Catalytic Methanol Carbonylation

The carbonylation of methanol to acetic acid is established as one of the major industrial applications of homogeneous catalysis. Since the introduction of a rhodium-catalyzed process by Monsanto four decades ago, there has been almost continuous activity aimed toward improving the process and gaining a deeper understanding of the underlying chemistry. Strategies to improve catalyst performance and process economics have been developed, resulting in both rhodium- and iridium-catalyzed systems that operate with high activity at reduced water concentration, making product purification less costly. This chapter describes important aspects of the commercial processes as well as potential strategies for enhancing catalyst activity, stability, and selectivity. A particular emphasis is placed on mechanistic aspects, with experimental studies being complemented in recent years by theoretical investigations. Attempts to anchor the rhodium catalyst and to influence activity and selectivity using phosphine ligands are reviewed. Some potential alternative catalytic routes to acetic acid and derivatives are also summarized.