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JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2, no.9, pp.1748-1752, 2001 (SCI-Expanded)
Substituted N-tritylamines undergo deamination in aqueous acidic solution containing organic cosolvents, and follow a pseudo first-order specific acid-catalysis rate law (k(obs) = k(0) + k(H)[H3O+]), the products are the corresponding trityl alcohols in equilibrium with the trityl carbenium ions, and ammonium ions. The change from 4,4'-dimethoxy- to 4,4',4"-trimethoxy-tritylamine increases reactivity by a factor of about 30 in both k(0) and k(H), but N-alkyl and N-aryl groups have much greater effects (ca. 10(6) for both k(0) and k(H) for 4,4'-dimethoxytritylamine) which are largely independent of the nature of the N-alkyl and N-aryl groups. The anions of the catalytic strong acids (perchlorate, chloride, bromide, and nitrate) have only small effects as also does the concentration of acetonitrile as cosolvent; ethanoic acid as cosolvent is mildly rate-enhancing. Substituents in the aniline residue of N-(4,4'-dimethoxytrityl)anilines have virtually no effect upon either k(0) or k(H) (p = 0 for both). The results are interpreted by a mechanism involving a pre-equilibrium heterolysis of the (substituted) tritylammonium ion to give an ion-molecule pair which may undergo diffusional or acid-catalysed dissociation before the (substituted) trityl cation undergoes equilibrium nucleophilic capture by water. Base strengths of some substituted N-tritylamines have been measured; the substituted N-trityl group causes all amines (aliphatic and aromatic) to be comparably strongly basic (pK(BH+) ca. 9).