Monolayer properties of fatty acids : II. Surface vapor pressure and the free energy of compression

The properties of monolayers spread at the air-water interface were measured for saturated, unsaturated, and hydroxy fatty acids, differing in the type and degree of unsaturation, geometric isomerism, and position of unsaturated and hydroxy groups. Surface vapor pressures, reflecting the equilibrium between “gaseous” and “liquid” monolayer states were determined, as were the free energies of compression, ΔF_c, from essentially infinite dilution (100,000 Ų/molecule) to the area per molecule, A_e at the equilibrium spreading pressure, π_e. Surface vapor pressures and free energies of compression for saturated and unsaturated fatty acids with a double bond, or bonds, change in a manner expected because of chain-chain interactions. Hydroxy and acetylenic acids produce relatively high surface vapor pressures, despite their tendency for strong chain-chain interaction. It is concluded that chain-water interactions are very significant for the acetylenic and hydroxy acids and less so for the saturated and ethylenic acids.     

Thermodynamics of weak interactions: excess enthalpies and excess Gibbs free energies of mixing

Excess enthalpies of chloroform + n-hexane, bromoform + n-hexane, bromoform + pyridine and bromoform + benzene and excess Gibbs free energies of mixing for bromoform + pyridine, chloroform + pyridine, bromoform + n-hexane, chloroform + n-hexane and bromoform + benzene have been determined at 308.15 K and the same factors have been examined for Barker's theory to understand the magnitude and nature of various interactions between the components of these mixtures.     

Synthesis and properties of alkyldicyclopentadienyl-vanadium(III) compounds

The compounds Cp₂VR (R = CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, CH₂C(CH₃)₃ or CH₂Si(CH₃)₃) have been prepared from Cp₂ VCl and RMgX in n-pentane. The air-sensitive compounds are stable at room temperature, but decompose between 65 and 138°C. The thermal stability decreases in the order R = CH₃ CH₂Si(CH₃)₃ > C₂H₅ > CH₂C(CH₃)₃ > n-C₅H₁₁ > n-C₄H₉ > n-C₃H₇. Compounds with R = i-C₃H₇ or t-C₄H₉ could not be obtained.     

Non-linear relaxation methods: III. Current-controlled perturbations

A functional expression is derived valid for evaluating all orders of perturbation in potential when a current of known profile is super-imposed. Generalised expressions for the distortion and the rectification potential are given. The problems of “iR-drop” and “charging current” compensation are also discussed.     

Voltammetry at microcylinder electrodes: Part III. Chronopotentiometry

Expressions for chronopotentiometry at stationary microcylinder electrodes are presented. The transition time, τ, is expressed as a function of a single parameter λ ( = nFc^*_RD / ia, where a is the radius of the electrode, D is the diffusion coefficient, i is the current density, n is the number of transferred electrons, F is the Faraday constant and c^*_R is the bulk concentration. When the values of λ are small, the transition-time constant, i√τ / c^*_R, depends linearly on λ, with the intercept predicted from the Sand equation. Conversely, when values of λ increase, the transition time also increases exponentially. Therefore transition necessarily occurs no matter how small a current flows. An approximate equation for the transition time is presented, from which one can evaluate the diffusion coefficient. Equations for the potential-time curve and the quarter-wave potential are also obtained. The equations were tested experimentally using carbon fiber electrodes (a = 4.1 μ m) and platinum wire electrodes (a = 10-100μ m). The transition times obtained experimentally were in good agreement with those predicted theoretically for various values of the applied current, for several different radii of the electrodes.     

The structure and magnetic properties of chromium(III) molybdate

Magnetic susceptibility measurements have shown that Cr₂(MoO₄)₃ orders magnetically at 42 K. Powder neutron diffraction experiments at 295 and 5 K indicate that Cr₂(MoO₄)₃ is chemically and magnetically isostructural with the L-type ferrimagnet Fe₂(MoO₄)₃, and has a magnetic moment of 2.5 ± 0.2 μ_B per cation at 5 K. The limitations imposed on powder neutron diffraction methods by particle-size effects are discussed.     

