A facile and efficient method for hydroxylation of azabenzanthrone compounds

A novel and facile method of introducing 4-hydroxyl group into the aromatic ring of azabenzanthrone compounds was carried out by reacting azabenzanthrone compounds with hydrazine hydrate or hydroxylamine hydrochloride and sodium hydroxide in diethylene glycol(DEG) solvent.The mechanism of reaction may involve an amino intermediate and follow a hydroxyl substitution process.     

Kinetic speciation of BCR reference materials

The accurate study of heavy metal speciation is important in environmental monitoring. There has been much work developing various operationally defined speciation methods for soil and sediment, but there is a need to compare the different approaches by evaluating them for the same sample. In this article, a kinetic method was applied for the heavy metal speciation of the two BCR reference materials, CRM601 and BCR701, which have been specifically developed as materials to evaluate the validated BCR three-step sequential extraction method. When EDTA was used as an extractant, 81.0% of Cd, 68.0% of Cu, 21.5% of Ni, 80.3% of Pb and 71.9% of Zn was extracted from CRM601. For BCR701, the removal ratios were 92.0, 52.3, 18.7, 50.6 and 67.5% with EDTA and 95.7, 25.2, 20.0, 52.4 and 68.5% with hydroxylamine hydrochloride as an extractant, for Cd, Cu, Ni, Pb and Zn respectively. A two-component kinetic model was applied to the extraction curve and the extractable metals were readily classified into two categories, namely, labile fraction and non-labile fractions. The rate constants obtained from the regression model were found to be useful in quantifying the lability of an element. The rate constants obtained from the labile fractions in BCR701 were higher than that of obtained from CRM601, which indicated the high lability of metals in BCR701. When compared with the sequential extraction data, it seemed that the lability of an element was positively correlated to the first step extraction fraction.     

用对氨基苯酚改性的碳纳米管糊电极同时测定羟胺和苯酚(英文)

A carbon paste electrode that was chemically modified with multiwall carbon nanotubes and p-aminophenol was used as a selective electrochemical sensor for the simultaneous detection of hydroxylamine (HX) and phenol. Cyclic voltammetry, double potential-step chronoamperometry, square wave voltammetry (SWV), and electrochemical impedance spectroscopy were used to investigate the use of p-aminophenol in the carbon nanotubes paste matrixes as a mediator for the electrocatalytic oxidation of HX and phenol in aqueous solution. The coefficient of electron transfer and catalytic reaction rate constant were determined using the electrochemical methods. Under optimized conditions, the electrocatalytic oxidation current peaks for HX and phenol increased linearly with concentration in the range of 0.5-180.0 and 10.0-650.0 μmol/L for HX and phenol, respectively. The detection limits for HX and phenol were 0.15 and 7.1 μmol/L, respectively. The anodic potential peaks of HX and phenol were separated by 0.65 V in SWV. Because of good selectivity and sensitivity, the present method provides a simple method for the selective detection of HX and phenol in practical samples such as water samples.     

Reactions of 3-(polyfluoroacyl)chromones with hydroxylamine. The first synthesis of 3-cyano-2-(polyfluoroalkyl)chromones

Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine proceeds via nucleophilic 1,4-addition followed by opening of the pyrone ring and subsequent cyclization to 4-(polyfluoroalkyl)-4H-chromeno[3,4-d]isoxazol-4-ols in good yields. On treatment with trifluoroacetic acid, the isoxazole ring of this annulated heterocyclic system opens to give 3-cyano-2-(polyfluoroalkyl)chromones. Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine hydrochloride occurs only at the carbonyl carbon atom connected to the R^F group to give the corresponding oximes in low yields.     

