Adsorption of tracer cations,and the separation of carrier-free95Nb from95Zr,XU1 from U and45Ca from46Sc on titanium phosphate column

Titanium phosphate as ion exchanger for column operation has been prepared by mixing TiCl₄ and H₃PO₄ in suitable proportion. The ratio of titanium: phosphate was obtained to be 1:2.02. The uptake of Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Sc³⁺, Co³⁺, Y³⁺, Tb³⁺, Zr⁴⁺ and Th⁴⁺ cations at very small concentrations has been studied on this exchanger. The data indicated that the different cations are adsorbed in the exchanger by different mechanisms. Radiochemical separations of carrier free⁹⁵Nb from⁹⁵Zr, UX₁ from U and⁴⁵Ca from⁴⁶Sc have been achieved by adopting very simple chemical procedures through a column of titanium phosphate. The -spectrum of the separated⁹⁵Nb, UX₁ and⁴⁶Sc showed that the products are of high radionuclidic purity. The individual separation procedures took less than 20 min and the yields are quantitative.     

Barreleneiridium(I) complexes. Crystal structures of [Ir(Me3TFB)(η6-C6H4Me2)]ClO4 and [Ir(TFB)(η5-PhNPh2)]BF4·CH2Cl2 (TFB = tetrafluorobenzobarrelene)

A new series of cationic areneiridium(I) complexes of formula [Ir(barrelene)(arene)]⁺ or [Ir(barrelene)(PhNRPh)]⁺ (R= Ph or H) have been synthesized from neutral iridium complexes of the type [IrY(barrelene)]_x (barrelene = Me₃TFB, Y = Cl or OMe (x = 2), Y = acac (x = 1); barrelene = TFB, Y = OMe (x = 2), Y = acac (x = 1)). The crystal structures of [Ir(Me₃TFB)(1,4-C₆H₄Me₂)]ClO₄ and [Ir(TFB)(PhNPh₂)]BF₄·CH₂Cl₂ have been determined by X-ray diffraction. They crystallize in the space groups Pbca and Pna2₁ respectively with lattice constants of 17.6947(11), 15.8072(10), 16.0019(11) Å and 9.8059(2), 20.8097(9), 14.3367(4) Å. Final R factors were 0.063 and 0.042 for the observed data. Both complexes show a staggered arrangement between the arene and the TFB moieties and deviation from planarity of the coordinated arene ligands. In the second complex the IrC and NC distances, the CNC angle, the type of arene puckering, and the spectroscopic data indicate a distortion of the coordinated arene towards a η⁵-coordinated iminocyclohexadienyl form.     

Kinetic and catalytic aspects of dimethylterephtalate transesterification also through the use of model molecules

Kinetic and catalytic aspects of DMT transesterification reaction, key step in the industrial production of polyethylenterephtalate (PET), have been deepened also through the use of model molecules such as CH₃COO–Ph–X. These molecules give the same reactions with ethylene glycol occurring in the DMT transesterification too. The use of model molecules in the study of this reaction seems therefore to be promising in perspective. As we observed, however, the nature of the para-substituent X has a very strong influence on the reaction rate, when salts of bivalent metals such as Zn, Cd, Co, Mg, Mn, are used as catalysts, while this influence is much smaller when a tetravalent metal, as Ti, is used. This fact suggests that the transesterification mechanism operating in the two cases is different and this suggestion has been confirmed by applying Hammett's approach to the available kinetic data. Experimental kinetic runs were all performed at 193°C, by withdrawing small samples of the reaction mixture at different reaction times. These samples were gaschromatographically analyzed. We found volcano shaped curves of the reaction rates as a function of the metal ion acidities and we obtained different trends with a maximum of activity shifted from a metal to another for different substrates. A comparison of the kinetic results obtained, respectively, with the model molecules and DMT will be reported too.     

Activation analysis of geological material using ruthenium as a multiisotopic comparator

The isotopes⁹⁷Ru,¹⁰³Ru and¹⁰⁵Ru, produced by reactor irradiation of elemental ruthenium, were applied as triple comparators in the activation analysis of rock FU-41, a basanitoid from Fuerteventura, Canary Island. The concentrations of the following elements were determined: Sm, Sc, Fe, Co, Na, La, Hf, Eu, Th and Cr. The aim of this work was the experimental control of the error theory of the multiple comparator method as well as the experimental check of the accuracy. Presented at the 3rd Symposium on the Recent Developments in Neutron Activation Analysis, Cambridge (U.K.), 2–4 July 1973.     

