Voltammetry in Undiluted Acetic Acid. In Situ Determination of Water

Water present in undiluted acetic acid can be monitored in situ with Pt and Au microelectrodes using differential pulse and square‐wave voltammetries. Both reduction and oxidation peaks can be obtained. The best quantitative analytical results were obtained for the anodic peak, the Pt microelectrode, and differential pulse voltammetry. The anodic water peak is located at +1.55 V vs. the quasi reference Pt electrode. The voltammetric peak obtained at Pt electrode is apparently not a diffusional one, however, the calibration plot obtained by employing this peak is linear over a wide concentration range, up to 4 mol dm^?3. The detection limit has been estimated as 2.3 mM or 0.0043 v/v%. The developed method may be particularly useful, since the Karl Fischer method can not be used to determine water in glacial acetic acid due to the estrification reaction of acetic acid with methanol. A voltammetric wave of undiluted acetic acid could not be obtained in the positive and negative ranges of potential.     

The direct conversion of carbamates to ureas using aluminum amides

The conversion of carbamates into ureas using aluminum amide complexes is reported. This reaction is a convenient method to prepare bi-, tri- and tetra-substituted ureas from carbamate-protected primary or secondary amines by reaction with primary or secondary amines in the presence of stoichometric quantities of trimethylaluminum. A reactivity trend of the various carbamates was observed and methyl and benzyl carbamates were reacted selectively in the presence of t-butyl carbamates.     

Solid Phase Synthesis of 4H-Pyrimido[2,1-b] Benzothiazol-4-ones from Resin-Bound Cyclic Malonic Ester

The solid phase synthesis of 4H-pyrimido[2,1-6] benzothizaol-4-ones has been reported.     

Notiz zur Darstellung von 4-Hydroxy-6-methyl-5,6-dihydro-2H-pyran-2-on

Meldrum's acid (2) is acylated by diketen affording the acylMeldrum's acid3. In aqueous bicarbonate its 3-oxogroup is selectively reduced by sodium tetrahydroborate giving the alcohol4, which readily undergoes cyclization in refluxing dioxane leading to the title pyrone7. Under identical conditions3 produces the pyrone6 with the pyrone carboxylic acid5 as intermediate.

     

Synthesis and structure of a new tetranuclear macrocyclic antimony(v) complex

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Heterocyclic analogs of pleiadiene. 70. Synthesis of 6-hydroxy-1,3-diazapyrenes

The regioselectivity of the reactions of perimidine with cinnamic acids in polyphosphoric acid (PPA) depends on the P₂O₅ content. Procedures were developed for the synthesis of 4(9)- and 6(7)-cinnamoylperimidines. Cyclization of the latter under the action of an excess of AlBr₃ was accompanied by dearylation to form 6-hydroxy-1,3-diazapyrene.     

A concise synthesis of (2S,4R)- and (2S,4S)-4-methylglutamic acid

A concise, multi-gram scale method for producing the bioactive and enantiomerically pure epimers, (2S,4R)- and (2S,4S)-glutamic acids, in a single synthetic scheme is described.     

Determination of the enantiomeric composition of chiral carboxylic acids using chiral derivatization and HPLC

Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol (“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid.     

Cloud point extraction equilibrium of lanthanum(III), europium(III) and lutetium(III) using di(2-ethylhexyl)phosphoric acid and Triton X-100

The cloud point extraction behaviors of lanthanoids(III) (Ln(III) = La(III), Eu(III) and Lu(III)) with and without di(2-ethylhexyl)phosphoric acid (HDEHP) using Triton X-100 were investigated. It was suggested that the extraction of Ln(III) into the surfactant-rich phase without added chelating agent was caused by the impurities contained in Triton X-100. The extraction percentage more than 91% for all Ln(III) metals was obtained using 3.0 × 10⁻⁵ mol dm⁻³ HDEHP and 2.0% (v/v) Triton X-100. From the equilibrium analysis, it was clarified that Ln(III) was extracted as Ln(DEHP)₃ into the surfactant-rich phase. The extraction constant of Ln(III) with HDEHP and 2.0% (v/v) Triton X-100 were also obtained.     

Solid-phase fluorescence spectroscopy for the determination of acetylsalicylic acid in powdered pharmaceutical samples

A rapid, simple and rugged procedure without requiring any prior sample treatment was developed for the determination of acetylsalicylic acid (ASA) in tablets formulations by solid-phase fluorescence spectroscopy. The method was carried out on powdered samples, consisting of an active substance dispersed in lactose, maize starch, talc and magnesium stearate. Previous knowledge of the sample bulk composition is needed for proper application of the method. Wavelengths for maximum excitation and emission were 288 and 318 nm, respectively, and the fluorescence intensity was linear with ASA concentration within the 50-170 mg g⁻¹ range. Detection and quantification limits were 2.2 and 7.3 mg g⁻¹, and the analytical frequency was 200 h⁻¹. For a typical sample, the relative standard deviation of results was estimated as 2.3% (n = 10). Accuracy was assessed by comparing the analytical results obtained with the proposed method with those related to a reference method recommended by British Pharmacopoeia: no differences between the methods were found at the 95% confidence level.