Abstract
Hydrogenated methylene dianiline (H12MDA) is a valuable precursor for thermoplastic polyurethane. Traditionally, H12MDA is obtained by hydrogenation of methylene dianiline (MDA). However, the route from aniline to MDA produces large acidic waste streams linked to the nitration of benzene and the HCl-catalyzed reaction with formaldehyde, as well as a poor selectivity for the 4,4′-isomer in the condensation reaction with formaldehyde. Herein, we report a green and efficient amination process for synthesis of H12MDA starting from (waste) bisphenols. Palladium on moderately acidic catalyst supports (carbon, Al2O3, ZrO2) provided excellent yields of H12MDA (>97%) in short reaction times (3 h) at 200 °C, with limited addition of H2 and NH3. It was found that the reaction partially proceeds via a secondary amine intermediate. A high dispersion of palladium is essential to achieve high yields of the desired H12MDA. Finally, the use of polycarbonate as an alternative feedstock for H12MDA was demonstrated via a tandem ammonolysis-amination process.
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