Aromatic Olefins Research Articles

Source profile study of VOCs unorganized emissions from typical aromatic devices in petrochemical industry

Volatile organic compounds (VOCs) are significant pollutants generated during the processes of petroleum refining and chemical production. Aromatic hydrocarbons, in particular, pose a great risk to human health. Nevertheless, unorganized emissions of VOCs from typical aromatics units remain poorly studied and reported. Therefore, it is vital to achieve precise control over aromatic hydrocarbons while managing VOCs. In this study, two typical aromatics production devices in petrochemical enterprises, namely aromatics extraction devices and ethylbenzene devices, were selected. The fugitive emissions of VOCs from the process pipelines in the units were investigated. Samples were collected and transferred using the EPA bag sampling method and HJ 644 and analyzed using gas chromatography–mass spectrometry. The results indicated that a total of 112 VOCs were emitted during the six rounds of sampling in the two types of devices, with alkanes (61 %), aromatic hydrocarbons (24 %), and olefins (8 %) being the primary types of VOCs emitted. The results also revealed the unorganized emissions characteristic substances of VOCs in the two types of devices, with slight differences in the types of VOCs emitted. The study found significant differences in the detection concentrations of aromatic hydrocarbons and olefins, as well as the types of detected chlorinated organic compounds (CVOCs), between the two sets of aromatics extraction units in distinct regions. These differences were closely related to the processes and leakages in the devices and can be effectively controlled by enhancing leak detection and repair (LDAR) and other measures. This article offers guidance for compiling VOCs emission inventories and improving the management of VOCs emissions in petrochemical enterprises by refining the source spectrum at the device scale. The findings are significant for analyzing VOCs unorganized emission factors and promoting safe production in enterprises.

Co single atoms and CoO clusters over nitrogen–doped hollow carbon spheres for synergistic oxidation of aromatic alkanes

Single atom catalysts have attracted mountainous attentions in the field of catalysis, owing to their unsaturated coordination environment and maximized utilization of metal atoms. However, single atom catalysts may suffer from low catalytic efficiency toward multistep reactions because of the single active site. Herein, we report a synergistic catalyst (n–Co/CoO@N–HMCS) to solve above problem through supporting Co single atoms (Co–SAs) and CoO clusters (CoO–CTs) on nitrogen–doped hollow carbon spheres for selective oxidation of aromatic alkanes. Among the as–prepared catalysts, 0.03–Co/CoO@N–HMCS exhibits the remarkable catalytic performance, with 96.6% conversion of ethylbenzene and 99.5% selectivity to acetophenone. Density functional theory calculation demonstrates that the synergistic effect between Co single atoms and CoO clusters significantly decreases the energy barrier of cleavage of the C–H bond of ethylbenzene, a rate–determining step for the oxidation of ethylbenzene, so that to accelerate the conversion of ethylbenzene into acetophenone. The strategy is applicable for oxidation of other aromatic alkanes as well.

Visible-Light Copper Catalysis for the Synthesis of α-Alkyl-Acetophenones by the Radical-Type Ring Opening of Sulfonium Salts and Oxidative Alkylation of Alkenes.

Direct difunctionalization of simple alkenes has been treated as a powerful synthetic strategy for the construction of highly functionalized skeletons. In this study, direct oxidative coupling of sulfonium salts with alkenes was achieved under mild conditions by a blue-light-driven photoredox process using a copper complex as a photosensitizer. This protocol allows regioselective synthesis of aryl/alkyl ketones from simple sulfonium salts and aromatic alkenes via selective C-S bond cleavage of sulfonium salts and oxidative alkylation of aromatic alkenes using dimethyl sulfoxide (DMSO) as a mild oxidant.

Access to cyclopropanes with geminal trifluoromethyl and difluoromethylphosphonate groups.

A synthetic route to the bench-stable fluorinated masked carbene reagent diethyl 2-diazo-1,1,3,3,3-pentafluoropropylphosphonate, bearing a trifluoromethyl and a difluoromethyl group is reported for the first time. Its application in CuI-catalyzed cyclopropanation reactions with aromatic and aliphatic terminal alkenes under mild reaction conditions is demonstrated. In total, sixteen new cyclopropanes were synthesized in good to very good yields.

