Nucleophilic activation of hydrogen peroxide. On the formation and the reactivity of 1H-1,2,4-triazoleperoxycarboxylic acid and O-p-nitrophenylmonoperoxycarbonic acid†

Abstract

Measurements of the infrared phosphorescence of singlet molecular oxygen (¹O₂) at 1270 nm have been employed to demonstrate the formation of ¹O₂ in the system N,N′-carbonyldi-1,2,4-triazole (CDT)–hydrogen peroxide and in the system 1H-1,2,4-triazolecarboxylic acid p-nitrophenyl ester (TCNP)–hydrogen peroxide in tetrahydrofuran. At hydrogen peroxide concentrations of [H₂O₂] ≥ 2 [CDT] or ≥ 2 [TCNP] one molecule of ¹O₂ is generated per molecule of CDT and TCNP, respectively. In both systems a very reactive peroxy-intermediate is formed. In the system CDT–H₂O₂ the 1H-1,2,4-triazoleperoxycarboxylic acid (1) is generated, in TCNP–H₂O₂ the p-nitrophenylmonoperoxycarbonic acid (4). For the epoxidation of cyclohexene in THF by 1 a rate constant k₁₅ ≈3 × 10⁰ dm³ mol^–1 s^–1 can be estimated. For 4 the corresponding rate constant was found to be k₂₀ ≈ 6 × 10^–2 dm³ mol^–1 s^–1. The Arrhenius parameters of the formation of 1 and 4, respectively, and in addition of their consecutive reactions with hydrogen peroxide were determined. The results are consistent with the assumption that the nucleophilic displacements by hydrogen peroxide at the carbonyl carbon atom are addition–elimination processes, which take the form of a B_AC2-mechanism.