Some new methods for preparing 2,3- and 3,4-diaminopyridines

New methods of preparing 2,3-diaminopyridine ( 13 ) from 2-chloro-3-nitropyridine ( 11 ) and 3,4-diaminopy-ridine ( 8 ) from 4-ethoxy-3-nitropyridine hydrochloride ( 5 ) have been explored and evaluated.     

Lithiation and electrophilic substitution of 8-chlorodibenz[b,f][1,4]-oxazepine-10-tert-butylcarbamate: The preparation of novel fused heterocyclic derivatives of 8-chlorodibenzoxazepine

Lithiation of 8-chlorodibenz[b,f][1,4]oxazepine-10-tert-butylcarbamate ( 1 ) is described. Electrophilic substitution of the resulting N-Boc dibenzoxazepine α- lithioamine 2 with ketones, aldehydes, nitriles, iso-cyanates and imines, followed by an in-situ cyclization, gave fused carbamates 5–26 , fused 2H-imidazol-2-ones 27–29 , fused hydantoins 30–32 , and fused ureas 33–35 , respectively, in 11–66% yield.     

Recent developments in zinc oxide target chemistry

Zinc oxide targets irradiated with high energy protons at the Los Alamos Meson Physics Facility (LAMPF) contain a number of radioactive spallation products in quantities large enough to warrant recovery. This paper describes methods for recovering⁷Be,⁴⁶Sc, and⁴⁸V from such targets and offers suggestions on possible ways to recover additional isotopes. The proposed methods are based on traditional precipitation and ion exchange techniques, are readily adaptable to hot cell use, and produce no hazardous waste components. The products are obtained in moderate to high yields and have excellent radionuclidic purity.     

Femtosecond intermolecular electron transfer in condensed systems

We have investigated the ultrafast intermolecular electron transfer (ET) from an electron-donating solvent (aniline (AN) or N, N-dimethylaniline (DMA)) to an excited dye molecule (oxazines (Nile blue and oxazine 1) or coumarins). A non-exponential time dependence was observed in AN and can be explained by solvent reorientation and nuclear motion of the reactants. However, in DMA, a single exponential process was observed for Nile blue (160 fs) and oxazine 1 (280 fs), which can be explained by assuming that the rate of ET is limited mainly by ultrafast nuclear motion. A clear substituent effect on intermolecular ET was observed for the 7-aminocoumarins. When the alkyl chain on the 7-amino group is extended and a hexagonal ring with the benzene moiety is formed, the rate of ET is reduced by three orders of magnitude. This effect can be explained by a change in the free energy difference of the reaction and by the vibrational motion of the amino group.     

A single crystal study of eight-layer barium managanese oxide,BaMnO3

A single crystal study of hydrothermally prepared eight-layer BaMnO₃ has been carried out which confirms the (Zhdanov notation) 121121 layer stacking scheme for the BaO₃ layers. The MnO₆ octahedra share faces in strings of four, and these strings are connected to each other by corner sharing. The compound has an hexagonal unit cell of dimensions a = 5.667 ± 0.003 and c = 18.738 ± 0.009 Å, probable space group $\text{P6}{}_3\text{mmc}\text{, Z = 8}$. Its structure has been determined from 352 independent reflections, of which 242 were considered observed, collected manually by a counter technique and refined to a conventional R value of 0.079.     

Mixtures of charged colloid and neutral polymer: influence of electrostatic interactions on demixing and interfacial tension

The equilibrium phase behavior of a binary mixture of charged colloids and neutral, nonadsorbing polymers is studied within free-volume theory. A model mixture of charged hard-sphere macroions and ideal, coarse-grained, effective-sphere polymers is mapped first onto a binary hard-sphere mixture with nonadditive diameters and then onto an effective Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)]. The effective model is defined by a single dimensionless parameter-the ratio of the polymer diameter to the effective colloid diameter. For high salt-to-counterion concentration ratios, a free-volume approximation for the free energy is used to compute the fluid phase diagram, which describes demixing into colloid-rich (liquid) and colloid-poor (vapor) phases. Increasing the range of electrostatic interactions shifts the demixing binodal toward higher polymer concentration, stabilizing the mixture. The enhanced stability is attributed to a weakening of polymer depletion-induced attraction between electrostatically repelling macroions. Comparison with predictions of density-functional theory reveals a corresponding increase in the liquid-vapor interfacial tension. The predicted trends in phase stability are consistent with observed behavior of protein-polysaccharide mixtures in food colloids.     

Synthesis of homoleptic Re(I) complexes of isocyano-carboranes and the X-ray structure of hexakis(p-carboran-1-yl-isonitrile)Re(I)

Two homoleptic Re(I) complexes of ortho and para-carborane isocyanide ligands were prepared as the first examples of a new class of metal-based BNCT and BNCS agents. The target compounds were prepared in low yield through the reaction of [Re₂(O₂CPh)₄Cl₂] and [Re₂(OAc)₄Cl₂] with 3-isocyano-1,2-dicarba-closo-dodecaborane and a para-carborane azetidine derivative respectively. The desired product from the latter reaction was characterized crystallographically and is only the second reported molecular structure of a homoleptic Re(I) isonitrile complex.     

Crystallographic parameters in α-UF5 and U2F9 by multiphase refinement of high-resolution neutron powder data

The crystal structures of α-UF₅ and U₂F₉ were refined with high-resolution neutron powder diffraction data from an $\text{α-}\text{UF}{}_5\text{U}{}_2\text{F}{}_9$ mixture. Refinement was achieved by a multiphase Rietveld profile refinement technique. The results are compared with previous X-ray and neutron powder studies.     

The Bond-Rotational Mobility of Guanidinium Ion

The NMR. spectrum of guanidinium ion 1 is studied in anisotropic liquid crystalline nematic solution. Assuming an HNH-angle of 120°, the distance ratio NH /NC = 0.784 is obtained, from which using NC = 1.330 Å (from X-ray data) NH = 1.043 Å results. An upper bound for the free energy of activation for bond rotation of ΔG⁺ ≤ 13 kcal/mol is deduced. The bondrotational mobility of 1 is also investigated using the MINDO/3-SCF-procedure. The results obtained for the three conceivable consecutive activation energies for bond-rotation indicate that the observed bond-rotational mobility of 1 does not involve cooperative two- or three-bond rotations. The ‘conjugative stabilization’ of 1 has been estimated to be of the order of 24–26 kcal/mol.