Showing papers in "Journal of The Iranian Chemical Society in 2007"

Application of N-halo reagents in organic synthesis

Abstract: This review article summarizes published data on the application of N-halo reagents (such as N-halo amines, N-halo amides and/or imides, N-halo sulfonamides and/or imides, and etc) in various organic functional group transformations such as: oxidation reactions, deprotection and protection of different functional groups, halogenation of saturated and unsaturated compounds, acylation of alcohols, phenols, amines or thiols, epoxidation of alkenes, aziridination and etc The main purpose of writing this review is encouraging of active researchers interested to this field for the synthesis of new N-halo reagents specially with different halogens and applications of these new N-halo reagents in organic reactions or finding more and more applications of existing N-halo reagents in organic synthesis

Synthesis of 2-substituted benzimidazoles and bis-benzimidazoles by microwave in the presence of alumina-methanesulfonic acid

Abstract: A microwave-assisted method for the synthesis of 2-substituted benzimidazoles in the presence of alumina-methanesulfonic acid (AMA) is reported. In addition, by this method some new bis-benzimidazoles from the direct reaction of phenylenediamine and dicarboxylic acid under microwave irradiation in good to excellent yields are described.

Efficient and eco-friendly synthesis of dihydropyrimidinones, bis(indolyl)methanes, and N-alkyl and N-arylimides in ionic liquids

Abstract: Dihydropyrimidinones, bis(indolyl)methanes, and N-alkyl and N-arylimides were synthesized efficiently under mild reaction conditions in the presence of two types of ionic liquids. In each section, effects of different ILs on the yield of reactions were investigated. The use of ionic liquids offer improvements for the synthesis of title compounds with regard to the yield of products, simplicity in operation, short reaction times and green aspects by avoiding toxic catalyst and organic solvents.

Ca(HSO4)2 mediated conversion of alcohols into N-substituted amides under heterogeneous conditions: A modified Ritter reaction

Abstract: Tertiary, secondary, and benzylic alcohols react efficiently with nitriles in the presence of the catalyst calcium hydrogen sulfate, Ca(HSO4)2, to produce amides in high yields. In this study, a modified Ritter reaction using this solid acid catalyst is found to be an environmentally safe method for converting 2,6-bis(hydroxymethyl)-4-halo anisole into the corresponding diamides in CH3CN.

One decade of research on ion-selective electrodes in Iran (1996–2006)

Abstract: This review presents a general overview about the development of ion-selective electrodes in Iran during the past decade (1996–2006). All of the reported ion-selective sensors (for cations, anions and organic species) are cited in this review. Sensors for 39 cations, 12 anions, and 23 organic compounds and drugs have been reported in this reivew. Some of the main group cations (e.g. beryllium) as well as most of the lanthanide ion (i.e., presidium, erbium, lutetium, cerium, neodymium, europium, gadolinium, terbium, dysprosium, holmium, ytterbium, and thulium) sensors have been reported for the first time. It is noticable that the best reported sensors for HPO4 2−, SO4 2−, Cl−, ClO4 −, Br−, and I3 − have been designed and constructed by the Iranian researchers.

Synthesis and electrochemistry of vanadium(IV) Schiff base complexes

Abstract: The electrochemical properties of vanadyl(IV) derivatives, namely salen Schiff base complexes of the type [VO(Salen)] (5-BrSalen, 5-NO2Salen, 5-MeOSalen, salpn (bis(salicylaldehyde)-1,3-propanediamine, 5-BrSalpn, 5-NO2Salpn, 5-MeOSalpn, Me2Salen, Salophen, 5-BrSalophen, and 5-MeOSalophen) were investigated. The equatorial Schiff base ligands affect the oxidation potentials via interaction with the d-orbitals of the vanadyl metal ion. The cathodic peak potential (Epc) becomes less negative according to the sequence MeO- < H- < Br- < NO2−.

Microwave-Assisted Michael Addition of Sulfonamides to α,β-Unsaturated Esters: A Rapid Entry to Protected β-Amino Acid Synthesis

Abstract: An efficient, clean and very simple procedure for the synthesis of protected β-amino acids is described. Michael addition of sulfonamides to α,β-unsaturated esters in the presence of K2CO3 and tetrabutylammonium bromide (TBAB) under microwave irradiation affords the title compounds in good to high yields and short reaction times. This new method affords protected β-amino acids in high yields and short reaction times.