Thermodynamics of molecular interactions in binary mixtures of non-electrolytes. Molar excess volumes

Molar excess volumes, V^E, for pyridine (A) + α-picoline (B), + β-picoline (B) and + γ-picoline (B) and benzene (A) + toluene (B), + o-xylene (B) and + p-xylene (B) and carbon tetrachloride (A) + n-heptane (B) have been measured dilatometrically as a function of temperature and composition and have been utilized to study B—B and B—B—B interactions in the presence of A via the Mayer—McMillan approach. A model has also been presented to account for these B—B and B—B—B interactions. The V^E data at 308.15 K have also been analysed in terms of the “graph theoretical” approach which describes the V^E data well for all these mixtures at 308.15 K. The “graph theoretical” approach has further been extended to successfully evaluate V^E data for a mixture at any temperature, T₂, when the V^E data at T₁ are known.     

Hydrodynamic voltammetry at channel electrodes: Part III. Theory of kinetic currents

A theory of kinetic currents at a channel electrode is developed without any assumption on the magnitude of the rate constant of the preceding chemical reaction. An approximate equation with reasonable accuracy which relates the limiting current to the rate constant, flow velocity and the electrode geometries, is presented. The validity of the equation derived from the concept of the thin reaction layer is also discussed.     

Metallocene basicity : V. Protonation of ferrocenophanes in strong and weak acids

Protonation of [3]-, [4]- and [5]ferrocenophanes has been examined in trifluoroboric acid, HBF₃OH, and the results are consistent with the previous models of a long-lived metal protonated species. Selective ring and bridge deuteration has permitted the assignment of proton resonances from which probable conformations of the species have been derived. NMR spectra of [3]- and [4]ferrocenophane in trifluoroacetic acid have been recorded and interpreted in terms of rapid exchange between solvent and ferrocene.     

Thermodynamics of solutions of methanol and solvating components

A model is proposed to correlate the excess Gibbs free energies and excess enthalpies of binary solutions of methanol and a solvating component. Solution nonideality from ideal solutions is given by the sum of the chemical contribution term, which is due to self-association of methanol and solvation between methanol and a nonassociating component, and the physical contribution term with allowance for the NRTL equation. The model uses the following data for methanol: two enthalpies for formation of the hydrogen bonds for the dimer and all larger polymeric species, three equilibrium constants of stepwise association for the dimer, trimer and other polymeric species, and an equilibrium constant for cyclic species of more than tetramer. The association model further includes an additional solvation equilibrium to allow for the interaction between the terminal hydroxyl group of methanol polymeric species and a solvating component. The model is extended to predict vapor—liquid equilibria, liquid—liquid equilibria and excess enthalpies for ternary solutions containing methanol and two nonassociating components from only binary information. Calculated results are in good agreement with experimental data as shown by selected illustrative examples.     

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

Paramagnetic organometallic molecules : III. Photolysis of dimanganese decacarbonyl

The photolysis of Mn₂(CO)₁₀ has been investigated over a range of solvents and temperatures and found to be more complicated than hitherto reported. Homolysis of the metal—metal bond in Mn₂(CO)₁₀ is the dominant photochemical process in all solvents are evidenced by trapping the Mn(CO)_5^. radical. A temperature dependent bifunctionality of the spin-trap 2,4,6-tri-t-butylnitrosobenzene was observed. The unstable adduct Mn(CO)₅O_2^., previously characterised in the solid state, is formed in non-polar solvents in the absence of a trap. A paramagnetic species giving rise to a broad, structureless signal at ambient temperatures is the major product in basic solvents; in certain polar solvents at low temperatures, hyperfine coupling to manganese (A(Mn) 88 G) could be distinguished. Both spectra are believed to derive from the solvated manganese(II) ion.The controversial six-line spectrum found on photolysis of Mn₂(CO)₁₀ in tetrahydrofuran also results from a manganese(II) species. The unusual properties of the Mn₂(CO)₁₀/THF system may be explained in terms of ion-pair formation between the Mn²⁺ and Mn(CO)_5^? ions in solution.     

