Showing papers in "Monatshefte Fur Chemie in 1995"

The ionic product of water in highly concentrated aqueous electrolyte solutions

Abstract: The ionic product of water, {Mathematical expression}, has been determined in aqueous NaCl (0.5-5.0 M), KCl (3.0 M), NaNO3 (3.0 and 5.0 M), and KNO3 (2.5 M) at 25 °C from high-precision potentiometric titrations carried out in cells with liquid junction using either glass or hydrogen electrodes. Measurements of Kw provide a set of self-consistent data that can be used in the estimation of activity coefficient changes and liquid junction potentials in the study of extremely concentrated electrolyte solutions. Where comparison is possible, results obtained by hydrogen electrode measurements are in excellent agreement (ca ± 0.005 in pKw) with other reliable experimental values and the predictions of the Pitzer activity-coefficient model. The glass electrode results are, as expected, routinely lower (by 0.03-0.05 pKw units), owing to interference by Na+ ions. This effect virtually disappears in solutions of potassium salts. Comparison of the experimental results with the Pitzer predictions shows that knowledge of the ternary interaction parameters is essential to account for specific ionic effects in the concentration dependence of pKw.

Inhibition of the corrosion of iron by oxygen and nitrogen containing compounds

Abstract: Corrosion inhibition by quinine, ephedrine, brucine, cinchonine, codeine, and harmaline with respect to the dissolution of iron in 2M sulphuric acid was measured using electrochemical methods Polarization curves indicated that these compounds act as mixed-type inhibitors,ie both the cathodic and anodic curves are affected The observed effect follows theTemkin adsorption isotherm The effect of the different structural features of these compounds on their inhibition efficiency has been studied Results indicate that the rate of corrosion of iron increases with increasing temperature over the range 30–50 °C both in the absence and in the presence of inhibitors Some thermodynamic functions were also computed and are discussed

The synthetic microporous tellurites Na2[Me 2(TeO3)3]·3H2O (Me=Zn, Co): Crystal structure, De- and rehydration, and ion exchange properties

Abstract: The crystal structure investigations of hydrothermally synthesized Na2[Zn2(TeO3)3]·3H2O (NZT) and Na2[Co2(TeO3)3]·3H2O (NCT) using single-crystal X-ray diffraction methods revealed a microporous framework structure of hexagonal symmetry with tubular channels running parallel to the c-axis (zemannite type). The statistically occupied sites of the Na+ ions and H2O molecules within the channels as well as the channel dimensions indicate a possible zeolitic behaviour of the compounds. Thermoanalytical investigations ofNZT show an irreversible breakdown of the framework already atT=533 K caused by complete dehydration. A reversible rehydration was solely observed for partially dehydratedNZT (T⩽493 K); a remarkable ion exchange rate from alkali-chloride solutions was observed only for Li+. Both the rehydration and the ion exchange properties are characterized by relatively long reaction times. The relatively poor zeolitic properties compared to typical zeolitic compounds could be related to the stereochemical activity of the lone-pair electrons of the Te4+ atoms which claim a certain volume within the channels and constrict the effective channel dimension to a free diameter of approximately 2.5 A.

Diethyl Acetonedicarboxylate - a Precursor for the Synthesis of New Substituted 4-Aminoquinolines and Fused 4-Aminopyridines*

Abstract: The reaction of cyclic enaminonitriles1 with diethyl acetonedicarboxylate (2) affords fused 4-amino-3-ethoxycarbonyl-2-ethoxycarbonylmethyl-pyridines4. The course of the reaction and the yield of cyclic products were promoted by tin(IV)chloride. N-substituted diethyl 3-aminoglutaconates3 seem to be intermediates of the cyclization reaction.