Effect of Poly(vinyl alcohol) on Catalytic Performance of Al-Pillared Clay in Alkylation of Aromatic Hydrocarbons with Olefins

It is vital to design and synthesize efficient catalysts for removing olefins from aromatics and prolonging reaction time. The catalytic properties of pillared clay for olefin removal from aromatic compounds can be enhanced noticeably by grafting organic polymer molecules due to modification of the clay porosity in the pillaring reaction. In the present work, a series of catalysts are prepared by pillaring raw bentonite and acid-treated bentonite with aluminum and poly(vinyl alcohol) (PVA) intercalation. Prepared samples are evaluated in the olefin removal process and characterized by X-ray diffraction patterns (XRD), temperature-programmed desorption (TPD) of NH3, and nitrogen adsorption–desorption isotherms. The BET results reveal that the pillaring reaction in an aqueous solution of PVA increases the clay’s surface area to greater than 200 m2.g–1. The pore volume of alumina-pillared acid-activated clay (Al-PAAC) is enhanced from 0.278 to 0.321 and 0.416 cm3.g–1 at the PVA concentrations of 30 and 50 wt %, respectively. The samples modified with PVA, as a precursor in the pillaring reaction, show an enhanced catalytic activity compared to the other samples due to a higher number of active sites. The olefin conversion of the pillared sample remains above 50% in the presence of 50 wt % PVA for more than 26 h. Furthermore, PVA could facilitate the reactant’s access to the active acid sites in the interlayer of the pillared clay. The adsorption of aromatic compounds and olefins by the pillared samples follows the intraparticle diffusion kinetic model. In addition, the Langmuir model fits the adsorption isotherm data well.

N,N’‐Difluoro‐2,2’‐bipyridinium Bis(tetrafluoroborate): a New Terminal Oxidant for Iodoarene‐catalyzed Fluorination Reactions

AbstractA new N−F reagent, N,N′‐difluoro‐2,2′‐bipyridinium bis(tetrafluoroborate), for iodoarene‐catalyzed fluorination reactions as a terminal oxidant is reported. This reaction is effective for the fluorination of simple alkenes, aromatic alkenes and 1,3‐dicarbonyl compounds, giving 1,2‐difluorinated alkanes, geminal difluorinated compounds, 2‐fluorinated‐1,3‐dicarbonyl compounds in good to high yields, respectively. This is a useful fluorination reaction that not only improves the issues of the fluorination reaction using conventional mCPBA as a terminal oxidant but also constructs a simpler catalytic cycle. The present N−F reagent can be recovered as 2,2’‐bipyridine.

Experimental Studies on the Thermal Properties and Decomposition Course of a Novel Class of Heterocyclic Anticancer Drug Candidates

The experimental studies on the thermal properties and decomposition course of a novel class of potential anticancer drugs (1-5) containing in their heterobicyclic structures the asymmetrical triazine template were performed with the use of differential scanning calorimetry (DSC) and simultaneous thermogravimetry/differential scanning calorimetry (TG/DTG/DSC) coupled online with Fourier transform infrared spectroscopy (FTIR) and quadrupole mass spectrometry (QMS) in inert and oxidizing conditions. All the compounds were thermally characterized in detail for the first time in this article. The DSC studies proved that the melting points of the tested compounds depended on the position and type of the substituent at the phenyl moiety, whereas they did not depend on the furnace atmosphere. All the tested polynitrogenated heterocycles proved to be molecules with high thermal stability in both atmospheres, and most of them (1, 3-5) were more stable in oxidizing conditions, which indicated the formation of a more thermally stable form of the compounds when interacting with oxygen. The simultaneous TG/FTIR/QMS analyses confirmed that their pyrolysis process occurred in one main stage resulting in the emission of volatiles such as NH3, HNCO, HCN, CO, CO2, H2O, NO2, aromatic amine derivatives, alkenes (for compounds 1-5), and HCl (for the compound 5). On the other hand, the oxidative decomposition process was more complicated and proceeded in two main stages leading to the emission of NH3, CO2, CO, HCN, HNCO, H2O, some aromatics (for compounds 1-5), HCl (for compounds 3-5) as well as the additional volatiles such as N2, NO2, NH2OH, and (CN)2. The type of the formed volatiles indicated that the decomposition process of the studied heterocycles under the influence of heating was initiated by the radical mechanism. Their decomposition was related to the symmetric cleavage of C-N and C-C bonds (inert conditions) and additional reaction of the volatiles and residues with oxygen (oxidizing conditions).

