Major Product Research Articles

Quantification of hydroperoxides in liquid fuels: A systematic comparison of titration and absorption methods and their coupling to HPLC

Hydroperoxides are major products in the autoxidation of fuels and play a central role in oxidation kinetics. Their presence affects the oxidation rate, even at low concentrations, and, in turn, the thermal stability of fuels. Standard techniques for the quantification of hydroperoxides (ROOH) in fuels involve the reduction of ROOH by I−, yielding iodine (I2), which can be quantified by titration. The ASTM titration method of ROOH is known to be poorly reproducible and have inadequate lower detection limits and limited dynamic ranges. In this work, several analytical methods for the quantification of hydroperoxides in fuels have been systematically compared for known concentrations of ROOH: titrations of iodine with thiosulfate (ASTM D3703) and triphenylphosphine (TPP) solutions, with colorimetric and potentiometric methods, and quantification of iodine by UV–visible absorption. n-decane was used as a surrogate fuel and tert-butyl hydroperoxide as the ROOH internal standard. Our systematic study shows that the ASTM method based on colorimetric titration using thiosulfate aqueous solution is the least accurate because of the non-miscibility of water and n-decane, which even makes the UV–visible spectroscopy method ineffective. The other titration method proposed in the literature, using TPP dissolved in n-decane as the titrant, does not have this miscibility problem. Potentiometric titration is found to be more reproducible and accurate than colorimetric titration. The UV–visible absorption reaches lower detection limits. We show that the combination of the potentiometric titration of iodine with TPP and UV–visible absorption enables ROOH concentrations to be determined with low detection limits and a large dynamic range. The advantages of iodometry and UV-absorption detection methods have been used to develop a new analytical method based on their coupling in HPLC with a post-column reactor.

Photocatalytic CO2 Reduction Using Ti3C2Xy (X = Oxo, OH, F, or Cl) MXene-ZrO2: Structure, Electron Transmission, and the Stability.

CO2 photoreduction using a semiconductor-based photocatalyst is a promising option for completing a new carbon-neutral cycle. The short lifetime of charges generated owing to light energy is one of the most critical problems in further improving the performance of semiconductor-based photocatalysts. This study shows the structure, electron transmission, and stability of Ti3C2Xy (X = oxo, OH, F, or Cl) MXene combined with a ZrO2 photocatalyst. Using H2 as a reductant, the photocatalytic CO formation rate increased by 6.6 times to 4.6 μmol h-1 gcat-1 using MXene (3.0 wt %)-ZrO2 compared to that using ZrO2, and the catalytic route was confirmed using 13CO2 to form 13CO. In clear contrast, using H2O (gas) as a reductant, CH4 was formed as the major product using Ti3C2Xy MXene (5.0 wt %)-ZrO2 at the rate of 3.9 μmol h-1 gcat-1. Using 13CO2 and H2O, 12CH4, 12C2H6, and 12C3H8 were formed besides H212CO, demonstrating that the C source was the partial decomposition and hydrogenation of Ti3C2Xy. Using the atomic force and high-resolution electron microscopies, 1.6 nm thick Ti3C2Xy MXene sheets were observed, suggesting ∼3 stacked layers that are consistent with the Ti-C and Ti···Ti interatomic distances of 0.218 and 0.301 nm, respectively, forming a [Ti6C] octahedral coordination, and the major component as the X ligand was suggested to be F and OH/oxo, with the temperature increasing by 116 K or higher owing to the absorbed light energy, all based on the extended X-ray absorption fine structure analysis.

