Synthesis and spectroscopic properties of soluble aza analogs of phthalocyanine and naphthalocyanine

The syntheses of aryl-substituted octaaza analogs of phthalocyanine — tetra-2,3-(4,5-diphenylpyrazino)porphyrazin and its vanadyl complex — and also of the vanadyl complex of tetra-2,3-(4-phenylquinolino)porphyrazin — a tetraaza analog of naphthalocyanine — are described. A modified singlestage method for the synthesis of the previously reported tetra-2,3-(5-tert-butylpyrazino)porphyrazin is put forward. The electronic absorption spectra of the compounds synthesized have been studied in organic solvents and acid media — in sulfuric acid solution and in organic solvents with the addition of phenol or trichloroacetic acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 58–63, January, 1993.     

Chain and monomolecular decomposition of hexogen in solutions

The decomposition of hexogen dissolved in alkylaromatic hydrocarbons, alcohols, ketones, ethers, chloroform, and some other solvents occurs via the chain mechanism. This mechanism is supported by slowing down of the reaction when inhibitors are added, the solvent deuterium kinetic isotope effect, and the dependence of the rate on the reactivity of the C—H bond in solvents. The chain reaction propagates through the transfer of a free valence from the primary N-radicals formed by N—NO₂ bond dissociation to the C-centered radicals of the solvent. The solvents are inert when the N—H bond dissociation energy is >380 or <200 kJ mol^–1, and hexogen decomposition in such solvents is monomolecular.     

Reaction of tetranitrodibenzo-18-crown-6 with sodium alkoxides

It is shown that the reaction of tetranitrodibenzo-18-crown-6 with sodium alkoxides in aprotic solvents at room temperature occurs with initial cleavage of the macroheterocycle and formation of an intermediate — substituted o-dinitrobenzene — whereas the reaction in protonated solvents occurs with substitution of the nitro groups. From among other derivatives of dibenzo-18-crown-6 containing azole rings linked to the benzene ring, only the furoxan-containing crown ether is cleaved under similar conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 37–40, January, 1989.     

Surface activity of amphiphiles in hydrogen fluoride — water solutions

Surface tension measurements were carried out in surfactant — hydrofluoric acid — water systems and surfactant — anhydrous hydrofluoric acid systems. Surface tension measurements show that surfactants in anhydrous hydrofluoric acid do not effect a detectable change in surface tension. Effects, known from other solvents, can only be observed when water addition takes place. The surface tension lowering, the free standard adsorption energy, and the maximum surface concentration of a surfactant increases with decreasing hydrofluoric acid concentrations. The space requirement of a separate surfactant molecule decreases at the phase border with decreasing hydrofluoric acid concentrations of the solvents. Simultaneously, the CMC values were changed to smaller surfactant concentrations.     

Diffusion control of the Diels—Alder reaction rate at elevated pressures

The influence of the temperature and external pressure on the rate of the Diels—Alder reaction between 9,10-dimethylanthracene and maleic anhydride was studied in the series of solvents with wide intervals of viscosity (0.3—43.2 mPa s), dielectric constant (2—38), and internal pressure (3—8.8 kbar). At a standard pressure these properties of the solvent exert a weak and irregular effect on the reaction rate constant and activation enthalpy and entropy. The effect of the external pressure on the rate constant was studied in a high-pressure (up to 1 kbar) optical cell in acetonitrile and silicon oil and in a barostat cell (up to 6 kbar, toluene, silicon oil). Close values of the activation volume were obtained in all solvents. In toluene the reaction rate increases smoothly in the whole pressure interval. In more viscous silicon oil a similar dependence is observed up to 3 kbar, and the reaction rate decreases sharply with the further increase in the pressure and viscosity because of the diffusion control of the process.     

Headspace analysis of chlorinated organic solvents in aerosol cans by gas chromatography

Summary A gas chromatographic (GC) method for the analysis of chlorinated solvents in chemical products in aerosol cans is described. Conditions for the sampling of chemical products from aerosol cans were optimized, so that the recovery of the solvents was better than 90%. Chlorinated solvents were identified by headspace GC—electron capture detection (ECD) as well as by GC — mass spectrometry. Headspace analysis employing the standard additions method and GC-ECD was used for the quantitation of chlorinated solvents. Analysis of 159 acrosol products, for various uses, revealed that 9% of these did not comply with the Danish Aerosol Regulations. The results of the study further indicated that aerosol products for haircare, paints and paint removers, and many others, can be formulated without chlorinated solvents.     

