Unsaturated Products Research Articles

α-C-H Functionalization of π-Bonds Using Iron Complexes: Catalytic Hydroxyalkylation of Alkynes and Alkenes.

The discovery of catalytic systems based on earth-abundant transition metals for the functionalization of C-H bonds enables streamlined and sustainable solutions to problems in synthetic organic chemistry. In this Communication, we disclose an iron-based catalytic system for the functionalization of propargylic and allylic C-H bonds. Inexpensive and readily available cyclopentadienyliron(II) dicarbonyl complexes were employedas catalysts for a novel deprotonative activation mode for C-H functionalization, an approach that allows for the direct union of unsaturated building blocks with aryl aldehydes and other carbonyl electrophiles to deliver a range of unsaturated alcohol coupling products under operationally simple and functional group tolerant reaction conditions.

Synthesis of Unsaturated Esters by Cross-Metathesis of Terpenes and Natural Rubber Using Ru-Alkylidene Catalysts

This study reports the cross-metathesis of bicyclic β-pinene, acyclic cis-3- methylpent-2-ene terpenes and the natural rubber with functionalized olefins, a route for the functionalization of the carbon-carbon double bond of natural products to obtain aliphatic unsaturated esters. The production of unsaturated esters from β-pinene and cis-3- methylpent-2-ene via cross-metathesis reaction with dimethyl maleate and diethyl maleate in the presence of the ruthenium-alkylidene [Ru(Cl)2(=CHPh)(1,3-bis(2,4,6- trimethylphenyl)-2-imidazolidinylidene)(PCy3)] (I), [Ru(Cl)2(=CH(o-isopropoxyphenylmethylene))( 1,3-bis(2,4,6-trimethylphenyl) -2-imidazolidinylidene)] (II) and rutheniumvinylidene [RuCl2(=C=CH(p-C6H4CF3))(PCy3)2] (III) was carried out. Results showed that the reaction of β-pinene with diethyl maleate using II catalyst produced unsaturated esters with 43 % selectivity. I and III catalysts showed low activity toward the cross-metathesis of β-pinene and dimethyl maleate. A survey about the cross-metathesis of acyclic cis-3-methylpent-2-ene with diethyl maleate by II catalyst was also studied. The formation of ethyl but-2-enoate and ethyl-3-methylpent-2-enoate products was highly selective by 63 %. The unsaturated esters formation from the cross-metathesis degradation of natural rubber (99.9 % cis-polyisoprene) with dimethyl maleate and diethyl maleate using I-III catalysts was accomplished as well. I and II catalysts showed high activity in the degradation of natural rubber with diethyl maleate to produce the low molecular weight of oligomers unsaturated ester products (Mn = 1 x 103 g mol-1) with isoprene units of m = 10 – 27 and yields ranging from 68 to 94 %.

Radiation-Thermal Degradation of Waste Plastics

The combination of dry distillation with irradiation with accelerated electrons can serve as a productive method for the conversion of waste plastics and their mixtures with cellulose wastes into liquid organic products. It was found that, on the combined distillation, plastics were mainly converted into soft wax and organic liquid. In turn, the lignocellulose fraction of mixed wastes was converted into furans (which can serve as raw materials for the subsequent synthesis of “green” plastics) and, in part, into phenolic inhibitors of reverse polymerization. The combined distillation is characterized by a lower yield of unsaturated and gaseous products, and it takes place at lower temperatures.

Catalytic Degradation of Poly(Vinyl Alcohol) by FexMnyCuzOw/γ-Al2O3 Nano-particles Catalyst Using Box-Behnken Design

