The kinetics and mechanism of the oxidation of formic acid by bromine in acid aqueous media

Abstract

The reaction between formic acid and bromine in strongly acid aqueous media at 298 K Br_2 + HCOOH → 2Br^- + 2H^+CO_2 was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = -d[Br_2]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br_2[(2.7–13.6) × 10^(−3)M], H^+ (0.03–2.0M), and Br^− (up to 0.6M). The mechanism HCOO^- + Br_2 → 2Br^- + H^+ + CO_2 HCOOH ^2⇌_(-2) HCOO^- + H^+ Br^- + Br_2 ^3⇌_(-3) Br_3^- with k_1 = 20.2 ± 1.2 M^(−1) sec^(−1), pK_2 = 3.76, pK_3 = −1.20, accounts for all experimental observations. Br_3^− and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species.

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