Conformational analysis3̄CXXIV: The conformation of ring A in the 4,4-dimethyl-3-androstanone system. The crystal structure of 4,4-dimethylandrostan-3-on-17β-yl benzoate

Molecular mechanics calculations indicate that the deformed chair and twisted-boat conformations are similar in energy for a 4,4-dimethyl-3-keto steroid. Earlier dipole moment work on such compounds is discussed. The crystal structure of 4,4-dimethylandrostan-3-on-17β-yl benzoate has been determined. The crystals are orthorhombic, P2₁2₁2₁, a = 17.096 (2), b = 22.136 (e), c = 6.217 (1) A. The structure was solved by direct methods and refined by least squares to R ? 0.039, R_XXX = 0.038, based on 2168 observed reflections. Ring A is shown to exist in a chair form, deformed as indicated by the calculations.     

HPLC–MS determination of the oxidation products of the reaction between α- and β-pinene and OH radicals

Biogenic non-methane hydrocarbons such as isoprene, alpha-pinene, and beta-pinene, are emitted by forests in very large quantities. To evaluate the role of alpha- and beta-pinene and their contribution to the global production of trace gases and especially aerosol precursors, a study of the oxidation mechanism of alpha- and beta-pinene with hydroxyl radicals must be conducted.The degradation products of both monoterpenes with hydroxyl radicals were identified and quantified in a fast-flow reactor. The products were collected on a liquid-nitrogen trap coated with a 2,4-DNPH solution to which two internal standards (benzaldehyde-2,4-DNPH and tolualdehyde-2,4-DNPH) had been added. The collection method was based on the in situ conversion of aldehyde and/or ketone compounds to their 2,4-dinitrophenylhydrazone derivatives. The derivatives were analyzed by HPLC-MS using APCI(-). TIC chromatograms and mass spectral data for the various oxidation products are presented.For alpha-pinene, pinonaldehyde is the most important degradation product, with smaller amounts of acetone, formaldehyde, campholenealdehyde, and acetaldehyde. For beta-pinene, nopinone and formaldehyde are the most abundant products, of almost equal importance, whereas acetone and acetaldehyde are minor compounds.     

The chemical effects of photo-oxidation on butadiene rubber

The photo-oxidation of butadiene rubber (BR) was studied in detail using films of a commercially available material, containing 33% cis-1,4-, 56% trans-1,4- and 12% 1,2-vinylic units. The spectral data of the products showed that during photo-oxidation the following functional organic groups are formed: hydroperoxides, alcohols, ketones, carboxylic acids and esters. ¹³C-NMR spectroscopic evidence for the formation of epoxides is presented. By comparison with spectra of model compounds, signals were assigned to ester and carboxylic acids in the allylic position of the oxidized polymer. The presence of ketones and carboxylic acids was also proved by chemical methods. It could be demonstrated that the formation of ketones, carboxylic acids and esters occurs from the photolysis of the OO bond of the hydroperoxides. Kinetic measurements with films containing benzophenone showed a strong increase in the quantum yield for the formation of products in comparison with the pure polymer sample. The opposite effect is observed with films containing the commercially used anti-oxidant, 2,6-di-t-butyl-p-hydroxytoluene. Also, the quantum yield for formation of the oxidation products decreases with increase in the light intensity. This result shows that cross-linking plays an important role in the photo-degradation of BR.     

The effect of molecular planarity on crystal non‐centrosymmetry in benzyl­idene–aniline derivatives

In the title compound, N‐(2‐methoxy­phenyl)‐4‐nitro­benzyli­deneamine, C₁₄H₁₂N₂O₃, the two phenyl rings make a dihedral angle of 48.0 (2)° and the nitro group is at an angle of 6.5 (1)° with respect to its attached phenyl ring. In the crystal structure, mol­ecules are related as centrosymmetric pairs through π–π interactions and are further connected through strong C—H?O hydrogen bonds [C?O 3.4259 (17) Å and C—H?O 167°], forming molecular stacks along [100]. These stacks associate further through longer C—H?O interactions, forming two‐dimensional networks. In the c direction, there are only weak van der Waals interactions. The relationship between the molecular planarity and its centrosymmetry is also briefly described.     

Kinetics of substitution of aquo ligands fromcis-diaquo-bis-(biguanide) cobalt(III) and chromium(III) ions by aspartic acid in ethanol—water mixtures

The kinetics of substitution of aqua ligands fromcis-diaqua-bis(biguanide)cobalt(III) and chromium(III) ions by aspartic acid in EtOH–H₂O media have been studied spectrophotometrically in the 30 to 45°C range. We propose the following rate law for the anation

Organo group VB chemistry: Part IV: on the NQR spectra of tertiary aryl group VB compounds (35Cl, 75As, 121Sb, 209Bi)

The NQR spectra for the nuclei ³⁵Cl, ⁷⁵As, ¹²¹Sb/¹²³Sb and ²⁰⁹Bi at 300°K in the series of compounds (4-XC₆H₄)₃M and (3-XC₆H₄)₃M (M = P, As, Sb, Bi; X = H, F, Cl) are measured. Hammet sigma constants are calculated. The bonding in these molecules is discussed.