Glyphosate- and aminomethylphosphonic acid (AMPA)-induced mortality and residues in juvenile brown trout (Salmo trutta f. fario) exposed at different temperatures

BackgroundGlyphosate is a broad-spectrum, non-selective systemic herbicide with a commonly assumed low potential for accumulation in biota. Nevertheless, glyphosate has been shown to bioaccumulate in the tissues of several organisms. To understand the bioconcentration dynamics of glyphosate in fish, brown trout (Salmo trutta forma fario) of different age were exposed to different concentrations of glyphosate, the formulation Roundup® LB Plus, and the major transformation product aminomethylphosphonic acid (AMPA) for two, three, or four weeks at different temperatures in the laboratory. Mortality rates were determined, and tissue samples were collected at the end of the experiment to ascertain concentrations of glyphosate and AMPA residues by liquid chromatography coupled to mass spectrometry (LC–MS/MS).ResultsBrown trout mortality during exposure to glyphosate or AMPA was considerably higher at 15 °C than at 7 °C. Also, a significant increase in glyphosate concentrations in samples containing muscle, head, backbone, and caudal fin tissue with increasing exposure concentrations and temperatures was observed. Six-month-old fish contained more glyphosate per kg wet weight after exposure than ten-month-old fish. The bioconcentration factors (BCFs) for glyphosate and AMPA were much higher at 15 °C than at 7 °C, but in both cases decreased with higher glyphosate concentrations. The BCF for glyphosate formulated in Roundup® was higher than the one for the parent compound. Approximately 30–42% of the organ-absorbed glyphosate and AMPA remained in the tissues even when the fish were kept in clean water lacking the test substances for three weeks after termination of exposure.ConclusionOur study demonstrated that there is an interaction between glyphosate and ambient temperature in terms of toxicity. Further it was shown that increasing concentrations of glyphosate and AMPA in the surrounding media lead to significantly increased concentrations of these substances in brown trout tissues, although neither bioconcentration nor bioaccumulation of glyphosate in animal tissues is expected due to the high water solubility of this chemical. As a consequence, the uptake of glyphosate by humans through the consumption of contaminated edible fish is very likely.

Bio-upcycling of even and uneven medium-chain-length diols and dicarboxylates to polyhydroxyalkanoates using engineered Pseudomonas putida

Bio-upcycling of plastics is an emerging alternative process that focuses on extracting value from a wide range of plastic waste streams. Such streams are typically too contaminated to be effectively processed using traditional recycling technologies. Medium-chain-length (mcl) diols and dicarboxylates (DCA) are major products of chemically or enzymatically depolymerized plastics, such as polyesters or polyethers. In this study, we enabled the efficient metabolism of mcl-diols and -DCA in engineered Pseudomonas putida as a prerequisite for subsequent bio-upcycling. We identified the transcriptional regulator GcdR as target for enabling metabolism of uneven mcl-DCA such as pimelate, and uncovered amino acid substitutions that lead to an increased coupling between the heterologous β-oxidation of mcl-DCA and the native degradation of short-chain-length DCA. Adaptive laboratory evolution and subsequent reverse engineering unravelled two distinct pathways for mcl-diol metabolism in P. putida, namely via the hydroxy acid and subsequent native β-oxidation or via full oxidation to the dicarboxylic acid that is further metabolized by heterologous β-oxidation. Furthermore, we demonstrated the production of polyhydroxyalkanoates from mcl-diols and -DCA by a single strain combining all required metabolic features. Overall, this study provides a powerful platform strain for the bio-upcycling of complex plastic hydrolysates to polyhydroxyalkanoates and leads the path for future yield optimizations.Graphical

Oxygen Vacancies Alter Methanol Oxidation Pathways on NiOOH.

A thorough comprehension of the mechanism underlying the methanol oxidation reaction (MOR) on Ni-based catalysts is critical for future electrocatalytic design and development. However, the mechanism of MOR on these materials remains a matter of controversy. Herein, we combine in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations to identify the active sites and determine the mechanism of MOR on monometallic Ni-based catalysts in alkaline media. The SEIRAS results show that formate and (bi)carbonate are formed after the commencement of the MOR with potential-dependent relative distributions. These spectroscopic results are in good agreement with the DFT-computed reaction profiles over an oxygen vacancy, suggesting that the MOR mainly proceeds through the formate-involving pathway, in which the early consumption of methanol yields formate as the major product, while increasing potential drives further oxidation of formate to (bi)carbonate. We also find a parallel pathway for the generation of (bi)carbonate at high potentials that bypasses the formation of formate. The two main pathways are thermodynamically more feasible than the one predominantly reported in the literature for MOR on NiOOH that involves CHO and/or CO as key intermediates. These DFT results are supported by spectroscopic evidence showing that no band associated with CHO or CO can be detected by SEIRAS, which is attributed to the nature of the oxygen vacancies as the active sites, suppressing deep dehydrogenation of CH2O to CHO. This work thus shows the promising role of defect engineering in promoting the electrocatalytic MOR activity and selectivity.

