Charge-Transfer Interactions of Aluminum Copper(I) Chloride with Polystyrene and Related Compounds

Interactions between polystyrene and aluminum copper(I) chloride (AlCuCl₄) were investigated by various spectroscopic measurements in order to elucidate the structure of polystyrene-AlCuCl₄ complex in solution and the mechanism of water resistance of the complex as a carbon monoxide absorbent. The chemical shift (101 ppm) and half line width (145 Hz) of AlCuCl₄ in benzene by ²⁷Al-NMR suggest a dimer structure bridged by two chlorine atoms, which is almost identical with that of aluminum chloride. The coordination of benzene or other aromatic compounds to AlCuCl₄ was confirmed by charge-transfer bands in UV and visible absorptions. The equilibrium constants (K) for complex formation of AlCuCl₄ with various aromatic compounds were determined by ¹³C-NMR spectroscopy. In the case of AlCuCl₄ and benzene in 1,2-dichloroethane, for example, K is 2.2 M ^?1 at 303 K. For the polymer complex solution and 1,3-diphenyl-propane solution, strong charge-transfer bands have been observed in the wavelength region at about 380 to 500 nm, where no band is observed in benzene derivatives. This strong charge-transfer band is considered to be due to the strong interaction of AlCuCl₄ with adjacent aromatic rings of polystyrene or 1,3-diphenylpropane of a chelate type, which, as a result, causes the water resistance of the present carbon monoxide absorbent system.     

Thermochemistry of molecular complexes. 5. Molecular complexes of I2 with ethylbenzenes andn-alkylbenzenes

The enthalpies of formation and equilibrium constants are reported for molecular complexes of I₂ with five ethylbenzene and ninen-alkylbenzene donor molecules in CCl₄. The wavelength of maximum absorbance for each complex is also reported. For ethylbenzene donor molecules, the formation enthalpy and equilibrium constant for the complexes depend strongly on the number of ethyl groups attached to the benzene ring, but only weakly on the position of the groups. For then-alkylbenzene donor molecules, both the formation enthalpy and equilibrium constant for complex formation are indenpendent of the length of the alkyl chain. These results are consistent with previous observations on weak complexes of I₂ with substituted benzene donors.     

Photoelectron spectra of electron donor—acceptor complexes between bromine and alkylamines

The photoelectron spectra of N,N-diethylmethylamine—Br₂, triethylamine—Br₂, tri-n-propylamine—Br₂ and tri-n-butylamine— Br₂ complexes were observed. The n orbitals of the alkylamines as electron donors were found to be stabilized by molecular complex formation, while the σ4p and π4p orbitals of the bromine molecule were destabilized. These results strongly support the charge-transfer mechanism for the complex formation.     

Reactivity of cobaloxime bound to polystyrene chain by carbon–cobalt σ bond

The (alkyl)-bis(dimethylglyoximato)pyridinecobalt attached to polychloromethylstyrene by a cobalt–carbon bond was prepared by the reaction of Co(II)(DH)₂Py with polychloromethylstyrene in benzene. The fraction of p-vinylbenzyl·Co(DH)₂Py introduced to the polymer was 8.1 and 2.1 mole %. The photodecomposition of the polymer-bonded cobaloxime was investigated by following the change of the visible spectrum. The rate constant k_dec of the polymer-bonded cobaloxime was 1.1 × 10^?2 sec^?1 in benzene; it is one-fourth of that of its monomeric analog, benzyl·Co(DH)₂Py. The k_dec values of the cobaloximes were also measured in benzene–dimethyl sulfoxide mixed solvents, and the polymer effects were discussed. The dependence of the photodecomposition on energy of the irradiation light was investigated, and it was found that the absorption band near 470 nm is important for the photodecomposition of the cobalt–carbon bond. Spectroscopic measurements of the ligand exchange reaction of polymer-bonded cobaloxime with pyridine in dimethyl sulfoxide gave a larger equilibrium constant (1.2 × 10⁴ liter/mole) than that of benzyl·Co(DH)₂Py (9.4 × 10² liter/mole). The kinetic data of the ligand exchange reaction indicated that the larger equilibrium constant for the polymeric system is due to the smaller rate constant of the reverse reaction. The thermodynamic parameters were also obtained.     

