Magnesium oxide, aldol condensations

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythritol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is foUowed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerythritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45°C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on siHca gel gives acrolein [107-02-8] (59). 

A magnesium enolate of 99 is susceptible to aldol condensation with 4-pentenal, and the crude product can be directly protected to give its ethyl carbonate 100. a-Hydroxylation of the carbonyl group yields the hydroxyl carbonate 101. Reduction of the carbonyl group generates a triol, and this compound can be simultaneously converted to carbonate 102. Swern oxidation of 102 gives ketone 103, which can be rearranged25 to produce lactone product 104 (Scheme 7-32). 

Zhang, G., Hattori, H. and Tanabe, K. Aldol condensation of acetone/acetone-d6 over magnesium oxide and lanthanum oxide. Appl. Catal., 1988, 40, 183. 

It has previously been reported that hydrotalcite catalyzes the aldol condensation of acetone (25). Polyoxometalates are known to dehydrate alcohols due to their acidic nature (IS ). In order to compare the relative basicity of polyoxometalate-pillared hydrotalcites to that of hydrotalcite itself, a variety of hydrotalcites were screened for 2-propanol conversion (Table II). This reaction is known to give propylene when the catalyst contains acidic sites (such as alumina) and acetone when the catalyst contains basic sites (such as magnesium oxide). 

A mixture of formalin and ethanol was passed at 240—320 C over various metal oxides supported on silica gel and metal phosphates. The main products were acrolein, acetaldehyde, methanol, and carbon dioxide. Acidic catalysts such as V-P oxides promoted the dehydration of ethanol to ethene. The best catalytic performances for acrolein formation are obtained with nickel phosphate and silica-supported tungsten, zinc, nickel, and magnesium oxides. With a catalyst with a P/Ni atomic ratio of 2/3, the yields of acrolein reach 52 and 65 mol% on ethanol basis with HCHO/ethanol molar ratios of 2 and 3, respectively. Acetaldehyde and methanol are formed by a hydrogen transfer reaction from ethanol to formaldehyde. Then acrolein is formed by an aldol condensation of formaldehyde with the produced acetaldehyde [40],... 

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