Functional characterisation of a new halotolerant seawater active glycoside hydrolase family 6 cellobiohydrolase from a salt marsh

Realising a fully circular bioeconomy requires the valorisation of lignocellulosic biomass. Cellulose is the most attractive component of lignocellulose but depolymerisation is inefficient, expensive and resource intensive requiring substantial volumes of potable water. Seawater is an attractive prospective replacement, however seawater tolerant enzymes are required for the development of seawater-based biorefineries. Here, we report a halophilic cellobiohydrolase SMECel6A, identified and isolated from a salt marsh meta-exo-proteome dataset with high sequence divergence to previously characterised cellobiohydrolases. SMECel6A contains a glycoside hydrolase family 6 (GH6) domain and a carbohydrate binding module family 2 (CBM2) domain. Characterisation of recombinant SMECel6A revealed SMECel6A to be active upon crystalline and amorphous cellulose. Mono- and oligosaccharide product profiles revealed cellobiose as the major hydrolysis product confirming SMECel6A as a cellobiohydrolase. We show SMECel6A to be halophilic with optimal activity achieved in 0.5X seawater displaying 80.6 ± 6.93% activity in 1 × seawater. Structural predictions revealed similarity to a characterised halophilic cellobiohydrolase despite sharing only 57% sequence identity. Sequential thermocycling revealed SMECel6A had the ability to partially reversibly denature exclusively in seawater retaining significant activity. Our study confirms that salt marsh ecosystems harbour enzymes with attractive traits with biotechnological potential for implementation in ionic solution based bioprocessing systems.

Top–down versus bottom–up oxidation of a neonicotinoid pesticide by OH radicals

Emerging contaminants (EC) distributed on surfaces in the environment can be oxidized by gas phase species (top-down) or by oxidants generated by the underlying substrate (bottom-up). One class of EC is the neonicotinoid (NN) pesticides that are widely distributed in air, water, and on plant and soil surfaces as well as on airborne dust and building materials. This study investigates the OH oxidation of the systemic NN pesticide acetamiprid (ACM) at room temperature. ACM on particles and as thin films on solid substrates were oxidized by OH radicals either from the gas phase or from an underlying TiO2 or NaNO2 substrate, and for comparison, in the aqueous phase. The site of OH attack is both the secondary >CH2 group as well as the primary -CH3 group attached to the tertiary amine nitrogen, with the latter dominating. In the case of top-down oxidation of ACM by gas phase OH radicals, addition to the -CN group also occurs. Major products are carbonyls and alcohols, but in the presence of sufficient water, their hydrolyzed products dominate. Kinetics measurements show ACM is more reactive toward gas phase OH radicals than other NN nitroguanidines, with an atmospheric lifetime of a few days. Bottom-up oxidation of ACM on TiO2 exposed to sunlight outdoors (temperatures were above 30 °C) was also shown to occur and is likely to be competitive with top-down oxidation. These findings highlight the different potential oxidation processes for EC and provide key data for assessing their environmental fates and toxicologies.

Valorization potential of Egyptian mango kernel waste product as analyzed via GC/MS metabolites profiling from different cultivars and geographical origins

