Mössbauer spectrometica analysis of thermal decomposition products of phosphate and oxalate coatings on steel

The deterioration of zinc, zinc—calcium and manganese phosphate coatings and oxalate coatings on steel on heating was investigated by conversion electron Mössbauer spectrometry. and the chemical change of the coatings was analysed on the basis of the thermal characteristics of Zn₃(PO₄)₂·4H₂O, Zn₂Fe(PO₄)₄·4H₂O, CaZn₂(PO₄)₂·2H₂O, Fe₃(PO₄)₂·8H₂O. (Mn, Fe)₅H₂(PO₄)₄·4H₂O and FeC₂O₄·2H₂O. The steel substrate beneath the coatings influenced the thermal decomposition and evaporation of coating materials under the various heating atmospheres. The heat resistance of these coatings and the state of the substrate were also investigated.     

Cidep study of radical-ion pair systems: Photooxidation reactions of carbazoles by maleic anhydride in alcohol solution

Photooxidation (charge transfer) reactions of carbazole derivatives by maleic anhydride (MA) in alcoholic media are studied by a time-resolved cw-ESR (TRESR) and Fourier transform ESR (FTESR) techniques. The CIDEP spectra observed in the systems (methyl-, ethyl-, and phenyl-substituted carbazoles with MA) remarkably depend on the MA concentration. Under the high concentration conditions, an emissive TM (triplet mechanism) polarization with a slight A/E (absorption/emission) pattern of the RPM (radical pair mechanism) is observed. In the low concentration of MA, a TM-like absorptive polarization is superimposed on the A/E pattern of the RPM. Since this reaction takes place exclusively through the triplet state, this spectral phase reveals that the singlet state of the radical-ion pair (RIP) has an energy higher than that of the triplet state, in other words, the sign of the apparent exchange interaction of the present RIP systems is positive. The total absorptive polarization observed in the low concentration of MA is tentatively explained by the polarization transfer from the excited triplet state of carbazoles in thermal equilibrium.     

Synthesis and two-electron redox behavior of diazuleno[2,1-a:1,2-c]naphthalenes

The Diels-Alder reaction of di-2-azulenylacetylene with tetraphenylcyclopentadienone afforded 7,8,9,10-tetraphenyldiazuleno[2,1-a:1,2-c]naphthalene in one pot via autoxidation of the presumed 1,2-di-2-azulenylbenzene derivative. In contrast, a similar reaction of bis(1-methoxycarbonyl-2-azulenyl)acetylene with tetraphenylcyclopentadienone gave the 1,2-di-2-azulenylbenzene derivative. The following cyclodehydrogenation reaction of the benzene derivative with iron(III) chloride afforded diazuleno[2,1-a:1,2-c]naphthalene 6,11-bismethoxycarbonyl derivative. The redox behavior of these novel diazuleno[2,1-a:1,2-c]naphthalenes was examined by cyclic voltammetry (CV). These compounds exhibited two-step oxidation waves at +0.22 to +0.71 V upon CV, which revealed the formation of a radical cation and dication stabilized by the fused two azulene rings under the electrochemical oxidation conditions. Since the 1,2-di-2-azulenylbenzene derivative was oxidized at higher oxidation potentials (+0.83 and +1.86 V), the fusion of the two azulene rings to naphthalene increased electron-donating properties because of the formation of a closed-shell dicationic structure. Formation of the radical cation was characterized by UV-vis spectroscopy under the electrochemical oxidation conditions, although no evidence was obtained for the presumed dication under the conditions of the UV-vis spectroscopy measurement.     

Ion-Pair Solvent Extraction of EDTA Anions with Tetraalkylammonium Ions in Various Organic Solvents

Summary.  The ion-pair solvent extraction behavior of ethylenediaminetetraacetate (EDTA) anion by various tetraalkylammonium ions was investigated at 25.0 ± 0.1°C. The extraction of EDTA exceeded 90% from the basic aqueous solution into the organic solvents such as n-hexane and benzene derivatives containing tri-n-octylmethylammonium chloride, but EDTA was hardly extracted from acidic solution. Among the chemical species of EDTA in aqueous solution, edta ⁴⁻ is the most extractable one. On the other hand, the extraction of EDTA was less than 1% into chloroform and 1,2-dichloroethane even from the basic aqueous solution. The effect of the structure of alkylammonium ion was also examined. Tetra-n-hexylammonium and tetra-n-octylammonium ions could not extract EDTA even from the basic aqueous solution, while the use of tri-n-octylmethylammonium and di-n-lauryldimethylammonium ions enhances the extraction of EDTA. These results suggest that the steric hindrance in the ion-pair of alkylammonium and EDTA anion in the organic phase affects the extractability of EDTA containing ion-pair. The solution structure of ion-pair in the organic phase was calculated by MMFF force field and the steric effect in the ion-pair was also suggested. From the extraction constants obtained, the possibility of the extraction separation of EDTA has been shown. Present address: Chemistry Department, Heilongjiang University, Harbin, China     