Molecular association of benzene with a new cyclophane receptor

Host/guest interactions in the cyclophane-2/benzene system have been investigated by absorption and fluorescence spectroscopy in dichloromethane. The cyclophane serves as a host and the benzene as a guest. Absorption and fluorescence titration experiments are carried out by holding either the concentration of the host or guest constant while varying the concentration of the other component. When the concentration of benzene is kept constant, an isostilbic point at 288 nm is observed in the fluorescence spectral data, suggesting that only two absorbing species are present in equilibrium. Keeping the concentration of cyclophane-2 constant while increasing the concentration of benzene results in a hyposchromic shift of the emission peaks in the range 275–360 nm. The shift is attributed to interaction of the cyclophane with benzene. The average association constant of cyclophane-2 with benzene, K _a = 425 ± 54 M^?1, obtains from fitting the absorption and the fluorescence spectral data to the Bourson et al. equation using non-linear regression analysis.     

Solvent effect on the equilibrium constant of the chain reversible reaction of <Emphasis Type="Italic">N,N</Emphasis>′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone

The temperature dependences of the equilibrium constant K of the reversible chain reaction of N,N′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone in benzene, chlorobenzene, anisole, benzonitrile, and CCl₄ were studied. The enthalpies and entropies of the reaction in these solvents were determined, and a linear dependence between them in aromatic solvents was found. The equilibrium constant depends on the solvent nature: the replacement of CCl₄ by benzene at T = 298 K increases K from 13.6 to 140. The solvation effects are caused by several types of intermolecular interactions of participants of equilibrium with the medium. The decrease in K in the benzene-anisole-benzonitrile series is related, to a great extent, to complex formation with hydrogen bonding between 2,5-dichlorohydroquinone and the solvents. In anisole a charge-transfer complex is formed between the solvent and reaction product (2,5-dichloroquinone). The constant and enthalpy of the complexation were estimated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2296–2302, December, 2007.     

Kinetic studies on the bromate ion oxidation of 12-tungstocobaltate(II) in aqueous acid

The oxidation of Co^IIW by bromine(V) is a complex process involving an induction period. The reaction was found to be first-order in both [Co^IIW] and [Br^v], and exhibits a complex dependence on [H⁺]. These observations were successfully explained by considering HBrO₂, one of the intermediates formed in the direct but slow reaction between Co^IIW and bromine(V), as the reacting species. The first-order limiting dependence in [H⁺] was due to the involvement of a protic equilibrium of HBrO₂. The induction period appears due to the scavenging effect of Br^– inadvertently present in the medium. It appears to be the first report where HBrO₂ was found to be the reacting intermediate in the oxidation of metal ions and complexes by BrO^– ₃.     

Influence of ionization density on radiolysis of cyclohexane-benzene mixtures

Cyclohexane-benzene mixtures were irradiated by ²¹⁰Po-α-radiation (LET = 200 eV/nm) with the effective energy of 3 MeV and the results were compared with those obtained by 1.25 MeV λ-irradiation of ⁶⁰Co (LET = 0.2 eV/nm). While during λ-irradiation—similarly to the data known from the literature—the G(c-C₆H₁₀) and the G((c-C₆H₁₁)₂) values were decreased even by a small amount of benzene, the yields of both products obtained by α-irradiation were in the same range practically constant, and began to decrease only above the benzene concentration of 0.3 mol dm^-3 (about 3 electron %).The “protection” in the case of λ-irradiation was interpreted by positive ion scavenging, S₁ excited cyclohexane molecule quenching and thermal H atoms scavenging. The low efficiency of all these three components of “protection” in α-radiolysis is attributed principally to the very high concentration of intermediates in the track/core compared to the relatively low concentration of benzene.The conclusions were also supported by comparison with the data obtained in cyclohexane-iodine systems.     

