Sulfur Heterocycles Research Articles

Molecularly imprinted polymer thin-film as a micro-extraction adsorbent for selective determination of trace concentrations of polycyclic aromatic sulfur heterocycles in seawater

A tailor-made porous molecularly imprinted polymer (MIP) thin-film was prepared by in situ photo-radical polymerization on a glass slide and used as a microextraction adsorbent. Detection was carried out using gas chromatography-mass spectrometry (GC–MS) to afford a method suitable for the selective determination of trace concentrations of polycyclic aromatic sulfur heterocycles (PASHs) in seawater. PASHs are one of the most problematic aromatic organic pollutants, as they are considered more persistent and toxic compared to other analogous aromatic compounds in the environment. The optimized thin-film consisted of a 2-thiophenecarboxaldehyde pseudo-template with 1-vinylimidazole (1-Vim) as the functional monomer, bisphenol A dimethacrylate (BPADMA) as the cross-linker, acetonitrile as the porogen, and polyethylene glycol to boost porosity through formation of interpenetrating polymer networks. The adsorption behaviours of the thin-film, including adsorption kinetics, binding isotherms, and selectivity of MIP thin-film were investigated in detail. The highest imprinting factors (2.3–3.0) and adsorption capacity for targeted PASHs were achieved at a template:monomer:cross-linker ratio of 1:4:8. The method with no sample or film pretreatment showed very good reproducibility for the extraction of PASHs from spiked seawater samples (RSDs ≤ 6.0%, n = 3), was linear (R2 > 0.9960) over a range of 0.5–40 µg L−1, and gave limits of detection n the range of 0.029–0.166 µg L−1.

Highly Efficient Oxidative Desulfurization Catalyzed by a Polyoxometalate/Carbonized Cellulose Nanofiber Composite

Oxidative desulfurization (ODS) is a promising method to remove the heterocyclic sulfur compounds from fuel and such process need high-performance catalysts. Polyoxometalates (POMs) have been proven to be excellent catalysts in the ODS reaction, which need to be immobilized on carriers to realize its industrial application. In this work, [β-SiMo3W9O40]n− has been loaded on a sustainable cellulose nanofiber (CNF)-based material, which was then calcined at 400 °C to form an POM-based composite material. CNF was modified by γ-(2,3-epoxypropoxy)propyltrimethoxysilane (GPTMS) and polyethyleneimine (PEI) so that the polyanions and protonated PEI could effectively interact with each other; therefore, POM could be well supported on the carrier. The catalytic results showed that in model oil with the sulfur concentration being 2000 ppm, the removal efficiency of dibenzothiophene, benzothiophene, and 4,6-dimethyldibenzothiophene were 99, 89, and 100%, respectively. In addition, infrared spectra analysis indicated t...

Palladium‐Catalyzed Synthesis of Benzothiophenes via Cross‐Dehydrogenative Coupling of 4‐Arylthiocoumarins and Pyrones

AbstractBenzothiophenes represent a pivotal class of sulfur heterocycles and their synthesis has attracted significant attention to generate bioactive scaffolds. Herein, we report a convergent, atom‐ and step‐economic method for the synthesis benzothiophenes by cross‐dehydrogenative coupling (CDC) of 4‐arylthiocoumarins in good to excellent yields. We further demonstrate cross‐dehydrogenative coupling of 4‐arylthio‐2‐pyrones to afford alternative substitution of benzothiophenes. The presence of a labile ester carbonyl moiety provides functional handle for further functionalization by coumarin deconstruction. Most crucially, the manuscript demonstrates that the use of readily accessible templated synthesis has a significant potential for the rapid assembly of sulfur heterocycles by dehydrogenative coupling mechanism.magnified image

Morphology‐Controlled Synthesis of CuO, CuO Rod/MWW Composite for Advanced Oxidation of Indole and Benzothiophene

