Synthesis of 5H-pyrido[2,3-a]phenoxazin-5-one and 5H-pyrido[3,2-a]phenoxazin-5-one derivatives

The 5H-pyrido[2,3-a]phenoxazin-5-one derivatives and 5H-pyrido[3,2-a]phenoxazin-5-one derivatives were prepared by the condensation of substituted 2-aminophenols with 6,7-dibromo-5,8-quinolinequinone followed by dehalogenation in the presence of sodium hydrosulfite dissolved in aqueous pyridine under a nitrogen atmosphere.     

Intermolecular methyl transfer on pyrolysis of carpronium chloride

The methyl transfer occurring in the production of methyl N,N-dimethyl-γ-aminobutyrate by pyrolysis of carpronium chloride was examined by means of pyrolysis gas chromatography mass spectrometry with the aid of some deuterated compounds. The mass spectra of methyl N,N-dimethyl-γ-aminobutyrate, produced from deuterated derivatives of carpronium chloride, showed inter alia, characteristic molecular ion peaks which indicated that the methyl of the trimethylammonium group transfers and displaces the methyl of the carbomethoxy group of the tertiary amino compound. The results show that an intermolecular methyl transfer occurs in part on pyrolysis of carpronium chloride, to form methyl N,N-dimethyl-γ-aminobutyrate in which the methyl oxygen is replaced by a methyl from the nitrogen of the original compound. The mechanism presented involves the bimolecular reaction between zwitterionic intermediates formed by ionic O-demethylation of carpronium chloride.     

Recent progress in the improvement of hydrothermal stability of zeolites

Zeolites have been successfully employed in many catalytic reactions of industrial relevance. The severe conditions required in some processes, where high temperatures are frequently combined with the presence of steam, highlight the need of considering the evolution of the catalyst structure during the reaction. This review attempts to summarize the recently developed strategies to improve the hydrothermal framework stability of zeolites.

This review attempts to summarize the recently developed strategies to improve the hydrothermal framework stability of zeolites.     

Preparation and characterization of polypropylene/mesoporous silica nanocomposites with confined polypropylene

Polypropylene (PP)/Ti-MCM-41 nanocomposites were prepared by isospecific propylene polymerization with Ti-MCM-41/Al(i-C₄H₉)₃ catalyst. The cross polarization/magic angle spinning (CP/MAS) ¹³C NMR spectrum of the composite was similar to that of the conventional isotactic PP, and the decrease in the pore volume of Ti-MCM-41 in the nanocomposites, as measured by N₂ adsorption, was consistent with the value calculated from the weight loss in the thermogravimetric analysis (TGA) curve; both these facts attest to propylene polymerization within the mesopores of Ti-MCM-41. Alkali treatment followed by extraction with o-dichlorobenzene allows us to extract the confined PP out of the Ti-MCM-41 mesopores. Although the PP/Ti-MCM-41 nanocomposites do not exhibit a crystalline melting point, the same PP when extracted from the mesopores showed a clear melting point at 154.7 °C; this indicates that the crystallization of PP confined in mesopores is strongly hindered. For the PP polymerized within the confinement, the molecular weight (M_w) and molecular weight distribution (M_w/M_n) were 84,000 and 4.3, respectively; these values were considerably smaller than those of the PP polymerized concurrently outside the Ti-MCM-41 mesopores (M_w = 200,000–450,000, M_w/M_n = 40–75). Therefore, the confinement also has a marked effect on the molecular weight of the PP. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3324–3332, 2003     

Temperature dependence of the mixed-valence state of57Fe-atoms produced in57Co-Labelled oxo-centered trinuclear iron acetate complexes

