Formation of citraconic anhydride via condensation of dialkyl succinates and formaldehyde Original Research Article

The formation of citraconic anhydride (CAN) from the condensation of succinic acid and its derivatives with formaldehyde over oxide catalysts is described. Alumina and aluminum phosphate are active catalysts that give selectivity to citraconic anhydride as high as 75% in an integral fixed bed reactor. Weakly acidic sites on the catalyst surface, particularly Lewis acid sites, are responsible for activating the desired reaction pathway. Strongly acidic sites lead to cracking and coking, while basic sites facilitate the Cannizzaro reaction of formaldehyde to carbon dioxide and methanol. Catalyst deactivation via coking occurs over the course of reaction, but activity is easily restored by regeneration in air at elevated temperatures. The reaction system under investigation is part of an overall process to produce itaconic acid from renewable resource-based succinic acid.