Catalyst Properties - One-step Aldol Condensations

The catalysts for these demanding ketone syntheses must possess at least mild basicity/acidity and a selective hydrogenation component(s). The presence of Lewis acid sites, which act as acceptors for the enolate intermediates that are formed at the basic sites, is beneficial when basic sites predominate. However, the majority of the selective catalysts appear to be mostly acidic in nature catalysts with strongly basic sites are typically non-selective to ketones,except at low ( 310-330 K) temperatures concomitant with low reaction rates and the inability to dehydrate the ketoalcohol (e.g, diamino-functionalized MCM-41, or quaternary ammonium ion exchange polymer).  

and Mo/V oxides appear to be acceptable hydrogenation metal pairs. The acid to aldehyde hydrogenation is known to be selective on Cu and Fe oxides. Cr and Fe oxides by themselves are usually insufficient for either complete dehydration or subsequent hydrogenation, except at higher tempearatures. 

While there is no question that the stronger acidic and basic oxides can speed up the typically slow aldol step, it is also true that few Bronsted-type acidic or basic sites are necessary. For example, dealumination of Pd/H-FAU or Pd/SAPO-11 molecular sieve catalysts was shown to increase activity by a factor of 5 in the acetophenone to 1,3-diphenylbutan-l-one reaction, or by 20 /o in 

Imanaka, K. Adachi, Y. Okamoto, S. Terenishi, Nippon Kagaku Kaishi, 1974, 862-866. 

Randery, Ceria Based Catalysts for Assymetric Ketone Production, M.S. Thesis, Louisiana State University, Baton Rouge (1999). 

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