The effect of the solvents on the specific intramolecular C-H...N interactions studied by1H NMR spectroscopy

The analysis of the effect of the solvents on the proton chemical shifts in¹H NMR spectra of 2-vinyloxypyridine indicates that the C—H...N interaction of weak intramolecular hydrogen bond type hinders the formation of intermolecular hydrogen C—H...X and C-H... bonds. The protonating solvents reduce the intramolecular C—H...N interaction due to association with the N atom of the pyridine cycle.Translated fromIzvestiya Akademii Nauk. Seriya Khimieheskaya, No. S, pp. 1202–1204, May, 1996.     

Dielectric properties for the binary mixture of dimethylsuphoxide and dimethylacetamide with 2-nitrotoluene at microwave frequencies

The dielectric properties of various organic solvents and binary solvent mixtures at different temperatures over the frequency range of 10 MHz–20 GHz, are investigated using the time domain reflectometry technique, at various temperatures from 15 to 45 °C. These solvent mixtures—dimethylacetamide–2-nitrotoluene and dimethylsulphoxide–2-nitrotoluene as well as pure solvents display a Debye type dispersion. Their frequency-dependent dielectric properties can be summarized by the three parameters in the Debye equation: a static permittivity, permittivity at high frequency and a dielectric relaxation time constant. The free energy of activation for dipolar relaxation process and the Kirkwood correlation factor were determined using these fitting parameters, for these solvent systems at various temperatures. By using these dielectric parameters, the excess permittivity and excess inverse relaxation time is obtained. The static permittivity increases with increase in volume percentage of 2-nitrotoluene in dimethylacetamide as well as dimethylsulphoxide whereas the relaxation time decreases for both the systems.     

Temperature Dependence of Solubility for Ibuprofen in Some Organic and Aqueous Solvents

The thermodynamic functions—Gibbs energy, enthalpy, and entropy of solution—were evaluated from the solubilities of ibuprofen determined at several temperatures in the pure solvents: octanol, isopropyl myristate, chloroform, cyclohexane, and water. The organic solvent-saturated aqueous media and water-saturated organic solvents were also studied, except for cyclohexane. In aqueous media, the solubility was determined at pH = 7.4 and an ionic strength 0.15 mol-L^–1 (physiological values). The excess Gibbs energy and the activity coefficients of the solutes were also determined. The solubilities are higher in organic media such as chloroform and octanol than in aqueous media and cyclohexane.     

Solvatochromism of thiocyanato-tetraazamacrocycle-manganese(III) complexes

Summary Solvent effects on thecharge-transfer bands of a series of thiocyanato-tetraazamacrocycle-manganese(III) complexes are reported, and discussed in terms of the donor and acceptor (hydrogen-bonding) properties of the respective solvents. The piezochromic behaviour of one of these complexes is also described.

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Solvatochromie von Thiocyanato-Tetraazamakrocyclo-Mangan(III) — Komplexen

Zusammenfassung Die Auswirkung von Lösungsmitteleffekten auf diecharge-transfer — Banden einer Reihe von Thiocyanato-Tetraazamakrocyclo-Mangan(III) — Komplexen wird im Zusammenhang mit den Donor- und Akzeptoreigenschaften des Lösungsmittels diskutiert. Das piezochrome Verhalten eines der Komplexe wird beschrieben.

     

Methods for the isolation and characterization of constituents of natural products : XXI. Use of a celite-potassium methylate column for rapid preparation of methyl esters from microgram amounts of glycerides

In a convenient, rapid procedure, a very small column of potassium methylate — Hyflo Super-Cel is used to convert microgram amounts of glycerides to methyl esters. Transesterification is complete in hydrocarbon but not in chlorinated solvents or in CS₂. The methyl esters can be recovered in 92–95% yield if desired. Regardless of the solvent used, the recovered methyl esters are representative of the original fatty acid composition of the glycerides.     