Michael addition of phthalimide and saccharin to α,β-unsaturated esters under solvent-free conditions

Abstract: An efficient, clean and simple procedure for the Michael addition of phthalimide and saccharin to various α,β-unsaturated esters in the presence of tetrabutylammonium bromide (TBAB) and 1,4-diazabicyclo[2,2,2]octane (DABCO) under solvent-free conditions is described. By this method, the Michael adducts are obtained in good to excellent yields in short reaction times under thermal and microwave conditions.

2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate as an efficient coupling reagent for the amidation and phenylhydrazation of carboxylic acids at room temperature

Abstract: The synthesis of amides and phenylhydrazides from the reaction of corresponding carboxylic acids with primary aliphatic, aromatic amines or phenylhydrazine in the presence of triethylamine or diisopropylethyl amine as a base using 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU) proceeds smoothly under mild conditions to afford the corresponding amides or phenylhydrazides in good to high yields in ethyl acetate at room temperature.

Preparation and operating conditions for cobalt cerium oxide catalysts used in the conversion of synthesis gas into light olefins

Abstract: Cobalt cerium oxides, prepared using a co-precipitation procedure, were studied as catalysts for the conversion of synthesis gas to light olefins (C2-C4). Specifically, we studied the effect of a range of preparation variables, including the molar ratio of the [Co]/[Ce] of the precipitation solution, ageing time and calcination temperature. In addition, the effects of supports and promoters on the catalysts’ activity and selectivity and a range of reaction temperatures using synthesis gas with different H2/CO molar feed ratios were investigated. The catalyst containing a molar ratio of 80% Co and 20% Ce, aged for 2 h, supported with 15 wt% SiO2 without any promoter, at an operating temperature of 450 °C and an H2/CO feed ratio of 2/1 (GHSV = 4500 h−1), performed optimally for the conversion of synthesis gas to light olefins. The characterization of both the precursors and the calcined catalysts by powder X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller specific surface area measurements and thermal analysis methods, including TGA and DSC, show that all the preparation variables influenced the catalyst precursor structure.

Quantitation of ranitidine in pharmaceuticals by titrimetry and spectrophotometry using potassium dichromate as the oxidimetric reagent

Abstract: Four new methods are described for the determination of ranitidine hydrochloride (RNH) in bulk drug and in formulations employing titrimetric and spectrophotometric techniques and using potassium dichromate as the oxidimetric reagent. In titrimetry (method A), RNH is treated with a measured excess of dichromate in acid medium, and the unreacted oxidant is back titrated with iron(II) ammonium sulfate. The three spectrophotometric methods are also based on the oxidation of RNH by a known excess of dichromate under acidic conditions followed by the determination of surplus oxidant by three different reaction schemes. In one procedure (method B), the residual dichromate is treated with diphenylcarbazide and the absorbance measured at 540 nm. Calculated amount of iron(II) is added to residual dichromate and the resulting iron(III) is complexed with thiocyanate and measured at 470 nm (method C). Method D involves reduction of unreacted dichromate by a calculated amount of iron(II) and estimation of residual iron(II) as its orthophenanthroline complex after raising the pH, and measuring the absorbance at 510 nm. In all the methods, the amount of dichromate reacted corresponds to the drug content. The experimental conditions are optimized. The titrimetric procedure is applicable over 5–10 mg range. In spectrophotometric methods, Beer’s law is obeyed in the ranges 5–50, 5–80, and 10–100 µg ml−1 for method B, method C, and method D, respectively. The methods were validated for accuracy, precision and recovery. The proposed methods were applied to the analysis of RNH in the tablet and the injection forms, and the results were in agreement with those obtained by the reference method.

Molecular modeling and QSAR analysis of some 4,5-dichloroimidazolyl-1,4-DHP-based calcium channel blockers

Abstract: The effects of the structural features of some 4,5-dichloroimidazolyl-1,4-dihydropyridine on their calcium channel antagonist activity have been studied using molecular modeling and quantitative structure activity-relationship analysis. Both symmetrical and asymmetrical dihydropyridine derivatives were used. AM1 semi-empirical quantum chemical calculation was used to find the optimum 3-D geometry of the molecules. Four different sets of descriptors, including chemical, topological, quantum chemical and substituent constant, were then calculated for each molecule. For each set of descriptors, the best multilinear QSAR equations were obtained by the stepwise variable selection method using leave-one-out cross-validation as selection criterion. Separate QSAR models were first obtained for symmetrical and asymmetrical derivatives, after which a general model was proposed for the entire set of molecules. This model has root mean square error of 0.45 and reproduces more than 82% of the variances in the calcium channel antagonist activity data. The sum of the negative charges, the energy of the highest occupied molecular orbital, molecular volume and the least negative charge were identified as the most significant descriptors.