Mode of coordination and stability of Cu(II) and Zn(II) complexes with adenosine, deoxyadenosine, cytidine and deoxycytidine

Abstract: Stability constants of Cu(II) and Zn(II) complexes with nucleosides have been determined from a computer analysis of potentiometric titration results. Spectral investigations prove that in acidic solution adenosine coordinates to Cu(II)via its N1 or N7 atoms, while atpH>7 only N7 is involved. Similar interactions are observed for dAdo complexes. Spectral and potentiometric studies suggest that Zn does not form stable complexes with dAdo. In the case of cytidine and deoxycytidine, the preferred site of coordination is the N3 atom of the nucleoside. Oxygen atoms from the carbonyl groups are not involved in Cu(II) or Zn(II) coordination. The results of the spectral investigation have excluded the ribose and deoxyribose moieties of all studied ligands from participation in the interactions. In general, the mode of coordination of nucleosides and deoxynucleosides with Cu(II) and Zn(II) has been found analogous.

Chemical interactions between 2-mercaptobenzazoles and π-acceptors

Abstract: 2-Mercaptobenzazoles (1a–c) interact with several π-acceptors such as tetracyanoethylene (TCNE) 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL) dicyanomethyleneindane-1,3-dione (CNIND), 2,3-dicyano-1,4-naphthoquinone (DCNQ), 9-dicyanomethylene-2,4,7-trinitrofluorene (DTF), and 2,3-dichloro-1,4-naphthoquinone (DCHNQ)via the formation of charge-transfer (CT) complexes to yield various heterocyclic compounds.

Synthesis and thermal decomposition of 3-aroyl-4-aryl-2-pyrazolines

Abstract: 3-Aroyl-4-aryl-2-pyrazolines (21–40) have been synthesized by the reaction of α,β-unsaturated ketones (1–20) with diazomethane. These 2-pyrazolines gave β-methyl-α,β-unsaturated ketones (41–46) on thermal denitrogenation.

Synthesis and reactions of 2,3-dimethylfuro[3,2-c]pyridines

Abstract: A number of substituted 2,3-dimethylfuro[3,2-c]pyridines was synthesized. 3-(4,5-Dimethyl-2-furyl)propenoic acid (1) was converted to the acid azide2, which in turn was cyclized to give 2,3-dimethyl-5H-furo[3,2-c]pyridine-4-one (3) by heating at 240°C in Dowtherm. The pyridone3 was chlorinated with phosphorus oxychloride to give4, which was reduced with zinc and acetic acid to 2,3-dimethylfuro[3,2-c]pyridine (5). Treatment of4 with several secondary heterocyclic amines led to compounds6a–6c. Reaction of pyridone3 with phosphorus pentasulfide rendered the thione7, which was methylated to8a. The 4-methoxy derivative8b was obtained from4 with sodium methoxide. 2,3,5-Trimethylfuro[3,2-c]pyridine-4-one (9) was obtained by reaction of3 with methyl iodide.

Synthesis of some new dispiro[dipyrano-(2,4′:6,4″)bidithiolo(4,5-b:4′,5′-e)-4,8-benzoquinones]

Abstract: The one pot reaction of acetylacetone, CS2, and tetrabromobenzoquinone in a 2:2:1 molar ratio affords 2,6-di-(1-acetyl-2-oxopropylidene)-bidithiolo-(4,5-b:4′5′-e)-4,8-benzoquinone (3) which was allowed to react with some active methylene reagents in a 1:2 molar ratio to give the dispiro derivatives5–11. The reaction is assumed to proceedvia a hydrolysis of the two acetyl groups in compound3 followed by a nucleophilic addition of the active methylene reagents at the two ethylenic bonds and subsequent cyclization.

Synthesis of pyrrolo[2′,3′:4,5]furo[3,2- c ]pyridines

Abstract: The synthesis of pyrrolo[2′,3′:4,5]furo[3,2-c]pyridines (6a–6d) is described. Substituted pyridones (4a–4d) were prepared by thermic cyclization of the corresponding acyl azides (3a–3d), available from substituted propenoic acids (2a–2d)via a one pot reaction with ethyl chloroformate and sodium azide. Upon treatment with phosphorus oxychloride the pyridones (4a–4d) gave substituted chloropyridines (5a–5d) which were reduced with zinc in acetic acid to yield the title compounds (6a–6d).

