Functional Group Transformations Research Articles

Decontamination of Cr(VI) facilitated formation of persistent free radicals on rice husk derived biochar

This study investigated the facilitation of Cr(VI) decontamination to the formation of persistent free radicals (PFRs) on rice husk derived biochar. It was found that Cr(VI) remediation by biochar facilitated the production of PFRs, which increased with the concentration of treated Cr(VI). However, excessive Cr(VI) would induce their decay. Biochar with high pyrolysis temperature possessed great performance to Cr(VI) removal, which was mainly originated from its reduction by biochar from Inductively Coupled Plasma Optical Emission Spectroscopy and X-ray Photoelectron Spectroscopy. And the corresponding generation of PFRs on biochar was primarily ascribed to the oxidization of phenolic hydroxyl groups by Cr(VI) from Fourier Transform Infrared Spectroscopy analysis, which was further verified by the H2O2 treatment experiments. The findings of this study will help to illustrate the transformation of reactive functional groups on biochar and provide a new insight into the role of biochar in environmental remediation.

A Facile Synthetic Route to Ether Diols Derived from 1,1-Cyclopentylenylbisphenol for Robust Cardo-Type Polyurethanes

An efficient scheme for the synthesis of 1,1-cyclopentylenylbisphenol (bisphenol CP) has been developed starting from dicyclopentadiene, a C5 byproduct from the petroleum cracking process. The synthetic steps leading to bisphenol CP consist of mostly isomerization and addition reactions, which are higher in their atom-economy efficiencies than those based upon condensation reactions. In addition, alkoxylation by cyclic carbonates converted bisphenol CP into ethoxylated and propoxylated ether diols. The transformation of hydroxyl functional groups from bisphenols to alkoxylated alcohols increased the reactivity of their hydroxyl groups toward isocyanates, as evidenced by achieving >3 times higher molecular weights of the segmented polyurethanes (PUs) in GPC analysis using alkoxylated diols as chain extenders instead of bisphenols. In addition, the incorporation of five-membered cardo-type groups onto the PU side chains through alkoxyl diols of bisphenol CP also significantly enhances the phase mixing of th...

Highly Selective Synthesis of 2-(2H-1,2,3-Triazol-2-yl)benzoic Acids

A selective and scalable synthesis of 2-(2H-1,2,3-triazol-2-yl)benzoic acid starting from 1-fluoro-2-nitrobenzene derivatives is presented. The four-step synthesis introduces the triazole at the start via N2-arylation of 4,5-dibromo-2H-1,2,3-triazole. A sequence of consecutive functional group transformations, namely hydrogenation, Sandmeyer iodination, and Grignard carboxylation, provides the target molecules in a reliable and scalable manner. The usefulness of this method is demonstrated by the synthesis of di- or tri(2H-1,2,3-triazol-2-yl)benzene derivatives, which are difficult to produce by other methods.

Decomposition of maize stover varies with maize type and stover management strategies: A microcosm study on a Black soil (Mollisol) in northeast China

Crop residue decomposition has an important impact on soil organic carbon (SOC) sequestration and CO2 emission. Residue quality and management strategies are two important factors regulating decomposition process and SOC mineralization and greenhouse gas emission. In this study, a microcosm experiment in field condition was conducted on a silty loam (a Black soil) in Northeast China to investigate stover decomposition and soil CO2 emission characteristics as influenced by different crop cultivars and stover field incorporation methods. Stover from two popular maize cultivars Xianyu335 (XY) and Liangyu99 (LY) were applied in two modes (soil surface application vs soil incorporation) at a rate of 11 t ha−1, and CO2 efflux was monitored during the decomposition duration of 144 days. The structural transformation of carbon functional groups in maize stover were evaluated using solid state 13C-CPMAS NMR and elemental analysis techniques. Results showed that up to 71.7%∼86.9% (weight basis) of C and N in soil-incorporated stover was decomposed during the study period, which was significantly greater than the losses (32.8%∼55.3%) of C or N from the surface-applied stover for both maize cultivars; decomposition rates of main C functional groups were significantly higher in soil incorporation (71.1%∼88.8%) than in surface application (20.9%∼60.2%) systems. The concentrations of SOC, total N, available N, and microbial biomass C and N in soil were also higher with stover incorporation than surface application. Stover incorporation resulted in a notably lower CO2 emission rate and accumulative CO2 efflux (53.9–55.4 mol m−2) during the stover decomposition compared with surface application (57.4–67.0 mol m−2). Between the two maize cultivars, the LY stover showed a higher decomposition rate and greater capacity for SOC sequestration when incorporated into soil. The LY stover induced higher (16.8%) CO2 emission than XY when applied on soil surface, but no significant difference was found between the two cultivars when incorporated into soil. The results suggested that cultivar selection and stover management strategies have great potential in reducing soil CO2 emission while improving soil biochemical properties. Incorporating the LY stover into soil rather than surface mulching could enhance SOC sequestration and reduce CO2 emission.

