Applying density functional theory on tautomerism in 3,4-dihydropyrimidin-2(1H)-ones

In the present study, the density functional theory (DFT) and Gibbs free energy calculations were performed to investigate the stability and tautomerism of C4-substituted-3,4-dihydropyrimidin-2(1H)-ones. Three different forms are possible for the ethyl 3,4-dihydropyrimidinones (ethyl 4-aryl-6-methyl-3,4-dihydropyrimidin-2(1H)-one-5-carboxylates, ethyl 4-aryl-2-hydroxy-6-methyl-1,4-dihydropyrimidine-5-carboxylates and ethyl 4-aryl-2-hydroxy-6-methyl-3,4-dihydropyrimidine-5-carboxylates) forms that the most stable form is ethyl 4-aryl-6-methyl-3,4-dihydropyrimidin-2 (1H)-one-5-carboxylates (keto-form). The obtained data showed that the substitution on the C4-substitut position can be effective on the equilibrium constant (K _eq).     

Sol–gel derived LaFeO3/SiO2 nanocomposite: synthesis,characterization and its application as a new,green and recoverable heterogeneous catalyst for the efficient acetylation of amines,alcohols and phenols

LaFeO₃/SiO₂ nanocomposite was synthesized by the sol–gel process from metal nitrates and tetraethyl orthosilicate (TEOS) as the SiO₂ source. The nanocomposite product was characterized by XRD, FT-IR, SEM, and surface area measurements and was used as a heterogeneous catalyst for the efficient acetylation of amines, alcohols and phenols to the corresponding acetates using acetic anhydride under solvent-free conditions. Among the various substrates, acetylation of amines was preceded rapidly, so that an amine group could be selectively acetylated in the presence of alcoholic or phenolic hydroxyl groups by the appropriate choice of reaction time. The catalyst can also be reused several times without the loss of activity. In addition, the catalytic activity of the LaFeO₃/SiO₂ nanocomposite was higher than that of the pure LaFeO₃ nanoparticles. The method is high yielding, clean, cost effective, compatible with the substrates having other functional groups and very suitable for the practical organic synthesis.     

ZnAl2O4 SiO2纳米复合催化剂用于无溶剂条件下乙酸酐与醇、酚和胺的乙酰化反应简

A ZnAl₂O₄@SiO₂ nanocomposite was prepared from metal nitrates and tetraethyl orthosilicate by the sol-gel process, and characterized by X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and N₂ adsorption-desorption measurements. The nanocomposite was tested as a heterogeneous catalyst for the acetylation of alcohols, phenols, and amines under solvent-free conditions. Under optimized conditions, efficient acetylation of these substrates with acetic anhydride over the ZnAl₂O₄@SiO₂ nanocomposite was obtained. Acetylation of anilines and primary aliphatic amines proceeded rapidly at room temperature, while the reaction time was longer for the acetylation of alcohols and phenols, showing that an amine NH₂ group can be selectively acetylated in the presence of alcoholic or phenolic OH groups. The catalyst can be reused without obvious loss of catalytic activity. The catalytic activity of the ZnAl₂O₄@SiO₂ nanocomposite was higher than that of pure ZnAl₂O₄. The method gives high yields, and is clean, cost effective, compatible with substrates having other functional groups and it is suitable for practical organic synthesis.     

ZnAl_2O_4@SiO_2纳米复合催化剂用于无溶剂条件下乙酸酐与醇、酚和胺的乙酰化反应(英文)

A ZnAl2O4@SiO2 nanocomposite was prepared from metal nitrates and tetraethyl orthosilicate by the sol-gel process,and characterized by X-ray diffraction,Fourier transform infrared,transmission electron microscopy,and N2 adsorption-desorption measurements.The nanocomposite was tested as a heterogeneous catalyst for the acetylation of alcohols,phenols,and amines under solvent-free conditions.Under optimized conditions,efficient acetylation of these substrates with acetic anhydride over the ZnAl2O4@SiO2 nanocomposite was obtained.Acetylation of anilines and primary aliphatic amines proceeded rapidly at room temperature,while the reaction time was longer for the acetylation of alcohols and phenols,showing that an amine NH2 group can be selectively acetylated in the presence of alcoholic or phenolic OH groups.The catalyst can be reused without obvious loss of catalytic activity.The catalytic activity of the ZnAl2O4@SiO2 nanocomposite was higher than that of pure ZnAl2O4.The method gives high yields,and is clean,cost effective,compatible with substrates having other functional groups and it is suitable for practical organic synthesis.     

Trace determination of EDTA from water samples using dispersive liquid–liquid microextraction coupled with HPLC-DAD

Dispersive liquid–liquid microextraction (DLLME) in conjunction with high-performance liquid chromatography-diode array detection (HPLC-DAD) has been applied to the extraction and determination of EDTA in sediments and water samples. The effect of extraction, nature and volume of disperser solvent, pH value of sample solution, extraction time and extraction temperature were investigated. Under the optimal conditions the analytical range of EDTA was from 3.0 to 50.0 μg L^?1 with a correlation coefficient of 0.9982 and a detection limit of 1.7 μg L^?1. The relative standard deviation (RSD) was less than 5.4% (n?=?5), and the recovery values were in the range of 89–95%. The simplicity, high enrichment, high recovery and good repeatability are the main advantages of the method presented. The DLLME-HPLC-DAD method was successfully applied to the analysis of EDTA in aqueous samples.     

Photo-oxidation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones

A variety of Biginelli 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones are efficiently oxidized to their corresponding pyrimidin-2(1H)-one derivatives upon UV irradiation under argon atmosphere in chloroform solution. The nature of the additional substituent on the phenyl ring located on C-4 of the heterocyclic ring influences the rate of reaction. An electron-transfer induced photoreaction is proposed based on the formation of HCl and CH₂Cl₂.     

Light-induced dehydrogenation of 3,4-dihydropyrimidin-2(1H)-ones

Abstract  

UV light irradiation of Biginelli 3,4-dihydropyrimidin-2(1H)-ones in chloroform in an argon atmosphere leads to dehydrogenation of these compounds to their corresponding pyrimidin-2(1H)-ones in excellent yields. Irradiation in the same solvent under an oxygen atmosphere generates, in addition, various hitherto unidentified products. A light-induced electron transfer from the substrate to the solvent is proposed as the initial event, supported by the detection of dichloromethane and hydrogen chloride in the photolysate.     

Preparation and application of the titania sol-gel coated anodized aluminum fibers for headspace solid phase microextraction of aromatic hydrocarbons from water samples

A novel titania sol-gel coating, including tetrabutyl orthototitanat (TBOT) as initial alkoxide, triethanolamine (TEA) as stabilizer, nitric acid as acid catalyst, and polyethylene glycol (PEG, 6000) as binder was prepared for the first time on an anodized aluminium wire and subsequently applied to headspace solid phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes (BTEX) with gas chromatography flame ionization detection (GC-FID). The analytical characteristics of the proposed porous titania sol-gel derived TBOT/PEG/TEA (41.6:16.0:42.4) fiber were comparable with reported fibers. The extraction temperature, extraction time, effect of salt addition, desorption temperature and desorption time were optimized. Under the optimized conditions and for all BTEX components, the linearity was from 20 to 800 μg L⁻¹, the RSD was below 8.2% and limit of detections (LODs) were between 5.4 and 14.8 μg L⁻¹. The recovery values were from 86.7% to 94.2% in water samples. The proposed HS-SPME-GC-FID method was successfully applied for the analysis of BTEX compounds from petrochemical wastewater samples.