NOESY,HOESY, T1 and solid‐state NMR studies on [RuH(η6‐toluene)(Binap)](CF3SO3): a molecule with a strongly distorted piano‐stool structure

Detailed solution‐NMR studies on the distorted ruthenium hydride complex [RuH(η⁶‐toluene)(Binap)](CF₃SO₃) (2) are reported. NOE‐spectroscopy, together with low‐temperature ¹H and ³¹P NMR data, reveals restricted rotation around a P—C bond for a specific axial P—phenyl ring with the activation energy determined via simulation. From ¹⁹F, ¹H HOESY data, the approach of the triflate anion relative to the hydride ligand is established. Comparison of the quadrupole coupling constant C_QF from both solution‐ and solid‐state MAS‐NMR on the deuteride [RuD(η⁶‐benzene)(Binap)](CF₃SO₃) (1‐D) provide information on the nature of the Ru—H bond. Copyright © 2003 John Wiley & Sons, Ltd.     

Charge Transfer Complex Role in the Formation of Chlorobenzene in the γ‐Irradiated Carbon Tetrachloride‐Benzene System

The formation of carbon tetrachloride‐benzene charge transfer complex was confirmed by UV and NMR spectrometric studies. A change in UV spectrum of benzene is observed upon addition of carbon tetrachloride. Whereas the appearance of new bands supports the formation of charge transfer complex. NMR study shows that, chemical shift of benzene pmr signal depends on the CCl₄‐C₆H₆ molar ratio. This observation is another criterion for the formation of benzene‐carbon tetrachloride charge transfer complex. Job's Continuous Variation method indicates that a 2:1 CCl₄‐C₆H₆ charge transfer complex (2:1 CTC) is formed. The association constants (K_2:1) of (2:1 CTC) was found to be 0.0197 M^?2. The maximum concentration of (2:1 CTC) was found to be in samples with 2:1 CCl₄‐C₆H₆ molar ratio (33% benzene mole). On the other hand the maximum yield of chlorobenzene was obtained, also, upon radiolysis of CCl₄‐C₆H₆ samples at a 2:1 molar ratio (33% benzene mole). Therefore, it could be concluded that (2:1 CTC) participates in the formation of chlorobenzene upon radiolysis of the benzene‐carbon tetrachloride system. This conclusion was supported by the dependence of the chlorobenzene yield of a γ‐irradiated carbon tetrachloride‐benzene system (2:1 molar ratio) on irradiation time according to a third order kinetic equation with a very good linearity (R² = 0.9977). Accordingly, the rate constant for the chlorobenzene formation under this condition was found to be ≈ 5.5 × 10^?7 L².mol^?2.h^?1. We propose a radiation chemical mechanism in which the 2:1 CTC plays a role in the formation of chlorobenzene.     

Thermodynamic ionization energies and charge transfer reactions in benzene and substituted benzenes

Ionization energies of 11 substituted benzenes of CS₂ related to the ionization energy of benzene were obtained by measurements of the charge exchange equilibrium constants for C₆H₅X⁺ + C₆H₅Y ? C₆H₅Y⁺ + C₆H₅X at 450 and K. Thermodynamic ionization energies of substituted benzenes, related to that of benzene, are found to be higher by 0.5–2.0 kcal/mole than the corresponding photoionization (0—0) values. Exothermic charge transfer reactions between substituted benzenes are found to proceed with rate constants of (1.3–1.6) × 10^?9 cm³/mol s, which agree well with calculated collision rates.     

