Modeling ofthe synthesis of mono-, di-, tri- and tetraesters by catalytic esterification of pentaerythritol with carboxylic acids C4–C10 under polar solvent conditions

Objectives. The study set out to establish the scientific basis for the catalytic esterification of aliphatic carboxylic acids C₄–C₁₀ with pentaerythritol in a polar solvent, sulfolane. The kinetic parameters of the forward and reverse reactions were determined along with the influence of the carboxylic acid structure on the rate of conversion and the component composition of the reaction products.

Methods. The process was carried out in a perfectly stirred tank reactor with an excess of carboxylic acid (the molar ratio of pentaerythritol to carboxylic acid was 1 to 8, respectively) in a temperature range of 383.2–403.2 K. A combination of sulfolane and methanesulfonic acid was used as a catalytic system. This combination, which was found to be more effective as compared to the self-catalytic process, manifested in a 600–800-fold increase in the reaction rate at optimal amounts of sulfolane (30% by weight of the reaction system) and methanesulfonic acid (1% by weight of the reaction substrate). The composition of the reaction products was monitored by gas–liquid chromatography with preliminary calibration using pure substances. Chromatographic analysis was performed using a Kristall 2000M chromatograph equipped with a capillary column (60 m × 0.32 mm × 0.5 μm) with a grafted stationary phase BP-1 (100% dimethylpolysiloxane).

Results. For the first time, the parameters of the Arrhenius equation for the forward and reverse reactions of the esterification of 14 aliphatic carboxylic acids C₄–C₁₀ of various structures with pentaerythritol in a sulfolane medium were obtained. The resulting kinetic models satisfactorily describe the experimental data as confirmed by standard statistical calculation methods (in our case, the Pearson test was chosen, which is sensitive to a sufficiently large array of experimental data; the test value was at least 96%, indicating the adequacy of the kinetic model used to describe the processes). The influence of the carboxylic acid structure on the process rate and the composition of the reaction products was evaluated.

Conclusions. The conducted studies revealed that the composition of reaction products under chemical equilibrium conditions under the selected conditions is virtually independent of the structure of the carboxylic acid: the chemical reaction rate is determined primarily by the structure of the carboxylic acid. The obtained data can be used to substantiate verified kinetic models that provide the possibility of rational design of the synthesis of target esters with a high degree of selectivity and predictable properties.

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