N-tritylhydroxylamines: Preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid

Canle M. L., Clegg W., Demirtas İ., Elsegood M. R. J., Haider J., Maskill H., ...More

Journal of the Chemical Society, Perkin Transactions 2, vol.9, pp.1742-1747, 2001 (Scopus) identifier


N-Trityl, N-(4-methoxytrityl), N-(4,4′-dimethoxytrityl), and N-(4,4′,4″-trimethoxytrityl) derivatives of hydroxylamine, O-methylhydroxylamine, and O-benzylhydroxylamine have been prepared and characterised. Additionally, N, O-ditrityl- and N, O-bis(4,4′-dimethoxytrityl)-hydroxylamines have been made, and the X-ray crystal structure of the former has been determined. The pKa value of O-benzylhydroxylammonium in water (6.2) and of its N-trityl analogue in aqueous acetonitrile (7.5) have been measured. The N-tritylhydroxylamines all decompose under aqueous acidic conditions to give the corresponding trityl alcohols, and rate constants for uncatalysed and hydronium ion catalysed reactions of N-(4,4′-dimethoxytrityl)-O-methylhydroxylamine have been measured by stopped flow kinetics at 25°C. This compound compares in reactivity with N-alkyl-N-(4,4′-dimethoxytrityl)amines rather than with 4,4′-dimethoxytritylamine. Attempted nitrosation of N-tritylhydroxylamine and its O-alkyl derivatives gave trityl alcohol, the intermediate N-nitroso compound being detectable but too unstable to isolate. From N-trityl-O-benzylhydroxylamine, attempted nitrosation led to the formation of triphenylmethane in addition to trityl alcohol, benzyl alcohol, and trityl benzyl ether. The mildly acidic conditions used for attempted nitrosation of methoxy-substituted N-tritylhydroxylamines led to deamination before addition of the nitrosating agent.