Tishchenko reaction over solid base catalysts

摘要

Catalytic behaviors of solid base catalysts for mixed Tishchenko reaction in which an equimolar mixture of two different aldehydes is allowed to react were investigated using benzaldehyde, pivalaldehyde, and cyclopropanecar-baldehyde as reactants. The selectivity to four Tishchenko dimers formed over MgO and CaO is determined primarily in the step of the nucleophilic addition of the active species (PhCH_2O~-, ~tBuCH_2O~-, and C_3H_5CH_2O~-) to the carbonyl carbon atoms of the aldehydes. The reaction of the aldehyde having a more positively charged and sterically less-hindered carbonyl carbon atom with the active species having a less-hindered oxygen atom proceeds faster. Besides, we have successfully applied CaO and SrO to the challenging Tishchenko reaction of furfural; almost quantitative esterification was accomplished over SrO at 353 K in 6 h. In addition, we found that the treatment of o-phthalaldehyde with MgO, CaO, and SrO at 313 K produces phthalide in excellent yields in a short time of 15 mm via the intramolecular Tishchenko reaction. gamma-Alumina also exhibited high activity for the intramolecular Tishchenko reaction of o-phthalaldehyde to furnish phthalide in almost quantitative yield at 313 K for 4 h.