Insight into the mechanism of 3,3′-dimethyl-4,4′-diaminodiphenylmethane synthesis over Hβ zeolite

•A novel method for synthesis of MDT catalyzed by acidic zeolites replacing mineral acids.•Hβ with strong Bronsted acidity and proper textural property showed good catalytic performance.•Synthetic process went through multiple steps involving several reaction intermediates.•The detailed interpretation to the mechanism of various intermediates reaction was presented.

Heterogeneous synthesis of 3,3′-dimethyl-4,4′-diaminodiphenylmethane (MDT) from o-tolylamine and formaldehyde on acidic zeolites HY, HZSM-5, Hβ and TS-1 was investigated. Hβ zeolite with strong Bronsted acidity and proper textural property demonstrated better catalytic performance than other three zeolites for this synthetic reaction. Yield and selectivity of product MDT from the catalytic reaction over Hβ strongly depended on temperature, and optimal reaction temperature appeared to be about 433 K. Based on analyses of LC/MS and 1H NMR for reaction intermediates, it was suggested that the synthetic process went through multiple steps involving intermediates o-tolylamino-methanol, methylene-o-tolylamine, N,N′-di-o-tolyl-methanediamine and 2-methyl-4-(o-tolylamino-methyl)-phenylamine. Interpretation to the mechanism of various intermediates formation and conversion was presented.

Graphical abstractOverview of reaction sequence for MDT synthesis over Hβ zeolite.Figure optionsDownload full-size imageDownload high-quality image (111 K)Download as PowerPoint slide