Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
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.
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