Direct catalytic asymmetric method for the synthesis of tetrahydropyranopyrazoles through allene zwitterion chemistry

The enantioselective synthesis of the tetrahydropyranopyrazole scaffold has been achieved. The quinidine catalyzed reaction of allenoates with arylidenepyrazolones proceeded with high enantio- and diastereoselectivity while the reactions of alkylidenepyrazolones were less efficient. Allene ketones also afforded tetrahydropyranopyrazole derivatives in high yields, however, with only moderate enantioselectivity. The primary adduct undergoes further functional group transformations without effecting the initially formed chiral centre.

Manipulation of Spiroindolenine Intermediates for Enantioselective Synthesis of 3-(Indol-3-yl)-Pyrrolidines.

By manipulating the reactivity of spiroindolenine species, a sequential Michael/retro-Mannich/Mannich reaction of ω-indol-3-yl α,β-unsaturated ketones was developed. In the presence of 10 mol % of a chiral phosphoric acid as the catalyst, a series of 3-(indol-3-yl)-pyrrolidines were synthesized in high yields (up to 91 %) with excellent stereoselectivities (up to 92 % ee, >19:1 d.r.). The products obtained here undergo diverse functional-group transformations. The mechanistic proposal of this reaction is supported by DFT calculations.

Experimental Study on NOx Reduction in Oxy-fuel Combustion Using Synthetic Coals with Pyridinic or Pyrrolic Nitrogen

Oxy-fuel combustion technology can capture carbon dioxide (CO2) in the large-scale and greatly lower nitrogen oxides (NOx) emission in coal-fired power plants. However, the influence of inherent minerals on NOx reduction still remains unclear and the impact of oxy-fuel combustion on the transformation of different nitrogen functional groups has yet to be fully understood. The present work aims to obtain a further understanding of the NOx reduction during oxy-fuel combustion using synthetic coals with pyrrolic or pyridinic nitrogen. Compared to pyridinic nitrogen, more of the pyrrolic nitrogen in synthetic coal was converted to NOx. The conversion ratio of nitric oxide (NO) first increased significantly with the rising oxygen content and then trended to an asymptotically constant as the oxygen (O2) content varied between 10–50%. The nitrogen dioxide (NO2) formation was roughly proportional to the oxygen content. The NO2 conversion was increased with particle size but the case of NO showed a non-monotonic variation. The catalytic effects of sodium carbonate (Na2CO3), calcium carbonate (CaCO3), and ferric oxide (Fe2O3) on the transformation of pyridinic nitrogen to NO were independent of the combustion atmosphere, while the alteration from air to the oxy-fuel combustion led to a change of mineral catalytic effect on the oxidation of pyrrolic nitrogen within the coal matrix.

