Volume 13, Issue 8 p. 2005-2016
Full Paper

Diethylene Glycol/NaBr Catalyzed CO2 Insertion into Terminal Epoxides: From Batch to Continuous Flow

Davide Rigo

Davide Rigo

Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venezia, Via Torino 155, 30172 Venezia, Mestre, Italy

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Roberto Calmanti

Roberto Calmanti

Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venezia, Via Torino 155, 30172 Venezia, Mestre, Italy

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Prof. Alvise Perosa

Prof. Alvise Perosa

Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venezia, Via Torino 155, 30172 Venezia, Mestre, Italy

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Prof. Maurizio Selva

Corresponding Author

Prof. Maurizio Selva

Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venezia, Via Torino 155, 30172 Venezia, Mestre, Italy

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Prof. Giulia Fiorani

Corresponding Author

Prof. Giulia Fiorani

Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venezia, Via Torino 155, 30172 Venezia, Mestre, Italy

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First published: 29 January 2021
Citations: 12

Graphical Abstract

Getting stuck with CO2 is terminal: CO2 insertion on terminal epoxides was performed under batch conditions and in continuous flow using an inexpensive and sustainable binary homogeneous mixture comprised of NaBr as the catalyst and diethylene glycol (DEG) as both solvent and catalyst activator. At complete conversion, cyclic carbonate products were obtained in up to 99 % selectivity from styrene oxide, 1,2-epoxyhexane and butyl glycidyl ether.

Abstract

CO2 insertion reactions on terminal epoxides (styrene oxide, 1,2-epoxyhexane and butyl glycidyl ether) were performed in a binary homogeneous mixture comprising NaBr as the nucleophilic catalyst and diethylene glycol (DEG) as both solvent and catalyst activator (cation coordinating agent). The reaction protocol was initially studied under batch conditions either in autoclaves and glass reactors: quantitative formation of the cyclic organic carbonate products (COCs) were achieved at T=100 °C and p0(CO2)=1–40 bar. The process was then transferred to continuous-flow (CF) mode. The effects of the reaction parameters (T, p(CO2), catalyst loading, and flow rates) were studied using microfluidic reactors of capacities variable from 7.85 ⋅ 10−2 to 0.157 cm3. Albeit the CF reaction took place at T=220 °C and 120 bar, CF improved the productivity and allowed catalyst recycle through a semi-continuous extraction procedure. For the model case of 1,2-epoxyhexane, the (non-optimized) rate of formation of the corresponding carbonate, 4-butyl-1,3-dioxolan-2-one, was increased up to 27.6 mmol h−1 equiv.−1, a value 2.5 higher than in the batch mode. Moreover, the NaBr/DEG mixture was reusable without loss of performance for at least 4 subsequent CF-tests.

Conflict of interest

The authors declare no conflict of interest.