Effect of Pd(II) Species on Decomposition Reactions of Pyrrolidone Derivatives by Ozone

Abstract

Decomposition reactions of N-dimethylpropyl-2-pyrrolidone (NDPP), which is one of pyrrolidone derivatives (NRPs), by O₃ have been examined in aqueous sulfuric acid solutions containing metal ions (Fe(II), Rb(I), Sr(II), Ba(II), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Y(III), Zr(IV), Ru(III), Rh(III), Pd(II), Mo(VI), Re(VII), and Te(VI)), respectively, under conditions, pH = 2.0 and Temp. = 298 K. It was found that Pd(II) ion has the highest efficacy for the decomposition of NDPP. Hence, the effect of Pd(II) ion on the decomposition reactions of NRPs (NDPP, N-neopentyl-2-pyrrolidone (NNPP), and N-n-pentyl-2-pyrrolione (NPP)) by O₃ has been studied kinetically under conditions, pH = 1.0–3.5 and Temp. = 288 K. As a result, it was found that the decomposition reactions of NRPs by O₃ in the system containing Pd(II) ion (abbreviated as NRPs/Pd(II)/O₃ reactions) are independent on concentrations of H⁺ ([H⁺]) and proceed through two paths, one is the path depending on [Pd(II)] and the dissolved O₃ concentration ([O₃]_D), and another is the path depending on only [O₃]_D. Furthermore, it was confirmed that the 1:1 complex is formed, Pd(II) + NRPs ⇌ [Pd(NRPs)]²⁺, under the conditions [NRPs]_T/[Pd(II)]_T = 1 ∼ 12 (subscript T means total concentration), and that the stability constants (K₁) for [Pd(NRPs)]²⁺ are also evaluated as 37.8 ± 0.46, 9.33 ± 0.15, and 1.63 ± 0.11 M⁻¹ for NPP, NDPP, and NNPP, respectively. Based on these results, it was found that the reaction rate is expressed as -d[NRPs]/dt = k_aK₁[O₃]_D[NRPs][Pd(II)]_T + k_b[O₃]_D[NRPs] (k_a: rate constants for the reactions between [Pd(NRPs)]²⁺ and O₃, k_b: rate constants for the reactions between NRPs and O₃, K₁: stability constants for [Pd(NRPs)]²⁺), and that the k_a values are (6.03 ± 0.69) × 10³, (4.33 ± 0.21) × 10³, and (7.61 ± 0.23) × 10³ M⁻¹s⁻¹ for NPP, NDPP, and NNPP, respectively. From these results, it was proposed that the path depending on [Pd(II)] in the NRPs/Pd(II)/O₃ reactions proceeds through the attack of O₃ to [Pd(NRPs)]²⁺.

Keywords:

• Ozone
• Organic nitrogen compounds
• Pyrrolidone derivatives
• Metal ions
• Kinetics
• Stability constant
• Catalytic Ozonation

ACKNOWLEDGMENTS

The authors would like to thank Dr. Masayuki Harada (Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology) and Dr. Kawasaki (Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology) for fruitful discussions and technical supports.