Ring-opened Products Research Articles

Epoxidation of light olefin mixtures with hydrogen peroxide on TS-1 in a laboratory-scale trickle bed reactor: Transient experimental study and mathematical modelling

Direct epoxidation of light olefin mixtures with hydrogen peroxide and titanium silicalite (TS-1) catalyst is interesting from a pure scientific viewpoint and it might have a considerable economic and environmental advantages. Direct epoxidation of olefin mixtures implies a significant process intensification as the separation steps of alkenes prior to the epoxidation process is avoided. Binary and ternary mixtures of ethene, propene and 1-butene were selectively epoxidized with hydrogen peroxide in the presence of TS-1 as the heterogeneous catalyst. Methanol was used as the solvent. Transient and stationary kinetic experiments were conducted in a laboratory-scale trickle bed reactor, which was operated under atmospheric pressure and isothermal conditions at 15–55 °C. The experiments were designed to investigate the kinetics of the epoxidation of light olefins at different temperatures, alkene-to-hydrogen peroxide molar ratios as well as gas and liquid residence times in the trickle bed reactor. The recorded transient responses of the reaction products confirmed that the components in the alkene mixtures are epoxidized simultaneously. The epoxide selectivity was 90 % or higher in most experiments; ring-opening products formed from the epoxides and methanol were observed as by-products. The concentration maxima of epoxides during the transient experiments were explained by accumulation of the epoxide products inside the catalyst, which resulted in partial blocking of active sites. After-treatment of the catalyst with methanol and nitrogen completely restored the initial activity. Kinetic modeling was applied, based on presumed elementary steps on the TS-1 surface to describe the behavior of the system at steady state conditions. The trickle bed reactor was described with a dynamic multiphase model, taking into account the kinetic and mass transfer effects. The numerical values of the activation energies, kinetic constants and mass transfer parameters were estimated by nonlinear regression analysis. The model gave a satisfactory description of the experimental data.

1,10-Phenanthroline ring-opening mediated bycis-{Re(CO)2} complexes

C–N bond cleavage of pyridine rings bonded to well-definedcis-dicarbonyl Re(i) complexes has been achieved, affording bipy and phen (for the first time) ring-opening products.

Unearthing the Subtleties of Rhodium(II)-Catalyzed Carbenoid Cycloadditions to Furans with an N-Sulfonyl-1,2,3-triazole Probe.

The rhodium(II)-catalyzed reaction of a model alkenyl donor/acceptor N-sulfonyltriazole with a wide selection of furans is reported. This investigation unearthed a range of structurally diverse carbocyclic and ring-opened products, in good to excellent yields. The products obtained are proposed to arise selectively via cyclopropanation or zwitterionic rearrangement pathways, which are highly dependent on both the structural and electronic features of the furan substrate.

Mechanical Force Enables an Anomalous Dual Ring-Opening Reaction of Naphthodipyran.

Multimodal mechanophores that exhibit complex mechanochromic behavior beyond the typical binary response are capable of distinguishing between multiple stress states through discrete changes in color. Naphthodipyran photoswitches contain two pyran rings fused to a central naphthalene core and represent a potentially promising framework for multimodal reactivity. However, the concurrent ring opening of both pyran moieties has previously proven inaccessible via photochemical activation. Here, we demonstrate that mechanical force supplied to naphthodipyran through covalently linked polymer chains generates the elusive dual ring-opened dimerocyanine product with unique near-infrared absorption properties. Trapping with boron trifluoride renders the merocyanine dyes thermally persistent and reveals apparent sequential ring-opening behavior that departs from the reactivity of previously studied mechanophores under the high strain rates imposed by ultrasound-induced solvodynamic chain extension.

Aluminium-Catalyzed Selective Hydroboration of Esters and Epoxides to Alcohols: C-O Bond Activation.

In this work, the molecular aluminium dihydride complex bearing an N, N'-chelated conjugated bis-guanidinate (CBG) ligand is used as a catalyst for reducing a wide range of aryl and alkyl esters with good tolerance of alkene (C=C), alkyne (C≡C), halides (Cl, Br, I and F), nitrile (C≡N), and nitro (NO2 ) functionalities. Further, we investigated the catalytic application of aluminium dihydride in the C-O bond cleavage of alkyl and aryl epoxides into corresponding branched Markovnikov ring-opening products. In addition, the chemoselective intermolecular reduction of esters over other reducible functional groups, such as amides and alkenes, has been established. Intermediates are isolated and characterized by NMR and HRMS studies, which confirm the probable catalytic cycles for the hydroboration of esters and epoxides.

