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Kinetic Study of the Bromine‐Catalyzed Isomerization of Methyl‐ and Chloro‐Maleic Acids in Aqueous Ce(IV)‐Br ‐H 2 SO 4 Medium
Author(s) -
Jwo JingJer,
Huang CheYuan,
Chang EngFen,
Wu Ru Rong
Publication year - 1987
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.198700038
Subject(s) - isomerization , chemistry , maleic acid , catalysis , aqueous solution , enthalpy , sulfuric acid , medicinal chemistry , itaconic acid , inorganic chemistry , organic chemistry , physics , quantum mechanics , copolymer , polymer
Methylmaleic (citraconic, CTA) acid and methylfumaric (measaconic, MSA) acid in aqueous sulfuric acid solution undergo bromine‐catalyzed reversible cis‐trans isomerization in the presence of ceric and bromide ions. The positional isomerization of CTA or MSA to itaconic acid (ITA) is not observed. The method of high performance liquid chromatography (HPLC) was applied to study the kinetics of this catalyzed isomerization. The major catalytic species is best expressed as the Br − 2 · radical anion. Under suitable catalytic conditions, there is a tendency for the [MSA]/[CTA] ratio to reach an equilibrium value of 4.10 at 25° for the CTA+Br − 2 · ⇄ MSA+Br − 2 · reaction. Chloromaleic (CMA) and chlorofumaric (CFA) acids undergo similar isomerization with an equilibrium [CFA]/[CMA] ratio of 10.3 at 25°. The isomerization of maleic acid (MA) to fumaric acid (FA) is essentially irreversible with 50 as the lower limit of the equilibrium [FA]/[MA] ratio. The substituent has an important effect on the reversibility of this catalyzed isomerization of butenedicarboxylic acids. The thermodynamic parameters ΔH ° and ΔS ° at 25° for the CTA+Br − 2 · ⇄ MSA+Br − 2 · reaction were found to be −5.1±0.7 kj/mol and −6.0±3.3 J/mol K, respectively. The present method gives a plausible way to measure the differences in enthalpy and entropy between the trans ‐ and cis ‐isomers of butenedicarboxylic acids (CRCO 2 H=CR'CO 2 H) in aqueous solution.