The reactivity of two series of compounds: alkyl x-oxoalkanoates (x = 2, 3, 4 and 6), and alkyl x-phenyl-y-oxoalkanoates (y = 2 and 4) has been studied in the catalytic transfer hydrogenation (CTH) over magnesium oxide as the catalyst. The catalytic tests have been performed either in liquid or vapor phase with secondary alcohols (2-propanol to 2-octanol) as hydrogen donors. A strong diminution of reactivity of the ketoesters in CTH has been observed, in contrast to simple aliphatic or aralkyl ketones. The occurrence of transalcoholysis between ketoesters and alcohols used as hydrogen donors resulted in the formation of new ketoesters as side products. The hydroxoesters, i.e. the products of the CTH reaction, have been obtained with only moderate to good yields (up to 50 %). It has been found that in the CTH of ketoesters with the carbonyl group in a c position, such as alkyl levulinates and benzoylpropionates, the appropriate lactones (c-valerolactone and 5-phenyl-c-valerolactone) have been formed.
The first aim of the research was to synthesize a pure Upsalite, which is an amorphous form of MgCO3, by modifying a procedure described in the literature, so that it would be the precursor of a high-surface, amorphous magnesium oxide. The results indicate that within the studied reaction conditions, the type of alcohol used as the reactant has the most pronounced effect on the yield of reaction. From the two alcohols that led to the highest yield of Upsalite, methanol gave a substantially larger surface area (794 vs. 191 m2 g−1). The optimized synthesis conditions of Upsalite were used to obtain MgO via thermolysis, whose activity in the transfer hydrogenation reaction (THR) from ethanol, 2-propanol and 2-pentanol to various carbonyl compounds was determined. The optimal conditions for the thermolysis were as follows: vacuum, T = 673 K as the final temperature, and a heating rate of 2 deg min−1. The high-surface, amorphous magnesia (SBET = 488 m2 g−1) was found to be a very selective catalyst to 4-t-butylcyclohexanone in THR, which led to a diastereoselectivity of over 94% to the E-isomer of 4-t-butylcyclohexanol for more than 3 h, with conversions of up to 97% with either 2-propanol or 2-pentanol as the hydrogen donor. In the case of acrolein and 2-n-propylacrolein being used as the hydrogen acceptors, the unsaturated alcohol (UOL) was the main product of the reaction, with higher UOL yields noted for ethanol than 2-propanol.
In this study, magnesium nitrate, chloride or sulphate were used in the synthesis of Mg(OH)2, the precursor of MgO. It was found that the counter ion strongly influences the purity of the Mg(OH)2, as well as the specific surface area of the obtained MgO. The latter is also strongly influenced by the calcination temperature. The choice of the precipitating agent can lead to the introduction of K+ or Na+ ions and hence NH3 (aq) is the best choice. A multistep precipitation procedure of Mg(OH)2 was proposed to lower the concentration of typical impurities (Fe, Ni and Mn) found in commercial p.a. purity Mg(NO3)2. The effect of the number of portions of water used for washing of Mg(OH)2 on the purity of the final product has also been investigated in detail. The stages of formation of grains of Mg(OH)2 and their subsequent thermal decomposition was described together with determination of the introduction of new impurities into the material. Large scale (1500 g) preparation of Mg(OH)2 with an improved purity was performed and described. Therefore, this study explains what measures should be taken to obtain pure magnesia catalysts and is a valuable resource for catalytic research in which magnesia is used.
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