A Method for the Acetylation of Alcohols Catalyzed by Heteropolyoxometallates

Summary. Esterifications of acetic acid with some linear, secondary, tertiary, and benzylic alcohols mediated by catalytic amounts of Keggin, Wells–Dawson, and Preyssler type heteropolyacids were carried out under reflux at mild reaction conditions with good to excellent yields. Among the examined catalysts, H₃PW₁₂O₄₀ and H₁₄NaP₅W₃₀O₁₁₀ revealed better results than other heteropolyacids. This work was performed with the aim of simplifying the esterification process by omitting any solvents and mineral acid catalysts. Easy work-up, low cost, and acidic waste reduction, which are all important features from the environmental and economical points of view, are distinct aspects of this protocol. Heteropolyacid catalysts could be separated after a simple work-up and reused for several times.     

Two New and a Known Compound from Lawsonia inermis

A new obtusafuran derivative, lawsonicin ( 1 ), and a new naphthaquinone, lawsonadeem ( 2 ), along with a known constituent, vomifoliol ( 3 ), were isolated from the aerial parts of Lawsonia alba and characterized by chemical transformation and spectroscopic experiments, including 2D‐NMR techniques.     

Spectrophotometric studies and analytical application of Ce(III) chelates with 1-(2-pyridylazo)-2-naphthol (PAN)

A sensitive procedure for spectrophotometric determination of cerium(III) has been developed. AtpH 10.2 cerium reacts with 1-(2-pyridylazo)-2-naphthol in 40% ethanol to form a red complex which has an absorption maximum at 545 nm. The molar absorptivity at 545 is 3.95·10³ mol^–1. Maximum stability of the complex was attained in pure ethanol. The stoichiometries and structures of the chelates were studied applying conductometric titration, visible spectrophotometry and IR spectrophotometry. The IR spectra revealed that coordination takes place through the N=N, C-OH and pyridyl group.

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Spektrophotometrische Untersuchungen und analytische Anwendung von Ce(III)-Chelaten mit 1-(2-Pyridylazo)-2-naphthol (PAN)

Zusammenfassung Es wurde eine empfindliche Methode zur spektrophotometrischen Bestimmung von Cer(III) entwickelt. Bei einempH von 10,2 reagiert Cer mit 1-(2-Pyridylazo)-2-naphthol in 40% Ethanol unter Bildung eines roten Komplexes mit einem Absorptionsmaximum bei 545 nm (=3 950). Der Komplex besitzt in reinem Ethanol ein Maximum an Stabilität. Die Stöchiometrien und Strukturen der gebildeten 1:1- und 1:2-Chelate wurden mittels konduktometrischer Titration, Elektronen- und IR-Spektrometrie untersucht. Die IR-Daten zeigen, daß die Koordination über N=N, C-OH und Pyridyl erfolgt.

     

Water as an Efficient Solvent for Oxygenation Transformations with 34% Hydrogen Peroxide Catalyzed by some Heteropolyoxometalates

Summary. A highly efficient, selective, fast, and cheap protocol is developed for oxidation of aromatic amines and alcohols utilizing 34% hydrogen peroxide in water catalyzed by some W- and Mo-based heteropolyoxometalates. Findings showed that dodecatungstophosphoric acid, H₃PW₁₂O₄₀, was the most efficient catalyst in the examined oxidation reactions. This methodology may prove to be a valuable alternative for eco-friendly green oxidation. Inherent simplicity, easy work up, and using regenerable catalysts were other key aspects of this oxidation protocol.     

Interaction of glucose oxidase with alkyl-substituted sepharose 4B

Glucose oxidase (GOD) is often used in immobilized forms for determination of glucose. To examine the possibility of its adsorption by hydrophobic interactions, palmityl-substituted Sepharose 4B (Sepharoselipid) was employed as an adsorptive matrix. Various conditions were used in tests to improve the limited immobilization of the enzyme observed under normal (native) conditions, including use of high concentrations of denaturing agents. Of the denaturants used, only the cationic detergent dodecyl trimethyl ammonium bromide was effective in denaturing the protein and exposing its hydrophobic sites for interaction with alkyl residues on the support. This, followed by the process of renaturation, provided catalytically active immobilized preparations. The apoenzyme, prepared by treatment of the holoenzyme with acidified (NH4)2SO4 or thermal denaturation, was totally immobilized on the support. Furthermore, it was shown that either flavin adenine dinucleotide (FAD) or the alkyl residues, not both, may interact with the nucleotide site at any given time. Results are discussed in terms of high rigidity of GOD molecule and limited exposure of hydrophobic sites in its native structure. The observations are in accord with suggestions in the literature that the FAD pocket is a very narrow channel of hydrophobic properties, adapted to accept its natural coenzyme.     

A di-μ-oxomolybdenum(V) complex of 6-acetonylisoxanthopterin,undergoing oxygen atom transfer with dimethyl sulphoxide

The new compound, Na[(Mo₂ ^VO₄)(pte)(OMe)(MeOH)₂] (pte = anion of 6-acetonylisoxanthopterin), has been prepared using the redox non-innocent title ligand in MeOH–H₂O, and characterized by elemental analysis and physico-chemical methods including e.s.m.s., i.r., u.v.–vis. and ¹H-n.m.r. spectra. Rate constants data (1.4 × 10^–3 s^–1 at 300 K) for its oxygen atom transfer with dimethyl sulphoxide tally with those of synthetic analogue systems reported earlier by different authors. The negative activation entropy (–206.3 J mol^–1 deg^–1) is consistent with an associative mechanism for this reaction.     

以金属硫酸氢盐为催化剂在无溶剂条件下高效合成3,4-二氢嘧啶-2(1H)-酮

以金属硫酸氢盐M(HSO4)n(Ca(HSO4)2,Zn(HSO4)2和过硫酸氢钾制剂oxone○R)为催化剂催化醛、1,3-二羰基化合物和尿素进行缩合反应,在90℃及无溶剂的条件下高收率、一锅法合成了3,4-二氢嘧啶-2(1H)-酮.     

SnCl4 and SbCl5 promoted aromatization of enamines

Aromatic amines have been synthesized efficiently from enamines using SnCl₄ and SbCl₅ in CH₂Cl₂ at room temperature.     

Insecticidal Activity and Free Radical Scavenging Properties of Isolated Phytoconstituents from the Saudi Plant Nuxia oppositifolia (Hochst.)

Chromatographic purification of the alcoholic extract from the aerial parts of the Saudi plant Nuxia oppositifolia (Hochst.), Benth., resulted in five isolated phenolic compounds. Two flavones, hispidulin (1) and jaceosidin (2), and the phenylethanoid glycosides, verbascoside (3), isoverbascoside (4), and conandroside (5), were identified and their chemical structures were determined by spectroscopic analyses. The insecticidal activity of compounds 1 and 2, in addition to 11 compounds isolated in a previous research (6–16), was evaluated against the Yellow Fever mosquito, Aedes aegypti. Four compounds displayed adulticidal activity with LD₅₀ values of 2–2.3 μg/mosquito. Free radical scavenging properties of the plant extracts and compounds (1–5) were evaluated by measuring the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate radical cation (ABTS^•+) scavenging activity. All compounds exhibited notable activity, compared with the positive control, l-Ascorbic acid. This study suggests that N. oppositifolia could be a promising source of secondary metabolites, some with lethal adulticidal effect against Ae. aegypti.