FexMnyCuzOw/γ-Al2O3 nanoparticles were prepared by a wet impregnation -calcination method and characterized by means of XRD, BET, SEM-EDS. Box-Behnken design was used to investigate the degradation of PVA in aqueous solution. Besides, the effect of different calcination temperature, FexMnyCuzOw/γ-Al2O3 dosage, H2O2 dosage, initial P VA concentration and initial solution pH on the removal of P VA were also studied. Results showed that P VA can be efficiently removed and oxidized by the heterogeneous Fenton-like process with appropriate amount of FexMnyCuzOw/γ-Al2O3 and H2O2. In this paper, the efficiency of P VA was above 90 % by FexMnyCuzOw/γ-Al2O3 nanoparticles at an initial P VA concentration below 25 g/l, temperature at 60 oC, initial pH from 1.0 to 6.0, H2O2 and catalyst dose of 60 ml/l and 0.5 g/l, respectively. In addition, chromatography (GPC) was applied to further analyze the degradation of P VA under different experimental conditions, which revealed that the backbone chain of P VA could be effectively broken and oxidized. Several unsaturated degradation products, including butanones, benzaldehydes, hexanals and acetic acids were also detected and identified by gas chromatography-mass spectrometry (GC-MS). Besides, the nano catalyst maintained favorable catalytic ability during the five-times utilization, which means it could be recycled by filtration and calcination.

Fosmidomycin biosynthesis diverges from related phosphonate natural products.

Fosmidomycin and related molecules comprise a family of phosphonate natural products with potent antibacterial, antimalarial and herbicidal activities. To understand the biosynthesis of these compounds, we characterized the fosmidomycin producer, Streptomyces lavendulae, using biochemical and genetic approaches. Surprisingly, we were unable to elicit production of fosmidomycin, instead observing the unsaturated derivative dehydrofosmidomycin, which we showed potently inhibits 1-deoxy-D-xylulose 5-phosphate reductoisomerase and has bioactivity against a number of bacteria. The genes required for dehydrofosmidomycin biosynthesis were established by heterologous expression experiments. Bioinformatics analyses, characterization of intermediates, and in vitro biochemistry show that the biosynthetic pathway involves conversion of a two-carbon phosphonate precursor into the unsaturated three-carbon product via a highly unusual rearrangement reaction, catalyzed by the 2-oxoglutarate dependent dioxygenase DfmD. The required genes and biosynthetic pathway for dehydrofosmidomycin differ substantially from that of the related natural product FR-900098, suggesting that the ability to produce these bioactive molecules arose via convergent evolution.

High-temperature oxidation of methyl isopropyl ketone: A shock tube experiment and a kinetic model

Pentanone has three types of isomers: 3-methyl-2-butanone (methyl isopropyl ketone, MIPK), 3-pentanone (diethyl ketone, DEK) and 2-pentanone (methyl propyl ketone, MPK). Since MIPK is the smallest branched ketone and a promising biofuel, it is important to fully understand its combustion kinetics. In this work, the ignition delay times were measured in the temperature range from 1150 to 1600 K at pressures from 1 to 5 bar and for the equivalence ratios of 0.5, 1.0 and 1.5 (Mixes 1–9). A high-temperature detailed combustion kinetic model for MIPK was developed via a hierarchical method. Previous theoretical computations of the H-atom abstraction by HO˙2 and O˙H from the tertiary carbon of MIPK were adopted, and the reaction rate coefficients of H-abstraction by H˙ from the MIPK tertiary carbon were calculated via quantum chemical techniques. The rate coefficients of the reactions that are related to the acetyl group and the isopropyl group of MIPK were estimated by analogy with MPK and DIPK, respectively. Eleven elementary reactions in the submodel that are related to MIPK were selected for the optimization due to the poor prediction performance of the raw model. The self-adaptive differential evolution algorithm was applied to optimize the raw kinetic model based on the ignition delay times of Mixes 1–6. The optimized MIPK model was validated against the ignition delay times of Mixes 7–9. A brute-force sensitivity analysis, in combination with a flux analysis, demonstrates that the amount of unsaturated fuel-related stable intermediate products is the key factor that determines the reactivity of MIPK and DEK.