Structure of Aqueous Gallium(III) Bromide Solutions Over a Temperature Range 80–333 K by Raman Spectroscopy, X-ray Absorption Fine Structure, and X-ray Diffraction

The structure and complex formation of concentrated aqueous gallium(III) bromide (GaBr₃) solutions have been investigated over a temperature range 80–333 K by Raman spectroscopy, X-ray absorption fine structure (XAFS), and X-ray diffraction. The Raman spectra obtained at various [Br^?]/[Ga³⁺] molar ratios and temperatures have shown that complex formation between Ga³⁺ and Br^? occurs as a predominant species, with [GaBr₄]^? at [Ga³⁺] as high as 1～2 M (M = mol?dm ^?3) and [Br^?]/[Ga³⁺] ratios > ～2, and that cooling of the solutions favors the formation of the aqua Ga³⁺. The intermediate species were not seen in the Raman spectra. The XAFS data have revealed that the aqua complex has a sixfold coordination as [Ga(H₂O)₆]³⁺ with a Ga³⁺–H₂O distance of (1.96 ± 0.02) Å, whereas the [GaBr₄]^? complex has a Ga³⁺–Br^? distance of (2.33± 0.02) Å, and that vitrification of the aqueous GaBr₃ solution at liquid nitrogen temperature shifts the equilibrium toward the aqua complex. The X-ray diffraction data at different subzero temperatures have shown a tendency of decreasing Ga³⁺–Br^? and increasing Ga³⁺–H₂O interactions with lowering temperature, confirming the preference of aqua Ga³⁺ in the supercooled liquid state as well as in the glassy state. The Ga³⁺–H₂O distance of ～1.8 Å for the tetrahedral coordination was found in a 2.01 M gallium(III) bromide solution with a [Br^?]/[Ga³⁺] ratio of 3.7 and gradually increased to a value of 1.92 Å for octahedral geometry with decreasing temperature, suggesting that equilibrium shifts from [GaBr₄]^? to [Ga(H₂O)₆]³⁺ through intermediate species, [GaBr _n ]^(3?n)+ (n = 2 and 3). The Ga³⁺–Br^? and Br^?–Br^? distances within [GaBr₄]^? with an almost tetrahedral symmetry are (2.35± 0.02) and (3.82± 0.03) Å, respectively. The Ga³⁺ has the second hydration shell at (4.03± 0.03) Å and the hydration of Br^? is characterized with a Br^?–H₂O distance of (3.35± 0.02) Å at all temperatures investigated.     

Synthetic studies of proanthocyanidins. Part 3: Stereoselective 3,4-cis catechin and catechin condensation by TMSOTf-catalyzed intramolecular coupling method

TMSOTf-catalyzed intramolecular condensation for catechin and epicatechin units are described. A potential electrophile and a nucleophile were connected with diester linkers and TMSOTf-catalyzed condensation was examined. In comparison with intermolecular catechin and catechin condensation, the intramolecular condensation required high reaction temperature and reversed 3,4-cis product was obtained. The condensed product was transformed into the natural 3,4-cis (+)-catechin-(4β→8)-(+)-catechin dimer.     

Novel syntheses of 2,3-dihydro-5H-1,4-benzoxathiepins and 1,2,3,5-tetrahydro-4,1-benzothiazepines

2,3-Dihydro-5H-1,4-benzoxathiepins were prepared by intramolecular Friedel-Crafts reactions of ethyl α-[2-(aryloxy)ethylthio]-α-chloroacetates or by acid-catalyzed cyclizations of ethyl α-[2-(aryloxy)ethylsulfinyl]-acetate. 1,2,3,5-Tetrahydro-4,1-benzothiazepines were similarly prepared.     

Stereoselective ring-opening polymerization of racemic lactide using aluminum-achiral ligand complexes: exploration of a chain-end control mechanism

Stereoselective polymerization of racemic lactide (rac-LA) was examined using Al-achiral ligand complexes. By introduction of substituents in aromatic rings of Schiff base ligands, a higher selectivity was obtained without any chiral auxiliaries in the catalyst via a chain-end control mechanism. The T(m) values (T(m) 170-192 degrees C) were comparable to or higher than that of homochiral polymer, poly(L-LA) (T(m) 162 degrees C), and a thermally more stable polylactide than poly(L-LA) was prepared from rac-LA.     

Borate adsorption at Pt(111) in acidic medium

The adsorption/desorption process of borate was studied at Pt(111) in acidic solution by cyclic voltammetry. A so-called butterfly wave in the cyclic voltammogram of Pt(111) in HClO₄ shifted to negative direction upon the addition of boric acid with the disappearance of its sharp spikes. The shift in potential was found to be −57 mV with a tenfold increase of boric acid concentration. This illustrates that this anomalous wave is due to borate adsorption/desorption by a one-electron transfer process. The borate adsorption/desorption wave was observed to shift by −63 mV/pH. At pH>3, the anomalous wave splits forming two separate waves, depending on the pH and the scan rate. The appearance of two waves is assigned to the change in the adsorption mode of borate or the participation of OH in the adsorption process.