Kinetic Modeling of Maleic Acid Isomerization to Fumaric Acid Catalyzed by Thiourea Determined by Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy

Abstract

Fumaric acid (FA) is an important commodity in the food and polymer industries; its main route of production is the chemical synthesis from maleic acid (MA). In this work, the isomerization of MA to FA catalyzed by thiourea was investigated. The experiments were performed in an automated reactor with temperature and stirring control, using methanol as the solvent to ensure a homogeneous system and to avoid a possible parallel hydration reaction to malic acid. The reaction kinetics was monitored in real time by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR/FT-IR). Studies on the influence of the catalyst concentration (1−20% of the initial molar concentration of MA) and the temperature (20−60 °C) were carried out in reaction times between 2 and 5 h. The kinetics of the reaction was modeled using an integral method over the infrared data, assuming a reaction mechanism that yielded a partial order of 1.41 for the MA concentration and a 0.99 order for the thiourea. These orders were similar to the ones found by the proposed mechanism for the acid-catalyzed isomerization, in which monomaleate is a nucleophilic reagent to react with the protonated MA. This may present a path for further studies regarding the correct reaction mechanism. The kinetic model provided an excellent correlation with the experimental data, and the observed activation energy of the reaction was calculated to be 43.1 kJ mol −1 . At higher temperatures, such as 60 °C, and with a thiourea concentration of 10% mol/mol (0.0502 mol L −1 ), the isomerization conversion was around 90% in 60 min. Accordingly, thiourea proved to be an appropriate catalyst for FA synthesis, and ATF/FT-IR proved to be a reliable technique for the kinetic study.

ATR-SEIRAS Investigation of the Electro-oxidation Mechanism of Biomass-Derived C5 Furanics on Platinum Electrodes

“…For MA, due to the lack of CO poisoning of the surface, this feature emerges at 0.7 V. Per studies in D 2 O previously discussed, we do not expect the HOH bending mode of water to be contributing to this feature. Prior ATR-FTIR studies of MA in methanol have identified features in this region as a CC stretch. However, we performed vibrational calculations for MA in a number of different geometries (shown in Figure S14 and S15) and observed that the carboxylic acid CO stretch can range widely (calculated anywhere from 1640 to 1727 cm –1 ) depending on the orientation of the molecule and interactions with the surface.…”

Combining Electro-, Photo-, and Biocatalysis for One-Pot Selective Conversion of Furfural into Value-Added C4 Chemicals

“…Currently, FA is commercially produced via thermal or catalytic isomerization of MA. , The thermal processes require high temperatures (150–200 °C) and high pressures (approximately 15.5 bar). In the catalytic processes, thiourea is the most commonly used at lower temperatures (50–100 °C).…”

A New Approach Utilizing Aza-Michael Addition for Hydrolysis-Resistance Non-Ionic Waterborne Polyester

“…Because the catalytic activity of Ti(OBu) 4 was the higher than both TsOH and DBTDL, the Entry 2L was the largest in molecular weight, but the excessive degradation reactions of Ti(OBu) 4 during polymerization process resulted the darkest color of the sample [37]. Moreover, the catalysts play an important in the isomerization process, which was usually used to manufacture fumarate from maleate [40], and the different isomerization extent using different catalysts may be related to the nucleophilicity [41] and rigidity [42] of the catalyst. In general, TsOH was more suitable as a polycondensation reaction catalyst in this work.…”