous system response to volatile naphthenes in rodents has been shown to be slightly different compared to other alkane analogues. To determine whether these differences may extend to systemic effects with less volatile naphthenes, rats were exposed to 1500, 3000 or 6000 mg/m3 of a C9-C11 aliphatic solvent containing 70% naphthenes, for 90 days. Effects were limited to adaptive liver enlargement in both sexes and kidney toxicity in the male rat. For comparative purposes, the results from this study were compared to published reports of a complex hydrocarbon solvent with a higher proportion of volatile C5/C6 naphthenes and a mono-constituent naphthene (decahydronaphthalene). The results indicate that the systemic effects of naphthenes are similar to the straight and branched chain analogues and that the effects that are most relevant for human health evaluations of alkanes are acute central nervous system effects.

Silylarene Hydrogenation: A Strategic Approach that Enables Direct Access to Versatile Silylated Saturated Carbo- and Heterocycles.

We report a method to convert readily available silylated arenes into silylated saturated carbo- and heterocycles by arene hydrogenation. The scope includes alkoxy- and halosilyl substituents. Silyl groups can be derivatized into a plethora of functionalities and find application in organic synthesis, materials science, and pharmaceutical, agrochemical, and fragrance research. However, silylated saturated (hetero- ) cycles are difficult to access with current technologies. The yield of the hydrogenation depends on the amount of the silica gel additive. This silica effect also enables a significant improvement of a previously disclosed method for the hydrogenation of highly fluorinated arenes (e.g., to all-cis-C6 H6 F6 ).

Copper-Catalyzed Carbonylative Coupling of Cycloalkanes and Amides.

Carbonylation reactions are a most powerful method for the synthesis of carbonyl-containing compounds. However, most known carbonylation procedures still require noble-metal catalysts and the use of activated compounds and good nucleophiles as substrates. Herein, we developed a copper-catalyzed carbonylative transformation of cycloalkanes and amides. Imides were prepared in good yields by carbonylation of a C(sp(3) )-H bond of the cycloalkane with the amides acting as weak nucleophiles. Notably, this is the first report of copper-catalyzed carbonylative C-H activation.

Aerobic biodegradation of cycloalkanes in non-aqueous extracted oil sands tailings.

Management of growing volumes of fluid fine tailings (FFT) is a significant challenge for oil sands industry. A potential alternative non-aqueous solvent extraction (NAE) process uses cycloalkane solvent such as cyclohexane or cyclopentane with very little water and generates smaller volumes of 'dry' solids (NAES) with residual solvent. Here we investigate remediation of NAES in a simulated bench-scale upland reclamation scenario. In the first study, microcosms with nutrient medium plus FFT as inoculum were amended with cyclohexane and incubated for ∼1 year, monitoring for cyclohexane biodegradation under aerobic conditions. Biodegradation of cyclohexane occurred under aerobic conditions with no metabolic intermediates detected. A second study using NAES mixed with FFT spiked with cyclohexane and cyclopentane, with or without additional nutrients (nitrogen and phosphorus), showed complete and rapid aerobic biodegradation of both cycloalkanes in NAES inoculated with FFT and supplemented with nutrients. 16S rRNA gene sequencing revealed dominance of Rhodoferax and members of Burkholderiaceae during aerobic cyclohexane biodegradation in FFT, and Hydrogenophaga, Acidovorax, Defluviimonas and members of Porticoccaceae during aerobic biodegradation of cyclohexane and cyclopentane in NAES inoculated with FFT and supplemented with nutrients. The findings indicate that biodegradation of cycloalkanes from NAES is possible under aerobic condition, which will contribute to the successful reclamation of oil sands tailings for land closure.

Iron-catalyzed decarboxylative alkenylation of cycloalkanes with arylvinyl carboxylic acids via a radical process.

A Fe(acac)3-catalyzed decarboxylative coupling of 2-(aryl)vinyl carboxylic acids with cycloalkanes was developed by using DTBP as an oxidant through a radical process. This reaction tolerates a wide range of substrates, and products are obtained in good to excellent yields (71-95%). The reaction also shows excellent stereoselectivity, and only trans-isomers are obtained.

Preparation of Pd Nanoparticles Stabilized by Modified Montmorillonite for Efficient Hydrodeoxygenation of Lignin-Derived Phenolic Compounds in Water.