Increasing attention has been given to mango (Mangifera indica) fruits owing to their characteristic taste, and rich nutritional value. Mango kernels are typically discarded as a major waste product in mango industry, though of potential economic value. The present study aims to outline the first comparison of different mango kernel cvs. originated from different localities alongside Egypt, e.g., Sharqia, Suez, Ismailia, and Giza. Gas chromatography–mass spectroscopy (GC–MS) post silylation analysis revealed that sugars were the major class being detected at 3.5–290.9 µg/mg, with some kernels originating from Sharqia province being the richest amongst other cvs. In consistency with sugar results, sugar alcohols predominated in Sharqia cvs. at 1.3–38.1 µg/mg represented by ribitol, iditol, pinitol, and myo-inositol. No major variation was observed in the fatty acids profile either based on cv. type or localities, with butyl caprylate as a major component in most cvs. identified for the first time in mango. Regarding phenolics, Sedeeq cv. represented the highest level at 18.3 µg/mg and showing distinct variation among cvs. posing phenolics as better classification markers than sugars. Multivariate data analyses (MVA) confirmed that the premium cvs “Aweis and Fons” were less enriched in sugars, i.e., fructose, talose, and glucose compared to the other cvs. Moreover, MVA of Zabdeya cv. collected from three localities revealed clear segregation to be chemically distinct. Sharqia originated mango kernels were rich in sugars (e.g., glucose and fructose), whilst sarcosine esters predominated in other origins.

Phototransformation of halobenzoquinones in aqueous solution under the simulate sunlight: Kinetics, mechanism and products

Halobenzoquinones (HBQs) are a novel family of unregulated disinfection byproducts (DBPs). Little is known about their phototransformation activities in natural water. Here, five HBQs with various halogenated substituent types, numbers, and structures positions were selected to investigate the kinetics of degradation in aqueous solutions at various concentrations and in the presence of common environmental variables (Cl−, NO2−, and humic acid). The results indicated that dichloride and dibromo-substituted HBQs were photolyzed, whereas tetrachloro-substituted HBQs showed little degradation. The photolysis rate constant (k) of HBQs decreased with increasing initial concentration. The presence of NO2− and Cl− promoted the degradation of HBQs mainly through the formation of hydroxyl radical (•OH), which were confirmed by electron paramagnetic resonance (EPR). In contrast, humic acid played a negative role on HBQs transformation due to the adsorption and quenching reactions. Possible conversion pathways for HBQs were proposed based on the identification of two major photodegradation products, hydroxylated HBQs and halogenated-benzenetriol, as well as reactive free radicals. This study provided meaningful insights into the environmental fates and risk assessments of HBQs in natural aquatic system.

B(OH)3‐Catalyzed Dual Friedel‐Crafts Type Reaction of Anilines and Aldehydes to Access Di‐ or Triarylmethanes (TRAMs)

AbstractThe catalytic influences of boric acid have been introduced on dual Friedel‐Crafts reaction between arylamines and aldehydes to install the Csp3‐center that leads to the formation of di‐ or tri‐substituted methanes. The described reaction conditions have directed the transformation to favor the para‐para substitution pattern to deliver the major products rather than the corresponding ortho‐para functionalization process. The devised transformation was examined by DFT calculation, which shows the favorable activation energy of transition states (TS) for the generation of highly substituted molecular scaffolds. The method was applicable over diversely substituted aldehydes and arylamines to afford the final products in excellent yields (60‐92 %) and selectivity. The proposed mechanism is supported by suitable control experiments, GC‐MS studies, and DFT calculations.

Phocaeicola acetigenes sp. nov., producing acetic acid and iso-butyric acid, isolated faeces from a healthy human.

An obligately anaerobic, non-motile, Gram-stain-negative, and rod-shaped strain KGMB11183T was isolated from the feces of healthy Koreans. The growth of strain KGMB11183T occurred at 30-45°C (optimum 37°C), at pH 6-9 (optimum pH 7), and in the presence of 0-0.5% NaCl (optimum 0%). Strain KGMB11183T showed 16S rRNA gene sequence similarities of 95.4% and 94.2% to the closest recognized species, Phocaeicola plebeius M12T, and Phocaeicola faecicola AGMB03916T. Phylogenetic analysis showed that strain KGMB11183T is a member of the genus Phocaeiocla. The major end products of fermentation are acetic acid and isobutyric acid. The major cellular fatty acids (> 10%) of this isolate were C18:1 cis 9, anteiso-C15:0, and summed feature 11 (iso-C17:0 3-OH and/or C18:2 DMA). The assembled draft genome sequences of strain KGMB11183T consisted of 3,215,271bp with a DNA G + C content of 41.4%. According to genomic analysis, strain KGMB11183T has a number of genes that produce acetic acid. The genome of strain KGMB11183T encoded the starch utilization system (Sus) operon, SusCDEF suggesting that strain uses many complex polysaccharides that cannot be digested by humans. Based on the physiological, chemotaxonomic, phenotypic, and phylogenetic data, strain KGMB11183T is regarded a novel species of the genus Phocaeicola. The type strain is KGMB11183T (= KCTC 25284T = JCM 35696T).

