In situ infrared study of oxidative carbonylation of aniline with methanol on Cu-based catalysts

Abstract

Oxidative carbonylation of amines with alcohols provides an environmentally benign pathway to isocyanates and carbamates. Currently, the most active catalysts for the oxidative carbonylation of aniline with methanol are Pd-based catalysts. To further improve the economic feasibility of the carbamate synthesis process, we have investigated the activity of CuCl₂–NaI, CuCl₂–NaCl, and CuCl–NaI at 438 K and 0.41 MPa by in situ infrared spectroscopy. The activity of the catalysts for carbamate synthesis increased in the order: CuCl₂–NaCl < CuCl–NaI < CuCl₂–NaI. The presence of promoter (i.e., NaI or NaCl) in the reactant–catalyst mixture is essential to promote carbamate synthesis. The formation of by-product, CO₂, can be suppressed by the sequential addition of NaI to CO/O₂/methanol/aniline/CuCl₂. Transient profiles of reactants/products obtained from in situ infrared spectroscopic studies revealed that CO₂ and carbamate were formed via two independent pathways. The infrared observation of a Cu⁰(CO)₂ species and O₂ participation in carbamate synthesis suggest that the carbamate synthesis reaction involves a redox cycle of Cu⁰/Cu^II.