An Efficient Synthesis of Thioesters Via TFA-Catalyzed Reaction of Carboxylic Acid and Thiols: Remarkably Facile C–S Bond Formation

Abstract

A general, facile, and efficient new synthetic path to thioesters was established by employing defined TFA-catalyzed reaction of carboxylic acid and thiol under mild conditions. The structure of the newly synthesized compounds was determined by infrared spectroscopy, nuclear magnetic resonance, and a single crystal X-ray crystallographic analysis.

Supplemental materials are available for this paper. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Preparative Electrochemical Liberation of Arenes and Heterocycles from Their Respective Ironcyclopentadienyl Complexes

Electrolysis of arene and heterocycle cyclopentadienyliron hexafluorophosphates led to the liberation of arenes or heterocycles in 69–90% yield. The procedure described gives yields comparable with or superior to the yields obtained from pyrolytic sublimation used previously.     

Optimization and validation of an RP-HPLC method for direct determination of metformin hydrochloride in human urine and in a dosage form

A simple, selective, sensitive, accurate, and precise method was developed for determination of metformin hydrochloride (MF) in human urine using RP-HPLC. The method depends upon using an octylsilyl (C8) 5 microm particle size column at ambient temperature with mobile phase consisting of 33 mM sodium dihydrogen phosphate containing 6.38 mM hexanesulfonic acid sodium salt and adjusted to apparent pH 3.0 with phosphoric acid-acetonitrile (93 + 7, v/v) at a flow rate of 1.5 mL/min. Quantitation was achieved with UV detection at 231 nm based on peak area with a linear calibration curve over the concentration range of 0.01-50 microg/mL. The proposed method was applied to the determination of the urinary excretion pattern of MF (the cumulative amounts excreted were calculated without pretreatment of the urine sample) and for determination of the dissolution pattern of MF tablets. The proposed method was completely validated according to the U.S. Food and Drug Administration guidelines.     

Electrical conduction mechanism in nanocrystalline CdTe (nc-CdTe) thin films

The present paper reports the electrical characterization of nc-CdTe thin films in different temperature ranges. Thin films of nc-CdTe are deposited on the glass substrates by Physical Vapor Deposition (PVD) using the Inert Gas Condensation (IGC) method. The Transmission Electron Microscopy (TEM) studies are made on the CdTe nanocrystals. The surface morphology and structure of the thin films are studied by the Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) measurements. Dark conductivity measurements are made on the nc-CdTe thin films in the temperature range 110–370 K in order to identify the conduction mechanism in this temperature range. The obtained results reveal three distinct regions at high, low, and sufficiently low temperature regions with decreasing activation energies. The analysis of the high temperature conductivity data is based on the Seto’s model of thermionic emission. At very low temperatures, dc conductivity (σ _d) obeys the law: lnσT ^1/2∝T ^?1/4, indicating variable-range hopping in localized states near the Fermi level. The density of the localized states N(E _F) and various other Mott’s parameters like the degree of disorder (T _O), hopping distance (R), and hopping energy (W) near the Fermi level are calculated using dc conductivity measurements at low temperatures. Carrier type, carrier concentration, and mobility are determined from the Hall measurements. The transient photoconductivity decay measurements are performed on the nc-CdTe thin films at different intensities in order to know the nature of the decay process.     

Chemometrics in pharmaceutical analysis: an introduction, review, and future perspectives

Chemometrics is the application of statistical and mathematical methods to analytical data to permit maximum collection and extraction of useful information. The utility of chemometric techniques as tools enabling multidimensional calibration of selected spectroscopic, electrochemical, and chromatographic methods is demonstrated. Application of this approach mainly for interpretation of UV-Vis and near-IR (NIR) spectra, as well as for data obtained by other instrumental methods, makes identification and quantitative analysis of active substances in complex mixtures possible, especially in the analysis of pharmaceutical preparations present in the market. Such analytical work is carried out by the use of advanced chemical instruments and data processing, which has led to a need for advanced methods to design experiments, calibrate instruments, and analyze the resulting data. The purpose of this review is to describe various chemometric methods in combination with UV-Vis spectrophotometry, NIR spectroscopy, fluorescence spectroscopy, electroanalysis, chromatographic separation, and flow-injection analysis for the analysis of drugs in pharmaceutical preparations. Theoretical and practical aspects are described with pharmaceutical examples of chemometric applications. This review will concentrate on gaining an understanding of how chemometrics can be useful in the modern analytical laboratory. A selection of the most challenging problems faced in pharmaceutical analysis is presented, the potential for chemometrics is considered, and some consequent implications for utilization are discussed. The reader can refer to the citations wherever appropriate.     