Macrocyclic Sulfur Ligand Stabilized Trans-Palladium Dichloride Complex: Syntheses, Structure, Chlorine Rotation, and Application in α-Olefination of Nitriles by Primary Alcohols.

Herein, we have reported the synthesis of a macrocyclic organosulfur ligand (L1) having a seventeen-membered macrocyclic ring. Subsequently, the corresponding trans-palladium complex (C1) of bulky macrocyclic organosulfur ligand (L1) was synthesized by reacting it with PdCl2 (CH3 CN)2 salt. The newly synthesized ligand and complex were characterized using various analytical and spectroscopic techniques. The complex showed a square planar geometry with trans orientation of two ligands around the palladium center. The complex possesses intramolecular SCH…Cl interactions of 2.648 Å between the macrocyclic ligand and palladium dichloride. The potential energy surface (PES) for the rotational process of C1 suggested a barrier of ~23.81 kcal/mol for chlorine rotation. Furthermore, the bulky macrocyclic organosulfur ligand stabilized palladium complex (C1) was used as a catalyst (2.5 mol %) for α-olefination of nitriles by primary alcohols. The α,β-unsaturated nitrile compounds were found to be the major product of the reaction (57-78 % yield) with broad substrate scope and large functional group tolerance. Notably, the saturated nitrile product was not observed during the reaction. The mechanistic studies suggested the formation of H2 and H2 O as only by-products of the reaction, thereby making the protocol greener and sustainable.

Cyclic Alkyl(amino) Carbene‐Induced Rearrangement of Ga‐Phosphaketene

AbstractReactions of LGa(Cl)P(cAAC) (L=HC[C(Me)N(2,6‐iPr2C6H3)]2, MecAAC (MecAAC=1‐(2,6‐di‐iso‐propylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene) with NaPCO and NaN3 gave LGa(PCO)P(MecAAC) (1) and LGa(N3)P(MecAAC) (2), respectively. DFT calculations on the nature of compounds 1 and 2 reveal a phosphaalkene rather than a carbene‐phosphinidene structure. The reaction of 1 with MecAAC resulted in a nucleophilic attack of the electron‐rich P atom on the γ‐C backbone of the β‐diketiminate ligand to give compound 3 as the major product and cyclic 1,2‐diphospha‐1,3‐butadiene LGa(P2OC)MecAAC (4) in minor yield.

Orchid bee collects herbicide that mimics the fragrance of its orchid mutualists

Abstract Male orchid bees store volatile compounds collected from their orchid mutualists and other sources to use in their courtship. Males of a naturalized orchid bee in Florida, Euglossa dilemma Bembé & Eltz (Hymenoptera: Apidae), intensively and habitually collected from substrates impregnated with triclopyr herbicide, most probably collecting its major breakdown product TMP (3,5,6-trichloro-2-methoxypyridine). Why this occurred and if the practice harmed the bees was considered. The chemical is thought to have low toxicity to bees and orchid bees collect and manage volatile chemicals so that they do not contact the interior of their bodies, both suggesting limited harm from the practice. Molecular similarity comparisons of TMP with 24 volatile compounds collected by E. dilemma found greater than 50 % structural similarities in four compounds according to the maximum common substructure, suggesting that TMP mirrors compounds needed by the bee in its courtship, and probably explains why the bees collect triclopyr. The bizarre but interesting collection of an herbicide by this orchid bee appears to be due to the similarity between the herbicide and chemicals that the bee needs in its courtship. The herbicide does not appear to harm the bee.

