Thermal studies on purine complexes. VII. 8-theophylline derivatives and their silver(I) complexes

Four theophylline derivatives: 8-ethyltheophylline (ETH), 8-isopropyltheophylline (IPH), 8-propyltheophylline (PRH), and 8-phenyltheophylline (FTH) have been synthesized and characterized by spectroscopic techniques and thermal analysis. The melting points of these theophylline derivatives increase with the molecular weight, from 263.8°C (ETH) to 384.7°C (FTH). The values of the fusion enthalpy increase in the same order, from 28.4 kJ mol⁻¹ (ETH) to 36.5 kJ mol⁻¹ (FTH).

The interaction of these theophylline derivatives with Ag(I) has been studied by means of spectroscopic techniques, TG, DTG and DSC. In all cases, the pyrolysis of these compounds gave metallic silver.     

Reactivity of cyclopalladated compounds: VIII. Synthesis of cyclometallated compounds with an oxygen as the donor atom. Crystal and molecular structure of (8-methylquinoline-C,N)-(1-methoxynaphthalene-8-C,O)palladium(II)

Treatment of 1-methoxynaphthalene (MXNH) with n-butyllithium in a diethyl ether/n-hexane solution gives 1-methoxynaphthalene-8-lithium (MXNLi) in 30% yield as an insoluble material. This compound reacts with PdCl₂(SEt₂)₂ to give bis(1-methoxynaphthalene-8-C,O)palladium(II) (I)_and with PtCl₂(SEt₂)₂ to give cis- and trans-(1-methoxynaphthalene-8-C,O)(1-methoxynaphthalene-8-C)(diethylsulfide)platinum(II) (II), which are non-rigid molecules in solution. With the cyclopalladated dimers [{$\text{Pd(CN}$)Cl₂}₂], MXNLi gives the palladobicyclic compounds: ($\text{N∩C)P}$$\text{d(C∩O}$) (III). An X-ray diffraction study of compound IIIa where N∩N = 8-methylquinoline-C,N reveals the planarity of the molecule, shows that it has a cis configuration with respect to the PdC bonds, and confirms that the oxygen atom of MXN is bonded to palladium: PdO 2.236(4) Å. The geometry of IIIa is maintained in solution, whereas the corresponding compounds IIIb and IIIc in which N∩C is benzo[h]quinoline-9-C,N and N,N-dimethyl-1-naphthylamine-8-C,N, respectively, appear to be mixtures of cis and trans isomers in solution. With PMe₂Ph I and II give trans-Pd(MXN)₂(PMe₂Ph)₂ and cis-Pt(MNX)₂(PMe₂Ph)₂, respectively, in which the methoxynaphthalene is bound to the metals via the 8-carbon of the naphthalene ring. Only one phosphine ligand adds to compounds IIIb and IIIc with displacement of the O → Pd bond. One carbon monoxide ligand can be added to the platinum compound II to give Pt(MXN)₂(SEt₂)CO which in solution exists as two isomers in equilibrium.     

π-Allymetal chemistry 8. Uncatalyzed cis-trans isomerization of n3-allyl (pentachloropehnyl) palladium (II) complex

Two geometrical isomers of an n³-crotyhlpalladium(II) complex, Pd(n³-crotyl)(C₆Cl₅)(PPh₃) have been found to undergo uncatalyzed mutual interconversion in benzene above room temperature. The rate constants of the isomerization have been determined by the ¹H NMR method at 45–67°C, and thermodynamic data calculated. The large decrease of the rate on adding free tripheylphosphine ligand is attributed to occurrence of a dissciative isomerization path involving a 3-coordinate intermediate. Reductive elimination of the complex takes place at much slower rates than the isomerization to afford MeCHCHCH₂C₆Cl₅ selectively.     

Fluorimetric detection of tautomeric equilibria in 8-aminoquinolines

The 1-methylquinolinium cations derived from 8-aminoquinoline and 8-amino-6-methoxyquinoline were prepared by methylation of the corresponding nitroquinolines and reduction of the nitro-compounds. The dissociation constants of the protonated species of these compounds are almost identical to those of doubly-protonated 8-aminoquinoline and 8-amino-6-methoxyquinoline, respectively, suggesting that the parent quinolines are exclusively first protonated at the ring nitrogen atom. However, the molar absorptivities of the 1-methyl derivatives at their longest-wavelength absorption maxima are substantially greater than the corresponding absorptivities of the unmethylated aminoquinolines, a result which suggests tautomerism of the singly-protonated parent quinolines, with a proportion of the population protonated at the amino group. Fluorescence spectroscopy reveals a single emission from the 8-amino-6-methoxy-1-methylquinolinium ion and two excitation-wavelength-dependent fluorescences from the 8-amino-6-methoxyquinolinium ion, confirming the occurrence of tautomerism and supporting choice of the absorptiometric approach rather than the titrimetric approach as the preferred method for the detection of tautomerism and the calculation of tautomeric equilibrium constants.     