OXYGEN COMPLEX FORMATION BY COBALT(II)-TRIS (2-AMINOETHYL) AMINE+

Abstract

The reversible oxygenation of the Co(II) complex of tris(2-aminoethyl)amine (TREN, L) has been studied in some detail. The equilibrium constant K _O2 =10^26.92 M^?2 atm^?1, corresponding to the quotient [H⁺] [L₂Co₂(O₂) (OH)³⁺]/[Co²⁺]² [L]² P_O2 was determined by potentiometric equilibrium measurements of hydrogen ion concentration. Values for the thermodynamic constants, ΔH° =–63 ± 9 kcal/mole and ΔS° =–100 ± 15 cal/deg. mol, were calculated from the temperature dependence of the equilibrium constant. Oxygen stoichiometry, measured with a polarographic sensor, indicated the formation of a binuclear (peroxo bridged) complex, and the potentiometric equilibrium data indicated the presence of a second, μ-hydroxo, bridge. Measurement of the kinetics of the fast reaction between the cobalt(II)-TREN complex and dioxygen gave the value of the second order rate constant for the formation of the dioxygen complex as k ₁ =2.8 × 10⁺³ sec^?1 mol^?1. The first order rate constant for the decomposition of the dioxygen complex measured by stopped-flow was found to be k _?2 =0.7 sec^?1. Kinetic and equilibrium data are discussed with respect to the probable structure and mechanism of formation of the dioxygen complex, and are compared with similar data previously reported for analogous complexes. The oxygen complex reported is unique with respect to its extremely slow rate of conversion to inert cobalt(III) complexes.     

Complex-radical terpolymerization of phenanthrene,maleic anhydride,and trans-stilbene

The radical terpolymerization of the donor-acceptor-donor monomer system, phenanthrene (P)—maleic anhydride (M)—trans-stilbene (S), was studied. These monomers are known to be nonhomopolymerizable. The terpolymerization was carried out in p-dioxane and/or toluene at 70°C in the presence of benzoyl peroxide used as the initiator. P and S were found to form charge transfer complexes (CTC) with M in p-dioxane at 35°C. The results obtained are discussed in terms of the free monomer and complex propagation models. It is shown that terpolymerization is carried out at a stage close to binary copolymerization of two complexomers. The reactivity ratio of P … M and S … M complexes was estimated by the Kelen-Tüdös method. Absorbance ratios at 1770 cm^?1 (v_C=0 of anhydride group), 764 cm^?1 (δ_CH in monosubstituted benzene of S), and 820 cm^?1 (δ_CH in disubstituted benzene of P) as a function of terpolymer composition were established. P—M—S terpolymers are shown to have high thermal stabilities. © 1995 John Wiley & Sons, Inc.     

Kinetics and Mechanism of Oxidation of Hydroquinone by Tetrabutylammonium Tribromide Ion in Aqueous Acetic Acid

The oxidation of hydroquinone by environmentally benign tetrabutyl ammonium tribromide (TBATB) was carried out in 50% V/V aqueous acetic acid medium under pseudo-first-order conditions, keeping a large excess of hydroquinone over the oxidant. The main reactive species of oxidant and substrate were found to be the Br₃^-\mathrm{Br}_{3}^{-} ion and hydroquinone, respectively. The reaction proceeds with prior complex formation between the reactants followed by its slow decomposition to generate semiquinone and bromine radicals. The complex formation was kinetically verified by its Michaelis–Menten plot. The solvent effect was verified by using Grunwald–Winstein equation which is consistent with an S_N2 mechanism. The formation constants for the complex and rate constant for the slow decomposition step were determined by studying the reaction at five different temperatures. The values of formation constant of the complex and the rate constant for its decomposition were determined at these temperatures. The activation parameters with respect to the slow step of the reaction have also been determined.     

Effect of addition of trifluoroacetic acid on the photophysical properties and photoreactions of aromatic imides

The UV and IR spectra of N-methyl-1,8-naphthalimide in benzene showed a two-step consecutive complexation (hydrogen bond formation) with trifluoroacetic acid (TFA). The equilibrium constant K₁ for the first complexation in benzene was determined from the UV spectrum to be 48 M⁻¹. The fluorescence intensities of the imide in benzene were found to be remarkably enhanced by the addition of TFA. Furthermore, photochemical cyclobutane formation of the imide with styrene in benzene was enhanced by the addition of TFA. Enhancement of the fluorescence intensity and the photoreaction of the imide by complexation with TFA was explained by a decrease of the efficiency of the intersystem crossing from ¹(ππ^∗) to ³(nπ^∗), that results from an increase in the energy of the ³(nπ^∗) level due to the complexation.     