Developing a new and efficient catalytic route for the production of alkanes by upgrading the aqueous phenolic biofuels still remains a challenge. Here, we designed and synthesized a bifunctional catalyst that uses natural montmorillonite (MMT) as support and combines metal active sites and BrÓ§nsted acid sites in the MMT via ion exchange and reduction roasting process. The catalytic activity of the as-synthesized Pd-MMT (H+) was evaluated by the hydrodeoxygenation (HDO) of a series of lignin-derived phenolic compounds in water. Our model reaction study reveals that the HDO of phenol undergoes an initial hydrogenation of aromatic rings to produce cyclohexanol and cyclohexanone, followed by the dehydration of cyclohexanol to provide intermediate cyclohexene and a final hydrogenation of cyclohexene to create a cyclohexane product. The combination of high metal catalytic activity and BrÓ§nsted acidity in Pd-MMT (H+) synergistically accelerated the HDO of phenol. Furthermore, good catalytic activity and recycling ability were also observed for other lignin-derived phenolic compounds.

Fluorinated Cycloalkyl Building Blocks for Drug Discovery.

The review covers various aspects of fluorinated cycloalkyl (C3 -C7 ) building blocks for drug discovery, including their synthesis, key physicochemical properties, and biological and medicinal applications of their derivatives. The discussed synthetic methods include classical nucleophilic fluorinations of various substrates, the addition of fluorine and another heteroatom to double bonds, cycloadditions and other transformations of fluorine-containing substrates, as well as some newer reactions like fluorination of non-activated and remotely activated C-H bonds, decarboxylative and deborylative fluorinations, etc. The known data on the effect of introducing the fluorinated cycloalkyl groups on the compound's key in vitro parameters (such as acidity/basicity, lipophilicity, conformational behavior, and short contact capabilities) are surveyed. Finally, applications of fluorinated cycloalkyl building block derivatives in the design of biologically active compounds (including marketed drugs Maraviroc, Ivosidenib, and Sitafloxacin) are covered, with a focus on the fluorination impact.

Occurrence and distribution of cyclic-alkane-consuming psychrophilic bacteria in the Yellow Sea and East China Sea.

Cyclic alkanes (c-alkanes) are toxic compounds that are abundant in subsurface oil reservoirs and spilled condensate; hence, their environmental risk is significant. Although numerous studies have focused on the decomposition of other compound classes, e.g., acyclic alkanes and aromatic hydrocarbons, very little is known about the biodegradation of c-alkanes in the marine environment. Here, we enriched methylcyclohexane (MCH)-degrading bacteria derived from the cold bottom water (10-20 °C) of China's marginal seas in summer and characterized the changes to the bacterial community using high-throughput amplicon sequencing. MCH-consuming bacteria failed to grow from the warmer surface water (25-29 °C) in the same geographic sites and seasons. Notably, MCH-consuming communities derived from the cold bottom water in the Yellow Sea exhibit distinct structures compared to the other treatments. Furthermore, almost all dominant species in this setting appear to be specifically adapted to deeper cold water as indicated by significantly negative correlations to temperature (P < 0.01). From these results, we proposed that the biodegradation of MCH is effectively limited to the colder waters (10-20 °C) of China's marginal seas, with uncultured psychrophiles acting as the key taxa for MCH decomposition. Overall, this study indicates key functions for uncultivated microbes in the marine environment.

Dehydrogenation of Cycloalkanes over N-Doped Carbon-Supported Catalysts: The Effects of Active Component and Molecular Structure of the Substrate.

Efficient dehydrogenation of cycloalkanes under mild conditions is the key to large-scale application of cycloalkanes as a hydrogen storage medium. In this paper, a series of active metals loaded on nitrogen-doped carbon (M/CN, M = Pt, Pd, Ir, Rh, Au, Ru, Ag, Ni, Cu) were prepared to learn the role of active metals in cycloalkane dehydrogenation with cyclohexane as the model reactant. Only Pt/CN, Pd/CN, Rh/CN and Ir/CN can catalyze the dehydrogenation of cyclohexane under the set conditions. Among them, Pt/CN exhibited the best catalytic activity with the TOF value of 269.32 h-1 at 180 °C, followed by Pd/CN, Rh/CN and Ir/CN successively. More importantly, the difference of catalytic activity between these active metals diminishes with the increase in temperature. This implies that there is a thermodynamic effect of cyclohexane dehydrogenation with the synthetic catalysts, which was evidenced by the study on the activation energy. In addition, the effects of molecular structure on cycloalkane dehydrogenation catalyzed by Pt/CN were studied. The results reveal that cycloalkane dehydrogenation activity and hydrogen production rate can be enhanced by optimizing the type, quantity and position of alkyl substituents on cyclohexane.