Effect of pressure grinding technology on the physicochemical and antioxidant properties of Tremella aurantialba powder

Tremella aurantialba powders (TAPs) with different grinding time were prepared by pressure grinding technology. The physicochemical and antioxidant properties of TAPs were evaluated. The results showed that the bulk density, fluidity, surface number mean, and volume surface of TAPs decreased with the extending of grinding time, the surface area and polysaccharide contents significantly increased (p < 0.05). Grind time from 0 min to 25 min, the stickiness, bitterness, roughness, and mouthfell of TAPs were significant reductions except for increasing sweetness (p < 0.05). The finer TAPs showed the brighter color and higher DPPH and ·OH scavenging effects, while scavenging effect was not significantly different. FTIR analysis showed that the transformation of no major functional groups happened during superfine grinding. Practical applications The pressure grinding treatment will provide the basis of coursework for biomaterial powder engineering, and have great potential for being scaled-up to a commercially processing of food materials from cost consideration. In addition, the development results in creating environmentally friendly processes.

Polyoxometalate Photocatalysis for Liquid-Phase Selective Organic Functional Group Transformations

Polyoxometalates (POMs), which are anionic metal oxide clusters, have recently attracted considerable attention as photocatalysts because of their unique photoinduced charge-transfer properties, redox properties, acid–base properties, and reactivities. In this Review, we present a summary of recent developments in POM photocatalysis for organic synthesis. Various organic functional group transformations can be selectively induced by photoirradiation in the presence of catalytic amounts of suitably designed POMs. In particular, many liquid-phase functional group transformations based on the activation of substrates by decatungstate have been reported. However, decatungstate photocatalysis requires irradiation with UV light because of the large energy gaps between the O2–-based highest occupied molecular orbitals (HOMOs) and the W6+-based lowest unoccupied molecular orbitals (LUMOs) therein. Various strategies have been developed in efforts to utilize visible light, including hybridization with photosensiti...

Optical property variations from a precursor (isoprene) to its atmospheric oxidation products

Isoprene is a crucial precursor of secondary organic aerosols (SOAs) that reacts with radicals or oxidants such as OH, O3, and NO3. The reaction mechanisms under various conditions have been elucidated through years of research. In this study, the UV–vis light absorptive ability of oxydates for isoprene was calculated at the PBE1PBE/6-311g (d) level using Gaussian 09. The results indicated that reactions of isoprene with OH and O3 would produce less absorptive organics; the intensity of the absorption peaks and the maximum absorption wavelength decreased relative to those of the precursor. The oxydates formed from isoprene through an NO3-initiated reaction had different light absorption properties. The optical properties of the oxydates exhibited a bathochromic shift and hyperchromic effect relative to those of the precursor. NO3 mainly originated from vehicular traffic, indicating that anthropogenic activity heavily affected the formation of oxydates and light absorption. The light absorption properties and irradiation effect of SOAs caused by isoprene heavily depended on the reaction route. Transformation of functional groups was the dominated factor in photobleaching and photoenhancement of oxidative products. This study provides a detailed mechanism that explains the changes in optical absorption properties during isoprene oxidation.

Sonochemical degradation of antibiotics from representative classes-Considerations on structural effects, initial transformation products, antimicrobial activity and matrix

In this work, the sonochemical treatment (at 354 kHz and 88 W L-1) of six relevant antibiotics belonging to fluoroquinolones (ciprofloxacin and norfloxacin), penicillins (oxacillin and cloxacillin) and cephalosporins (cephalexin and cephadroxyl) classes was evaluated. Firstly, the ability of the process to eliminate them was tested, showing that sonodegradation of these antibiotics is strongly chemical structure-dependent. Thus, correlations among initial degradation rate of pollutants (Rd), solubility in water (Sw), water-octanol partition coefficient (Log P) and topological polar surface area (TPSA) were tested. Rd exhibited a good correlation with Log P (i.e., the hydrophobicity degree of antibiotics). The considered penicillins had the fastest elimination and from the constitutional analysis using Lemke method was clear that the functional groups arrangement on these antibiotics made them highly hydrophobics. The penicillins were degraded closer at cavitation bubble than the fluoroquinolones or cephalosporins. The investigation of degradation products showed that sonogenerated hydroxyl radical primary attacked the β-lactam ring of cloxacillin and cephalexin, whereas on norfloxacin induced a decarboxylation. On the other hand, the evolution of antimicrobial activity was also followed. It was evidenced the process capacity to remove antimicrobial activity from treated solutions, which was associated to the transformations of functional groups on antibiotics with important role for interaction with bacteria. Additionally, degradation of antibiotics having the highest (the most hydrophobic, i.e., cloxacillin) and lowest (the most hydrophilic, i.e., cephadroxyl) Rd, was performed in synthetic matrices (hospital wastewater and seawater). Ultrasound degraded both antibiotics; for cloxacillin in such waters higher eliminations than in distilled water were observed (probably due to a salting-out effect exerted by matrix components). Meanwhile, for cephadroxyl a moderate inhibition of degradation in hospital wastewater and seawater respect to distilled water was found, this was related to competition by hydroxyl radical of the other substances in the matrices. These results show the quite selectivity of high frequency ultrasound to eliminate antibiotics form different classes even in complex matrices.