Catalyst Complexity in a Highly Active and Selective Wacker-Type Markovnikov Oxidation of Olefins with a Bioinspired Iron Complex

Palladium-catalyzed Wacker-type reactions occupy a central place in organic synthesis with important implications in industry. Pursuing more benign protocols by replacing palladium with first-row transition metals allowed the identification of iron as a privileged one in the last few years. Although the anti-Markovnikov selectivity for iron catalysts is well developed, the Markovnikov-selective reactions still afford significant quantities of alcohol side-products, and identification of reaction intermediates has remained elusive so far. Herein, we present an iron catalyst that affords Markovnikov ketone products from (hetero)aromatic and aliphatic olefins in up to 99% selectivity under ambient conditions with 190,000 turnover numbers and turnover frequencies of 74 h–1 at 50 °C. The catalyst design is based on the promiscuous activity encountered in the family of the cytochromes P-450 enzymes, and it enables the formation of iron-hydride species under catalytically relevant reaction conditions. Substrate scope assessment and mechanistic investigations suggest that the Markovnikov-selective catalytic cycle competes with unprecedented three additional catalytic cycles (alcohol formation, hydrogenation, and reductive homo-coupling) depending on the nature of the olefin and the reaction conditions.

Waste to Treasure: Preparation of Functional Polymeric Particles from Waste Olefins in Carbolic Oil by Self-Stabilized Precipitation Polymerization

Carbolic oil is a fraction of coal tar with an enormous reserve, 40% of which are aromatic olefins such as indene, coumarone, styrene, etc. However, it is an underutilized r esource due to the lack of deep processing technology. In this study, we copolymerized olefins in the carbolic oil with maleic anhydride (MAh) by self-stabilized precipitation polymerization (2SP) method, to obtain uniform carbolic oil–maleic anhydride copolymer (CMA) particles with high yield (≥90%). Uniform CMA particles with a number-average molecular weight (Mn) in the range of 4400–24,100 g·mol–1 and particle sizes in the range of 150–2800 nm could be conveniently obtained by tuning the reaction factors. CMA exhibited good solubility in common organic solvents and possessed good thermal stability. After chemical modification of anhydride groups, CMA could be further converted into water-soluble carbolic oil–maleamic acid copolymers (CMAA), and heat-resistant and hydrophobic carbolic oil–maleimide copolymers (CMI). Overall, this research had provided a facile and green strategy for the effective utilization of waste olefins in carbolic oil, and the obtained copolymers had broad application prospects.

Carbamoyl manganese complexes for epoxidation of alkenes and cycloaddition of epoxides to carbon dioxide

There is no precedent for the usage of transition metal carbamoyl complexes (typical hydrogenase models) as pre-catalysts for oxidation or CO2 utilization purposes. In this work, we describe that carbamoyl-Mn(I) complexes are capable of selectively catalyzing both epoxidation of olefins and epoxides with carbon dioxide to form cyclic carbonates. The dual-role catalytic system was well adapted to a wide range of aromatic olefins, and the desired cyclic carbonates were obtained in moderate to excellent yields. Mechanistic investigations indicated that active Mn(II)-oxo and Mn(III)-oxo species were involved in the oxidation process.

CeO2‐Nanorods‐Catalyzed Protoboration of Alkenes and Alkynes with Bis(pinacolato)diboron

AbstractThe protoboration of alkenes and alkynes with B2pin2 (pin=OCMe2CMe2O) using a heterogeneous CeO2 nanorods catalyst has been developed to afford the corresponding alkyl and vinyl boronate esters in 41–99% yield under mild reaction conditions. A series of aromatic and aliphatic alkenes and alkynes with synthetically important functional groups were well tolerated. In both the systems, the catalyst could be reused for up to six runs without significant loss in activity. Stoichiometric reactions revealed that the protoboration may proceed through the in situ formed catalytically active boryl species.magnified image

Engineering Cytochrome P450BM3 Enzymes for Direct Nitration of Unsaturated Hydrocarbons.