Influence of Proton Transfer on the Formation of Hydrogen-Bonded Complexes of Higher Stoichiometry and on their Dissociation into Free Ions

Proton transfer in a given H-bond A—H—B—(H)A_–— H⁺—B—(H) considerably enhances the strength of the electron donor sites of the first partner and that of proton donor sites possibly present in the second one. This leads to the formation of complexes of higher stoichiometry of the type B— H⁺—(A^–—H—A--H—A--H--)or A^–---(H—B⁺—H----B—H—B—H----) where the self-association bonds are much strengthened. This is due to the high stability of the homoconjugated anions or cations in the corresponding ion pairs. In polar solvents like acetonitrile, the ion pairs may dissociate into free ions. The variety of the entities that can be formed necessitates a diversification of the quantitative concepts connected with the proton transfer process. Besides the average value x₁ of the fractions of the various complexes in the ionized form, other quantities are defined that can also be used in the case of partial dissociation: (1) the percentage of ionized base molecules and (2) the fraction of donor molecules AH ionized after direct interaction with B. A further characteristic used in this generalized treatment is the average number n of proton donor molecules perturbed by one base molecule. Examples of determinations of these various parameters from calorimetric, infrared, or NMR data from the literature are presented and new quantitative correlations established.     

Extraction of C60 from fullerene-containing carbon soots

Extraction of fullerene-containing carbon soots with various organic solvents has been studied at room temperature. Yields and compositions of toluene-soluble carbon soot fractions have been determined. Extracts of different carbon soot samples treated according to the toluene—trichlorobenzene—nitrobenzene scheme are studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1223–1225, July, 1995.The authors are grateful to E. B. Yagubskii and I. S. Krainskii for helpful discussion and help in the work.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-18705).     

Modification of the polytrimethylsilylpropine adsorption layer in open capillary columns

Modification of adsorption open capillary columns coated with polytrimethylsilylpropine (PTMSP) was experimentally studied. The modification of PTMSP by solvents (chlorobenzene, pentanol) and hot ethanol improves (up to 40%) the efficiency of capillary columns with a slight (3—7%) decrease in the retention factor.     

Towards a modellisation of the solvation energy in multi-component solvents. The interesting case of a charged solute imbedded in a polymer-containing electrolyte solution

In this paper we propose a mean-field theory to calculate the solvation free energy of a charged solute imbedded in a complex multi-component solvent. We considered a solvent made up of a mixture of small (electrolyte solution) and large (polymer) components. The presence of macromolecules ensures reduced mixing entropy among the different solvent components, an effect due to polymer connectivity. The reduced entropy favours strong preferential distribution of a particular solvent even in the presence of weak preferential solute–solvent interactions. In addition, two energy terms must be considered: (a) the interaction between the solute electrostatic potential and the electrolyte solution and (b) the formation of a polymer–solute interface. Because of the different dielectric permittivity of the solvent components, the electrolyte and polymer distribution functions are strongly coupled: ions, indeed, are more solvated in regions of higher local dielectric permittivity arising from the inhomogeneous mixing of solvent and polymer. We combined together the different energy terms in the framework of the de Gennes free energy functional for polymer solutions along with a generalised Poisson–Boltzmann equation developed for inhomogeneous dielectric media. Moreover, the preferential electrolyte solvation in regions of greater polarity was considered by an extension of the Born equation. Setting the polymer dielectric permittivity smaller than the solvent one and making null the specific polymer–solute interactions, we calculated enhanced electrolyte concentration and reduced polymer concentration near the solute surface on raising the solute surface charge density. The theory shows also the breakdown of the widely used separation between electrostatic and surface tension-dependent contributions to solvation energy when non-ideal mixed solvents are considered. In fact, according to the model, the surface tension of such mixed solvents strongly depends on the solute surface charge density: at high potentials the interfacial tension may increase rather than decrease on raising the polymer volume fraction. The theoretical results have been compared with experimental data on polymer+electrolyte solution surface tension and with solubility data of colloidal particles. The comparison evidences the complex behaviour of multi-component solvents going well beyond the trivial weighted average of the dielectric permittivity and surface tension of the isolated chemical components. Deviations from the simple behaviour predicted by an average picture of multi-component solvents could be understood by developing more sophisticated, but still simple, approaches like that proposed in this paper.Contribution to the Jacopo Tomasi Honorary Issue. This paper is dedicated to Jacopo Tomasi. I learned much of the difficult art of transforming complex problems into simple models after reading his early works on solvation energy.     