AbstractVarious morphologies of copper (II) oxide (CuO) such as dandelion, sea anemone, walnut, leaf, dendrite, rod, fiber, feather, and flake were synthesized and characterized by different methods. The oxidation of indole (IND) and benzothiophene (BT) in mild conditions was studied by various morphologies of CuO. Walnut with the lowest surface area 7.928 (m2g−1) and rod with a high surface area 41.237 (m2g−1) had efficiencies of 5.93% and 91.44% for IND and 0.53% and 88.29% for BT at 4 h, respectively. Zeolite MWW was synthesized by microwave and hydrothermal method on which CuO rod was loaded via wet impregnation method. The results indicated that CuO rod/MWW composite considerably outperformed CuO rod. The oxidations of IND and BT by CuO rod/MWW composite for 75 min was 99.99 and 97.67%, respectively. Based on the results across all experiments, the oxidation of the IND was higher than that of BT. CuO rod/MWW composite was shown to be an efficient catalyst for oxidation of nitrogen and sulfur heterocycles.

Microwave-Assisted Synthesis of Sulfurated Heterocycles with Herbicidal Activity: Reaction of 2-Alkynylbenzoic Acids with Lawesson's Reagent.

The reactivity of 2-alkynylbenzoic acids toward Lawesson's reagent (LR) under microwave irradiation (300 W, 100 °C, CH2 Cl2 ) was assessed. It was found that, depending on reaction conditions, either a dithionation- or a monothionation-cycloisomerization process takes place with formation of important sulfurated heterocycles. In particular, using 1 equivalent of LR for 1 h, dithionation occurred, with formation of benzo[c]thiophene-1(3H)-thiones or 1H-isothiochromene-1-thiones, while with 0.5 equiv. of LR for 10-30 min, monothionated products were selectively obtained (benzo[c]thiophen-1(3H)-ones or 1H-isothiochromen-1-ones). The regiochemical output of the process strongly depended on the substitution pattern of the starting 2-alkynylbenzoic acid derivatives. These compounds were also assayed as potential herbicides by assessing their phytotoxic activity on seedling growth and development of the model species Arabidopsis thaliana. All compounds, to different extents, influenced the morpho-physiological parameters that were monitored; in particular, the fresh weight (FW) was significantly affected, with ED50 values ranging from 4.81-63.7 μM.

Recent Advances in the Synthesis and Reactivity of Isothiazoles

AbstractIsothiazoles represent an important class of five‐membered sulfur heterocycles that are widely utilized in medicinal chemistry and organic synthesis due to the unique properties of two electronegative heteroatoms in a 1,2‐relationship. However, in contrast to other 1,2‐azoles, the facile assembly of isothiazoles has always been considered a substantial challenge. In the last decade, major advances have taken place in the fields of synthesis and functionalization of isothiazoles that make them accessible to a wide range of interested chemists through unprecedented pathways. New condensation methods have emerged that address the challenges posed by unstable thiohydroxylamine. New metal‐catalyzed approaches have been reported that deliver densely decorated isothiazoles bearing various sensitive functional groups. New functionalization strategies have been developed through both cross‐coupling and direct C−H activation chemistry. Finally, the emergence of novel heterocyclic architectures based on isothiazole opens the door for future investigations of this versatile heterocyclic scaffold. This review covers the period from January 2004 to December 2018 and is intended as a sequel to the review on isoxazoles, which represent another class of synthetically‐important 1,2‐azoles (see Adv. Synth. Catal. 2015, 357, 2583–2614).magnified image

Design of stable platinum(II) complexes exhibited various colors via auxiliary ligand and electron-donating/withdrawing groups: A theoretical investigation

Abstract The short operation lifetime is a major factor which hinders the large-scale commercialization of phosphorescent organic light-emitting diodes (OLEDs). Unveiling the intrinsic degradation mechanism of phosphorescent material may be a feasible method for exploring the determined factors of operation lifetime. In this article, the ligand dissociation reactions and phosphorescent quantum yields of various bidentate Pt (II) complexes were investigated by means of the density functional theory (DFT) and time-dependent (TD)-DFT. The calculated results indicate for phosphorescent quantum yields, sulphur heterocycle can facilitate the radiative decay process and suppress the temperature-dependent nonradiative channel. In the aspect of ligand dissociation reactions, the corresponding dissociations of Pt (II) complexes can be effectively avoided via changing the coordinate forms of ligands. In addition, the relationship between geometric tailor and stability, emission color was also taken into account. An analysis of computed results can conclude that the electron-withdrawing and electron-dominating substituents can tune the emissive wavelengths from 477 to 624 nm and cause minor effect on the stability. This investigation could some meaningful information for designing stable Pt (II) complexes.