Synthesis and properties of fringelite D (1,3,4,6,8,10,11,13-octahydroxy-phenanthro[1,10,9,8, o , p , q , r , a ]perylene-7,14-dione)

Abstract: Fringelite D was synthesized from 1,3,6,8-tetramethoxyanthracen-9-olvia two different efficient routes. The first one involved demethylation and subsequent dimerization. The other one started with dimerization to yield octamethylfringelite D and subsequent demethylation. The starting material was prepared in four steps from commercially available educts, the key step being a benzamideortho-lithiation. The spectroscopic properties of fringelite D were measured and are discussed. The dissociation, deprotonation, and protonation equilibria of fringelite D were characterized by their respectivepK values in ground and excited states and compared with those of hypericin. Homo- and heteroassociation properties of fringelite D were found to be similar to those of hypericin.

Hydrogen bonding in 2-hydroxybenzoic, 2-hydroxythiobenzoic, and 2-hydroxydithiobenzoic acid. A structural and spectroscopic study

Abstract: X-ray structural data are reported for 2-hydroxythiobenzoic acid (T=200 K;P21/a;a=14.903(5) A,b=5.203(3) A,c=9.114(6) A, β=92.40(4)°;Z=4;R=0.049) and 2-hydroxydithiobenzoic acid (T=297 K;P21/a;a=14.416(3) A,b=13.447(3) A,c=3.947(1) A, β=90.96(2)°;Z=4;R=0.047). In 2-hydroxythiobenzoic acid, each two molecules form cyclic dimersvia S-H...O=C hydrogen bonds, analogous to the association pattern of 2-hydroxybenzoic acid. In 2-hydroxydithiobenzoic acid, the molecules are linked to chains by S-H...O(H)-C hydrogen bonds. Solid state IR, and solution IR and NMR spectroscopic data of 2-hydroxybenzoic acid, 2-hydroxythiobenzoic acid, and 2-hydroxydithiobenzoic acid are summarized. The main characteristics of the intramolecularly associated phenolic O-H groups of the three title compounds are\(\bar v_{OH} = 3230, 3120, 2750 cm^{--1} \) for the solids,\(\bar v_{OH} = 3210, 3185, 2945 cm^{--1} \) for solutions (CCl4), and δOH=10.21, 10.53, 12.20 ppm for solutions (CCl4:CDCl3=5:1).

Characterization of Copper(II), nickel(II), cobalt(II) and palladium(II) complexes of vicinal oxime-imine ligands; induced chelate isomerism in the same molecule of the nickel(II) complex

Abstract: Metal complexes of the title ligands were characterized in order to determine the factors influencing the stability of chelate isomerism in the same molecule. The ligands were prepared by 1:1 condensation of isonitrosoacetylacetone (Hiso) with eithero-aminophenol (H2 isoaph),p-aminophenol (H2 isopph), or aniline (Hisoanil). The following complexes have been synthesized: [(isoaph)Cu]4, (Hisoaph)2Co, (Hisopph)2 M·nH2O (M=Ni(II), n=2;M=Pd(II), n=0;M=Co(II), n=2), [(isopph) Cu·H2O]2, and (isoanil)2 M (M=Ni(II), Cu(II), Co(II), or Pd(II)). Both chelate rings in these metal complexes are five-membered. Transimination of one −C=N−C6H5 group to −C=NH in (isoanil)2Ni produced a six-membered chelate ring in (isoim)Ni(isoanil). The induced chelate isomerism is ascribed to intermolecular hydrogen bonding of the imino-hydrogen and the basic nitrogen of the same six-membered chelate ring of an adjacent square planar molecule. Other types of hydrogen bondings with the oximato oxygen (intra- or intermolecular) favour the formation of five-membered chelate rings. Analytical, spectroscopic, and magnetic moment data are in accordance with the suggested formulations.