Enhancement of the analytical properties and catalytic activity of a nickel hexacyanoferrate modified carbon ceramic electrode prepared by two-step sol-gel technique: application to amperometric detection of hydrazine and hydroxyl amine

The electroless sol-gel technique was used for the construction of nickel hexacyanoferrat (NiHCF) modified carbon composite electrodes (CCEs).This involves two steps: formation of a carbon ceramic electrode fabricated by nickel powder and then immersing the electrode into a sodium- hexacyanoferate solution for the immobilization of NiHCF films. The cyclic voltammety of the resulting modified CCEs prepared under optimum conditions, shows a well defined surface redox couple due to the [Ni^IIFe^III/II(CN)₆]^−2/−1 system. The effect of different alkali metal cations in supporting electrolyte on the behavior of the modified electrode were studied. The charge transfer coefficient (α) and charge transfer rate constant (k_s) for modified films were calculated. Hydrazine and hydroxylamine have been chosen as a model to elucidate the electocatalytic ability and analytical parameters of NiHCF modified CCE prepared by one and two-step sol-gel techniques and these compounds determined amperometically at the surface of modified electrodes. The latter shows a good electocatalytic activity towards the oxidation of hydrazine and hydroxylamine in the pH range 3-8 in comparison with CCEs modified by homogeneous mixture of graphite powder, Ni(NO₃)₂ and Na₂[Fe(CN)₆], (one-step sol-gel technique). Furthermore, the catalytic rate constant, linear dynamic range, limit of detection, and sensitivity for hydrazine and hydroxylamine detections were evaluated and compared with CCEs prepared with one-step sol-gel method. The modified CCEs containing NiHCF shows good repeatability, short response time, t 90%<3 s, long term stability (3 months) and excellent catalytic activity. Furthermore, the method of preparation is rapid and simple and the modified electrodes are renewed by simple mechanical polishing and immersing in [Na₃Fe(CN]₆] solution.     

粘土中游离氧化铁的分离及其测定

研究了盐酸羟胺-草酸-草酸铵体系提取粘土中游离氧化铁及其测量,试验表明,用此体系提取拈土中的游离氧化铁,其测量结果与DCB法一致,而提取及测量所需的时间却较前者短。相对标准偏差RSD≤2．0％。     

A modular approach to α,β-unsaturated N-aryl ketonitrones

A modular approach to α,β-unsaturated N-aryl ketonitrones has been developed. Specifically, condensation of anilines and enals followed by alkylation of the resulting α,β-unsaturated imines provided N-allyl anilines, which were subjected to oxidation with Oxone® to form α,β-unsaturated N-aryl ketonitrones. This modular approach is general and provides rapid access to diversely substituted α,β-unsaturated N-aryl ketonitrones with a single purification step in good yields.     

Facile synthesis of 3-aryl/alkylamino 5-aryl/alkyl 1,2,4-oxadiazoles from acylthiourea

Facile and selective synthesis of 3-aryl/alkylamino 5-aryl/alkyl 1,2,4-oxadiazoles starting from N-acylthioureas has been demonstrated. The regio-selectivity is achieved by simply selecting an appropriate base used for the generation of hydroxyl amine from the corresponding hydrochloride salt. This method also avoids the use of toxic cyanogen bromide. The structure of the synthesized oxadiazoles has been resolved by tandem mass spectral studies.     

A convenient procedure for the solid-phase synthesis of hydroxamic acids on PEGA resins

An efficient method for the solid-phase synthesis of hydroxamic acids is described. The method comprises the nucleophilic displacement of esters immobilized on PEGA resins with hydroxylamine/sodium hydroxide in isopropanol. The hydroxyaminolysis protocol is compatible with a broad range of PEGA-supported peptide and peptidomimetic esters. The methodology was found to be compatible with two new strategies for the synthesis of solid-supported lactams and diketopiperazines, respectively, both relying on the high inter- and intramolecular reactivity of cyclic N-acyliminium ions with electron-rich aromatics and heteroaromatics, ultimately affording hydroxamic acid derivatives in high purities.     

From 4,5,6,7-tetrahydroindoles to 3- or 5-(4,5,6,7-tetrahydroindol-2-yl)isoxazoles in two steps: a regioselective switch between 3- and 5-isomers

(4,5,6,7-Tetrahydroindol-2-yl)alkynes, synthesized by cross-coupling of 4,5,6,7-tetrahydroindoles with aroyl(hetaroyl)bromoalkynes or ethyl bromopropynoate in the presence of K₂CO₃, regioselectively cyclize with hydroxylamine to either 3- or 5-(4,5,6,7-tetrahydroindol-2-yl)isoxazoles depending on the acidity of the reaction mixture: in the presence of acetic acid 3-isomers are formed (ca. 100% selectivity), while under neutral conditions the reaction is switched to 5-isomers (94–97% selectivity).