Kinetic and mechanistic studies of oxidation of amine-N-polycarboxylates complexes of cobalt(II) by periodate ions in aqueous medium

Abstract: The kinetics and mechanism of interaction of periodate ion with [CoIIL(H2O)]2-n [L = trimethylenediaminetetraaceticacid (TMDTA)] and ethylene glycol bis(2-aminoethyl ether) N,N,N’,N’-tetraaceticacid (EGTA) have been studied spectrophotometrically by following an increase in absorbance at λmax = 550 nm in acetate buffer medium as a function of pH, ionic strength, temperature, various concentration of periodate and [CoIIL(H2O)]2-n under pseudo-first order conditions. The experimental observations have revealed that the intermediates having sufficiently high half life are produced during the course of both the reactions which finally get converted into a corresponding [CoIIIL(H2O)]3-n complexes as a final reaction product. The reaction is found to obey the general rate law Rate = (k2 [IO4 −] + k3 [IO4 −]2) [CoIIL(H2O)]2-n. This rate law is consistent with a four step mechanistic scheme (vide supra) where electron transfer proceeds through an inner sphere complex formation. The value of rate constant k2 is independent of pH over the entire pH range which suggest that unprotonated form of [CoIIL(H2O)]2-n is the only predominant species. The value of k2 is invariant to ionic strength variation in both the systems. The value of k3 is also found to be almost invariant to ionic strength in case of [CoIITMDTA(H2O)]2−-[IO4]− system but it decreases considerably in case of [CoIIEGTA(H2O)]2−-[IO4]− system with the corresponding decrease in ionic strength. The activation parameters have been computed and given in support of proposed mechanistic scheme.

Highly Regioselective N-Alkylation of Benzotriazole under Solvent-Free Conditions

Abstract: An efficient, simple and solvent-free method for highly regioselective N-alkylation of benzotriazole in the presence of SiO2, K2CO3 and tetrabutylammonium bromide (TBAB) under thermal and microwave conditions has been described. In this method, 1-alkyl benzotriazoles were obtained regioselectively in moderate to high yields and short reaction times.

Synthesis and calcium channel antagonist activities of new derivatives of dialkyl 1, 4- dihydro -2, 6-dimethyl-4- (5-phenylisoxazol-3-yl) pyridine-3,5-dicarboxylates

Abstract: The new analogues of nifedipine, in which 2-nitrophenyl group at position 4 is replaced by phenylisoxazolyl substituent, were synthesized. The symmetrical dialkyl 1,4-dihydro-2,6-dimethyl-4-(5-phenylisoxazol-3-yl)pyridine-3,5-dicarboxylates were prepared by classical Hantzsch condensation, and the asymmetrical analogues were synthesized using a procedure reported by Dagnino that involved the condensation of alkyl acetoacetate with alkyl 3-aminocrotonate and 5-phenylisoxazole-3-carboxaldehyde. The structure of all compounds was confirmed by IR, 1H NMR and Mass spectra. In vitro calcium channel antagonist activities were evaluated as calcium channel antagonists using the high K+ concentration of guinea-pig ileum longitudinal smooth muscle (GPILSM) assay. These compounds exhibited moderate calcium antagonist activity (IC50 = 10−7 to 10− 5 M range) relative to the reference drug nifedipine (IC50 = 1.10 ± 0.40 × 10−8 M).

The effect of atomic hydrogen adsorption on single-walled carbon nanotubes properties

Abstract: We investigated the adsorption of hydrogen atoms on metallic single-walled carbon nanotubes using ab initio molecular dynamics method. It was found that the geometric structures and the electronic properties of hydrogenated SWNTs can be strongly changed by varying hydrogen coverage. The circular cross sections of the CNTs were changed with different hydrogen coverage. When hydrogen is chemisorbed on the surface of the carbon nanotube, the energy gap will be appeared. This is due to the degree of the sp3 hybridization, and the hydrogen coverage can control the band gap of the carbon nanotube.

Molecular iodine-catalyzed efficient n-cbz protection of amines

Abstract: An efficient and selective protection of various structurally and electronically divergent aryl and aliphatic amines with Cbz-Cl in the presence of a catalytic amount of molecular iodine (2 mol%) in methanol with high yields at ambient temperature is presented.