Heterogeneous Catalytic Oxidation of Amides to Imides by Manganese Oxides

Herein, we report a one-step peroxide mediated heterogeneous catalytic oxidation of amides to imides utilizing a series of manganese oxides. Among them, Cs/Mn2O3 was found to be the most active catalyst for the selective partial oxidation of N-benzylbenzamide to diphenyl imide. We have been able to apply an optimized oxidation method to other aromatic substrates. The feasibility of using air as an oxidant, the heterogeneous nature, inexpensive catalytic materials, respectable turnover numbers, and chemoselectivity to imides make this methodology an attractive choice for functional group transformations of amides to imides.

Transformation of functional groups and environmentally persistent free radicals in hydrothermal carbonisation of lignin

In this study, lignin was selected as the main component of waste biomass to synthesise carbonaceous adsorbents with environmentally persistent free radicals (EPFRs) through hydrothermal carbonisation (HTC) under different conditions. The HTC method with Fe(III) doping was superior for promoting dehydration and decarboxylation of lignin hydrochar than that with HTC Cu(II) doping. The deconstruction of oxygen-containing groups of lignin was reduced while esterification was enhanced by Fe(III). The Fe(III) addition was conducive to the formation of EPFRs as carbon-centred radicals with an adjacent oxygen atom and oxygen-centred radicals. A comparison of lignin with cellulose and d-xylose suggests that the formed EPFRs on lignin hydrochar were derived from their phenolic hydroxyl groups. A high removal efficiency of bisphenol A by lignin hydrochar was observed owing to oxygen-centred radicals, which activated H2O2 to produce OH. These results will facilitate the design and application of novel hydrochar materials with EPFRs.

Molecular Conjugation for the "Diazido Probe" Method

Target identification of screening hit compounds with unknown mechanisms of action obtained from chemical libraries by phenotypic assays has played an important role in the development of innovative drugs that work based on novel mechanisms. To improve the usability of the target identification based on the photoaffinity labeling method, we have studied the "diazido probe" method, wherein a photoreactive aromatic azido and relatively photostable aliphatic azido groups are sequentially used for photoreaction and introduction of a latent detectable tag via the Staudinger ligation or click reactions, and related synthetic methods that enable expeditious preparation of molecular probes. To facilitate the development of diazido probes, we established short synthetic routes to diazido building blocks with different connectable groups based on sequential iridium-catalyzed C-H borylation and copper-catalyzed azidation of 1,3-disubstituted benzenes, and subsequent diverse functional group transformations leaving the azido groups untouched. To improve the utility of click chemistry for efficient introduction of a latent detectable tag, we developed a transient protection method of cyclooctynes from cycloaddition with an azide by 1 : 1 complexation with a cationic copper(I) salt. Application of this protection method using a cationic copper salt to a cyclooctyne bearing a terminal alkyne allowed for the selective click conjugation with an azide at the terminal alkyne moiety, which rendered functionalized cyclooctyne derivatives easily synthesizable.

Thirty Years of (TMS)3SiH: A Milestone in Radical-Based Synthetic Chemistry.

This review is an update on tris(trimethylsilyl)silane, TTMSS, in organic chemistry, focusing on the advancements of the past decade. The overview includes a wide range of chemical processes and synthetic strategies under different experimental conditions, including functional group insertion and transformations, as well as preparation of complex molecules, natural products, polymers, surfaces, and new materials. These results reveal how TTMSS has matured over the past 30 years, and they further establish its value as a free radical reagent with widespread academic and industrial applications.

