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

Abstract

At T ≥ 200 • C, in the presence of K 2 CO 3 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 CO 2 . The K 2 CO 3 -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.

Continuous‐Flow O‐Alkylation of Biobased Derivatives with Dialkyl Carbonates in the Presence of Magnesium–Aluminium Hydrotalcites as Catalyst Precursors

“…Solketal and glycerol formal (1a and 2a/2a')c ouldb ec onverted quantitatively into the correspondingm ethyl and ethyl ethers( 1b and 2b/2b')b yu sing DMC and DEC as O-alkylating agents. The reaction productivity,c alculated from the isolated yield, allowed further remarkable considerations:c ompared with the P values of 0.01-0.02 g prod g cat À1 h À1 )f or the syntheses of compounds 1b and 2b/2b' by our previously reported batchwise (autoclave) method, [16] the CF procedure boosted the productivity by af actor of 100-200 [to % 2g prod g cat À1 h À1 ); Ta ble 3, entries 1a nd 2] and, thereby, substantiated the synthetic potential of such ap rotocol. Methyl and ethyl ethers 2b/2b' and 2e/2e' were obtained at 220 and 275 8C, respectively,w hereas 1b and 1e formed at the lower temperatures of 210 and 250 8C( compare Table 3, entries 1 and 2w ith 6a nd 7).…”

“…[16] GC-MS (EI, 70 eV) analyses were performed with an HP5-MS capillary column (L = 30 m, Ø = 0.32 mm, film = 0.25 mm), and GC analyses with af lame ionisation detector (CG/FID) were performed with an Elite-624 capillary column (L = 30 m, Ø = 0.32 mm, film = 1.8 mm). If not otherwise specified, they were employed without further purification.…”

“…[10,16] In particular, the experiments were performed in the ranges T = 200-275 8Ca nd p = 5-50 bar.E ach of the investigated catalysts was used to fill the inner volume of the CF reactor as uniformly and completely as possible. The temperature and pressure for the initial tests were selected according to our previousr esults obtained for the batch alkylation and CF transesterification reactions of glycerol acetalsw ith dialkyl carbonates.…”

Kinetic modelling of the solventless synthesis of solketal with a sulphonic ion exchange resin

“…Reduced gum formation and improvement of the octane index was observed when using up to 5% volume of solketal to gasoline [16], while addition of said ketal to biodiesel not only improved its viscosity, but also complied with the flash point and oxidation stability specifications as enacted by European and American Standards (EN 14214 and ASTM D6751, respectively) [17]. Even further reactions of solketal have been explored to yield new potential additives, namely: its upgrade to benzyl alcohol ether [18] or the synthesis of solketal o-methylesters by making solketal react with dialkyl carbonates under basic conditions [19].…”

Acid functionalized carbon–silica composite and its application for solketal production

“…Olefins such as butene or alcohols such as tertiary butyl alcohol are commonly used as etherifying agents of glycerol, but the main drawback involved in the use of olefin is the formation of undesired di-olefins and the formation of huge amount of water in case of using alcohols [23][24][25][26][27]. Esterification with low molecular weight acids, transesterification with low molecular weight esters and acetalization with aldehydes or ketones are the other promising and economically viable alternative routes for the conversion of glycerol [28][29][30][31][32]. Acetalization with ketones, especially acetone is gaining importance due to the fact that acetone is widely produced from biomass conversion as well as from the chemical process of cumene cracking.…”