Ring opening of cyclopropyl ketones with 1,3-diketones for the synthesis of 1,6-diketone derivatives

A series of 1,6-diketone derivatives were prepared by first copper (II) trifluoromethanesulfonate catalysed ring-opening of cyclopropyl ketones with 1,3-diketones followed by DBU-promoted retro-Claisen-type reactions. The acyclic 1,3-diketones selectively worked as carbon-nucleophiles to add to the donor–acceptor cyclopropanes. The ring-opening products underwent CC bond cleavage to afford 1,6-diketone derivatives concisely.

Oxidative treatment of bisphenol A by Fe(VI) and Fe(VI)/H2O2 and identification of the degradation products

Bisphenol A (BPA) is classified as a xenoestrogen compound and has caused adverse effects in humans and animals. Ferrate(VI) (Fe(VI)) and the combination of Fe(VI) and hydrogen peroxide ( H 2 O 2 ) were investigated to degrade BPA in water. This study evaluated the impact of BPA initial concentration (50, 200, and 1, 000 μ g L −1 ) and background anions ( Cl − , PO 4 3 − , and NO 3 − ) on the degradation efficiency of the combined oxidants. The results showed that Fe(VI)/H 2 O 2 performed significantly better than Fe(VI) or H 2 O 2 alone. BPA degradation ( 50 μ g L −1 ) using Fe(VI)/H 2 O 2 was recorded at 99.8% within 60 min at pH 8.0 with [Fe(VI)]/[H 2 O 2 ] molar concentration ratio of 250:2,500. At the same initial concentration of BPA and pH condition, the degradation of BPA using Fe(VI) and H 2 O 2 was recorded as 89% ([Fe(VI)]/[BPA]=5) and 33.5% ([H 2 O 2 ]=2, 500 μ g L −1 ), respectively. BPA degradation using Fe(VI)/H 2 O 2 was 99.8%, 85.3%, and 43.8% for an initial concentration of 50, 200, and 1, 000 μ g L −1 , respectively. The presence of Cl − and NO 3 − ions had no obvious effects on BPA degradation; however, a considerable reduction in the degradation efficiency was observed for PO 4 3 − ( 350 μ g L −1 ) due to the complexation between PO 4 3 − ion and ferric oxy/hydroxides. There were eleven intermediates detected in BPA degradation using Fe(VI)/H 2 O 2 , and three degradation pathways were proposed, including hydroxylation, cleavage of the C-C bond, and oxidation to form ring opening products. A reduction in ecotoxicity was observed after 60 min of reaction for both Fe(VI) and Fe(VI)/H 2 O 2 . • Bisphenol A (BPA) degradation using Ferrate(VI) (Fe(VI)) and Fe(VI)/H 2 O 2 was studied. • Nearly a complete degradation of BPA in water was achieved with Fe(VI)/H 2 O 2 . • BPA degradation by Fe(VI)/H 2 O 2 was affected by PO 4 3 − , but not by Cl − and NO 3 − . • Eleven intermediates in the BPA degradation were detected. • BPA degradation pathways during the oxidative treatments were proposed.

Theoretical Validation of In Chemico Skin Sensitization Assay "ADRA" Using the Products Formed by Nucleophilic Reagents and Chemicals.

Amino acid derivative reactivity assay (ADRA) is an in chemico assay for assessing the skin sensitization potential of chemicals by evaluating the reactivity of nucleophilic reagents that mimic skin proteins. N-(2-(1-Naphthyl)acetyl)-l-cysteine (NAC) and α-N-(2-(1-naphthyl)acetyl)-l-lysine (NAL), used as nucleophilic reagents, are small-molecule derivatives of two different amino acids, each with a naphthalene ring attached. The rate of decrease in the amount of NAC or NAL in the reaction solution is evaluated in this assay as an indicator of the test substance's skin sensitization ability. However, the products formed between the nucleophilic reagent and the test substance, which play an important role in vivo, are not directly identified. Therefore, six highly reactive chemicals, including the proficiency substances listed in the OECD Test Guidelines─squaric acid diethyl ester, 2-methyl-2H-isothiazol-3-one (MI), p-benzoquinone, palmitoyl chloride, diphenylcyclopropenone (DPCP), and imidazolidinyl urea (IU)─were used to determine each formed product. Samples were prepared according to the standard ADRA method, and the formed products were predicted on the basis of the reaction mechanism. Excluding DPCP, the estimated structures were validated using mass spectrometry and nuclear magnetic resonance spectrometry on the synthesized samples. In this manner, the products of each nucleophile were confirmed for all examined test substances. The estimated structure products were obtained through a series of reactions initiated by the nucleophilic attack of NAC's thiol group or NAL's amino group on the test substance's electron-deficient carbonyl carbon. However, contrary to expectations, disulfide-linked-type ring-opened products were detected in the case of MI, and products with free formaldehyde in solution were detected in the case of IU. In summary, all skin sensitizers tested herein reacted with NAC and/or NAL to give products. This supports the theoretical validity of ADRA, which provides an indirect evaluation of the formed products based on a decrease in nucleophilic reagents.