Reflectance near-infrared spectroscopic method with Chemometric techniques for simultaneous determination of Chondroitin, glucosamine, and methyl sulfonyl methane

Reflectance near-IR (RNIR) spectroscopy was used for the simultaneous determination of chondroitin (CH), glucosamine (GO), and methyl sulfonyl methane (MSM) in tablets. Simple sample preparation was done by grinding, sieving, and compression of the tablets for improving RNIR spectra. Principal component regression and partial least squares (PLS-1 and PLS-2) were successfully applied to quantify the three components in the studied mixture using information included in RNIR spectra in the range of 4350-9100 cm(-1). The calibration model was developed with drug concentration ranges of 14.5-44.2% (w/w) for CH, 18.4-55.3% (w/w) for GO, and 6-18.6% (w/w) for MSM with addition of tablet excipients to the calibration set in the same ratio as in the tested tablets. The calibration models were evaluated by internal validation, cross-validation, and external validation using synthetic and pharmaceutical preparations. The proposed method was applied for analysis of six batches of the pharmaceutical product. The results of the proposed method were compared with the results of the pharmacopoeial method for the same batch of the pharmaceutical product. No significant differences between the results were found. The RNIR method is accurate and precise, and can be used for QC of pharmaceutical products.     

Dielectric spectroscopy of some heteronuclear amino alcohol complexes

The temperature dependent dielectric spectroscopic properties of two heteronuclear complexes of monoethanolamine (MEA) at a wide temperature range (303-413 K) were investigated by impedance spectroscopy, in the frequency range from 100 Hz to 100 kHz. The frequency dependence of the impedance spectra plotted in the complex plane shows semi-circles. The Cole-Cole diagrams have been used to determine the molecular relaxation time, tau. The temperature dependence of tau is expressed by thermally activated process. Relaxation frequencies corresponding to the rotation of the molecules about their long axes are expected to lie above 10 MHz and exhibit Arrhenius behavior, where a single slope is observed with activation energy values equal to 0.67 and 0.78 eV. The ac conductivity sigma(ac) (omega) is found to vary as omega(s) with the index s相似文献   

Reaction of 4‐substituted thiosemicarbazides with (2,4,7‐trinitro‐9H‐fluoren‐9‐ylidene)propanedinitrile

4‐Substituted thiosemicarbazides 4a‐c reacted with (2,4,7‐trinitro‐9H‐fluoren‐9‐ylidene)‐propanedinitrile ( 2 ) in pyridine with admission of air to form spiro[fluorene‐9,3′‐(1,2,4‐triazole)]derivatives 5a‐c and (4‐substituted thiosemicarbazono)propanedinitriles 6a‐c in modest yields. 2,4,7‐Trinitro‐9‐fluorenone ( 8 ) as well as one reduction product thereof and of 2 , namely compounds 9 and 10 , respectively are also found. A rationale for the conversions observed is presented.     

Liquid chromatography determination of citalopram enantiomers using beta-cyclodextrin as a chiral mobile phase additive

A reliable and specific method for the determination of citalopram enantiomers was developed and validated. Chromatographic resolution of citalopram enantiomers was made on a Shim-pack (5 microm particle size) cyanopropyl column with beta-cyclodextrin (beta-CD) as an effective chiral mobile phase additive. The composition of the mobile phase was (90 + 10, v/v) aqueous 0.1% triethylammonium acetate buffer, pH 4.0 (adjusted with acetic acid), and acetonitrile, containing 12 mM beta-CD. The flow rate was 0.8 mL/min with ultraviolet detection at 240 nm. The effects of the mobile phase composition, concentration of beta-CD, and pH of the triethylammonium acetate buffer on peak shape and resolution of the enantiomers were investigated. The calibration graphs were linear (r = 0.9999, n = 8) in the range of 1-40 microg/mL for S(+) citalopram and R-(-) citalopram. The limit of detection values were 5.51 x 10(-3) and 4.35 x 10(-3) pg/mL, while the limit of quantification values were found to be 1.84 x 10(-2) and 1.45 x 10(-2) microg/mL for S-(+) citalopram and R-(-) citalopram, respectively.     

Design of Organoiron Macromolecules Based on Upper Rim Functionalized Calix[4]arenes

The versatility of cationic cyclopentadienyliron complexes is demonstrated for the generation of calix[4]arene‐based dendrimers and polymers. Dendrimers were prepared from a branched organoiron calix[4]arene through subsequent reactions of azo dyes and organoiron complexes. The resulting azo dye‐containing metallocalix[4]arenes were soluble in polar organic solvents and displayed λ_max ranging between 430 and 456 nm. Upon addition of various acids, the λ_max shifted to higher wavelengths (513–535 nm). In the solid state and in solution, the azo dye‐containing metallocalix[4]arenes reversibly changed colour in the presence of acid and base, indicating their potential use as acid sensors. Cyclic voltammetric studies showed that the iron centres of the metallocalix[4]arenes were reversibly reduced at E_1/2 = −1.49 V. When non‐branching organoiron‐based calix[4]arene were reacted with dithiols, polymers containing calix[4]arenes either in their side chains or main chains were obtained. The polymers possessed weight average molecular weights between 35 000 and 53 000. The polymers were determined to be thermally stable with backbone decomposition occurring above 500 °C.