Liquid—liquid distribution in reversed micellar systems

The equilibrium distribution of a hydrophilic solute (M^z+ between an aqueous phase and a reversed micellar organic phase (consisting of a surfactant HA with aggregation number x, and dissolved in a hydrocarbon diluent) is analyzed quantitatively by treating the reversed micelles as a pseudophase. It is shown that when the M—A complex is strongly solubilized by the micellar pseudophase, the distribution coefficient (D) has a first-order dependence on the concentration of micellized surfactant (C_s). On the other hand, when the M—A complex is not solubilized by the reversed micelles, a plot of log D versus log C_s has a slope of (z/x); in this case the monomeric species HA is the active extractant and any effect that decreases surfactant aggregation (e.g. low aggregation number, small aggregation equilibrium constant) leads to an increase in the distribution coefficient.     

Determination of Lanthanide (III) Ions by Using a Flotation - Spectrophotometric Method

Abstract

This paper reports our attempt at determining Ln (III) ions by using a flotation-spectrophotometric method and our findings. When a ternary ion-association complex of Ln (III) coordinated by thiocyanate (SCN^?) and diantipyryl methane (DA[Mdot]) is separated by a mixed solvent containing benzene and chloroform at pH 3.1 – 4.2, a third phase is observed between the aqueous and organic phases. The solid ternary complex can be dissolved in acetone that contains thenoyltrifluoroacetone (TTA). The individual Ln (III) ion can be determined by using the 4th derivative spectra directly. The equilibrium constant of the ternary composition ratio of Ln(II1) to ligand is estimated by the equilibrium shift method. The mole ratio of Ln(II1) to DAM and to SCN^? is 1:3 each. The composition of the tcrnary complex seems to be Ln(III):DAM:SCN^?=1:3:3.     

Triplet—triplet absorption of benzene and some methylated derivatives

The CNDO/S method of del Bene and Jaffé has been applied to the study of the triplet—triplet absorption of benzene and some methylated derivatives. The first allowed triplet—triplet transition in benzene is assigned to the ³E⁽⁺⁾_2g la ³B⁽⁺⁾_1u transition.     

Extraction Equilibria between Benzene and Water of Uni- and Bivalent Metal Picrates with Lariat 16-Crown-5: Effect of the Side Arms on the Extraction Ability and Selectivity

The overall extraction constants (K_ex) of uni- andbivalent metal picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5(L16C5) were determined between benzene and water at 25°C. TheK_ex values were analyzed into the constituent equilibriumconstants, i.e., the extraction constant of picric acid, the distributionconstant of the crown ether, the stability constant of the metalion–crown ether complex in water, and the ion-pair extraction constantof the complex cation with the picrate anion. The K_ex valuedecreases in the orders Ag⁺ > Na⁺ >Tl⁺ > K⁺ > Li⁺ andPb²⁺ > Ba²⁺ > Sr²⁺ for theuni- and bivalent metals, respectively, which are the same as those observedfor 16C5. The extraction selectivity was found to be governed by theselectivity of the ion-pair extraction of the L16C5–metal picratecomplex rather than by that of the complex formation in water. Theextraction ability of L16C5 is smaller for all the metals than that of 16C5,which is mostly attributed to the higher lipophilicity of L16C5. Differencesin the extraction selectivity between L16C5 and 16C5 were observed for thebivalent metals but little for the univalent metals. The side-arm effect onthe extraction selectivity was interpreted on the basis of the negativecorrelation between the effect on the complex stability constant in waterand that on the ion-pair extraction constant.