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air–aqueous interface

Abstract. Water-soluble brown carbon in the aqueous core of aerosol may play a role in the photochemical aging of organic film on the aerosol surface. To better understand the reactivity and photochemical aging processes of organic coating on the aqueous aerosol surface, we have simulated the photosensitized reaction of organic films made of several long-chain fatty acids in a Langmuir trough in the presence or absence of irradiation. Several chemicals (imidazole-2-carboxaldehyde and humic acid), PM2.5 samples collected from the field, and secondary organic aerosol samples generated from a simulation chamber were used as photosensitizers to be involved in the photochemistry of the organic films. Stearic acid, elaidic acid, oleic acid, and two different phospholipids with the same carbon chain length and different degrees of saturation, i.e. 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC), were chosen as the common organic film-forming species in this analysis. The double bond (trans and cis) in unsaturated organic compounds has an effect on the surface area of the organic monolayer. The oleic acid (OA) monolayer possessing a cis double bond in an alkyl chain is more expanded than elaidic acid (EA) monolayers on artificial seawater that contain a photosensitizer. Monitoring the change in the relative area of DOPC monolayers has shown that DOPC does not react with photosensitizers under dark conditions. Instead, the photochemical reaction initiated by the excited photosensitizer and molecular oxygen can generate new unsaturated products in the DOPC monolayers, accompanied by an increase in the molecular area. The DSPC monolayers did not yield any photochemical oxidized products under the same conditions. The spectra measured with polarization modulation-infrared reflection–absorption spectroscopy (PM-IRRAS) were also consistent with the results of a surface pressure–area isotherm. Here, a reaction mechanism explaining these observations is presented and discussed. The results of PM2.5 and SOA samples will contribute to our understanding of the processing of organic aerosol aging that alters the aerosol composition.

Highly pH-Dependent Chemoselective Transfer Hydrogenation of α,β-Unsaturated Aldehydes in Water

The pH-dependent selective Ir-catalyzed hydrogenation of α,β-unsaturated aldehydes was realized in water. Using HCOOH as the hydride donor at low pH, the unsaturated alcohol products were obtained exclusively, while the saturated alcohol products were formed preferentially by employing HCOONa as the hydride donor at high pH. A wide range of functional groups including electron-rich as well as electron-poor substituents on the aryl group of α,β-unsaturated aldehydes can be tolerated, affording the corresponding products in excellent yields with high TOF values. High selectivity and yields were also observed for α,β-unsaturated aldehydes with aliphatic substituents. Our mechanistic investigations indicate that the pH value is critical to the chemoselectivity.

Influence of boiling on radiolysis of oxygen-containing liquids

The radiolysis of propanol, diglyme, acetone, 2-butanone and 4-methyl-2 pentanone is compared at boiling and at ambient conditions. Boiling affects the composition and yields of radiolytic products. Keto-enol tautomerization is manifested as a reason for increasing the yield of water, acids and some oxygen-containing unsaturated products in irradiated boiling ketones. The yield of ketone degradation at room temperature is almost 1/3 lower than that of alcohol and ether, primarily due to the difference in the mechanism of ionic processes. The increased degradation of boiling solvents is due to the dissociation of unstable radicals and the reactions of the resulting fragmentary radicals with a solvent. Radiolytic degradation of boiling ketones is further intensified due to their participation in radical chain oligomerization.

Combining agriculture and energy industry waste products to yield recyclable, thermally healable copolymers of elemental sulfur and oleic acid

ABSTRACTSulfur and oleic acid, two components of industrial waste/byproducts, were combined in an effort to prepare more sustainable polymeric materials. Zinc oxide was employed to serve the dual role of compatibilizing immiscible sulfur and oleic acid as well as to suppress evolution of toxic H2S gas during reaction at high temperature. The reaction of sulfur, oleic acid, and zinc oxide led to a series of composites, ZOSx (x = wt % sulfur, where x is 8–99). The ZOSx materials ranged from sticky tars to hard solids at room temperature. The ZOSx compositions were assessed by 1H NMR spectrometry, FTIR spectroscopy, and elemental microanalysis. Copolymers ZOS59‐99, were further analyzed for thermal and mechanical properties by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Remarkably, even ZOS99, comprising only 1 wt % of zinc oxide/oleic acid (99 wt % S) exhibits at least an eightfold increase in storage modulus compared to sulfur alone. The four solid samples (59–99 wt % S) were thermally healable and readily remeltable with full retention of mechanical durability. These materials represent a valuable proof‐of‐concept for sustainably sourced, recyclable materials from unsaturated fatty acid waste products. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1704–1710