Reductive amination of aldehydes with sodium borohydride and lithium aluminum hydride in the presence of lithium perchlorate

Abstract: A one-pot high yielding reductive amination of aldehydes with primary and secondary amines using LiClO4/NaBH4 and LiClO4/LiAlH4 as reducing agents in diethyl ether is described.

Solid phase extraction and flame atomic absorption spectroscopic determination of trace amounts of iron(iii) using octadecyl silica membrane disks modified with 2-mercaptopyridine-1-oxide

Abstract: A simple and selective method for rapid extraction and determination of trace amounts of iron(III) using octadecyl-bonded silica membrane disks modified with 2-mercaptopyridine-1-oxide and flame atomic absorption spectroscopy is presented. The factors influencing extraction efficiency were evaluated, including the nature of the counter anion, pH of the sample solution, amount of ligand, flow rate of the sample and type of stripping solution. The maximum capacity of the membrane disk, modified by 10 mg of the ligand, was found to be 926 ± 6 μg of iron(III). The breakthrough volume was greater than 2500 ml. Iron(III) was completely recovered (>99%) from water with a preconcentration factor of more than 166. The limit of detection of the proposed method was 0.63 ng ml−1. The various cationic interferences had no effect on the recovery of iron(III) from the binary mixtures. The proposed method was applied to the determination of iron(III) from three different water samples.

An efficient protocol for acetalization of carbonyl compounds using zr(hso4)4 at room temperature under solvent-free conditions

Abstract: Zr(HSO4)4 as a solid acid was applied for the acetalization of carbonyl compounds, at room temperature, under solvent-free conditions with good to excellent yields. The low cost and availability of the reagents, versatile procedure and easy work-up make this method attractive for the organic synthesis of these compounds.

Comparison of techniques for the extraction of the hypotensive drugs geniposidic acid and geniposide from eucommia ulmoides

Abstract: The extraction of geniposidic acid and geniposide from Eucommia ulmoides was carried out by Soxhlet extraction, enzyme-assisted aqueous extraction, semi-bionic extraction and supercritical fluid extraction techniques and the extracts were analyzed by high performance liquid chromatography. The results showed that the best methods for extraction of geniposidic acid and geniposide are enzyme-assisted aqueous extraction and semi-bionic extraction. Compared with various extraction methods, the semi-bionic extraction was more efficient, yielding the highest amount of geniposidic acid and geniposide. In semi-bionic extraction, no organic solvent was used. Semi-bionic extraction was performed at the same pH as that of the human body. The results indicated that semi-bionic extraction was the best method for large-scale efficient extraction of geniposidic acid and geniposide from plant materials. The supercritical fluid extraction process required more time than the other methods, and gave the lowest yields of geniposidic acid and geniposide.

A New Diclofenac Membrane Sensor Based on Its Ion Associate with Crystal Violet. Application to Diclofenac Determination in Urine and Pharmaceuticals

Abstract: A novel diclofenac ion-selective electrode has been prepared and used in pharmaceutical analysis. The ion-associate of diclofenac with basic dye (crystal violet) was used as the membrane carrier. Among the four different solvent mediators tested, dibutylphthalate (DBP) exhibited proper behavior including the Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of 59 ± 1 mV decade−1 for diclofenac in the concentration range 5.0 × 10−5-5.0 × 10−2 M with the limit of detection of 2.5 × 10−5 M. The electrode displays good sensitivity with the respect to a number of common inorganic and organic species. It can be used in a pH range of 6–11. The membrane sensor was successfully applied to the determination of diclofenac in capsules and for its recovery from urine samples.

Effect of two isomeric tetrapyrazolyl ligands on the catalytic oxidation of 3,5-di-tert-butylcatechol

Abstract: Copper(II) salts were combined with a tetrapyrazolyl ligand ({N,N,N’,N’-tetrakis-[(3,5-dimethylpyrazol-1-yl)methyl)-1,4-phenylenediamine}L1 or {N,N,N’,N’-tetrakis-[(1,5-dimethylpyrazol-3-yl)methyl)-1,4-phenylenediamine}L2) and assessed as oxidation catalysts. The corresponding dioxygen complexes were generated in situ by mixing the copper salt and the pyrazolyl donor ligand in air. The oxidation of 3,5-di-tert-butylcatechol (DTBC), which affords 3,5-di-tert-butylquinone (DTBQ), was studied. The reaction rate was found to depend essentially on the nature of the junction linking two pyrazolyl neighbours.

