Synthetic Hydroxyapatites as Inorganic Cation-Exchangers; Exchange Characteristics for Pb2+ and Sn2+ Ions in Acidic Solution

Abstract

The cation-exchange characteristics between Pb²⁺ ions of aqueous solutions containing counter-anions (F^?, C1^?) and Ca²⁺ ions of synthetic hydroxyapatite samples have been investigated in detail under the conditions of low pH values (3.0, 4.0 and 5.0) by a normal batch method. Even at the low pH value of 3.0 the apatite structure in a solution containing F^? or C1^? ions was maintained via a concurrent ion-exchange effect of Pb²⁺ ions together with F^? or C1^?ions, which are known to be exchangeable with OH- ions of the apatite. Moreover, it was found that Ca²⁺ ions in the apatite sample can easily be exchanged for Pb²⁺ ions almost without distinction between MI and M2 sites, assisted by the loosening effect of protons even at room temperature. Next, it was found that the hydroxyapatite samples are transformed into amorphous states by the reactions between Ca ²⁺ ions in the samples and Sn ²⁺ ions in the SnC1₂ acidic aqueous solutions with pH of 3.0 or below with a molar ratio of Sn²⁺/Ca²⁺ -1.0. The existence of hydroxyapatite as amorphism in acidic aqueous solutions such as SnC1₂ is quite interesting, because in general the hydroxyapatite has been found to be dissolved in acidic aqueous solutions. Moreover, the obtained amorphism are found to be stable up to at least 500 to 6OO°C but to be unstable in alkaline solutions. The characteristics of Sn²⁺ ions are found to have been found to form crystalline Pb ²⁺ apatite even in be quite different from those of homologous Pb²⁺ ions which have been found to form crystalline pb²⁺ apatite even in such an acidic atmosphere.     

Preparation of Metallaiminophosphoranes and Their Reactivity

Treatment of [Cp*(CO) 2 M{P(NHPh)(OMe) 2 }]PF 6 (M = Fe and Ru) with NaNH 2 gives metallaiminophosphoranes, Cp*(CO) 2 M{P(NPh)(OMe) 2 }. The x-ray structures and reactivity of the complexes are reported.     

Influences of aging on thermal decomposition mechanism of high performance oxidizer ammonium dinitramide

Ammonium dinitramide (ADN) is one of the several promising new solid propellant oxidizers. ADN is of interest because its oxygen balance and energy content are high, and it also halogen-free. One of the most important characteristics of a propellant oxidizer, however, is stability and ADN is known to degrade to ammonium nitrate (AN) during storage, which will affect its performance. This study focused on the effects of aging on the thermal decomposition mechanism of ADN. The thermal behaviors of ADN and ADN/AN mixtures were studied, as were the gases evolved during their decomposition, using differential scanning calorimetry (DSC), thermogravimetry–differential thermal analysis-infrared spectrometry (TG–DTA-IR), and thermogravimetry–differential thermal analysis-mass spectrometry (TG–DTA-MS). The results of these analyses demonstrated that the decomposition of ADN occurs via a series of distinct stages in the condensed phase. The gases evolved from ADN decomposition were N₂O, NO₂, N₂, and H₂O. In contrast, ADN mixed with AN (to simulate aging) did not exhibit the same initial reaction. We conclude that aging inhibits early stage, low temperature decomposition reactions of ADN. Two possible reasons were proposed, these being either a decrease in the acidity of the material due to the presence of AN, or inhibition of the acidic dissociation of dinitramic acid by NO ₃ ^? .     

Synthesis of cis-3-arylated cycloalkylamines through palladium-catalyzed methylene sp carbon–hydrogen bond activation

Methylene sp³ carbon–hydrogen bond activation of N-picolinoylcycloalkylamines provides a useful method for synthesizing cis-3-arylated cycloalkylamine derivatives. Pd(II) species catalyzed the γ-arylation of N-picolinoylcycloalkylamines with aryl iodides in the presence of silver carbonate to afford cis-3-arylated N-picolinoylalkylamines in up to 87% yield. Hydrolysis of the amide linkage to give the corresponding cis-3-arylated cycloalkylamines was also demonstrated.     

Synthesis of N-labeled 4-oxo-2,2,6,6-tetraethylpiperidine nitroxide for EPR brain imaging

A scalable synthetic route for ¹⁵N-labeled 4-oxo-2,2,6,6-tetraethylpiperidine nitroxide (¹⁵N-TEEPONE) is described. This ¹⁵N-labeled nitroxide is suitable for electron paramagnetic resonance imaging of brain, and its higher sensitivity compared with that of its ¹⁴N-counterpart is an important advantage of the labeled derivative.     

Oxidative Bond Cleavage of the Silicon–Silicon Bond of a Pentacoordinated Disilicate

The Si Si bond of a pentacoordinated disilicate was readily cleaved by treatment with 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone in the presence of sodium carbonate under mild conditions. The bond cleavage did not proceed under the same conditions after conversion of the disilicate into the corresponding monoanionic silylsilicate and neutral disilane by protonation. The difference in the charges of the Si Si bond compounds affects the reactivity toward an oxidant, resulting in the Si Si bond cleavage, considering that all of these compounds have a bond between pentacoordinated silicon atoms.     

Rate constant measurements for initial addition reactions of radicals at the propagation step of photo‐polymerization as studied by pulsed EPR spectroscopy

Pulsed EPR spectroscopy was employed to determine reaction rate constants at an early stage of addition reactions in radical polymerizations triggered by four initiator radicals, which were generated by photodissociation of four parent molecules. Two monomers (tert‐butylacrylate and tert‐butylmethacrylate) were examined as reactant. Stern–Volmer analysis on the measured decay time of electron spin echo intensity of reacting radicals provides rate constants for addition reactions. We focused on rate constants for the second step reaction between monomer and adduct radical that is produced by the first step addition reaction between initiator radical and monomer. The rate constant measured by pulsed EPR was evaluated by theoretical calculations in the light of (1) enthalpy difference between product radical and reactants and (2) charge transfer interaction between reacting radical and monomer. Copyright © 2016 John Wiley & Sons, Ltd.