Sequentially Regulating the Structural Transformation of Copper Metal-Organic Frameworks (Cu-MOFs) for Controlling Site-Selective Reaction.

Regulating atomically precise sites in catalysts to achieve site-selective reactions is remarkable but challenging. In this work, a convenient and facile solid-gas/liquid reaction strategy was used to construct controllable active sites in metal-organic frameworks (MOFs) to guide an orientation site-selective reaction. A flexible CuI-MOF-1 with dynamics originating from an anionic and tailorable framework could undergo a reversible structural transformation to engineer a topologically equivalent mixed-valent CuICuII-MOF-2 via a solid-gas/liquid oxidation/reduction process. More importantly, CuI-MOF-1 and CuICuII-MOF-2 could further execute the solid-gas/liquid reaction under ammonia vapor/solution to generate CuII-MOF-3. Furthermore, the transformation from CuI-MOF-1 to CuICuII-MOF-2 and CuII-MOF-3 served as controllable catalysts to facilitate site-selective reactions to realize direct C-N bond arylations. The results demonstrated that CuI-MOF-1 and CuII-MOF-3 possessed well-defined platforms with uniformly and accurately active sites to attain a "turn-on/off" process via different reaction routes, providing the desired site-selective ring-opening products.

Stereoselective Activation of Small Molecules by a Stable Chiral Silene.

The reaction of the dilithium salt of the enantiopure (S)-BINOL (1,1'-bi-2-naphthol) with two equivalents of the amidinate-stabilized chlorosilylene [LPh SiCl] (LPh =PhC(NtBu)2 ) led to the formation of the first example of a chiral cyclic silene species comprising an (S)-BINOL ligand. The reactivity of the Si=C bond was investigated by reaction with elemental sulfur, CO2 and HCl. The reaction with S8 led to a Si=C bond cleavage and concomitantly to a ring-opened product with imine and silanethione functional groups. The reaction with CO2 resulted in the cleavage of the CO2 molecule into a carbonyl group and an isolated O atom, while a new stereocenter is formed in a highly selective manner. According to DFT calculations, the [2+2] cycloaddition product is the key intermediate. Further reactivity studies of the chiral cyclic silene with HCl resulted in a stereoselective addition to the Si=C bond, while the fully selective formation of two stereocenters was achieved. The quantitative stereoselective addition of CO2 and HCl to a Si=C bond is unprecedented.

MgI2-Catalyzed Nucleophilic Ring-Opening Reactions of Donor-Acceptor Cyclopropanes with Indoline-2-thiones.

MgI2-catalyzed nucleophilic ring-opening reactions of donor-acceptor cyclopropanes with indoline-2-thiones as easy-to-handle sulfur nucleophiles were investigated. A series of functionalized γ-indolylthio butyric acid derivatives were synthesized in good to excellent yields under mild reaction conditions. Furthermore, the thioether functionalized ring-opening products could be transformed to sulfone and methionine analogues.

Controllable Polymerization of N -Substituted β-Alanine N -Thiocarboxyanhydrides for Convenient Synthesis of Functional Poly(β-peptoid)s

Controllable Polymerization of <i>N</i> -Substituted β-Alanine <i>N</i> -Thiocarboxyanhydrides for Convenient Synthesis of Functional Poly(β-peptoid)s

Regio- and stereo-chemical ring-opening reactions of the 2,3-epoxy alcohol derivative with nucleophiles: Explanation of the structures and C-2 selectivity supported by theoretical computations

