Novel tetrapodal molecules and reticular polyamides based on tetraphenylmethane

A series of tetrapodal derivatives of tetraphenylmethane were synthesized and characterized. Crystals obtained from tetrakis(4-acetamidophenyl)methane (1c) and from tetrakis[4-(4-aminobenzamido)phenyl]methane (2b) were analyzed by X-ray diffraction. The analyses pointed to the crystal packing problems faced by molecules of this kind by showing that the crystals, with composition1c·2DMF·2H₂O and2b·2DMSO, respectively, contained cocrystallized solvent molecules. The solvent molecules were found in both cases to be held in place by H bonds; in the case of2b·2DMSO they occupied channels running along theb axis. Tetrakis(4-aminophenyl)methane (1b) was used in polycondensation reactions with terephthalic acid, under modified Yamazaki conditions, to produce rigid aromatic polyamide networks. The networks were obtained as gels encompassing the whole volume of the reaction mixture. The volume of the gels did not vary noticeably upon changing the solvent (1-methyl-2-pyrrolidone) with less polar solvents, but the gels collapsed upon drying. No crystallinity was observed.     

Gas-phase ion chemistry in the ternary SiH(4)-C(3)H(6)-PH(3) system

Propene-phosphine and the silane-propene-phosphine gaseous mixtures were studied by ion trap mass spectrometry. For the binary mixture the variation of ion abundances under different partial pressures and the mechanisms of ion-molecule reactions are reported. Moreover, the rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-phosphine mixture the mechanisms of formation of Si(m)C(n)P(p)H(+)(s) ion clusters were elucidated, but the complexity of the system and the low abundances of the ions usually isolated by successive steps prevented the determination of rate constants. The hydrogenated ternary ions are mainly formed by reactions of Si(r)P(s)H(+)(t) ions with propene, whereas a minor contribution comes from reactions of Si(m)C(n)H(+)(p) ions with phosphine. The C(v)P(w)H(+)(z) ions show very low reactivity with silane. The formation processes of these species are discussed in relation to their possible role as precursors of amorphous silicon carbides doped with phosphorus obtained by deposition from properly activated silane-propene-phosphine mixtures.     

Soft electron impact ionization in crossed molecular beam reactive scattering: the dynamics of the O((3)P)+C(2)H(2) reaction

Soft ionization by low-energy, tunable electrons is implemented for the first time in crossed molecular beam reactive scattering experiments with mass-spectrometric detection. The power of the method, which permits the suppression of the dissociative ionization of interfering species, is exemplified with the study of the O((3)P)+C(2)H(2) multichannel reaction.     

Anodic characterization of mercury microelectrodes for determinations of anions in real samples

The anodization of mercury microelectrodes was investigated in synthetic samples containing several strong and weak electrolytes at different concentrations. In particular, the effects on mercury anodization due to the presence of NaOH, HClO₄, NaCl, NaI, NaF, Na₂SO₄, NaHCO₃, Na₂CO₃, tartaric and citric acids, were studied in solutions containing either each species or mixtures of them, and without addition of supporting electrolyte. Some of the electrode processes studied led to linear calibration plots e.g. 1 × 10⁻⁵ − 1 × 10⁻⁴M Cl⁻, 1 × 10⁻⁶ − 1 × 10⁻⁵M I⁻, 5 × 10⁻⁴ − 3 × 10⁻³M SO₄²⁻, 5 × 10⁻⁴ − 2 × 10⁻²M HCO₃⁻, with typical correlation coefficients of 0.998–0.999. The anodization of mercury microelectrodes was also investigated directly in wine, rain, tap and mineral water, without pretreatment and without addition of supporting electrolyte. In the real samples only the ions Cl⁻ and HCO₃⁻ could be quantified, and the values found were in agreement, within 3–5%, with the reference values obtained by using Italian standard methods for food.     

Apparent formation constants of dithiooxamide and substituted dithiooxamide complexes of cobalt(II,III), nickel(II) and copper(II) in strongly acidic media

The apparent stability constants of the complex species formed between cobalt(II, III), nickel(II) or copper(II) and dithiooxamide or some N,N′- and tetra-substituted dithiooxamides have been determined in strongly acidic media at 25 ° C. The configuration of the complexes in solution is discussed on the basis of the electronic spectra.     