Stabilization of furanics to cyclic ketone building blocks in the vapor phase

Furanics are produced in high abundance from the decomposition of biomass. The thermal and chemical instability of these species leads to the formation of humins upon condensation. The ring rearrangement of furfural to form 2-cyclopentenone and cyclopentanone is known to occur in the condensed aqueous phase, but this requires operation in condensed acidic media where humin formation readily occurs. High hydrogen pressures are typically used to offset rapid polymerization reactions, limiting the yields of stable unsaturated products that result. Here we report that furfural can be selectively converted to 2-cyclopentenone and cyclopentanone in a single step over supported TiO2 catalysts with both model compounds and real biomass-derived streams in the vapor phase. Selectivity for ring rearrangement vs. CO cleavage over TiO2 supported Ru and Pd catalysts can be tuned by manipulating the water partial pressure. The formation of these products in the absence of a condensed acidic stream also enables the tuning of reaction environments to favor the selective formation of unsaturated ketones, which could be valuable diolefin precursors. The incorporation of a TiO2 support in the catalysts tested leads to the suppression of CC hydrogenolysis/decarbonylation and enhancement of ring rearrangement reactions. The nature of the active sites for selective CO cleavage as well as vapor phase ring rearrangement are discussed.

Improved lipid production via fatty acid biosynthesis and free fatty acid recycling in engineered Synechocystis sp. PCC 6803

BackgroundCyanobacteria are potential sources for third generation biofuels. Their capacity for biofuel production has been widely improved using metabolically engineered strains. In this study, we employed metabolic engineering design with target genes involved in selected processes including the fatty acid synthesis (a cassette of accD, accA, accC and accB encoding acetyl-CoA carboxylase, ACC), phospholipid hydrolysis (lipA encoding lipase A), alkane synthesis (aar encoding acyl-ACP reductase, AAR), and recycling of free fatty acid (FFA) (aas encoding acyl–acyl carrier protein synthetase, AAS) in the unicellular cyanobacterium Synechocystis sp. PCC 6803.ResultsTo enhance lipid production, engineered strains were successfully obtained including an aas-overexpressing strain (OXAas), an aas-overexpressing strain with aar knockout (OXAas/KOAar), and an accDACB-overexpressing strain with lipA knockout (OXAccDACB/KOLipA). All engineered strains grew slightly slower than wild-type (WT), as well as with reduced levels of intracellular pigment levels of chlorophyll a and carotenoids. A higher lipid content was noted in all the engineered strains compared to WT cells, especially in OXAas, with maximal content and production rate of 34.5% w/DCW and 41.4 mg/L/day, respectively, during growth phase at day 4. The OXAccDACB/KOLipA strain, with an impediment of phospholipid hydrolysis to FFA, also showed a similarly high content of total lipid of about 32.5% w/DCW but a lower production rate of 31.5 mg/L/day due to a reduced cell growth. The knockout interruptions generated, upon a downstream flow from intermediate fatty acyl-ACP, an induced unsaturated lipid production as observed in OXAas/KOAar and OXAccDACB/KOLipA strains with 5.4% and 3.1% w/DCW, respectively.ConclusionsAmong the three metabolically engineered Synechocystis strains, the OXAas with enhanced free fatty acid recycling had the highest efficiency to increase lipid production.

Microalgae as rich source of polyunsaturated fatty acids

Abstract Microalgae are rich source of poly unsaturated fatty acids and therefore, extraction and purification of poly unsaturated fatty acids from algal strains are emerging steeply to nourish the nutritional needs of the population. Recently, various cost-effective and efficient approaches are being explored to increase the poly unsaturated fatty acids yield in algae. In this juncture, this article attempted to connect extraction of lipid using different methods, and accumulation of lipid under various stress conditions, and accumulation of poly unsaturated fatty acids under various stress conditions. Initially, extraction of lipid from various algal strains using different techniques was discussed in detail. Then, accumulation of lipid in microalgae under the influence of various stimuli has been critically flagged, in order to enable researchers to choose an optimal lipid induction condition for food and fuel production. Later, impact of various factors or culture condition on the poly unsaturated fatty acids accumulation in algae has been extensively assessed and presented in the perspective of increasing its production for food supplement. Finally, recent literature pertaining to the lipid and poly unsaturated fatty acids production in microalgae is reviewed, and summarized.