Front Cover: A new approach for predicting gas chromatography retention indices of polycyclic aromatic sulfur heterocycles

Front Cover: A new approach for predicting gas chromatography retention indices of polycyclic aromatic sulfur heterocycles

Optically transparent chitosan hydrogels for selective sorption and fluorometric determination of dibenzothiophenes

Solid-phase extraction of polycyclic aromatic sulfur heterocycles (PASHs) and their rapid determination in oil fuel without tedious sample pretreatment are of high interest. We propose porous and optically transparent hydrogels prepared from the covalently crosslinked chitosan (CS) as the basis for a sensor system for the rapid and robust monitoring of PASHs. We efficiently combined the ability of the crosslinked CS to sorb PASHs, the capacity of microcavities in a molecularly imprinted polymer to selectively recognize and trap analytes, and the optical transparency of CS materials for selective sorption and solid-phase fluorometric determination of dibenzothiophenes. For the screening of PASHs in organic nonpolar media, ortho-phtalic dialdehyde appeared to be the most appropriate crosslinker. Synthetic and analytical procedures performed in microplate mode allowed obtaining CS hydrogels with suitable reproducible properties and their further time- and labor-efficient applying in analysis (particularly, as little as 2 μM dibenzothiophene oxide can be determined).

Refining of Diesel and Ship Fuels by Extraction and Combined Methods. Part 1. Use of Ionic Liquids as Extractants

Modern and perspective environmental requirements to the quality of diesel and ship fuels are considered. Data on the selectivity and solvency of ionic liquids with respect to aromatic hydrocarbons and heterocyclic sulfur- and nitrogen-containing compounds, obtained using gas-chromatographic data on the limiting activity coefficients of model mixture components in ionic liquids, are discussed. Experimental data on the liquid-liquid phase equilibrium in model systems consisting of a saturated hydrocarbon, an aromatic sulfur- or nitrogen-containing compound, and an ionic liquid and on the component distribution ratios and separation factors are presented. The advantages and drawbacks of ionic liquids as extractants in selective refining of diesel fractions and vacuum gasoils to obtain raffinates meeting perspective environmental requirements to diesel and ship fuels are considered.

A new approach for predicting gas chromatography retention indices of polycyclic aromatic sulfur heterocycles

AbstractHere we present a novel and simple approach for predicting retention indices of polycyclic aromatic sulfur heterocycles on (5%‐Phenyl)‐methylpolysiloxane stationary phase using a new set of structural descriptors based on substituent positions. The prediction method modeled correlations between retention indices and structural parameters for alkyl substituted benzothiophenes and dibenzothiophenes. Five models were created: two for uni‐ and di‐ substituted benzothiophenes homologous series, and three for the following non‐homologous series: (i) uni‐ to tri‐ substituted benzothiophenes; (ii) uni‐ to tetra‐substituted dibenzothiophenes and (iii) isomers of benzo[b]naphtha[2,1‐d]thiophene and benzo[b]naphtha[1,2‐d]thiophene. Retention was highly correlated with structural parameters, and all models had high correlation coefficients, low root mean‐squared errors, and low mean absolute percentage errors for the homologous series. For non‐homologous models, R‐values were 0.998 for dibenzothiophenes, 0.995 for benzothiophenes, and 0.991 for benzo[b]naphtha[2,1‐d]thiophene and benzo[b]naphtha[1,2‐d]thiophene, lower than for homologous series. Our approach represents a simple strategy for the prediction of experimental retention indices values without the need for state‐of‐the‐art technology.