Activity coefficients of electrolytes from the E.M.F. of liquid membrane cells. I. The method—Test measurements on KCl

A new electrochemical cell is described, in which two permselective liquid membranes, one anionic the other cationic, are interposed between the subsidiary electrodes and the solution of the electrolyte under examination By means of this kind of cell it is possible to measure activity coefficients of salts of cations and anions for which reversible electrodes are not available, with great accuracy even at high dilutions never accessible before (down to ≊10⁻⁴ mol-dm⁻³). The cell performance has been tested by measuring the activity coefficients of KCl for which accurate data are available in literature.     

High-performance liquid chromatographic analysis of chlorophylls, pheophytins and carotenoids in virgin olive oils: chemometric approach to variety classification

This work evaluate the possibility to get from the quali-quantitative determination of the pigments contained in monovarietal olive oils (chlorophylls, pheophytins and carotenoids) and from the multivariate statistical analysis of these measures, parameters able to distinguish within the cultivars. The chemometric variables used have concurred to obtain preliminary interesting results. Liquid-phase distribution and solid-phase extraction/purification procedures has been compared: recoveries for both are resulted higher than 94% for all the pigment classes and the R.S.D. values were below 10%. HPLC analysis, allowing the simultaneous pigment determination, and fluorescence detection, allowing a better green pigments measure (detection limits from 5 to 80ppb), are revealed a fundamental solution.     

Electroanalytical investigation on the stability of tetracoordinate nickel(I) complexes

The stability of tetracoordinate nickel(I) complexes, of the type [Ni(CN)₂P₂]^? (P=substituted phosphine), generated by cathodic reduction of the parent nickel(II) complexes, has been studied by cyclic voltammetry and double potential step techniques. Evidence has been obtained that nickel(I) complexes decay to the dimeric species Ni₂(CN)₂P₄ via a first order chemical reaction the rate determining step being the release of a cyanide ion leading to the radical species [Ni(CN)P₂]. The experimental trend obtained for the first order kinetic constants has been explained on the basis of the different “trans-effect” induced by a cyanide ligand in comparison with that induced by a phosphine group and taking into account the different basic character of the phosphine ligands.     

Synthesis and configuration of trans-1-amino-4-benzyl-2,6-dimethylpiperazine as an intermediate of semi-synthetic rifamycins

The synthesis of trans-1-amino-4-benzyl-2,6-dimethylpiperazine (1b), trans-4-benzyl-2,6-dimethylpiperazine (VIIb) and trans-2,6-dimethylpiperazine (IIb) are described, by condensation of N-benzyl-1,2-propanediamine with α-bromopropionate and successive thermal cyclization and reduction with lithium aluminum hydride. The assignment of the cis, trans configuration to the isomers was based on a thorough examination of the ring proton nmr signals of the two isomers of 4-benzyl-2,6-dimethylpiperazine (VIIa and VIIb) interpreted in terms of conformational considerations.     

Copper(II) complexes of 2-amino-1,3,4-thiadiazole and 2-ethylamino-1,3,4-thiadiazole

Summary Some copper(II) complexes of 2-amino-1,3,4-thiadiazole (atz) and 2-ethylamino-1,3,4-thiadiazole (eatz) have been prepared and studied by electronic, i.r. and e.p.r. spectra and by magnetochemical and conductometric methods. The CuX₂ · atz (X=Cl, Br) and CuCl₂ · eatz complexes are presumably six-coordinate with bridging ligand molecules and asymmetrically bridging halide ions, while the CuX₂ · 2 atz (X=Cl, Br) complexes probably have a flattened tetrahedral N₂X₂ moiety with apical interactions. The CuBr₂ · 5/3 eatz · 2/3 MeOH and Cu(OAc)₂ · L (L=atz or eatz) complexes have subnormal magnetic moments (1.53-1.40 B.M.). The acetato-complexes have a dimeric structure with bridging acetato-groups, copper-copper interactions and apical ligand molecules. The ligands bond principally through the amine nitrogen atom and, when bridging, also through one ring-nitrogen.