Kinetics and mechanisms of reactions of the nitrate radical (NO3) with substituted phenols in aqueous solution

Abstract

Second order rate constants were obtained for the reactions of the nitrate radical (NO₃) with substituted phenols in aqueous solutions at 298 K and pH = 0.5. The following compounds were investigated and the corresponding rate constants are reported: (1) 2-hydroxyphenol [k₁ = (5.6 ± 0.8) × 10⁸ M⁻¹ s⁻¹]; (2) 2-methylphenol [k₂ = (8.5 ± 0.2) × 10⁸ M⁻¹ s⁻¹]; (3) 2-ethylphenol [k₃ = (6.7 ± 0.4) × 10⁸ M⁻¹ s⁻¹]; (4) 2-methoxyphenol [k₄ = (1.1 ± 0.1) × 10⁸ M⁻¹ s⁻¹]; (5) 2-nitrophenol [k₅ = (2.3 ± 0.4) × 10⁷ M⁻¹ s⁻¹]; (6) 2-cyanophenol [k₆ = (3.1 ± 0.3) × 10⁸ M⁻¹ s⁻¹]; (7) 2-fluorophenol [k₇ = (5.5 ± 0.4) × 10⁸ M⁻¹ s⁻¹]; (8) 2-chlorophenol [k₈ = (2.9 ± 0.3) × 10⁸ M⁻¹ s⁻¹]; (9) 2-bromophenol [k₉ = (2.7 ± 0.1) × 10⁸ M⁻¹ s⁻¹]; (10) 2-phenylphenol [k₁₀ = (2.4 ± 0.4) × 10⁸ M⁻¹ s⁻¹]; (11) 4-hydroxyphenol [k₁₁ = (8.8 ± 0.5) × 10⁸ M⁻¹ s⁻¹]; (12) 4-aminophenol [k₁₂ = (8.1 ± 0.3) × 10⁸ M⁻¹ s⁻¹]; (13) 4-chlorophenol [k₁₃ = (1.7 ± 0.2) × 10⁹ M⁻¹ s⁻¹]; (14) 4-bromophenol [k₁₄ = (1.0 ± 0.4) × 10⁹ M⁻¹ s⁻¹]; (15) 4-hydroxybenzen ethyl ester [k₁₅ = (8.0 ± 0.4) × 10⁸ M⁻¹ s⁻¹]. Moreover, the temperature dependence of the reaction of NO₃ with four ortho-substituted phenols, (a) 2-methylphenol, (b) 2-ethylphenol, (c) 2-hydroxyphenol and (d) 2-methoxyphenol were investigated in the temperature range of 278 ≤ T ≤ 318 K and the corresponding activation parameters were obtained for the first time. A comparison of the reactivity of NO₃ towards other aromatics present in the tropospheric aqueous phase such as substituted benzenes and substituted benzoic acid was undertaken.