Computational Screening of Lewis Acid Catalysts for the Ene Reaction between Maleic Anhydride and Polyisobutylene

Polyisobutenyl succinic anhydrides (PIBSAs) and their succinimide derivatives are one of the most important additives in lubricant and fuel formulations. These additives are commonly synthesized through the ene reaction between maleic anhydride (MAA) and polyisobutene (PIB). Although this reaction is thermodynamically feasible, it requires elevated temperatures to overcome kinetic limitations. In this regard, Lewis acids are shown to be prominent catalysts for the ene reaction by making the enophile more electron-deficient. Despite the industrial importance of PIBSA in the automotive industry, a computational methodology to screen potential Lewis catalysts for the ene reaction between MAA and PIB has not been established. Herein, we report the detailed mechanism of the Lewis acid-catalyzed ene reaction based on first principles calculations. We demonstrated that the most favorable pathway for the ene reaction between MAA and PIB is through a concerted reaction mechanism. By screening different Lewis acid catalysts, we developed activity relationships relating the activation energy with the adsorption/desorption energies of the species from the catalyst. Turnover frequency calculations revealed that, among the Lewis acid chloride-based catalysts studied, AlCl3 exhibits the highest catalytic activity. Overall, our work introduced catalytic activity relationships that can accelerate the discovery of Lewis acid catalysts for ene reactions of industrial importance.

Automated summary

Polyisobutenyl succinic anhydrides (PIBSAs) and their succinimide derivatives are important additives in lubricant and fuel formulations, synthesized through the ene reaction. This study reports the mechanism of Lewis acid-catalyzed ene reaction and finds that AlCl3 exhibits the highest catalytic activity among the studied catalysts. The work introduces catalytic activity relationships that can accelerate the discovery of Lewis acid catalysts for industrial ene reactions.