Abstract
The aim of the work was to study the unusual regularities of propylene carbonate prepared by carboxylation of propylene oxide in the presence of the catalytic system ZnBr2/Et4N+Br−. Using the kinetic method, a long induction period was detected, followed by the rapid formation of propylene carbonate in a quantitative yield, where the maximum turnover frequency (TOF) values reached 21,658 h−1. The regularities of the influence of the main process parameters on the induction period duration and the reaction rate were established. Based on the results obtained and considering the literature, assumptions about the mechanism of the process were proposed and ways for its further study were outlined.
Highlights
IntroductionAmongst the numerous catalysts used for carrying out these processes, from a practical point of view, zinc compounds in combination with quaternary ammonium salts ZnX2 /R4 N+ X− (X = Hal, R = Alk) are very promising [3,4]
The catalytic carboxylation of α-oxides is one of the most effective methods for producing cyclic carbonates, which are widely used as electrolytes for Li-batteries, solvents, monomers, etc. [1,2].Amongst the numerous catalysts used for carrying out these processes, from a practical point of view, zinc compounds in combination with quaternary ammonium salts ZnX2 /R4 N+ X− (X = Hal, R = Alk) are very promising [3,4]
The components of the catalytic system were placed into the autoclave, and after sealing, it was evacuated and propylene oxide was loaded using a siphon from a measuring vessel, and CO2 was supplied at the required pressure, followed by the closure of the gas supply valve
Summary
Amongst the numerous catalysts used for carrying out these processes, from a practical point of view, zinc compounds in combination with quaternary ammonium salts ZnX2 /R4 N+ X− (X = Hal, R = Alk) are very promising [3,4]. It is known that each of the components of these systems, as a rule, is a low-active catalyst in this reaction, but their combined use significantly increases the rate and ensures mild processing conditions. It should be noted that these reactions are typically studied by determining the yield of the final product, whereas the observation of changes in processing parameters (pressure and temperature) over time are usually not carried out. The preparation of propylene carbonate (PC) by the carboxylation of propylene oxide (PO) was carried out together with the continuous automatic recording of the pressure and temperature using electronic sensors. Since the studied reaction was used to obtain the PC labeled with a stable carbon isotope 13 C (an intermediate product in the synthesis of the diagnostic drug 13 C-urea [5]) [6,7,8]
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