Applications of the peroxidase activity of cytochrome P450 enzymes in synthetic chemistry remain largely unexplored. We present herein a protein engineering strategy to increase cytochrome P450BM3 peroxidase activity for the direct nitration of aromatic compounds and terminal aryl-substituted olefins in the presence of a dual-functional small molecule (DFSM). Site-directed mutations of key active-site residues allowed the efficient regulation of steric effects to limit substrate access and, thus, a significant decrease in monooxygenation activity and increase in peroxidase activity. Nitration of several phenol and aniline compounds also yielded ortho- and para-nitration products with moderate-to-high total turnover numbers. Besides direct aromatic nitration by P450 variants using nitrite as a nitrating agent, we also demonstrated the use of the DFSM-facilitated P450 peroxidase system for the nitration of the vinyl group of styrene and its derivatives.

Water-Soluble Pd Nanoparticles for the Anti-Markovnikov Oxidation of Allyl Benzene in Water

The catalytic activity and selectivity of two different water-soluble palladium nanoparticles capped with 5-(trimethylammonio)pentanethiolate and 6-(carboxylate)hexanethiolate ligands are investigated using the catalytic reaction of allyl benzene. The results show that the regioselective transformation of allyl benzene to 3-phenylpropanal occurs at room temperature and under atmospheric pressure in neat water via a Tsuji-Wacker type oxidation. Conventionally, the Tsuji-Wacker oxidation promotes the Markovnikov oxidation of terminal alkenes to their respective ketones in the presence of dioxygen. Water-soluble Pd nanoparticles, however, catalyze the anti-Markovnikov oxidation of allyl benzene to 3-phenylpropanal in up to 83% yields. Catalytic results of other aromatic alkenes suggest that the presence of benzylic hydrogen is a key to the formation of a p-allyl Pd intermediate and the anti-Markovnikov addition of H2O. The subsequent b-H elimination and tautomerization contribute to the formation of aldehyde products. Water-soluble Pd nanoparticles are characterized using nuclear magnetic resonance (NMR), UV-vis spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Catalysis results are examined using 1H NMR and/or GC-MS analyses of isolated reaction mixtures.

Iridium-Catalyzed Branch-Selective Hydroalkylation of Simple Alkenes with Malonic Amides and Malonic Esters

We report the iridium-catalyzed branch-selective hydroalkylation of simple alkenes such as aliphatic alkenes and aromatic alkenes with malonic amides and malonic esters under neutral reaction conditions. A variety of aliphatic alkenes and aromatic alkenes bearing bromine, chlorine, ester, 2-thienylcarboxylate, silyl, and phthalimide groups were all found to be suitable for this hydroalkylation. The combination of this method with Krapcho dealkoxycarbonylation realized a one-pot synthesis of β-substituted amide and ester from β-amide ester and malonic ester. The hydroalkylated products derived from malonic amides are suitable for further transformation. The finely tuned reaction conditions realized the selective transformation of hydroalkylated products to 1,3-diamines or monoamides with the same reagent. Deuterium labeling experiments and measurement of the kinetic isotope effect indicated that the catalytic cycle involves a reversible step and cleavage of the C-H bond is not a rate-determining step. Density functional theory calculations provided insight into the reaction mechanism, where the carboiridation step is followed by C-H reductive elimination.

Conversion of Polystyrene Plastic into Aviation Fuel through Microwave-Assisted Pyrolysis as Affected by Iron-Based Microwave Absorbents

As recycling plastics through microwave-assisted pyrolysis becomes gradually popular, the selection of microwave absorbents is therefore of great importance because plastics generally have low microwave absorption capacities, and microwave absorbents are then required to improve the heating and pyrolysis processes. In this study, conversion of polystyrene plastic into aviation fuel through microwave-assisted pyrolysis as affected by iron-based microwave absorbents (Fe, Fe3O4, and FeS2) was studied and reported for the first time. The heating performance, product yields, oil higher heating values, and aviation oil compositions with different microwave absorbents, microwave powers, and microwave absorbent loads were detailed. The results showed that Fe3O4 exhibited the highest average heating rate of 119.23 °C/min, and Fe had good selectivity for cycloalkenes, while FeS2 had good selectivity for olefins. The highest oil yield (97.67 wt %) was obtained at a pyrolysis temperature of 460 °C, microwave power of 650 W, and Fe load of 90 g, and the oil compositions were mainly monocyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons, olefins, and cycloalkenes with abundant C8–C16 hydrocarbons of 52.041–77.880 area%. The results indicated that polystyrene can be well converted into aviation fuel through microwave-assisted pyrolysis by screening the iron-based microwave absorbents.

