Carbocation/Polyol Systems as Efficient Organic Catalysts for the Preparation of Cyclic Carbonates

Abstract

Carbocation/polyol systems are shown to be highly efficient catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa CO pressure. The best activity was shown by the combination of crystal violet and 1,1'-bi-2-naphthol (BINOL), which could be recycled five times with no loss of activity. The presence of specific interactions between the amino groups of the carbocation and the hydroxyl protons was confirmed by NMR experiments. The Job plots for the crystal violet iodide/BINOL and brilliant green iodide/BINOL systems showed that the catalytic systems consist of one molecule of the carbocation and one molecule of BINOL. Mechanistic studies using a deuterated epoxide indicate that there was some loss of epoxide stereochemistry during the reaction, but predominant retention of stereochemistry is observed. On this basis, a catalytic cycle is proposed.

Efficient transformation of CO2 to cyclic carbonates using bifunctional protic ionic liquids under mild conditions

“…[12][13][14] As one of a few successfully industrial products that efficiently utilize CO2 as a carbon feedstock, cyclic carbonate can be wildly used as solvents in chemical processes, [15][16][17] electrolyte components in lithium batteries, 18 useful monomers for acyclic carbamates 19,20 and carbonates, 21 and intermediates in the production of fine chemicals, etc. 22,23 To date, various catalysts have been developed for the synthesis of useful cyclic carbonates from CO2 and epoxides, such as metal-based catalysts, [24][25][26][27][28][29][30][31][32][33][34] organocatalysts, [35][36][37][38][39][40][41][42][43][44] and ionic liquids etc. [45][46][47][48][49][50][51][52][53] Although most of the catalyst systems show a good yield to produce carbonates, high temperatures (>100 °C) and/or high CO2 pressures are always needed in these studies.…”

Recent developments in organocatalysed transformations of epoxides and carbon dioxide into cyclic carbonates

“…In 2017, Belokon et al discovered that triarylmethane dyes, acting as carbocations, could catalyse the formation of cyclic carbonates in the presence of polyols. 125 The iodide salts of the commercially available dyes: malachite green, brilliant green and crystal violet, acted as bifunctional catalysts in which the iodide was the nucleophile and the carbocation provided a Lewis acidic centre. Low to moderate conversions (<1-45%) were reported for styrene carbonate synthesis using the dyes alone, albeit with high selectivity (>99%) under moderate conditions (50 o C, 50 bar of carbon dioxide and 1-2 mol% of catalyst for 24 h).…”

Salen‐decorated Periodic Mesoporous Organosilica: From Metal‐assisted Epoxidation to Metal‐free CO2 Insertion

“…The obtained results motivated us to develop a heterogeneous catalyst to promote the coupling of carbon dioxide/epoxide more efficiently and under relatively milder conditions, preferably, in the absence of a co‐catalyst. Based on the CO 2 uptake capability of the Salen‐PMO material and the presence of protic phenolic substituents, which are known to have co‐catalyzing properties for cyclic carbonate synthesis, [3e,16] the catalytic ability of the Salen‐PMO material in the preparation of cyclic carbonates was studied. Epichlorohydrin was chosen as a model substrate.…”