The ring-opening reactions of (1aS,2S,6bR)-5-ethyl-2-hydroxyhexahydro-4H-oxireno[2,3-e]isoindole-4,6(5H)-dione were investigated under very mild and nonchelated conditions. C-2 selective ring-opening products were obtained with nucleophilic additions such as Cl−, Br− and N3−. The exact configuration of (3aS,4R,5R,6S,7aS)-5-chloro-2-ethyl-4,6-dihydroxyhexahydro-1H-isoindole-1,3(2H)-dione was determined by X-Ray diffraction analysis which was obtained from the reaction of epoxy alcohol with HCl . On the other hand, theoretical computations were carried out to explain the regioselectivity in the ring opening reaction of epoxy alcohols. The results showed that the ring-opening reaction of both epoxy alcohols proceeds in a kinetically controlled manner and regioselectivity occurs depending on the transition state.

2,6-Dichloro-1,4-benzoquinone formation from chlorination of substituted aromatic antioxidants and its control by pre-ozonation in drinking water treatment plant

Halobenzoquinones are frequently detected as disinfection by-products in drinking water. Among identified halobenzoquinones, 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) is particularly toxic and is frequently detected in drinking water. Synthetic aromatic antioxidants discharged to source water may increase the risk of 2,6-DCBQ formation, as many studies suggest that aromatic compounds are the most likely precursors to 2,6-DCBQ. Herein, we investigated the formation of 2,6-DCBQ from chlorination of three model aromatic antioxidants, including 3-tert-butyl-4-hydroxyanisole (BHA), 2,6-di-tert-butyl-4-methylphenol (BHT) and bis(4-tert-butylphenyl)amine (BBPA). Only BBPA produced 2,6-DCBQ under chlorination, while chlorination of BHA and BHT formed α, β-unsaturated C4-dicarbonyl ring-opening products and phenolic compounds. Based on mass balance and intermediate transformation analysis, mechanisms for the formation of 2,6-DCBQ from BBPA chlorination involved hydrolysis, tert-butyl group cleavage, chlorine substitution, desamination and oxidation. Mitigating aromatic compounds will be an efficient method for 2,6-DCBQ control, such as pre-ozonation, because the intermediates involved in 2,6-DCBQ formation were aromatic compounds. Real water samples from two drinking water treatment plants (DWTPs), one with pre-ozonation (DWTP 2) and the other without pre-ozonation (DWTP1), were analyzed. The two DWTPs were built along the Yangtse river in Nanjing city. Raw water parameters from the two DWTPs, including dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254) and NH3–N, indicated the water quality between these sources was similar. Pre-ozonation in DWTP 2 vanished 2,6-DCBQ in raw water. Concentrations of 2,6-DCBQ in finished water from DWTP 1 (5.69 ng/L) was higher than concentrations generated from DWTP 2 (1.31 ng/L). These results demonstrate that pre-ozonation, granular activated carbon (GAC) and quartz sand treatments at DWTP 2 remove more 2,6-DCBQ precursors than the conventional quartz sand and GAC treatments in DWTP 1. These results suggest the pre-ozonation, GAC and quartz sand treatments can help minimize concentrations of 2,6-DCBQ generated in DWTPs.

Retro-aza-Michael reaction in continuous flow. Approaches to synthesis of adaline and euphococcinine related products

A retro-aza-Michael ring opening reaction of tropinone and granatanone (pseudopelletierine) in flow setup was investigated and the resulting products were utilized as key intermediates in approaches to adaline and its analogues. The enantioselective flow-reaction gave products of ring opening of granatanone with enantiopurity up to 98% ee. Attempts to elaborate the retro-aza-Michael product to alkaloids are described. Lithiated carbamate derivative of tropane was converted to a tropane analogue of euphococcinine, an adaline related alkaloid (a methyl and tropane homologue of adaline 19). Reactivity of the retro-aza-Michael product under Morita-Baylis-Hillman conditions was also briefly investigated.

Furfural hydrogenation over Cu, Ni, Pd, Pt, Re, Rh and Ru catalysts: Ab initio modelling of adsorption, desorption and reaction micro-kinetics

Hydrogenation, hydrodeoxygenation and ring opening of biomass-derived furfural were studied by using Pd/C, Pt/C, Re/C, Ru/C, Rh/C, Ni/C and Cu/C catalysts. Based on experiments, a generalized micro-kinetic model was developed, describing kinetics of tested catalysts well. Pd/C could unselectively hydrogenate furfural’s ring, aldehyde group or both and was the most active tested catalyst. Selective aldehyde group hydrogenation, followed by deoxygenation was observed with other catalysts. This route was also favorable thermodynamically according to density functional theory (DFT) calculations. Only Ru/C could form methyltetrahydrofuran (45.3 % yield) and ring opening products at 200 °C. Reaction conditions were optimized in silico for most promising catalysts (Pd, Pt, Re, Ni on carbon), by fixing the kinetic parameters obtained by regression analysis and subsequently maximizing the objective function, i.e. the yield of the product of interest. Validation experiments confirmed a high Pd/C hydrogenation activity already at 40 °C, forming predominantly tetrahydrofurfural (85 % yield), while 95 % yield of 2-methyltetrahydrofuran was obtained by using a cheap Ni/C at 212 °C.

