- 作者: 卓靜哲; 陳義雄
- 作者服務機構: Department of Chemistry, National Cheng Kung University, Tainan, Taiwan 700
- 中文摘要: The presence of ceric and bromide ions catalyzes the isomerization of maleic acid (MA) to fumaric acid (FA) in aqueous sulfuric acid. A kinetic study of this bromine-catalyzed reaction was carried out. The reaction between ceric ion and maleic acid is first order with respect to Ce(IV). For [Ce(IV)]0=5.0×10… M, [H2SO4]0=1.2M, μ=2.0 M (adjusted by Naclo4), and [MA]0=(0.5-1.0)M, the observed pseudo-first-order rate constant (k01) at 25° is k01=7.622×10… [MA]0/(1+0.205[MA]0). The reaction between ceric and bromide ions is first order with respect to Ce(IV). For [Ce(IV)]0=5.0×10…M, [H2SO4]0=1.2M, μ=2.0M, and [Br¯]0=(0.025-0.150)M, the pseudo-first-order rate constant (k02) at 25° is k02=(4.313±0.095)×10…[Br¯]2+(2.060±0.119)×10…[Br¯]. The reaction of Ce(IV) with maleic acid and bromide ion is also first order with respect to Ce(IV). For [Ce(IV)]0=5.0×10…M, [MA]0=0.75M, [H2SO4}=1.2M, μ=2.0M, and [Br¯]0=(0.025-0.150)M, the pseudo-first-order rate constant (k03) at 25° is k03=(5.286±0.045)×10…[Br¯]2+(3.568±0.056)×10…[Br¯]. For [Ce(IV)]0=5.0×10…M, [Br¯]0=0.050M, [H2SO4]0=1.2M, μ=2.0M, and [MA]0=(0.15-1.0)M at 25°, k03=(2.108×10…+2.127×10…[MA]0)…1+0.205[MA]0). A mechanism is proposed to rationalize the results. The effect of temperature on the reaction rate was also studied. The energy barrier of Ce(IV)—Br¯ reaction is much less than that of Ce(IV)—MA reaction. Merleic and fumaric acids have acids have very different mass spectra. The mass spectrum, of fumaric acid exhibits a strong metastable peak at m/e66.5.
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