H-point standard addition method for simultaneous determination of cobalt(II) and zinc(II) ions

Abstract: The H-point standard addition method (HPSAM) was applied to the simultaneous determination of zinc(II) and cobalt(II). This method is based on the difference in the absorbance of methylthymol blue complexes of Zn(II) and Co(II) at pH 6 using different wavelength pairs. The results showed that Zn(II) and Co(II) can be determined simultaneously with concentration ratios of 20:1 and 1:7.5. Under working conditions, the proposed method was successfully applied to the simultaneous determination of zinc and cobalt in synthetic, drinking water and vitamin samples.

Hydrated Ferric Perchlorate, Fe(ClO4)3.XH2O in Organic Synthesis. A Short Review

Abstract: In this short review, we wish to present an overview of the applications of hydrated, ferric perchlorate, Fe(ClO4)3.XH2O as an available and inexpensive reagent amd catalyst in organic synthesis.

Catalytic effects of some Keggin-type heteropoly acids and polyoxometalates on selective nitration of phenols

Abstract: Catalytic amounts of heteropoly acids and polyoxometalates promoted mononitration of phenolic compounds using iron(III) nitrate nonahydrate and bismuth(III) nitrate pentahydrate in dichloromethane at room temperature. Tungstophosphoric acid cesium salt, Cs2.5H0.5PW12O40, in a heterogeneous phase, exhibited significant rate enhancement of reactions as well as ortho selectivity without over-nitration and oxidation byproducts.

Synthesis and immunomodulatory activity of some novel amino acid germinates

Abstract: Amino acid germanate compounds are synthesized by the chemical reaction of germanium dioxide with a selected amino acid in the presence of an alkali medium at a suitable elevated temperature. Amino acids included in the novel synthesis include histidine, methionine and glutathione. The study evaluated their effects on induction of interleukin-12 and interferon-γl in Swiss albino Webster rats. The new germanium compounds, especially bis-methionino germanate, are considered as good interferon inducer that significantly enhance the immunologic function.

Spectrophotometric determination of trace amounts of beryllium using 1,8-dihydroxyanthrone as a new chromogenic reagent

Abstract: A simple, rapid, and sensitive spectrophotometric method for the trace level determination of beryllium based on the formation of a 1:2 complex with anthralin (1,8-dihydroxyanthrone) as a new reagent is developed. A spectrophotometric method was used to determine the acidity constant and stepwise proton dissociation of the reagent. The experimental conditions for determining beryllium including the influences of pH, reagent concentration and time were evaluated and optimized. Under the optimum experimental conditions, the molar absorptivity of the complex is 0.47 × 104 l mol−1 cm−1 at 545 nm. Calibration graph was linear in the range of 0.04–1.04 μg ml−1 with a detection limit of 0.012 μg ml−1 and a %RSD of 0.43%, for 5 replicate determinations at 0.48 μg ml−1 of Be(II). The interferring effect of some cations and anions was also studied. The method was applied for the determination of beryllium in beryl, silicate rock and alloys. Ethylenediaminetetraacetic acid (EDTA) was used for masking interfering ions.

Electrocatalytic oxidation of methanol on a glassy carbon modified electrode by bis(1,2-phenylenediamine) nickel(ii) complex

Abstract: Electrocatalytic oxidation of methanol on a glassy carbon electrode coated with Ni(II)-(1,2-phenylendiamine)2 (GC/NiOPD), conditioned by the potential recycling in a potential range of 100–650 mV (vs. SCE) is studied by cyclic voltammetry in an alkaline medium (0.10 M NaOH). The results show that the NiOPD layer formed at the surface of the electrode behaves as an efficient electrocatalyst for the oxidation of methanol in the alkaline medium via the Ni(III) species with a cross exchange reaction occurring throughout the layer at a low concentration of methanol. The effects of various parameters such as potential scan rates, methanol concentration and NiOPD surface concentration on the electro-oxidation of methanol are also investigated.

Deprotection of trimethylsilyl ethers to corresponding alcohols promoted by silica chloride: a heterogeneous and eco-friendly protocol

Abstract: Silica chloride as an efficient solid acid can serve as an eco-friendly and high-capacity reagent for the deprotection of trimethylsilyl ethers to their corresponding alcohols under mild and heterogeneous conditions. The yields are excellent and the procedure is simple and convenient, with the higher catalytic efficiency of a heterogeneous system.