Improving Thermo-Oxidative Stability of Nitrile Rubber Composites by Functional Graphene Oxide.

Graphene oxide (GO), modified with anti-aging agent p-phenylenediamine (PPD), was added into nitrile rubber (NBR) in order to improve the thermo-oxidative stability of NBR. The modification of GO and the transformation of functional groups were characterized by Fourier transform infrared spectroscopy (FTIR), Raman, and X-ray diffraction (XRD). Mechanical performances of NBR composites before and after the thermo-oxidative aging were recorded. The results of dynamic mechanical analysis (DMA) show an increased storage modulus (G’) and a decreased value of area of tan δ peak after introducing modified GO into NBR. It indicates that filler particles show positive interaction with molecular chains. The thermo-oxidative stability of composites was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). Then, the thermo-oxidative aging kinetic parameters were obtained by the Flynn–Wall–Ozawa (FWO) equation. The results of aging tests show that the thermo-oxidative stability of rubber matrix increases obviously after introducing GO–PPD. In addition, mechanical properties (tensile strength and elongation at break) of both before and after aged NBR/GO–PPD composites were superior to that of NBR. This work provides meaningful guidance for achieving multifunction thermo-oxidative aging resistance rubber composites.

Unexpected formation of 1-[4-chloromethylphenyl]-5-[4-(methylsulfonyl)benzyl]-1H-tetrazole and 1-[4-chloromethylphenyl]-5-[4-(aminosulfonyl)phenyl]-1H-tetrazole: Crystal structure, bioassay screening and molecular docking studies

During the cyclization reaction of benzyl alcohol containing amides, using NaN3 and SiCl4, additional unique chlorination development was observed to yield the novel azoles 1-[4-chloromethylphenyl]-5-[4-(methylsulfonyl)benzyl]-1H-tetrazole (3a) and 1-[4-chloromethylphenyl]-5-[4-(aminosulfonyl)phenyl]-1H-tetrazole (3b). Control experiments showed that the SiCl4 or SiCl3N3 has the major role for such functional group transformation in such a clean reaction and quantitative yield. Their molecular structures have been ascertained using the X-ray crystallography technique in addition to the spectroscopic analyses. Both compounds 3a and 3b crystallize in the monoclinic space group P21/c. The cell parameters of azole 3a are a = 22.3827 (8), Å, b = 5.1602 (2) Å, c = 13.4994 (5) Å3, β = 95.2352 (14)°, V = 1552.67 (10) Å3, and Z = 4. While the cell parameters of azole 3b are a = 20.582 (2), Å, b = 5.8947 (7) Å, c = 13.0796 (16) Å3, β = 104.376 (4)°, V = 1537.2 (3) Å3, and Z = 4. The central tetrazole ring of both compounds is planar and bears (4-chloromethylphenyl) at position one (N-1) of the central moiety. However, the substituents 4-(methylsulfonyl)phenyl and 4-(aminosulfonyl)phenyl of azoles 3a and 3b, respectively, are attached to the C-5 of the same central unit. The phenyl rings at N-1, (C2C7) and C9C14 in (3a); (C2C7) and (C8C14) in (3b) are inclined compared to the tetrazole ring with dihedral angles of 21.74° and 83.94° in 3a and 25.85° and 65.13° in 3b. The two phenyl rings, at N-1 and C-5, are rotated against each other by 87.73° (in 3a) and 72.21° (in 3b). In the crystal, intermolecular interactions between molecules of 3a,b are dominated by CH⋯O and CH⋯N hydrogen bonds. Additional Cl…π interactions add extra supramolecularity. All intermolecular interaction motifs consolidate a three dimensional network lattice. The molecular docking studies were carried out to understand the interaction of compounds 3a and 3b within the active site of the cyclooxygenase-2 enzyme, followed by a comparison study with the celecoxib drug as a reference compound. The in vitro bioassay screenings of azoles 3a and 3b showed that both compounds have poor selectivity and weak inhibition potency toward cyclooxygenase-2 enzyme.