Chalcogenisation of unsaturated organohalogen compounds by elemental chalcogens and their metal derivatives

The presented review addresses the prospects for application of organochalcogen compounds in various fields of technology, medicine, agriculture and organic synthesis. The unsaturated chalcogenisation products appear to be of much greater interest compared to their saturated analogues, especially in organic synthesis. This study observes halogen derivatives of ethene, propene, propyne and butene subjected to chalcogenisation as unsaturated substrates. The indicated reagents are related either to large-tonnage products of industrial organochlorine synthesis or waste products of organochlorine production with their disposal presenting an important environmental task. According to analysed publications, chalcogenisation processes are based on the application of elemental chalcogens (sulphur, selenium, and tellurium) or their available metal derivatives (Na2S, etc.). In the reactions of chalcogens with unsaturated halogen derivatives, the elements both in an accessible form and in a free state are subjected to reductive activation resulting in the formation of anionic nucleophilic reagents. Complex metal hydrides, chalcogenide anions and rongalite are exampled for application in terms of reducing agents. The review emphasises the prospects of basic reduction systems based on hydrazine hydrate in activation processes. Special aspects in the introduction of caustic alkalis and an monoethanolamine organic amine as bases in these systems are described. For the considered chalcogenisation processes, conditions are specified providing the most optimal yield of certain products. In some particular cases, the stereochemistry of the obtained compounds is presented considering the formation conditions for the stereoisomers of a certain configuration. For a number of the obtained compounds, the prospects of practical application are provided. In general, the current review is intended for specialists working in the field of organic synthesis and application of organochalcogen compounds. The authors declare no conflict of interests regarding the publication of this article.

Palladium-Catalyzed Dearomative syn-1,4-Diamination

Herein we report a dearomative syn-1,4-diamination protocol using simple nonactivated arenes and amines. This one-pot method utilizes arene-arenophile para-cycloadducts, formed via visible-light-mediated [4+2]-photocycloaddition that undergoes formal allylic substitution with amine nucleophiles under Pd-catalysis. The products are obtained with exclusive syn-1,4-selectivity; the method permits enantioselective desymmetrization of naphthalene, as well as elaborations of amine-containing drug molecules. Furthermore, the resulting unsaturated products are amenable to numerous options for diversification. Overall, this novel dearomative functionalization strategy offers rapid and straightforward access to complex building blocks, which are difficult to prepare otherwise, from simple arenes.

Mild-thermal fabrication and phase conformation of chopped glass fiber-reinforced low-density unsaturated polyester resin with NH4HCO3

Chopped glass fiber-reinforced low-density unsaturated polyester resin product (CFR-LDUPRP) was fabricated utilizing chopped glass fiber and ammonium bicarbonate through an innovative mild-thermal process featuring an ideal phase conformation. Based on the mild-thermal mechanism and preliminary experiments, an orthogonal experiment was conducted to obtain the optimal conditions of CFR-LDUPRP fabrication. The optimal fabrication temperature of 76.0 °C, 20.00 phr of 3 mm chopped glass fiber, 2.50 phr of NH4HCO3 and 1.50 phr of tert-butylperoxy benzoate (TBPB) comprised the optimal conditions for CFR-LDUPRP fabrication. Under this condition, the density (ρ), compressive strength (P), and specific compressive strength (Ps) of CFR-LDUPRP specimen were 0.63 ± 0.02 g cm− 3, 24.29 ± 0.73 MPa, and 38.56 ± 1.02 MPa g− 1 cm3, in the given order. The analyses of nonisothermal DSC and semi-quantitative FTIR revealed that NH4HCO3 neutralized the residual acid in the resin, leading to an early polymerization of resin and a prolonged curing process of UPR. The endothermic decomposition of NH4HCO3 and the vaporization of water enabled a mild-thermal mechanism, which was beneficial for the growth of bubbles and for the distribution of chopped glass fiber in the resin. Proper phase conformation of the resin, bubbles, chopped glass fiber together with cracks and microvoids in the resin matrix, characterized by SEM and 1H NMR, facilitated the polymerization of UPR and improved properties of CFR-LDUPRP. Bubbles diameter ranged from 0.27 to 0.61 mm without linking or destroyed bubbles.