Untersuchungen über benzylübergangsmetallverbindungen : III. Darstellung und eigenschaften des tetrabenzylthoriums

Tetrabenzylthorium can be obtained in crystalline form by interaction of benzyllithium with thorium tetrachloride. All properties of the compound indicate σ-bonds between the metal atom and the benzyl groups. The IR spectrum of tetrabenzylthorium is discussed together with that of tetrabenzylzirconium.     

Thermodynamics of tetraalkyl- and bis- tetraalkylammonium bromides: II. Heat capacities of solid state from 273 to 373 K

The solid phase heat capacities of a number of hydrocarbon containing salts have been determined in the temperature range 273 to 373 K using a differential scanning calorimeter. The salts studied include tetramethyl-, tetraethyl-, and tetrabutylammonium bromide and the bis-tetraalkylammonium bromide series of the general formula [R₃N(CH₂)_nNR₃]Br₂, where n = 2,3… 10, and R = ethyl or allyl. With the exception of n-Bu₄NBr, the heat capacities of the salts were found to increase linearly with temperature over the range investigated. DSC curves of the bis-tetraalkylammonium series indicated that some of them have broad thermal transitions occurring between 365 K and their decomposition point, n-Bu₄NBr was the only tetraalkylammonium salt to show any anomalous thermal transitions in the solid phase. The origin of these transitions may be due to mesophase formation.     

Transport and kinetics at microheterogeneous electrodes: Part III. Application to the photoelectrochemical decomposition of water

The transport and kinetics in a system involving two sets of microheterogeneous electrodes, which are designed to use solar radiation to split water into H₂ and O₂, are described. A reaction scheme involving fourteen different processes is considered. The conditions for an efficient system are derived. It is shown that the main problems are electrode selectivity and the loss of H₂ and O₂ by back reactions.     

Cleavage by halogens of carboncobalt bonds in organometallic complexes of cobalt(III) : II. Organobis(dimethylglyoximato)cobalt(III) complexes

The reaction between organocobaloximes and ICl in chloroform has been studied. In absence of an excess of added chloride ion the reaction is electrophilic in character; in presence of an excess of chloride ion both oxidative dealkylation and radical attack can occur.     

Calcium alkoxyalanates : III. Reduction of organic functional groups by calcium tetrakis(alkoxy)alanates

Calcium tetrakis(alkoxy)alanates obtained from different alcohols reduce aldehydes, ketones, acids, esters, acid chlorides and anhydrides to alcohols in high yields. Good results are achieved in the reduction of amides to amines. The reductions of nitrile and oxime groups and dehalogenation reactions are more difficult. Selectivity is possible in the reduction of organic epoxides.     

Water in polymer membranes. Part III : Water sorption and pore volume in cellulose acetate films

Changes in waveguide properties of several cellulose acetate membranes and one polyimide membrane were measured as a function of their exposure to varying levels of relative humidity. The volume fraction of water in the films and the occupied pore volumes were determined from refractive index and thickness changes. The dependence of the refractive index on water absorption is related to a competition between two processes: one of filling pores with no film expansion and one of “free expansion” where the film expands to completely accommodate the added water volume. The term “pore” is taken to mean a volume with molecular and not macroscopic dimensions. The hydration properties of these dense cellulose acetate membranes were affected by degree of acetylation, casting temperatures and annealing treatments. Annealing CA398 membranes at 180°C decreased film water concentration by reducing the amount of free expansion. Annealed CA398 membranes that were tested in a reverse osmosis cell were found to have high salt rejection compared to unannealed films. The hydration characteristics of a polyimide membrane are compared to cellulose acetate membranes.     

Thermodynamics of complex formation in ternary liquid mixtures containing acetonitrile

Vapor—liquid and liquid—liquid equilibria and excess enthalpies for ternary mixtures formed from acetonitrile, benzene, n-heptane, toluene, and carbon tetrachloride are successfully correlated with a modified version of the associated solution theory proposed by Lorimer and Jones in 1977, which assumes two types of self-association for acetonitrile and binary complexes between acetonitrile and unsaturated hydrocarbons and does not include any ternary parameters.