Chemistry of organosilicon compounds XCIV. Preparations of 8-silatricyclo[3.2.1.02,4]oct-6-enes,new photochemical silylene generators

The reaction of siloles with cyclopropene afforded products representative of a new organosilicon ring system, 8-silatricyclo[3.2.1.0^2,4]oct-6-ene, which proved to be photolytic silylene generators.     

Non-stoichiometric molybdenum oxides as cathodes for lithium cells: Part IV. Factors influencing the performance of Li/Mo8O23 batteries

Mo₈O₂₃ was further investigated as a cathode material suitable for secondary Li batteries. Within the channels present in the basic slabs of its ReO₃-type structure, it can accept up to 1.0 Li⁺/Mo through an octahedrical coordination of Li⁺ by O. The oxide performance in primary cells was seen to be largely dependent on cathode formulation and solution volume. As a secondary cathode it give single-cycle recharge efficiencies as high as 95% at 1.0 mA cm^?2 and 0.5 e/Mo. Prolonged cycling in button cells at 1.0 and 2.0 mA cm^?2 also gives satisfactory results. X-ray analysis shows that after cycling the structure does not suffer from significant distortions.     

Solid state reaction between thallous carbonate and 8-hydroxyquinoline

The solid state reaction between thallous carbonate and 8-hydroxyquinoline has been studied. The energy of activation for surface migration was found to be 8.8 kcal/mole whereas for inner penetration it was 14.6 kcal/mole. The reaction product was characterized by elemental analysis and ir spectral studies.     

Cristallisation de LiFe5O8 dans un verre 0,9 Li2B2O4 - 0,1 LiFe5O8

X-Ray diffraction, transmission electron microscopy, and magnetic measurements are used to study the crystallization of an amorphous compound: Li₂B₂O₄ (90 mole%)-LiFe₅O₈ (10 mole%). The crystalline phase which first appears in the amorphous matrix is LiFe₅O₈. The average particle size (50 to 300 Å) may be controlled by varying the temperature of annealing and/or the time of annealing. The crystallization kinetics are similar to those of metallic glasses. The fraction transformed, x, as a function of time, satisfies the Johnson-Mehl-Avrami equation with an exponent n of 0.75. The activation energy for the crystallization process is approximately 0.6 eV. Both these values characterize a primary crystallization.     

Zur kenntnis nichtmetallischer iminverbindungen : LXXVII. Dimeres aminodiiminophosphoran

(Ph₃P)₂ Pt or (Ph₃ P)₂ Pd insertion into the mercury-germanium, or tin bond was achieved to afford new chains of four metal atoms. The starting compounds were (C₆ F₅)₃ MHgR, M = Ge, Sn; R = C₂ H₅, Ge(C₆ F₅)₃, Sn(C₆ F₅)₃. The pentafluorophenyl derivatives prepared are very stable in air and acids. Photolysis of these compounds in benzene or boiling in trifluoroacetic acid results in demercuration.     

The isostructural γ-sulfur phase of selenium-sulfur,SenS8−n

Two new selenium-sulfur species, Se_1.1S_6.9 (yellow) and Se_3.7S_4.3 (orange), have been isolated as single crystals, and the corresponding structures have been determined. The space group is P2c, and the parameters are a = 8.34 A?, b = 13.11 A?, c = 9.30 A?, β = 123.9° and a = 8.40 A?, b = 13.26 A?, c = 9.37 A?, β = 124.5°, respectively. They are isostructural with γ-sulfur, having two distinct pairs of eight membered rings in the unit cell. The selenium and sulfur atoms appear scrambled throughout all atomic positions, but are not scrambled equally. When atomic site occupancy data are combined with other data from the literature, a wide compositional continuum of γ-sulfur isostructures is revealed that extends from γ-sulfur to SeS. It appears unlikely that selenium-sulfur crystals exist having the γ-sulfur structure with more than half the atoms as selenium.     