Beiträge zur Chemie der Pyrrolpigmente, 3. Mitt.1: Die NH-Tautomerie von substituierten Pyrromethenen: Protonenresonanzspektrometrische Untersuchungen

NMR-spectra of several pyrromethenes were measured at different temperatures, concentrations and in different solvents. The chemical shifts of all protons were assigned and long range coupling constants determined. This variation of temperature, concentration and solvent provided evidence forintra- andinter-molecular proton transfer. In all pyrromethenes investigated the tautomeric NH exchanges are too fast—even at –100°C—to be measured by NMR.

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Mit 2 Abbildungen     

Enhancement and quenching of fluorescence of metal chelates of 8-hydroxyquinoline-5-sulfonic acid

Fluorescence enhancement of 8-hydroxyquinoline-5-sulfonic acid complexes of Mg, Ca, Sr, Ba, Al, Zn and Cd were studied in micellar and hydroorganic solvents. Al is extraordinarily amenable to both types of fluorescence enhancement, an order of magnitude to two order of magnitude enhancement of fluorescence intensity has been observed with aqueous hexadecyltrimethylammonium chloride (HTAC) and certain mixed aqueous-organic solvents. Fe(III) appears to be an unusually powerful fluorescence quencher in these systems — the effect is noticeable in low micromolar concentrations and is greatly amplified by cationic surfactants such as HTAC.     

Microgels and ionic associations in solutions of cellulose diacetate

Solutions of cellulose diacetate (CDA) from two sources (cotton linters and wood pulp Floranier) were analysed in various solvents by size exclusion chromatography (SEC). Without special precautions, the SEC chromatograms presented three peaks — or prehumps — before the main polymer peak. The first prehump which could be eliminated by ultracentrifugation corresponded to microgels whose sugar composition was determined. These microgels were also investigated by electron microscopy, X-ray and electron diffraction analysis. They corresponded mainly to cellulose triacetate (CTA-II) in the case of CDA from cotton linters and a mixture of CTA-II and xylan diacetate (XDA) in the case of CDA from the wood pulp Floranier. The second and third prehumps could be attributed to ionic effects corresponding to the association of remaining sulfate groups on the CDA molecules with residual calcium. It was found that these ionic effects could be eliminated by the addition of LiBr or LiCl to the elution solvents. This led to chromatograms devoid of prehumps.Presented in part at the Cellulose '91 meeting in New Orleans.     

Electrochemical Amination of Benzene in Aqueous Solutions of Sulfuric Acid and an Organic Solvent

Electrolysis of the Ti(IV)–NH₂OH–C₆H₆ system in 11 M H₂SO₄ reveals that out of four organic solvents—methanol, formic acid, acetonitrile, and acetic acid—only the last two meet conditions imposed on solvents to be used in indirect cathodic amination of aromatic compounds. They improve the aromatic substrate solubility in the catholyte and affect the process mechanism, determining, together with other factors, the substitution's rate and selectivity.     

Surface analysis methods in the investigation of corrosion inhibitor performance

Summary Being economical and easily applied, organic corrosion inhibitors are finding increasing use. The efficacy of inhibitors is normally investigated by gravimetric and electrochemical methods. For further information — for example, on the thickness, composition and structure of protective films, or the binding states of the inhibitor and metal — surface analysis methods, such as ESCA, AES, SIMS and LAMMA, must be used. The system copper/ benzotriazole or tolyltriazole in tap water is investigated as an example of interface inhibition. A quasipolymeric film with a thickness of only a few molecular layers is formed from Cu(I) and inhibitor and is remarkably resistant even to air and solvents. Phosphonic acids act as membrane inhibitors on iron in cooling water. Together with corrosion products and ions from the water they form layers with a thickness of about 20–40 nm. As their growth then ceases, they cause no hindrance to heat transfer.

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Oberflächenanalytische Methoden zur Untersuchung der Wirksamkeit von Korrosionsinhibitoren