Extending the freshness of tilapia surimi with pulsed electric field modified pea protein isolate-EGCG complex

The development of natural polyphenol-protein complexes for preserving surimi holds great promise. The effects of pea protein isolate (PPI) - (−)-Epigallocatechin-gallate (EGCG) non-covalent and covalent complexes modified by pulsed electric field (PEF) on the preservation of tilapia surimi were evaluated. Results showed that the PEF-treated PPI-EGCG non-covalent complex extended the shelf life of surimi by more than 6 days. This complex reduced the microbial activity and delayed the lipid and protein oxidation of surimi during chilled storage. Total viable count (TVC), thiobarbituric acid reactive substances (TBARS), and total volatile base nitrogen (TVB-N) of surimi with PEF-treated PPI-EGCG non-covalent complex on day 15 were 31.65 %, 68.67 %, and 54.46 % lower than untreated surimi, respectively. Moreover, the rate of colour deterioration and off-odour development were also delayed. The major products of lipid oxidation in surimi were reduced by 37.91 % for hexanal, 43.14 % for pentanal, 73.24 % for 1-octen-3-ol, and 39.32 % for 1-penten-3-ol on day 15. Structural analyses and computer simulations revealed that PEF was able to unfold the structure of PPI, thereby exposing more binding sites for EGCG. PEF-treated PPI-EGCG non-covalent complex allowed the slow dissociation of EGCG from PPI and maintained the antimicrobial and antioxidant activities of EGCG in a long storage time. Therefore, PEF-treated PPI-EGCG non-covalent complex was considered as a potential preservative in fish and fish products.

Isopropanol production via the thermophilic bioconversion of sugars and syngas using metabolically engineered Moorella thermoacetica

BackgroundIsopropanol (IPA) is a commodity chemical used as a solvent or raw material for polymeric products, such as plastics. Currently, IPA production depends largely on high-CO2-emission petrochemical methods that are not sustainable. Therefore, alternative low-CO2 emission methods are required. IPA bioproduction using biomass or waste gas is a promising method.ResultsMoorella thermoacetica, a thermophilic acetogenic microorganism, was genetically engineered to produce IPA. A metabolic pathway related to acetone reduction was selected, and acetone conversion to IPA was achieved via the heterologous expression of secondary alcohol dehydrogenase (sadh) in the thermophilic bacterium. sadh-expressing strains were combined with acetone-producing strains, to obtain an IPA-producing strain. The strain produced IPA as a major product using hexose and pentose sugars as substrates (81% mol-IPA/mol-sugar). Furthermore, IPA was produced from CO, whereas acetate was an abundant byproduct. Fermentation using syngas containing both CO and H2 resulted in higher IPA production at the specific rate of 0.03 h−1. The supply of reducing power for acetone conversion from the gaseous substrates was examined by supplementing acetone to the culture, and the continuous and rapid conversion of acetone to IPA showed a sufficient supply of NADPH for Sadh.ConclusionsThe successful engineering of M. thermoacetica resulted in high IPA production from sugars. M. thermoacetica metabolism showed a high capacity for acetone conversion to IPA in the gaseous substrates, indicating acetone production as the bottleneck in IPA production for further improving the strain. This study provides a platform for IPA production via the metabolic engineering of thermophilic acetogens.

Bottom-Up Formation of Antiaromatic Cyclobutadiene (c-C4H4) in Interstellar Ice Analogs.

Antiaromatic cyclobutadiene (c-C4H4) is the simplest prototype of [n]annulenes and a key reactive intermediate with significant ring strain, serving as the model compound for antiaromatic systems in organic chemistry. Here, we report the first bottom-up formation of cyclobutadiene in low-temperature acetylene (C2H2) ices exposed to energetic electrons. Cyclobutadiene was isolated and detected in the gas phase upon sublimation utilizing vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry along with ultraviolet photolysis studies. These findings advance our fundamental understanding of the exotic chemistry and preparation of highly strained antiaromatic cycles through non-equilibrium chemistry in interstellar environments, thus affording a possible route for the formation of highly strained molecules such as the hitherto elusive tetrahedrane (C4H4). Because acetylene is a major product of the photolysis and radiolysis of methane (CH4) ice, an abundant component of interstellar ices, our results suggest that cyclobutadiene can likely be formed in methane-rich ices of cold molecular clouds.

