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Pyridine, pyridazine, pyrimidine and pyrazine were investigated in their reaction with ozone. These compounds are archetypes for heterocyclic aromatic amines, a structural unit that is often present in pharmaceuticals, pesticides and dyestuffs (e.g., enoxacin, pyrazineamide or pyrimethamine). The investigated target compounds react with ozone with rate constants ranging from 0.37 to 57 M −1 s −1 , hampering their degradation during ozonation. In OH radical scavenged systems the reaction of ozone with pyridine and pyridazine is characterized by high transformation (per ozone consumed) of 55 and 54%, respectively. In non scavenged system the transformation drops to 52 and 12%, respectively. However, in the reaction of pyrimidine and pyrazine with ozone this is reversed. Here, in an OH radical scavenged system the compound transformation is much lower (2.1 and 14%, respectively) than in non scavenged one (22 and 25%, respectively). This is confirmed by corresponding high N -oxide formation in the ozonation of pyridine and pyridazine, but probably low formation in the reaction of pyrimidine and pyrazine with ozone. With respect to reaction mechanisms, it is suggested that ozone adduct formation at nitrogen is the primary step in the ozonation of pyridine and pyridazine. On the contrary, ozone adduct formation to the aromatic ring seems to occur especially in the ozonation of pyrimidine as inferred from hydrogen peroxide yield. However, also OH radical reactions are supposed processes in the case of pyrimidine and in particular for pyrazine, albeit negligible OH radical yields are obtained. The low compound transformation in OH radical scavenged system can prove this. As a result of negligible OH radical yields in all cases (less than 6%) electron transfer as primary reaction pathway plays a subordinate role. [ABSTRACT FROM AUTHOR]

Anilines as archetypes for aromatic amines, which play an important role in the production of, e.g., dyestuffs, plastics, pesticides or pharmaceuticals were investigated in their reaction with ozone. Due to their high reactivity towards ozone (1.2 × 10 5 –2.4 × 10 6 M −1 s −1 ) the investigated aniline bearing different substituents are readily degraded in ozonation. However, around 4 to 5 molecules of ozone are needed to yield a successful transformation of aniline, most likely due to a chain reaction that decomposes ozone without compound degradation. This is inferred from OH radical scavenging experiments, in which compound transformation per ozone consumed is increased. Mechanistic considerations based on product formation indicate that addition to the aromatic ring is the preferential reaction in the case of aniline, p -chloroaniline and p -nitroaniline (high amounts of o -hydroxyaniline, p -hydroxyaniline, chloride, nitrite and nitrate, respectively were found). For aniline an addition to the nitrogen happens but to a small extent, since nitroso- and nitrobenzene were observed as well. In the case of N -methylaniline and N , N -dimethylaniline, an electron transfer reaction from nitrogen to ozone was proven due to the formation of formaldehyde. In contrast, for p -methylaniline and p -methoxyaniline the formation of formaldehyde may result from an electron transfer reaction at the aromatic ring. Additional oxidation pathways for all of the anilines under study are reactions of hydroxyl radicals formed in the electron transfer of ozone with the anilines (OH radical yields = 34–59%). These reactions may form aminyl radicals which in the case of aniline can terminate in bimolecular reactions with other compounds such as the determined o -hydroxyaniline by yielding the detected 2-amino-5-anilino-benzochinon-anil. [ABSTRACT FROM AUTHOR]

Piperidine, piperazine and morpholine as archetypes for secondary heterocyclic amines, a structural unit that is often present in pharmaceuticals (e.g., ritalin, cetirizine, timolol, ciprofloxacin) were investigated in their reaction with ozone. In principle the investigated compounds can be degraded with ozone in a reasonable time, based on their high reaction rate constants with respect to ozone (1.9 × 10 4 –2.4 × 10 5 M −1 s −1 ). However, transformation is insufficient (13–16%), most likely due to a chain reaction, which decomposes ozone. This conclusion is based on OH scavenging experiments, leading to increased compound transformation (18–27%). The investigated target compounds are similar in their kinetic and stoichiometric characteristics. However, the mechanistic considerations based on product formation indicate various reaction pathways. Piperidine reacts with ozone via a nonradical addition reaction to N -hydroxypiperidine (yield: 92% with and 94% without scavenging, with respect to compound transformation). However, piperazine degradation with ozone does not lead to N -hydroxypiperazine. In the morpholine/ozone reaction, N -hydroxymorpholine was identified. Additional oxidation pathways in all cases involved the formation of OH with high yields. One important pathway of piperazine and morpholine by ozonation could be the formation of C-centered radicals after ozone or OH radical attack. Subsequently, O 2 addition forms unstable peroxyl radicals, which in one pathway loose superoxide radicals by generating a carbon-centered cation. Subsequent hydrolysis of the carbon-centered cation leads to formaldehyde, whereby ozonation of the N -hydroxy products can proceed in the same way and in addition give rise to hydroxylamine. A second pathway of the short-lived peroxyl radicals could be a dimerization to form short-lived tetraoxides, which cleave by forming hydrogen peroxide. All three products have been found. [ABSTRACT FROM AUTHOR]

This paper deals with reactions occurring in the aqueous system of 2-propanol/ozone. The considered reactions are discussed from thermodynamic and kinetic points of view. The major finding refers to the fact that 2-propanol reacts with O 3 mainly via hydride transfer: (HO)(H 3 C) 2 C H + O 3 → [(HO)(H 3 C) 2 C + + HO 3 − ] cage → (HO)(H 3 C) 2 C + + HO 3 − → (H 3 C) 2 C O + H 2 O + O 2 Arguments supporting this proposed mechanism are: high exergonicity of reaction (ΔG = −234 kJ mol −1 for the first two steps), low HO yield - (2.4 ± 0.5)% and high acetone yield - (87.2 ± 1.5)%. Other oxidation products detected within the system are acetaldehyde - (1.4 ± 0.1)%, formaldehyde - (4.0 ± 0.1)%, acetic acid - (2.8 ± 0.2)%, formic acid - (0.6 ± 0.2)% and hydrogen peroxide - (1.5 ± 0.1)%. The temperature dependence of the second order rate constant for the reaction 2-propanol + O 3 → products is ln k II = 29.64–8500 × T −1 . The activation energy and pre-exponential factor derived from this relationship are (71 ± 3) kJ mol −1 and (7.5 ± 6.4) × 10 12 M −1 s −1 , respectively. At 23 °C, the second order rate constant is k II = (2.7 ± 0.1) M −1 s −1 . The low reaction rate can be explained by the transfer of one hydride ion from 2-propanol to electrophilic ozone. [ABSTRACT FROM AUTHOR]