Selective ammonolysis of carboxylic acid derivatives
To fully take advantage of the potential of bio-based molecules, selective modification chemistry on different functional groups is needed. Among the all, unsaturated diacid has been recognized as a high value-added category. The unsaturated bonds provide the position for further modification, and the diacid structure has various application in the polymer industry. However, the selective amination pathway between C-C double bonds and carboxylic acid groups has not been fully discussed in the literature. The goal of this work was to provide the chemistry information of selective amination pathways from bio-based unsaturated acids.
This work focused on the ammonolysis of more reactive acid derivative, esters, to demonstrate the ammonolysis reaction pathways. Dimethyl fumarate ammonolysis was conducted in both an ammonium hydroxide solution and an ammonia/methanol solution, the side reactions—hydrolysis and conjugate addition—were discussed respectively. We concluded that the conjugate addition reactivity differences between esters and amides can simplify the ammonolysis and conjugate addition into competing reactions. Additionally, we showed that temperature is a key factor to improve the yield of the unsaturated by reducing the side reaction.
More esters were tested to study different structural effects in ammonolysis reactions. The selectivity differences between geometric isomers were addressed by comparing dimethyl fumarate and dimethyl maleate ammonolysis. To demonstrate the feasibility of producing unsaturated amides, dimethyl 3-hexedioate was tested. A higher selectivity to unsaturated amide had been achieved. Finally, a hypothesis that unsaturated bonds near the ester groups accelerate the ester ammonolysis had been made.