Scheme 4.12 Modes of adsorption (III and IV) of DMC over Na-exchanged faujasites.

patterns (for simplicity, Scheme 4.13 considers only one adsorption mode for both reagents).

Then, contrary to our previous hypothesis,23 the reaction proceeds via a BAl2 displacement of aniline on DMC. The product, mono-N-methyl aniline (PhNHMe), plausibly adsorbs into the zeolite in a different way with respect to aniline, because different H-bonds (N—H ••• O-zeolite) take place with the solid. As recently reported by Su et al.,32 N-methyl amines also may interact with NaY by H-bonding between the protons of the methyl group and the oxygen atoms of the zeolite: this probably forces the molecule a bit far from the catalytic surface in a fashion less apt to meet DMC and react with it. This behavior can account for the mono-N-methyl selectivity observed, which is specific to the use of DMC: in the presence of alkali metal exchanged faujasites; in fact, the bis-N-methylation of primary aromatic amines occurs easily with conventional methylating agents (i.e., dimethyl sulfate).33

Scheme 4.13 BAl2 displacement of aniline on DMC within the NaY supercage.
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