SOLID BASE-CATALYZED REACTION OF NITRILES WITH METHANOL TO FORM ALPHA,BETA-UNSATURATED NITRILES

Solid acid and base properties of magnesium oxides activated by transition metal ions, MMgO, which are effective catalysts for the reaction of nitriles with methanol to form corresponding α,β-unsaturated nitriles, were studied by temperature-programmed desorption of CO2 and the reaction of isopropyl alcohol, and the reaction mechanism was studied by isotopic tracer methods. The surface base property of magnesium oxide was modified by the addition of a metal ion; the addition of a metal ion with larger ionic radius than Mg2+ increases the amount of surface base site, whereas the addition of a metal ion with an ionic radius smaller than that of Mg2+ induces surface acid sites without any appreciable changes in the amount of surface base site. Active catalysts were formed in the latter case but not in the former case. It was thought that a surface acid property as well as a surface base property played an important role in the course of the reaction. Reaction of deuterium-substituted acetonitrile and methanol revealed that the exchange reaction between hydroxyl hydrogen of methanol and methyl hydrogen of acetonitrile took place readily under the conditions of acrylonitrile synthesis and the isotopic distribution in acetonitrile after the reaction was very close to that of isotopic equilibrium. No exchange reaction between methyl hydrogen of methanol and that of acetonitrile was observed. It was found, on the other hand, that the isotopic exchange reaction between methyl hydrogen of deuterated methanol and light methanol can occur under the same conditions. The reaction mechanism appears to be dehydrogenation of methanol to adsorbed formaldehyde which then reacts with the acetonitrile anion and, after dehydration, yields acrylonitrile. © 1990.