Microwave-assisted synthesis of solketal from glycerol and acetone

Herein, microwave-assisted synthesis of solketal from glycerol and acetone in the presence of montmorillonite modified with aqueous solution of 0.25 mol/l HCl (0.25M HCl/MM) was demonstrated. The reaction was studied in a methanol solution at an acetone/glycerol molar ratio of 2.45–7.53, a catalyst concentration of 1.2–2.8 wt.% (based on the mass of loaded glycerol), and 30–56 °C. Solketal was shown to be the major product with 96.1–99.2 % selectivity. The maximum solketal yield of 91.3 % with 98.6 % selectivity was obtained in 15 min of the reaction at an acetone/glycerol molar ratio of 7.53, a catalyst loading of 2.3 wt.% and 56 °C. The catalytic properties of 0.25M HCl/MM in the reaction under MW heating and thermal conventional heating were compared. It was found that the yield of solketal in the MW-assisted synthesis is 2 times higher compared to the process with conventional heating.

Cyclometalated platinum(II) complexes bearing eugenol as effective catalyst for hydrosilylation of phenylacetylene by triethoxysilane

The catalytic activities of the platinacyclic complexes bearing eugenol (EugH) including [Pt(μ-Cl)(Eug)]2 (1) and [PtCl(Eug)(amine)] (2–4) [amine: pyridine/2, 4-methylpyridine/3, quinoline/4] for hydrosilylation of phenylacetylene by triethoxysilane have been studied for the first time. The results showed that the complexes 1–4 exhibited good catalytic abilities. With loading 0.5 mol% each of the catalysts 1–4 at 70 oC without solvents and any other additives in the air for 2 hours, the triethoxysilane was completely converted to (E)-triethoxy(styryl)silane) (β(E) – the major product) and (triethoxy(1-phenylvinyl)silane) (α – the minor product) with the α/β(E) molar ratio ranging from 1 : 2.6 to 1 : 2.8. At the same reaction conditions with loading 0.1 mol% each of the catalysts 2–4, the conversion of triethoxysilane slightly reduced with an efficiency of 97–99% and the α/β(E) molar ratio of 1 : 2.6 indicating the important role of the Pt-(C=Calkene) in 1–4 for their catalytic activity. Furthermore, the verification of structures of complexes 2–4 by 13C NMR spectroscopy indicated that in chloroform-d1, complex 3 formed two distinct structural forms due to strong intermolecular interactions between the chloroform solvent and the complex, including a Cl3C-H...ClPt(II) hydrogen bond and a Cl2HC-Cl...Pt(II) halogen bond.

Enhancing RDX Thermal Decomposition in Al@RDX Composites with Co Transition Metal Interfacial Layer

In this study, an Al/Co@RDX composite was meticulously prepared through a combination of planetary high-energy ball-milling and a spray-drying technique. The thermal reactivity of these Al/Co@RDX composites was comprehensively investigated and compared using the TG/DSC technique. It is shown that the initial decomposition temperature of RDX in the DSC curve was decreased by 26.3 °C in the presence of Al/Co, which could be attributed to the nano-sized Co transition metal catalyzing the decomposition reaction of nitrogen oxides in RDX decomposition products. The decomposition peak temperature of RDX and the heat released by the thermal decomposition of RDX in the Al/Co@RDX composite were decreased by 26.3 °C and increased by 74.5 J·g−1, respectively, in comparison with those of pure RDX. The types of major gaseous products released from Al/Co@RDX were found to be identical to those of pure RDX, encompassing N2O, CH2O, CO2 and HCN. However, the concentrations of those gaseous products for Al/Co@RDX were higher than those observed for pure RDX, which may owe to the fact that the Al/Co composite can interact with the –CH2 and –NO2 within RDX molecules, which leads to the weakening of the C-N and N-N bonds. In addition, the decomposition of RDX in the Al/Co@RDX composite was observed as a one-step process with an apparent activation energy (Ea) of 115.6 kJ·cm−3. The decomposition mechanism of the RDX in the Al/Co@RDX composite was identified to follow the chain scission model (L2), whereas the two-step decomposition physical models observed for pure RDX were found to closely resemble the L2 and autocatalytic models.