Catalytic ketonization over oxide catalysts: X. Transformations of various alkyl heptanoates Original Research Article

The 20 wt.% MOx/Al2O3 catalysts, where M = Mn, Ce or Zr have been studied in ketonization of alkyl esters of heptanoic acid. A series of esters with the general formula C6H13COOR, where R = Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, s-Bu and t-Bu, was used as substrates. At high conversions, manganese catalyst showed the highest selectivity. For heptanoates with primary and secondary alkyl groups the maximum yield of 7-tridecanone was observed in the 673–698 K temperature range. In the case of n-alkyl heptanoates the value of maximum yield increased with the elongation of the n-alkyl chain. The highest reactivity was observed for t-butyl heptanoate. In the presence of manganese catalyst, its quantitative conversion and the theoretical yield of 7-tridecanone were observed already at temperatures above 548 and 573 K, respectively. On the basis of XRD and TPR measurements of freshly prepared manganese catalyst, it was concluded that its active phase contains image-MnO2 which is almost quantitatively reduced to MnO during contact with ethyl or t-butyl heptanoates. TPD measurements of ethyl and t-butyl heptanoates revealed dominant CO2 desorption peak for both esters and lesser peaks for octan-2-one, heptanal, 1-heptanol and 7-tridecanone, and the substrates. Ethene, diethyl ether and ethanol, and 2-methylpropene were found to be desorbates for ethyl and t-butyl ester, respectively.