Synthesis of hexamethylene-1,6-dicarbamate by methoxycarbonylation of 1,6-hexamethylene diamine with dimethyl carbonate over bulk and hybrid heteropoly acid catalyst

Synthesis of HDC by methoxycarbonylation of HDA with DMC was carried out over the bulk and hybrid heteropoly acid (HPA) catalyst. The catalysts were systematically characterized by XRD, FTIR, SEM and NH₃-TPD techniques. The by-products produced in the reaction were identified and a possible reaction pathway was proposed based on the by-products analysis. The performances of bulk and hybrid HPA catalysts were evaluated. The H₄[SiW₁₂O₄₀] catalyst revealed high performance compared with other catalysts and its high performance was attributed to its acidic properties. Effects of reaction parameters and reusability of the H₄[SiW₁₂O₄₀] catalyst were also investigated. Under the optimized reaction conditions, HDA conversion reached 93.2% with 64.8% HDC selectivity and only 3.8% by-product selectivity. Moreover, a possible reaction mechanism was proposed for the synthesis of HDC over H₄[SiW₁₂O₄₀] catalyst.     

Synthesis and properties of symm-triazines. 3. Reactions of 2-alkyl-4,6-bistrichloromethyl-symm-triazines containing higher alkyl groups with ammonia and aliphatic amines

The reaction of 2-alkyl-4,6-bistrichloromethyl-symm-triazines containing higher alkyl groups with ammonia or aliphatic amines results, depending on the reaction conditions, in the replacement of one or both trichloromethyl groups. On heating these symm-triazines with aqueous ammonia or dimethylamine, 2-oxo-4-amino-6-alkyl-1(3)H-symm-triazines are obtained.For communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1557–1563, November, 1985.     

Synthesis of 4-azafluorenes substituted at the position 9 based on 9,9-diphenacyl(phenacylidene)-4-azafluorene

Functionally substituted 4-azafluorenes were synthesized by the modification of the carbonyl groups of 9,9-diphenacyl-4-azafluorene. The usual reductive cleavage of 9,9-di(-bromophenacyl)-4-azafluorene by hydrazine, leading to the formation of diphenylpyridazine, was found. A method for the oxidation of methiodides of 9-substituted 4-azafluorenes to the corresponding indenopyridones was developed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1512–1515, November, 1993.     

A note on the essential pseudospectra and application

In this research article, we work with the notion of essential pseudospectra of closed, densely defined linear operators in the Banach space. We start by giving the definition and we investigate the characterization, the stability and some properties of these essential pseudospectra.     

Secondary metabolites from Paronychia argentea

Two new oleanane saponins (1 and 2) and one new flavonol glycoside (3) together with six known flavonoids, were isolated from the aerial parts of Paronychia argentea. Their structures were elucidated by 1D and 2D NMR experiments including 1D-TOCSY, DQF-COSY, NOESY, HSQC, and HMBC spectroscopy, as well as ESI-MS analysis.     

A new biflavonoid and an isobiflavonoid from Rhus tripartitum

A new biflavonoid masazinoflavanone (1) and the isobiflavonoid calodenone (2) have been isolated and characterized from the methanolic aerial part extract of the plant Rhus tripartitum. Their structures have been deduced from extensive spectral analysis (NMR and MS). Interpretation of the nuclear overhauser effects (NOESY) permitted us to establish relative stereochemistry of these natural products.     

Effect of boron on order-disorder transformation of some heat-treated Cu-Ni-Zn-Mn alloys

Atomic ordering of the alloy Cu_3.23NiZn_1.27Mn_0.016 was studied for different heat-treatment conditions. The effect of addition of boron (0–1 at %) on the order-disorder transformation was tested. Heat capacity measurement techniques were used to follow the progress of the solid state order-disorder transformation. The C_p values were measured during cooling or heating of heat treated specimens (3 hr, 1073 K) using a Perkin-Elmer DSC-2 calorimeter. The experimental results show that there exists a minimum and/or a maximum in the specific heat curve, C_p(T) vs T. These critical values (min. or max. C_p, together with the temperature ranges in which the solid-state transformations (order/disorder) occur, depend on both the heat-treatment and the boron content of the alloy.