Infrared study of solvent-solute interactions of 1-substituted 2-pyrrolidinones and related compounds

Abstract: The wavenumbers of the carbonyl stretching vibrations of 2-pyrrolidinone (P), 1-methyl-2-pyrrolidinone (MP), 1-isopropyl-2-pyrrolidinone (IPP), 1-(2-hydroxyethyl)-2-pyrrolidinone (HEP), 2-oxobenzothiazole (OBT), and 3-octyl-2-oxobenzothiazole (OOBT) were measured inn-hexane/CDCl3, acetonitrile/D2O, methanol/D2O, and 2-butoxyethanol/D2O mixtures and compared with similar data for 1-cyclohexyl-2-pyrrolidinone (CHP) and dimethylacetamide (DMA). The dependencies of the wavenumbers on the mole fraction of the less polar cosolvent in binary mixtures allow a distinction and assignment of all species resulting from weak solute-solvent and solute-solute interactions. The slopes of the dependencies of the wavenumbers on the mole fraction for similar intermolecular species inn-hexane/CDCl3 mixtures correlate well with the relative hydrogen bond basicities (i.e. hydrogen bonding abilities with phenol) and reveal that the solvent sensitivities significantly depend on the steric requirements in the vicinity of the C=O group. On the other hand, the slopes of similar dependencies in acetonitrile/D2O mixtures are proportional to the electron donating effects of alkyl groups attached to the nitrogen atom of the pyrrolidinone ring. In the case of mixtures formed by two strongly hydrogen bonding cosolvents (alcohols/D2O), a competitive equilibrium occurs between the hydrogen bonding tendency of both cosolvents and 1-substituted 2-pyrrolidinones. In solutions of 1-substituted 2-pyrrolidinones in water-rich 2-butoxyethanol/D2O mixtures, microheterogeneous domains occur before classic mixtures of two polar liquids are formed.

Cyclic voltammograms of iron and C-steels in oxalic acid solutions and investigation of the effect of phenyl phthalimide as corrosion inhibitors

Abstract: The electrochemical behaviour of Fe and C-steel samples in oxalic acid solutions was studied by the use of cyclic voltammetry. Two peaks were observed; the first one was the anodic peak and the second one an unexpected reductive dissolution peak which could be observed in the cathodic branch of cyclic voltammograms of all electrodes studied. The carbon content was found to increase the active dissolution of steels and to decrease their tendency towards passivation. The inhibitive efficiency of phenyl phthalimide derivatives on the active dissolution of Fe and steel samples in 0.1M oxalic acid were investigated.

Reaction of 3-phenyl-5-aminopyrazole with carbon disulfide: A novel synthesis of 3-(3′-phenylpyrazol-5′-yl)-4-phenylpyrazol-2-thione as well as of pyrazolo[3,4- d ]thiazole and pyrano[2,3- d ]thiazole derivatives

Abstract: 3-Phenyl-5-aminopyrazole (1) reacts with carbon disulfide, followed byin situ reaction with α-haloketones3a–c, to afford5,7a, and7b, respectively. Compounds5 and7 were further utilized for the formation of heterocycles and their fused derivatives.

Total syntheses and antimicrobial activities of pyridine alkaloids from Rubiaceae

Abstract: Pyridine alkaloids from Rubiaceae were prepared by palladium-catalyzed cross-coupling reactions of methyl 5-bromonicotinate (6) with various organometallic reagents. Baker's yeast reduction of the ketone8 gave the levorotatory alcohol (S)-1. On this basis, the naturally occurring alcohol (+)-1 was assigned to be (R)-configurated. The alkaloids1 and4 show weak antimicrobial activities.

