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  • 1
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the synthesis of p-hydroxybenzonitrile as a herbicide intermediate the nitrile formation is the most important reaction step. Possible feed compounds could be pure p-cresole, cresole mixtures or OH-protected cresoles like methoxy- or acetoxytoluenes. The ammoxidation of m- and p-methoxytoluene and a m,p-methoxytoluene-mixture over vanadium-titanium oxide catalysts has been investigated using flow reactors in a temperature range of 630-703 K. On comparable reaction conditions the conversion of pure compounds leads to a higher selectivity of p-methoxybenzonitrile (approx. 70%, conversion 85 mol-%) than that of the m-compound (only 35%, conversion 45 mol-%). For synthesis of the p-nitrile the feedstock can be p-methoxytoluene obtained by methylation of p-cresole, but it is also possible to use a m,p-methoxytoluene mixture obtained by methylation of an industrial cresole mixture. The ammoxidation of such a mixture affords a higher reactivity of the p-isomer and p-methoxybenzonitrile as the main reaction product, whereas m-methoxytoluene remains unreacted for the most part. Generally, the results obtained show that an amount of approx. 79% of the converted p-methoxytoluene was transformed into p-methoxybenzonitrile, whereas the corresponding transformation into the m-isomer was lower than 36%. An important part of the m-isomer was degraded by oxidation towards CO, CO2 and HCN.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9028
    Keywords: ammoxidation ; vanadium phosphate catalysts ; catalyst/feed interaction ; reaction mechanism ; FTIR spectroscopy ; TAP technique ; isotope experiments ; TPD ; TPRS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction pathway of the ammoxidation of toluene on (VO)2P2O7 used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH3 is chemisorbed on the catalyst surface, forming three different species, i.e., NH 4 + ions located on BrØnsted sites, coordinatively bound NH3 on Lewis sites and NH 2 − groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of VIV=O groups generates a V...O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH 4 + ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.
    Type of Medium: Electronic Resource
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