Biodegradation of dibenzothiophene by efficient Pseudomonas sp. LKY-5 with the production of a biosurfactant

A potent bacterial strain capable of degrading dibenzothiophene (DBT) was isolated and evaluated for its characteristics. The strain, designated as LKY-5, is rod-shaped, gram-negative, and occurs mainly in clusters. It was identified as belonging to the Pseudomonas genus based on the 16S rDNA sequence and phylogenic analysis. Determination of its DBT depletion efficiency by gas chromatography revealed that the isolate was able to completely degrade up to 100 mg L−1 DBT within 144 h. The pH values, DBT concentrations, and biomasses in the medium varied significantly in the initial 24 h. A biosurfactant produced by LKY-5 was extracted and identified as a di-rhamnolipid with the formula Rha-Rha-C8-C8:1 by HPLC-ESI-MS/MS. There were 26 metabolites in the DBT degradation process. Pseudomonas sp. LKY-5 exhibited unusually high DBT degradation efficiency via multiple metabolic pathways. Compared with the reported 4S and Kodama pathways, two more expanded metabolic pathways for the degradation of DBT are proposed. The polycyclic aromatic sulfur heterocycles (PASHs) in diesel, such as C1-DBT, C2-DBT, C3-DBT, 4,6-DMDBT, and 2,4,6-TMDBT, can also be degraded with 28.2–42.3% efficiency. The results showed that LKY-5 is an excellent bacterial candidate for the bioremediation of PASH-contaminated sites and sediments.

Simple, green approach for the synthesis of solid support‐embedded PdNPs for ligand exchange

Green approaches have the potential to significantly reduce the costs and environmental impact of chemical syntheses. Here, the authors used green tea (GT) leaf extract to synthesise and anchor palladium nanoparticles (PdNPs) to silica. The synthesised PdNPs in GT extract were characterised by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. PdNPs primarily formed as capped NPs dispersed in GT extract before reduction completed after 24 h. This capped phytochemical solution was employed as a green precursor solution to synthesise PdNP-embedded solid supports. The morphology of PdNPs anchored to silica differed to that of PdNPs in solution. Silica-embedded PdNPs was employed as a new ligand exchanger to isolate trace polycyclic aromatic sulphur heterocycles from a hydrocarbon matrix. The isolation efficiency of the new, greener ligand exchanger was the same as an efficient chemical ligand exchanger and may, therefore, hold promise for future applications.

Recent application of elemental sulfur in the synthesis of S-heterocycles (microreview)

Sulfur-containing heterocycles represent an important class of organic compounds. Elemental sulfur plays a significant role in the synthesis of sulfur heterocycles. This microreview discusses some interesting examples published in 1999, 2014, and in the period from 2017 to 2019.

A formal [4 + 2] cycloaddition of sulfur-containing alkylidene heterocycles with allenic compounds

A convenient enantioselective synthesis of sulfur heterocycles containing the dihydro-2H-pyran moiety by quinidine catalyzed formal [4 + 2] cycloaddition of 3-alkylidene benzo[b]thiophenes and allenoates is reported.

Development and application of two-dimensional liquid chromatography for the analysis of polycyclic aromatic sulfur heterocycles in heavy oil

A two-dimensional liquid chromatographic (2D LC) system was developed for the analysis of polycyclic aromatic sulfur heterocycles (PASHs) in heavy oil. The first dimension is a ligand-exchange chromatographic column packed with a palladium chloride/silica (PdCl2-SiO2) stationary phase, while the second dimension is a Spherisorb-NH2 column. The PASHs in vacuum gas oil were enriched online, and polycyclic aromatics hydrocarbons (PAHs) were separated according to their aromatic ring numbers. These separated fractions were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and detailed molecular characterization of PASHs and PAHs was achieved. Typical molecular structures of PASHs and PAHs in these fractions could be provided, and the side chain as well as the core structures were predicted. It is significant for the feedstocks selection and optimization of the hydrodesulfurization process by using these molecular characterization information.

A quantitative XPS examination of UV induced surface modification of TiO2 sorbents for the increased saturation capacity of sulfur heterocycles

UV pretreatment has proven effective in enhancing the sulfur heterocycle specificity and saturation capacity of TiO2 adsorbents. Previous efforts in our laboratory have shown this effect to persist for over two weeks and were attributed to increased densities of surface hydroxyl groups as assessed by XPS and FTIR evaluations. This paper presents further evidence of the previous assertion by tracking the UV-induced conversion of adsorbed water and lattice oxygen into surface hydroxyls as monitored by XPS. Two different commercial TiO2 adsorbents (@ 163 and 70 m2/g) were investigated at various hydration levels as determined by TGA. Deconvolution of the XPS spectra demonstrated both the qualitative nature and quantitative conversion of adsorbed water and lattice oxygen according to the following stoichiometry, where one lattice oxygen is converted into two surface hydroxyls.O(lattice)2 -+ H2O(ads)→UV2OH-Eight different reaction cases were examined using the 163 and 70 m2/g supports at four different hydration levels each. The measured stoichiometry for the above-noted conversion varied from 1.83 to 2.15 with an average value of 1.98 and a standard deviation of 0.10.Samples removed from the XPS chamber and stored in laboratory conditions showed that photo-generated surface hydroxyls could persist for over two weeks with or without handling.