Emission Mössbauer spectra of mixedvalence trinuclear complexes,⁵⁷Co-labelled [CoFe₂O(CH₃CO₂)₆(H₂O)₃] and [CoFe₂O(CH₃CO₂)₆ (py)₃]py were compared with that of [CoCr₂O(CH₃CO₂)₆ (py)₃]py. It was found that the⁵⁷Fe atoms produced in⁵⁷Co-labelled [CoFe₂O(CH₃CO₂)₆(H₂O)₃] and [CoFe₂O(CH₃CO₂)₆ (py)₃]py showed a temperature-dependent mixed-valence state as observed in the absorption Mössbauer spectra of [Fe₃O(CH₃CO₂)₆ (H₂O)₃] and [Fe₃O(CH₃CO₂)₆ (py)₃]py, respectively, while⁵⁷Co-labelled [CoCr₂O(CH₃CO₂)₆ (py)₃]py showed a temperature-independent divalent iron/II/ state. The results indicate that the decayed atoms keep their position at the sites of original⁵⁷Co atoms and that the valence electrons are transferred through the intramolcular bondings.     

Pyrolysis reaction of carpronium chloride and its structurally related compounds. 2—a mass spectrometric study of the lactonization mechanism

The mechanism of the pyrolysis reaction of carpronium chloride [(CH₃)₃N⁺? (CH₂)₃? COOCH₃CI^?] leading to γ-butyrolactone and tetramethylammonium chloride was investigated by means of thermal analysis, pyrolysis gas chromatography mass spectrometry and field desorption mass spectrometry, using deuterium labelling. The results indicated that carpronium chloride pyrolysed to yield equimolar amounts of γ-butyrolactone and tetramethylammonium chloride, methyl transfer occurred between N and O during the pyrolysis process. The mechanism is discussed on the basis of the experimental results, and with the aid of the theoretical results calculated by the CNDO/2 method. The mechanism presented is as follows. γ-Butyrolactone is formed by the intramolecular migration of the π-orbital of C?O to the carbon adjacent to [(CH₃)₃N]⁺ via a 5-membered ring transition state, accompanied by a bimolecular reaction between [(CH₃)₃N]⁺ and the CH₃ of O? CH₃, resulting in the formation of tetramethylammonium chloride in an amount equimolar with γ-butyrolactone.     

On the spin relaxation of57Fe(III) species produced through EC-decay in diamagnetic57Co-labelled Co(III) compounds

Absorption Mössbauer spectra of high-spin⁵⁷Fe(acac)₃ incorporated in diamagnetic Co(acac)₃ and in paramagnetic Mn(acac)₃ and of the γ-ray irradiated (⁵⁷Fe, Co) (acac)₃ and (⁵⁷Fe, Mn) (acac)₃ were compared with emission spectra of⁵⁷Co-labelled Co(acac)₃. Magnetic hfs is found in the spectra of (⁵⁷Fe, Co) (acac)₃ at 78 to 195 K, whereas such hfs is observed neither for the spectrum of⁵⁷Co-labelled Co(acac)₃ nor for that of γ-ray irradiated (⁵⁷Fe, Co) (acac)₃). The absence of magnetic hfs in the spectrum of diamagnetic⁵⁷Co-labelled cobalt(III) compounds was ascribed to the spin-spin interaction due to the radicals produced in the vicinity of the decayed atom.     

Separation of fatty acid methyl esters by comprehensive two-dimensional supercritical fluid chromatography with packed columns and programming of sampling duration

Fatty acid methyl esters from various fats and oils were separated by comprehensive two-dimensional supercritical fluid chromatography with conventional packed columns and FID detection. The first dimension was a silica gel column and the second dimension was an ODS column. This combination was largely orthogonal for the separation of fatty acid methyl esters. The first dimension separations were primarily based on the number of double bonds while the second dimension separations were based on the chain length. The highly-ordered chromatograms and improved resolution allowed the easy detection and identification of minor components. Although the first dimension separations were performed under isobaric conditions where the peak width increased in proportion to the retention, the programming of the sampling duration allowed us to maintain the optimum re-injection frequency (3–4 times) per peak into the second dimension and so to minimize the total analysis time without deteriorating the resolution.