Issue 1, 2012

Selective catalytic etherification of glycerol formal and solketal with dialkyl carbonates and K2CO3

Abstract

At T ≥ 200 °C, in the presence of K2CO3 as a catalyst, an original etherification procedure of non-toxic acetals such as glycerol formal (GlyF) and solketal has been investigated by using dialkyl carbonates as safe alkylating agents. The effects of parameters including the temperature, the reaction time, and the loading of both the catalyst and the dialkyl carbonate have been detailed for the model case of dimethyl carbonate (DMC). Both GlyF and solketal were efficiently alkylated by DMC to produce the corresponding O-methyl ethers with selectivity up to 99% and excellent yields (86–99%, by GC). The high selectivity could be accounted for by a mechanistic study involving a combined sequence of methylation, carboxymethylation, decarboxylation and hydrolysis processes. The O-methylation of GlyF and solketal could be successfully scaled up for multigram synthesis even operating with a moderate excess (5 molar equiv.) of DMC and in the absence of additional solvent. Notwithstanding the advantageous reduction of the process mass index, scale up experiments provided evidence that prolonged reaction times may induce the decomposition of DMC mainly by the loss of CO2. The K2CO3-catalyzed etherification of solketal with other carbonates such as dibenzyl and diethyl carbonate (DBnC and DEC, respectively), proceeded with the same good selectivity observed for DMC. However, at 220 °C, the solketal conversion did not exceed 81% since both DBnC and DEC were extensively consumed in competitive decarboxylation and hydrolysis reactions.

Graphical abstract: Selective catalytic etherification of glycerol formal and solketal with dialkyl carbonates and K2CO3

Supplementary files

Article information

Article type
Paper
Submitted
05 Jul 2011
Accepted
07 Oct 2011
First published
16 Nov 2011

Green Chem., 2012,14, 188-200

Selective catalytic etherification of glycerol formal and solketal with dialkyl carbonates and K2CO3

M. Selva, V. Benedet and M. Fabris, Green Chem., 2012, 14, 188 DOI: 10.1039/C1GC15796E

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