N-Tritylhydroxylamines: preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid

Abstract

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 pK_a 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.