Perylene diimide supermolecule (PDI) as a novel and highly efficient cocatalyst for photocatalytic degradation of tetracycline in water: A case study of PDI decorated graphitic carbon nitride/bismuth tungstate composite

Employing perylene diimide supermolecule (PDI) as metal-free cocatalyst, a novel PDI/g-C3N4/Bi2WO6 (PCB) photocatalyst was constructed for the effective degradation of antibiotics. Both the photocatalytic activity and photostability of g-C3N4/Bi2WO6 (gCB) were further improved after loading PDI. Under simulated sunlight illumination, the apparent rate constant of tetracycline (TC) degradation by PCB reached 2.6 times that of gCB. The photocatalytic activity of PCB still kept over 80% after 4 cycle experiments, while gCB only remained around 21%. The superior activity of PCB was ascribed to the synergism between the extended visible light absorption range through the participation of PDI cocatalyst and facilitated gCB-to-PDI photoelectron transfer. TC would finally be transformed into non-toxic ring opening products and mineralized. This work demonstrated that PDI was an excellent metal-free cocatalyst and exhibited great potential to boost the activity of photocatalysts.

Insights into the effect of flue gas on synergistic elimination of toluene and NOx over V2O5-MoO3(WO3)/TiO2 catalysts

The impact of the complex flue gas (containing SO2, NO, NH3, O2 and H2O) on the synergistic elimination of toluene and NOx over over V2O5-MoO3(WO3)/TiO2 in the SCR section was systematic researched for the first time. NO and SO2 proved to be mutually repressive in reaction and competitive in absorption. Moreover, NH3 was identified as the key factor responsible for reducing the COx selectivity in the catalytic oxidation of toluene. It promoted the generation of nitriles and indirectly inhibited the generation of benzoic acid, nitrobenzene, and maleic acid (the product of benzene ring opening). In addition, 16 types of polycyclic aromatic hydrocarbons (PAHs) were detected in the exhaust emissions from the flue gas, among which the content of naphthalene was the highest. The V2O5-MoO3(WO3)/TiO2 catalysts displayed low selectivity and generated a lot of by-products with high environmental risk, even though it had a high VOCs removal rate.

Photoinduced Etherification of Less-Strained Cycloketoxime Esters Enabled by C–C Bond Cleavage

We report a general, scalable, and convenient photochemical process for diversities of distal oxygenated nitriles from corresponding less-strained ketoxime esters allowing one-step introductions of ether and cyano groups, which avoids the utilization of toxic cyanide reagents. A wide range of ketoxime esters involving five-membered to eight-membered cycloketoxime esters and linear ketoxime esters participate smoothly under operately simple and mild conditions, affording structurally variable ring-opening products.

Photochemistry of 3,6-Didehydropyridazine Biradical─An Untraceable Para Benzyne Analogue.

We report matrix isolation infrared spectroscopic studies to characterize 3,6-didehydropyridazine 6, a heterocyclic analogue of para benzyne, combined with computations. In this regard, we have utilized 3,6-diiodopyridazine 11 as a photolytic precursor. The experiments toward the generation of the biradical are carried out in argon and nitrogen matrices at 4 K. Instead of the elusive biradical, we have observed a ring-opening product maleonitrile (Z)-7 upon irradiation at 254 nm. In contrast, prolonged irradiation at 254 nm leads only to Z-E isomerization, forming fumaronitrile (E)-7. The mechanistic aspects of ring-opening, product selectivity, and Z-E photoisomerization steps have been investigated in detail using high-level ab initio computations. These studies have found that 3,6-didehydropyridazine 6 is an untraceable intermediate, and the ring-opening step leading to maleonitrile is barrierless. In addition, we have proposed the involvement of the S1 (π-π*) state via conical intersection in the Z-E photoisomerization of maleonitrile.