Neue 1H-Tetrazol-5-thiol-Derivate als Pestizide, 2. Mitt. Cyanimidodithiokohlensäureester

Abstract: Ausgehend von 1H-Tetrazol-5-thiol-Derivaten wurden — abhangig von den Reaktionsbedingungen — Tetrazole und Tetrazoline hergestellt. Der Heteroring wurde mit Cyanimidodithiocabonaten entweder durch -S-CH2-S- oder durch -S-CH2-N=- Reste substituiert. Zahlreiche Derivate zeigten Fungizidaktivitat.

Ritigalin, a new thiocarbonic acid imide fromGlycosmis species

Abstract: From the lipophilic leaf extracts ofGlycosmis mauritiana andG. parviflora (Rutaceae-Aurantioideae), the novel thiocarbonic acid derived imide ritigalin was isolated as major component by MPLC and TLC. The structure was elucidated by spectroscopic evidence (1H,13C NMR; MS; IR; UV).

Synthesis of new fused heterocycles by annelation of thiopyrano[4′,3′:4,5]thieno[2,3- c ]pyrimidines

Abstract: Appropriately substituted thieno[2,3-c]thiopyrans (2, 3, 5, 6, 10, 11) were converted into 1,5,6,8-tetrahydro-2H-thiopyrano[4′,3′:4,5]thieno[2,3-d]pyrimidin-4(3H)-ones (4, 7, 12). These in turn were used as key intermediates for annelations of thiazolo and 1,3-thiazino moieties to yield the tetracyclic target structures7, 8, 9, and13, derived from two novel heterocyclic ring systems.

Inhibition of copper corrosion by arylazotriazoles in nitric acid solution

Abstract: Summary. A study has been made to investigate the effect of some azoheterocyclic dyes of the type 3-arylazo 1,2,4-triazole (AT) on the corrosion of copper exposed to 0.5M nitric acid solution at different temperatures and at different AT concentrations. Using potentiodynamic polarization and Tafel electrochemical methods, it can be shown that AT compounds are good inhibitors of copper corrosion in HNO 3 solution. The kinetic and thermodynamic parameters of the inhibited system were determined. The high inhibition efficiency of these compounds may be due to the adsorption of the additive itself and/or the adsorption of the formed Cu(II)-AT complexes at the polarized electrode interface. Cathodic polarization measurements showed that AT dyes are predominantly cationic

Synthesis of functionalized 3,4-dihydro-2H-pyrans by hetero —Diels-Alder reaction of an enaminoketone with enol ethers

Abstract: The hetero —Diels-Alder reaction of 3-(N-acetylbenzylamino)-2-cyano-1-phenyl-2-propen-1-one (3) with enol ethers (4) leads to diastereoisomeric cycloadducts5 and6 in good yields. The structure of the products is discussed in terms of configuration and preferred conformation. Reaction of5 with sulfuric acid yields 3-benzoyl-1,2-dihydropyridin-2-one (7).

Synthese und Geruch von (Z)-Dehydro-homo-β-santalol

Abstract: Guided by molecular modeling studies, the synthesis of the title compound is described. The organoleptic evaluation proved the predicted real sandal like odour of (Z)-dehydro-homo-β-santalol.

The scandium(III) ion as a template for the synthesis of a hexaazaSchiff base macrocyclic ligand

Abstract: The condensation of 2,6-diacetylpyridine andm-phenylenediamine in the presence of scandium(III) perchlorate as a template agent affords a new 20-membered macrocyclic complex of formula ScL(ClO4)3·4H2O, whereL is Me4bzo2pyo2[20]octaene-N6

A new synthesis of thes-triazolo[1,5-a]pyridine ring system

Abstract: A novel and efficient synthesis ofs-triazolo[1,5-a]pyridines was elaborated by reacting 1,2-diaminopyridinium salts with aldehydes.

