Chemistry Letters
Online ISSN : 1348-0715
Print ISSN : 0366-7022
ISSN-L : 0366-7022
Volume 35 , Issue 2
Showing 1-45 articles out of 45 articles from the selected issue
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  • Toshihide Baba, Koji Inazu
    2006 Volume 35 Issue 2 Pages 142-147
    Published: 2006
    Released: December 27, 2005
    JOURNALS RESTRICTED ACCESS
    The heterolytic dissociation of CH4 over silver cationic clusters (Agn+) in Ag+-exchanged zeolites leads to the formation of silver hydride (Agn–H) and methyl cations, which then reacts with C2H4 to form C3H6. This process provides methane conversion of 13.2% at 673 K to afford higher hydrocarbons, such as toluene. Under these reaction conditions, H–ZSM-5 only catalyzes ethene conversion to higher hydrocarbons, such as butenes, and no methane conversion occurs. The reaction of CH4 with benzene also proceeds to form toluene and xylenes over Ag–ZSM-5 at 673 K. Zeolites prepared by exchange with other metal cations, including In and Ga, also activate CH4 in the presence of C2H4. Using 13C-labeled methane (13CH4) as a tracer, propene is shown to be a primary product for the ethene reaction based on the observation of a significant proportion of singly 13C-labeled propene (13CC2H6). In–ZSM-5 catalyzes the formation of not only propene, but also benzene and toluene. 13C label atoms are not found in the benzene thus produced, indicating that benzene originates entirely from C2H4. However, the occurrence of singly 13C-labeled toluene (13CC6H8) implies that toluene is formed by the reaction of benzene with 13CH4. The alternative reaction path, involving 13CC6H8 formation by reaction of propene with n-butenes generated by ethene dimerization, can be refuted by confirmation of the toluene origin through direct reaction of 13CH4 with benzene.
  • Ilya D. Gridnev
    2006 Volume 35 Issue 2 Pages 148-153
    Published: 2006
    Released: December 28, 2005
    JOURNALS RESTRICTED ACCESS
    Complete chiral crystallization and absolute chiral synthesis are both fascinating phenomena shedding light on the possible origins of homochirality in nature and opening perspectives for efficient preparations of optically pure materials. Originally these two phenomena have been considered mechanistically quite different belonging to the hetero- and homogeneous systems, respectively. However, the results of the active research in both fields undertaken in the last few years suggest that there may be a much closer likeness of the most important mechanistic features of these two phenomena. In the present review, we bring together the latest data on the complete chiral crystallization and absolute chiral synthesis including our own data on the mechanism and spontaneous break of chirality in the Soai asymmetric autocatalysis.
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