Photoluminescence spectroscopy of anthrathiophenes and benzonaphthothiophenes in Shpol'skii matrixes

The dispersion of harmful oil components into the ocean waters could pose long-term risks to flora and fauna. Due to the complexity of oil-contaminated sites, the unambiguous identification and quantitation of environmental pollutants often requires the sequence of high-performance liquid chromatography and gas chromatography-mass spectrometry. A classic example is the analysis of polycyclic aromatic hydrocarbons. This article tackles a different aspect of environmental analysis as it focuses on the Shpol'skii spectroscopy of polycyclic aromatic sulfur heterocycles, specifically those belonging to the subgroups often known as anthrathiophenes and benzonaphthothiophenes. Photoluminescence measurements were made with a commercial spectrofluorimeter equipped with a continuous wave excitation source for steady state measurements and a pulsed excitation source for time-resolved measurements in the phosphorescence time domain. To the extent of our literature search, this is the first report on the 4.2 K fluorescence and phosphorescence spectra of anthrathiophenes and benzonaphthothiophenes, and the 77 K and 4.2 K phosphorescence lifetimes of benzonaphthothiophenes. 77 K and 4.2 K analytical figures of merit revealed the possibility to detect the studied compounds at the parts-per-billion (ng mL−1) concentration levels. The spectral and lifetime data gathered in this article provides the required information to choose an appropriate photoluminescence technique for the analysis of four-ring polycyclic aromatic sulfur heterocycles in complex environmental extracts.

Optimization of biodegradation of polycyclic aromatic sulfur heterocycles in soil using response surface methodology

This paper uses response surface methodology based on the Box-Behnken design to investigate the influence of substrate concentration, inoculation quantity and temperature on the biodegradation of polycyclic aromatic sulfur hydrocarbons in oil-contaminated soil by Pseudomonas sp. LKY-5. Substrate concentration is identified as the most important factor through the analysis of variance. The maximum degradation of PASHs can be achieved at the conditions of substrate concentration of 75.77 ml/kg, inoculation quantity of 20.4% and temperature of 30 °C.

Characterization of aromatic hydrocarbons and sulfur heterocycles in Saudi Arabian heavy crude oil by gel permeation chromatography and ultrahigh resolution mass spectrometry

The characterization of petroleum crude oil samples remains an overwhelming task for any single analytical technique. Additionally, the compositional complexity of crude oil typically increases with increase in sulfur content and decrease in API gravity. In the present investigation we employed gel permeation chromatography (GPC) for separating Arabian Heavy crude oil into clearly defined fractions, and atmospheric pressure photo ionization Fourier transform-ion cyclotron resonance mass spectrometry (APPI FT-ICR MS) for elucidating the structural commonalities through in-depth characterization of the fractions. The work involved the development of a GPC method by the selection of suitable columns, mobile phase, and optimization of separation conditions. Toluene was found to be suitable as a mobile phase for the analysis of nonpolar aromatic compounds as well as compatible with the subsequent APPI FT-ICR MS measurement. The GPC fractionated aromatic compounds based on the number of carbon atoms in alkyl chains. Compounds with a higher number of carbon atoms in their alkyl chains elute earlier in the GPC separation. This observation was true for aromatic hydrocarbons (HC), mono-sulfur (S1) and di-sulfur (S2) containing compounds. Using respective planar aromatic cores as parent structures, we systematically calculated the average number of alkyl carbon atoms present in each GPC fraction. The average number of alkyl carbon atoms were found to be 36, 27, 17, 9 and 5 in successive GPC fractions (from early to late elution), with only two alkyl carbon atoms overlap between successive fractions.