Synthesis and efficiency of 5-(2-hydroxyphenylazo)-indazoles as new reagents for the determination of vanadium

Abstract: Four azo compounds based on 5-aminoindazole have been synthesized and characterized by elemental analysis as well as different spectroscopic techniques. The potentiality of the prepared compounds as new chromophoric reagents for the spectrophotometric determination of VO 2 + was studied by extensive investigation of optimum conditions favouring the formation of the coloured complexes. The effect of interfering ions on the determination of VO 2 + was investigated.Beer's law is obeyed in the concentration range of 1.0–12 µg/ml. The detection limits are 0.8, 0.9, 0.7, and 1.1 µg/ml using reagent1a,1b,1c, and1d, respectively. The standard deviations of the proposed method are 0.098, 0.111, 0.089, and 0.078. The molar absorptivities are 5.8, 6.7, 6.1, and 8.2×103l·mol−1·cm−1 for1a–d, respectively, whereasSandell sensitivities are found to be 0.0187, 0.0163, 0.0174, and 0.0146 µg·cm−2 using the same reagents. The ability of using these reagents as metallochromic reagents in complexon III titrations was also studied.

1,4-Diacyl-3-acylamino-5-aryl-4,5-dihydro-1H-1,2,4-triazoles: Ring closure products of aromatic carbaldehyde (diaminomethylene) hydrazones with acylating agents

Abstract: Treatment of aromatic carbaldehyde (diaminomethylene)hydrazones1 with hot acetic anhydride or benzoyl chloride affords 1,4-diacyl-3-acylamino-5-aryl-4,5-dihydro-1H-1,2,4-triazoles2. In contrast, a new type of 0,N-acetal with an 1,2,4-triazole substructure (3) is obtained from 4-pyridine-carbaldehyde (diaminomethylene)hydrazone (li) by using a similar reaction procedure. The structures of all novel compounds were confirmed by spectroscopic data (1H and13C NMR, MS, IR); some representative compounds were also studied by X-ray analysis.

Chiral nucleation@@@Chirale Nukleierung

Abstract: SummaryThe crystallization of agitated aqueous solutions of sodium chlorate and sodium bromate was nucleated with levo- or dextrorotatory crystal powders of sodium chlorate and sodium bromate to furnish new crystals with a high degree of chiroptical purity.ZusammenfassungDie Kristallisation aus agitierten wässrigen Lösungen von Natriumchlorat und-bromat wurde mittels levo- und dextrorotatorischem pulverförmigem Natriumchlorat und -bromat nukleiert. Es entstanden Kristalle mit einem hohen Grad an optischer Reinheit.

Synthesis and fluorescent properties of some new unsymmetricbis-benzothiazolyl furans and thiophenes

Abstract: Some newmono- andbis-benzothiazolyl compounds with furan or thiophene nuclei were synthesized by multistep reactions from the corresponding furan and thiophene aldehydes. The data obtained from emission spectra show a large influence of the benzothiazole rings on the relative quantum efficiency of the compounds under investigation.

Crystal structure of diaquatetrakis (μ-2,6-dichlorobenzoato-o,o′)dicopper(II)

Abstract: A new copper(II) complex of the formula [Cu(C7H3O2Cl2)2·H2O]2 crystallizes in the triclinic system (space group P\(\bar 1\)). The cell parameters area=7.267(3),b=10.687(3),c= 10.934(3) A, α=99.88(3), β=96.25(3), γ=94.78(3)°,V=827.1(5)A3,Z=1,Dc=1.853(1), andDm=1.85 Mg/m3. The two copper atoms in the molecule are held together by the four carboxylate groups of the organic ligands, and each copper atom is further bonded to a water molecule, resulting in a square pyramidal geometry. The Cu-O(carboxylate) distances are in the range of 1.955(2)-1.975(2)A, and Cu-O(water) and Cu-Cu distances are 2.166(2) and 2.605(1)A, respectively.