One-Pot, Metal-Free Synthesis of Dimethyl Carbonate from CO2 at Room Temperature

Santosh Khokarale,Thai Bui,Jyri-Pekka Mikkola

doi:10.3390/suschem1030020

Santosh Khokarale, Thai Bui + Show 1 more

Open Access

https://doi.org/10.3390/suschem1030020

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Journal: Sustainable chemistry	Publication Date: Nov 13, 2020
Citations: 2	License type: CC BY 4.0

Affiliation: Umeå University, Åbo Akademi University

Abstract

Herein, we report on the metal-free, one-pot synthesis of industrially important dimethyl carbonate (DMC) from molecular CO2 under ambient conditions. In this process, initially the CO2 was chemisorbed through the formation of a switchable ionic liquid (SIL), [DBUH] [CH3CO3], by the interaction of CO2 with an equivalent mixture of organic superbase 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) and methanol. The obtained SIL further reacted with methyl iodide (CH3I) to form DMC. The synthesis was carried out in both dimethyl sulfoxide (DMSO) and methanol. Methanol is preferred, as it not only served as a reagent and solvent in CO2 capture and DMC synthesis, but it also assisted in controlling the side reactions between chemical species such as CH3I and [DBUH]+ cation and increased the yield of DMC. Hence, the use of methanol avoided the loss of captured CO2 and favored the formation of DMC with high selectivity. Under the applied reaction conditions, 89% of the captured CO2 was converted to DMC. DBU was obtained, achieving 86% recovery of its salts formed during the synthesis. Most importantly, in this report we describe a simple and renewable solvent-based process for a metal-free approach to DMC synthesis under industrially feasible reaction conditions.

Highlights

Dimethyl carbonate (DMC) is a commercially important organic carbonate, considering its valuable and widespread industrial applications
It was confirmed that CH3I played a role as a reagent in a similar way to methanol in DMC synthesis instead of as a promotor, while the base assisted in the activation of methanol molecules [15]
CO2 was initially activated via the synthesis of switchable ionic liquid (SIL), which is considered as a well-practiced process for the capture of CO2

Summary

Introduction

Dimethyl carbonate (DMC) is a commercially important organic carbonate, considering its valuable and widespread industrial applications. Methyl iodide (CH3I) and potassium metals containing base catalysts such as K2CO3, CH3OK, or KOH were successfully applied in the direct conversion of CO2 to DMC, whereupon the applied reaction conditions were milder than in the case of the previously discussed catalyzed processes [16,17] In this case, the previous studies explained that the methyl carbonate anion formed after interaction between the basic catalyst, methanol, and molecular CO2, which further interacted equivalently with CH3I upon formation of DMC. It was confirmed that CH3I played a role as a reagent in a similar way to methanol in DMC synthesis instead of as a promotor, while the base assisted in the activation of methanol molecules [15] Even though this base-catalyzed direct CO2 conversion approach emerged as an alternative to metal-oxide- and organotin-catalyzed processes, the catalyst deactivation and loss of the methoxide anion to the dimethyl ether (DME) as a byproduct caused the low reaction yield. ScShcehmeme e1.1S. ySnytnhtehseissisofo(fa()as)wswitcithcahbalbeleioinoincilciqliuqiudi,d[,D[BDUBUHH] []C[HCH3C3COO3]3,],anandd(b(b) )didmimetehtyhlycl acrabrobnoantaet,e, (C(HCH3O3O)2)C2COO

Materials and Methods

Amount of Chemical Species in the Reaction Mixture

Results and Discussion