One‐Electron Injection‐triggered Radical Reaction of Alkyl Benzoates Promoted by 1,4‐Bis(diphenylamino)benzene Photocatalysis

AbstractThe ester group is one of the most ubiquitous functional groups in natural products and synthetic organic molecules. Herein, we describe the photocatalytic generation of alkyl radicals from readily accessible alkyl benzoate esters. The excited organic photocatalyst 1,4‐bis(diphenylamino)benzene (BDB) plays a vital role as a one‐electron injector. The present photoredox‐catalytic system realizes the hydroxy‐1,1‐dialkylfluoroethylation of aromatic alkenes. Finally, a strategy is developed for generation of fluoroalkyl radicals from the corresponding readily available 2‐fluorinated 1,1‐dialkylethanols.

Base-mediated C-B bond activation of benzylic boronate for the rapid construction of β-silyl/boryl functionalized 1,1-diarylalkanes from aromatic alkenes.

The effect of tBuOK on the existing state of benzylic boronates in the solution phase has been investigated in detail by NMR analysis and DFT calculations. It was determined that simply using an excess of tBuOK (2.0 equivalents) can result in the full deborylation of benzylic boronates to afford free benzyl potassium species. These mechanistic insights were leveraged for the facile construction of β-silyl/boryl functionalized 1,1-diarylalkanes from aromatic alkenes via the combination of base-mediated silylboration or diborylation of aromatic alkenes and nucleophilic-type reactions with various electrophiles. Based on further machine-learning-assisted screening, the scope of electrophiles for this transformation can be generalized to the challenging aromatic heterocycles. Late-stage functionalization performed on several drug-relevant molecules generates the highly valuable 1,1-diaryl framework.

Towards "homeopathic" palladium-catalysed alkoxycarbonylation of aliphatic and aromatic olefins.

Palladium-catalysed alkoxycarbonylation of alkenes allows for atom-efficient synthesis of esters from easily available alkenes in an industrially viable manner. One of the major costs associated with this process is the consumption of the catalyst system. Hence, for economic and ecologic reasons it is desirable to minimize the amount of metal and ligands wherever possible. Herein, we report "a homeopathic" palladium-catalysed alkoxycarbonylation of olefins under comparably mild conditions. The key to success is the homemade ligand LIKATphos providing good to excellent yields of ester products with catalyst turnover numbers in the range of 106.

Applications of sulfonyl hydrazides in radical cyclization of alkenes.

Radical cyclization is regarded as a powerful and promising strategy for the assembly of diverse important cyclic structures because of its high atom- and step-economy. As excellent radical acceptors, alkenes offer two potential directions, pushing the research domain of radical cyclization. In this context, as a radical precursor, sulfonyl hydrazide plays an important role in accomplishing radical cyclization of alkenes in a facile and efficient way. This review focuses on the applications of sulfonyl hydrazides in radical cyclization of alkenes, which generally has two radical conversion modes, sulfonyl radicals and sulfoxide radicals. In particular, the section of sulfonyl radicals consists of eight parts containing aromatic rings, alkenes, alkynes, cyanides, aldehydes, carboxylic acids, amides, and small ring compounds, according to the objects of cyclization after addition with alkenes. Within each category, representative instances are presented and discussed in terms of their general mechanistic perspectives when needed.

Transition metal- and solvent-free anti-Markovnikov selective protoboration of alkenes with bis(pinacolato)diboron.

An efficient anti-Markovnikov selective transition metal- and solvent-free Lewis base-mediated protoboration of aromatic and aliphatic alkenes with bis(pinacolato)diboron (B2pin2) as the boron reagent is reported. This protocol is practical and demonstrates broad substrate scope and good functional-group tolerance on alkenes to give synthetically useful alkyl boronate esters in excellent yields under mild reaction conditions. The gram-scale reaction further highlighted the usefulness of this method.