Transformation of functional groups in the reduction of NO with NH3 over nitrogen-enriched activated carbons

In recent years, activated carbon technology has been applied in various industrial flue gas purifications, with a high desulfurization efficiency but a relatively low denitrification efficiency. To strengthen the denitrification performance and further clarify which physicochemical property factor dominates the reduction of NO over activated carbon, this study used four kinds of nitrogen-enriched additives to modify the activated carbon, and the denitrification efficiency increased. The results from porosity analysis and Raman spectra showed that modification reduced the specific surface area and total pore volume of the activated carbon but promoted the disorder of graphite microcrystalline structure providing the adsorption and reaction active center for NO and NH3. The oxygen-containing and nitrogen-containing functional groups were detected by X-ray photoelectron spectrometry before and after the reaction. The results revealed that the phenolic hydroxyl oxygen was transformed to carbonyl oxygen of quinone, and pyridine, pyrrole and quaternary nitrogen functional groups were converted to pyridine N-oxides and amines. The transient response experiment was employed to investigate the adsorption state of NO and NH3 in denitrification reaction by abruptly cutting off the intake of NO or NH3 under steady-state reaction. The results revealed that the reduction of NO with NH3 at 110 °C follows the Langmuir-Hinshelwood (L-H) mechanism, while at 150 °C with Elay-Rideal (E-R) mechanism and L-H mechanism. The pyridine, pyrrole and quaternary amine groups can adsorb NO in the gaseous state, and the phenolic hydroxyl group acts as the adsorption site of NH3 to produce quinones and N2 and complete the SCR reaction.

Correlation of Intermolecular Acyl Transfer Reactivity with Noncovalent Lattice Interactions in Molecular Crystals: Toward Prediction of Reactivity of Organic Molecules in the Solid State.

Intermolecular acyl transfer reactivity in several molecular crystals was studied, and the outcome of the reactivity was analyzed in the light of structural information obtained from the crystals of the reactants. Minor changes in the molecular structure resulted in significant variations in the noncovalent interactions and packing of molecules in the crystal lattice, which drastically affected the facility of the intermolecular acyl transfer reactivity in these crystals. Analysis of the reactivity vs crystal structure data revealed dependence of the reactivity on electrophile···nucleophile interactions and C-H···π interactions between the reacting molecules. The presence of these noncovalent interactions augmented the acyl transfer reactivity, while their absence hindered the reactivity of the molecules in the crystal. The validity of these correlations allows the prediction of intermolecular acyl transfer reactivity in crystals and co-crystals of unknown reactivity. This crystal structure-reactivity correlation parallels the molecular structure-reactivity correlation in solution-state reactions, widely accepted as organic functional group transformations, and sets the stage for the development of a similar approach for reactions in the solid state.

A chiral pool approach for asymmetric syntheses of both antipodes of equol and sativan

For the first time, both antipodes of the isoflavans, equol and sativan were synthesized in >98% ee with good overall yields starting from readily available starting materials. The chiral isoflavan, (−)-equol is produced from soy isoflavones, formonentin and daidzein by the action of intestinal bacteria in certain groups of population and other chiral isoflavans are reported from various phytochemical sources. To produce these chiral isoflavans in gram quantities, Evans' enantioselective aldol condensation was used as a chiral-inducing step to introduce the required chirality at the C-3 position. Addition of chiral boron-enolate to substituted benzaldehyde resulted in functionalized syn-aldol products with >90% yield and excellent diastereoselectivity. Functional group transformations followed by intramolecular Mitsunobu reaction and deprotection steps resulted the target compounds, S-(−)-equol and S-(+)-sativan, with high degree of enantiopurity. By simply switching the chiral auxiliary to (S)-4-benzyloxazolidin-2-one and following the same synthetic sequence the antipodes, R-(+)-equol and R-(−)-sativan were achieved. Both enantiomers are of interest from a clinical and pharmacological perspective and are currently being developed as nutraceutical and pharmacological agents. This flexible synthetic process lends itself quite readily to the enantioselective syntheses of other biologically active C-3 chiral isoflavans.