Ionic conductivity of Li2MgSn3O8 ramsdellite

The ionic conductivity of polycrystalline pellets of Li₂MgSn₃O₈ with ramsdellite-type structure was measured by complex impedance technique. The conductivity is 1.2 × 10^?8 (Ω cm)^?1 at 300°C and 2.3 × 10^?4 (Ω cm)^?1 at 450°C. The results are discussed in relation to structural properties.     

Nitroso compounds : III. The reaction of bromomagnesium diphenylcuprate and phenylcopper reagents with nitrosobenzene

Bromomagnesium diphenylcuprate reagent reacts with nitrosobenzene to give diphenylhydroxylamine, biphenyl, diphenylamine, azoxybenzene and phenol. It reacts with alkyl nitrites to give the above products as well as the corresponding alkanols. Phenylcopper reagent behaves similarly but somewhat sluggishly. A mechanism involving an initial electron-transfer process is proposed.     

Organocuivreux vinyliques : II. Deuterolyse,iodolyse, couplage et alcoylation stereospecifiques des vinyl-cuivres

Vinylcopper derivatives, obtained by stereospecific addition of alkylcopper compounds to 1-alkynes, are transformed with retention to various ethylenic structures; 1-deutero-1-alkenes, symmetrical conjugated dienes, 1-iodo-1-alkenes, di- or tri-substituted alkenes and primary or secondary allylic alcohols.     

Anodic Protection. Theory and Practice in the Prevention of Corrosion.: O.L. Riggs,Jr. and C.E. Locke,Plenum Press,New York, 1981, 284 pp., US$39.50.

The specific adsorption of chloride, bromide, iodide, azide, and thiocyanate has been studied at an electropolished polycrystalline silver-aqueous interface using differential capacitance measurements. For chloride, bromide, and azide, quantitative estimates of the surface concentration of specifically adsorbed anions were obtained from capacitance-potential data in mixed fluoride electrolytes having a constant ionic strength of 0.5. The dependence of the measured capacitance upon the ionic strength of sodium fluoride was also investigated in order to check the behavior of the polycrystalline surface in comparison with the predictions of conventional double-layer models. Estimates of the specifically adsorbed charge densities of chloride, bromide, and thiocyanate anions were also obtained from a “kinetic probe” technique which entailed monitoring the response of the outer-sphere reduction rate of CO(NH₃)₅F²⁺ and Co(NH₃)₆³⁺ to the addition of the appropriate adsorbing anion. At the average potential of zero charge for the polycrystalline silver surface, the standard free energies of adsorption ? Δ₃^o for chloride, bromide, and azide were found to be within ca. 5 kJ mol^?1 of the corresponding quantities obtained at mercury electrodes. However. significantly greater increases in ? Δ₃^o in the sequence Cl^? < N₃^? < Br^? are seen at silver compared to mercury. Electrochemical roughening in chloride media, giving silver surfaces displaying intense surface Raman scattering, yields only minor changes in the surface concentration of specifically adsorbed chloride anions.     

Dielectric relaxation in cyano complexes of the K4Me11(CN)6·3H2O type. II. Isotopic effect

The dielectric relaxation of deuterated K₄Me¹¹(CN)₆·3H₂O doped with NH₄¹ has been investigated in the vicinity of the transition temperature. In all cases the dielectric band appeared to be non-symmetrical and may be described by means of the Williams-Watts empirical decay function ?(Φ) ? exp[?(?/τ_-)]. A mechanism for the asymmetry of the dielectric absorption due to fluctuation of the “Glarum defects” is proposed. Also, the nature of the dielectric absorption in the crystals is discussed.     

Professor K.S.G. Doss in honour of his reaching his seventieth year

Recent studies have clearly demonstrated the importance of including the sphericity of the dropping mercury electrode in the theoretical analysis of certain polarographic phenomena. Experimental effects of sphericity on second harmonic a.c. polarograms¹ and on polarograms for reversible electrode reactions with amalgam formation^2.3 have been successfully described using a theoretical treatment augmented by computer simulation. The simulation procedure we present here allows one to simulate diffusion phenomena at the growing mercury drop (sphere) electrode without modification of other simulation operations, e.g. computation of surface boundary conditions⁴ or of homogeneous kinetics⁵. We treat two cases: “External” diffusion where the diffusing species, A, is in the solution phase with the boundary condition A_x=0=0 for t>0; and “internal” diffusion where the diffusing species is in the mercury phase with the same boundary condition.