Catalytic hydroconversion of oxydibenzene to cyclohexane over bifunctional Ni/Hβ

ABSTRACTAn active bifunctional Ni/Hβ was prepared by decomposing Ni(CO)4 to dispersive metallic Ni onto Hβ and applied in hydroconversion of oxydibenzene (ODB), which was used as a model reaction for the catalytic hydroconversion (CHC) of lignin or lignin oligomers to hydrocarbon fuels. The effects of reaction temperature, initial H2 pressure (IHP), and reaction time on the CHC of ODB was studied. Ni/Hβ was found to be effective for converting ODB into cyclohexane at 200°C under higher IHP. The mechanism for the CHC of ODB was discussed and the difference in mechanism under lower and higher IHP can be ascribed to the hydrogen-accepting abilities of unsaturated hydrocarbon products.

Iron-Mediated Coupling of Carbon Dioxide and Ethylene: Macrocyclic Metallalactones Enable Access to Various Carboxylates.

Treatment of (iPrPDI)Fe(N2)2 (iPrPDI, 2,6-(2,6-iPr2C6H3N═CMe)2C5H3N) with CO2 and ethylene resulted in the formation of a homologous series of saturated and unsaturated iron carboxylate products, (iPrPDI)Fe(O2CR), the distribution of which depends on the ratio of the reagents. The solid-state and electronic structures of a saturated product, (iPrPDI)Fe(O2CC2H5), were elucidated. Product distributions, deuterium labeling studies, and stoichiometric experiments support initial formation of a five-membered metallalactone intermediate, which undergoes subsequent ethylene insertions to generate macrocyclic metallalactones. Competitive β-hydride elimination, CO2 insertion, or reaction with H2 determines the fate of the metallalactone, the latter accounting for formation of iron complexes with saturated carboxylates. Similar reactivity was observed upon addition of propiolactone and ethylene to (iPrPDI)Fe(N2)2, supporting C-O oxidative addition and C-C bond formation through metallacycle intermediates.

Influence of Boiling on the Radiolysis of Diglyme

The radiolysis of diethylene glycol dimethyl ether (diglyme) in a boiling state has been studied for the first time. Boiling facilitates the cleavage of internal C–O bonds, weakens the cage effect and diglyme regeneration processes, and facilitates the exchange and dimerization reactions of radicals. As compared with radiolysis at room temperature, the amount of unsaturated products of diglyme fragmentation formed during irradiation in the boiling state is smaller by a factor of 4, and the disproportionation products of heavy radicals are found in negligible amounts, if any. The yield of radiolytic decomposition of diglyme under boiling conditions is ∼15 molecule/100 eV, which is higher than that at room temperature by a factor of almost 1.5.

Radiation-chemical transformations of diethylene glycol dimethyl ether at room temperature and at boiling point

Diethylene glycol dimethyl ether (diglyme) is interesting as a representative of ethers with several oxygen bridges in the molecule and as a model alternative fuel. A comparative study of the diglyme radiolysis at room temperature and at the boiling point was carried out. Boiling facilitates the cleavage of internal C‒O bonds, weakens the cage effect and diglyme regeneration processes, and also favors radical exchange and dimerization reactions. Unlike radiolysis at room temperature, irradiation at the boiling point generates four times less unsaturated fragmentation products and practically does not give disproportionation products of heavy radicals. The yield of radiolytic decomposition of boiling diglyme reaches 15.5 molecules/100 eV, which is almost 1.5 times higher than at room temperature.