Carbocycle-Based Organogelators: Influence of Chirality and Structural Features on Their Supramolecular Arrangements and Properties.

The rational design and engineer of organogel-based smart materials and stimuli-responsive materials with tuned properties requires the control of the non-covalent forces driving the hierarchical self-assembly. Chirality, as well as cis/trans relative configuration, also plays a crucial role promoting the morphology and characteristics of the aggregates. Cycloalkane derivatives can provide chiral chemical platforms allowing the incorporation of functional groups and hydrophobic structural units able for a convenient molecular stacking leading to gels. Restriction of the conformational freedom imposed by the ring strain is also a contributing issue that can be modulated by the inclusion of flexible segments. In addition, donor/acceptor moieties can also be incorporated favoring the interactions with light or with charged species. This review offers a perspective on the abilities and properties of carbocycle-based organogelators starting from simple cycloalkane derivatives, which were the key to establish the basis for an effective self-assembling, to sophisticated polycyclic compounds with manifold properties and applications.

Catalytic conversion of enzymatic hydrolysis lignin into cycloalkanes over a gamma-alumina supported nickel molybdenum alloy catalyst.

The efficient depolymerization and hydrodeoxygenation of enzymatic hydrolysis lignin are achieved in cyclohexane solvents over a gamma-alumina supported nickel molybdenum alloy catalyst in a single step. Under initial 3 MPa hydrogen at 320 °C, the highest overall cycloalkane yield of 104.4 mg/g enzymatic hydrolysis lignin with 44.4 wt% selectivity of ethyl-cyclohexane was obtained. The reaction atmosphere and temperature have significant effects on enzymatic hydrolysis lignin conversion, product type and distribution. The conversion of enzymatic hydrolysis lignin was also investigated over different nickel and molybdenum-based catalysts, and the gamma-alumina supported nickel molybdenum alloy catalyst exhibited the highest activity among those catalysts. To reveal the reaction pathways of alkylphenol hydrodeoxygenation, 4-ethylphenol was tested as a model compound. Complete conversion of 4-ethylphenol into cycloalkanes was achieved. A two-step mechanism of 4-ethylphenol dihydroxylation - hydrogenation is proposed, in which the benzene ring saturation is deemed as the rate-determining step.

Bio-Based Cycloalkanes: The Missing Link to High-Performance Sustainable Jet Fuels.

The development of sustainable energy solutions that reduce global carbon emissions, while maintaining high living standards, is one of the grand challenges of the current century. Transportation fuels are critical to economic development, globalization, and the advancement of society. Although ground vehicles and small aircraft are beginning a slow transition toward electric propulsion with energy sourced from solar radiation or wind, the extreme power requirements of jet aircraft require a more concentrated source of energy that is conveniently provided by liquid hydrocarbon fuels. This Review describes recent efforts to develop efficient routes for the conversion of crude biomass sources (e. g., lignocellulose) to cycloalkanes. These cycloalkanes impart advantageous properties to jet fuels, including increased density, higher volumetric heat of combustion, and enhanced operability. The combination of bio-based cycloalkanes and synthetic paraffinic kerosenes allows for the preparation of 100 % bio-based fuels that can outperform conventional petroleum-based fuels. In this Review methods are described that convert biomass-derived small molecules, including furfural, furfuryl alcohol, 5-hydroxymethylfurfural, cyclic ketones, phenolics, acyclic ketones, cyclic alcohols, furans, esters, and alkenes to high-density cycloalkanes. In addition to describing the chemical transformations and catalysts that have been developed to efficiently produce various cycloalkanes, this Review includes summaries of key fuel properties, which highlight the ability to generate fuels with customized performance metrics. This work is intended to inspire other researchers to study the conversion of sustainable feedstocks to full-performance aviation fuels. An acceleration of this research is critical to reducing the carbon footprint of commercial and military aviation on a timescale that will help blunt the impacts of global warming.