Kinetic and Mechanistic Studies on Reactions of Pyrrolidone Derivatives with Ozone

Abstract

Reactions of various pyrrolidone derivatives (NRPs = 2-pyrrolidone (2P), N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N-n-propyl-2-pyrrolidone (NProP), N-n-butyl-2-pyrrolidone (NBP), N-iso-butyl-2-pyrrolidone (NiBP), N-n-pentyl-2-pyrrolidone (NPP), N-neopentyl-2-pyrrolidone (NNPP), N-dimethylpropyl-2-pyrrolidone (NDPP), N-cyclohexyl-2-pyrrolidone (NCP)) with O₃ have been studied under pseudo–first-order conditions with excess O₃ in aqueous solution of pH 2.0 at various temperatures (278–298 K). It was found that the reaction rates is expressed as –d[NRPs]/dt = k[NRP][O₃], that the second-order rate constants (k) slightly increase with increasing the effective charges in order of NMP, NEP, NProP, NBP and NPP, and that the k values of NBP and NPP are larger than those of more bulky NiBP and more bulky NNPP and NDPP, respectively. In these reactions, the ΔH^‡ values are consistent with each other, while the ΔS^‡ values decrease with decreasing length of alkyl groups. Furthermore, it was found that reactions of NRPs (NMP, NEP, NProP, NBP, and NPP) with O₃ show the linear relationship between the obtained ΔS^‡ values and the softness of NRPs. From these results, it was proposed that the reactions of NRPs with O₃ proceed through the interaction between O₃ and N atom of NRPs. The analyses of products in the reactions of NRPs with O₃ were also carried out by ¹³C-NMR and GC/MS measurements, and indicated that N-alkylsuccinimide and N-acyl-2-pyrrolidone are produced through intramolecular side-chain oxidations of α-carbon of NRPs. From these results, it is proposed that the reactions of NRPs with O₃ proceed through the mechanism with the selective attacks of O₃ to N atom of NRPs.

Keywords:

• Ozone
• Organic nitrogen compounds
• Pyrrolidone derivatives
• Kinetics
• DV-Xα calculation

ACKNOWLEDGMENTS

The authors appreciate Dr. Masayuki Harada (Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology) for his technical supports and Mrs. Masayo Ishikawa (Chemical Resources Laboratory, Tokyo Institute of Technology) for operating GC/MS measurements.

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