Kinetic and mechanistic studies of the ozonation of alicyclic amines

Studies about the ozonation of the polar and mobile alicyclic amines pyrrol idine, piperidine, morpholine and piperazine were carried out in model wate r at pH 7.0. According to a pseudo-first order rate law the reaction-rate c onstants were determined from the decrease of the amine concentration vs, t he reaction time. The order of degradation of the alicyclic amines by ozone , resulting from the kinetic constants obtained, is piperazine > morpholine >>> piperidine > pyrrolidine. The pH value of the water, the chemical stru cture of the amines and their pK(A) values are recognized to be parameters influencing the reaction-rates of the amines. Using a radical scavenger (tert-butanol) it could be shown that the degrada tion of amines by ozone in neutral solution is caused by direct oxidation w ith the ozone molecule. According to that, the alicyclic amines are oxidize d by ozone electrophilicly at the activated C-N-(pyrrolidine, piperidine, p iperazine) as well as C-N- and C-O-bonding (morpholine), respectively. Afte r cleavage of the ring system, low molecular weight compounds are formed. The amount of free amines (non-protonized species) determined by the degree of protonation of the amines plays the dominant role for the different rea ction-rates of the compounds. For piperazine, as an example it was demonstr ated that partly protonized species can also be oxidized by ozone.