Nitrosation of 2-hydroxyethylpiperidine

Abstract

The kinetics of the nitrosation of 2-hydroxyethylpiperidine have been studied in acidic (0.05–0.30 mol dm⁻³ HClO₄) aqueous media. The reaction rate is first order with respect to nitrite and amine and independent of acidity and shows an experimental isotope effect of 1.73. The most plausible mechanism involves the fast formation of an alkyl nitrite in the protonated amine (equilibrium constant estimated as 0.014 dm³ mol⁻¹). The loss of a proton from this intermediate is the rate-limiting step, and it is followed by a fast internal nitroso group transfer from the oxygen to the nitrogen atom to give the corresponding N-nitroso compound. A comparison of this nitrosation pathway of secondary amines in acid media with the nitrosation of thiomorpholine and piperidine, and with that of amines by alkyl nitrites in basic media is also discussed.