Alkaline earth oxides, acetone condensation

A number of solid base catalysts have been reported in the literature to be active for acetone condensation. These include alkali oxides (NajO, K O, CsjO) (7), alkaline earth oxides (MgO, CaO, BaO) (1,4-6), transition metal oxides (7) and phosphates (8-11), ion-exchange resins (12), zeolites (13) and clay minerals and hydrotalcites (HTC) (14,15). A suitable catalyst for the acetone-to-MIBK reaction must have several properties the condensation of acetone to DAA is catalyzed by either basic or acidic sites, the dehydration of DAA to MO is acid-catalyzed, and the selective hydrogenation of MO to MIBK requires appropriate metal sites (7,8). 

Aldol Addition and Condensation. Alkaline earth oxides show high activities for aldol addition of acetone to diacetonealcohol at 273 K The order of the catal3dic activity is BaO > SrO > CaO > MgO. La203 and Zr02 are also active (74). The product, diactcetonealcohol often vmdergoes dehydration and further condensation to give mesityl oxide, phorone, and mesitylene. Alkaline earth oxides are also active for aldol condensation of butyraldehyde. Alumina also shows an activity but its activity was lower than that of MgO and CaO (75). 

Various nitro compounds have been condensed with carbonyl compounds in reactions catalyzed by alkaline earth metal oxides and hydroxides 145). It was found that the reactivities of the nitro compounds were in the order nitro-ethane > nitromethane > 2-nitropropane, and those of carbonyl compounds were propionaldehyde > isobutyraldehyde > pivalaldehyde > acetone > benzaldehyde > methyl propionate. Among the catalysts examined, MgO, CaO, Ba(OH)2, and Sr(OH)2, exhibited high activity for nitroaldol reaction of nitromethane with propionaldehyde. In reactions with these catalysts, the yields were between 60% (for MgO) and 26% (for Sr(OH)2) at 313 K after 1 h in a batch reactor. On Mg(OH)2, Ca(OH)2, and BaO, the yields were in the range of 3.8% (for BaO) and 17.5% (for Mg(OH)2). Investigation of the influence of the pre-treatment... 

Besides oxidative coupling of methane and double bond isomerization reactions (242), a limited number of organic transformations have been carried out with alkali-doped alkaline earth metal oxides, including the gas-phase condensation of acetone on MgO promoted with alkali (Li, Na, K, or Cs) or alkaline earth (Ca, Sr, or Ba) (14,120). The basic properties of the samples were characterized by chemisorption of CO2 (Table VI). 

Condensation of butanal has been carried out on alkaline earth metal oxides at 273 K[52 53] yielding 2-ethyl-3-hydroxy-hexanal as a main product the order of activity per unit surface area was equal to that in the case of self-condensation of acetone and in agreement with the order of basicity of the solids, namely, SrO > CaO > MgO. The authors found that for aldol condensation of w-butyraldehyde, the active sites are the surface O2 ions and the rate-determining step is the z-hydrogcn abstraction. The differences in rate-determining step and active sites in the condensation of butyraldehyde and self-condensation of the acetone were attributed to differences in acidity of the z-hydrogcn in the two molecules. CaO was slightly... 

Other transformations for which alkaline earth metal oxides are active include the hydrogenation of alkenes, the addition of amines to dienes, and the aldol condensation of acetone (312). 

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