Download Author Version (PDF)
Total Page：16
File Type：pdf, Size：1020Kb
RSC Advances This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. This Accepted Manuscript will be replaced by the edited, formatted and paginated article as soon as this is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/advances Page 1 of RSC4 Advances RSC Advances Dynamic Article Links ► Cite this: DOI: 10.1039/c0xx00000x www.rsc.org/xxxxxx Communication Catalytic etherification of hydroxyl compounds to methyl ethers with 1,2-dimethoxyethane a,b a a,b a Penghua Che, Fang Lu,* Xiaoqin Si and Jie Xu* Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX 5 DOI: 10.1039/b000000x 1,2-Dimethoxyethane is explored for the first time as In this work, DMET is explored for the first time as etherification agent for the acid-catalyzed synthesis of 50 etherification agent for the acid-catalyzed synthesis of methyl methylethers from biomass-derived hydroxyl compounds. ethers from biomass-derived alcohols. The aliphatic alcohols (n- H3PW12O40 catalyst can provide the formation of isosorbide butanol and n-hexanol) and isohexides (isosorbide, isomannide 10 methylethers with 80% GC yield from isosorbide. The acid and isoidide) with two hydroxyl groups were chosen as model catalyst type and acid amount are of critical importance in compounds. The synthesis in good yields of methyl ethers can be o improving etherification reactivities of hydroxyl groups with 55 performed by reaction of the alcohols with DMET at 150 C in 1,2-dimethoxyethane. the presence of heteropolyacid as catalyst. Manuscript With declining reserves of readily accessible fossil energy, 15 efficient conversion of biomass into fuels and chemicals has come into the research spotlight worldwide.1 The biomass polymers, such as cellulose and hemicellulose, usually contain Scheme 1 Etherification of isosorbide with DMET catalyzed by acid. numerous hydroxyl groups. Therefore, various strategies have been developed to functionalize hydroxyl groups for efficient The reaction of hydroxyl groups in isosorbide with DMET 2 o 20 utilization of biomass. 60 took place at 150 C in the presence of acid catalyst. Typically, Especially, catalytic methylation of hydroxyl groups in three predominant methyl ether products of isosorbide were biomass-derived platform chemicals, such as glucose,3 glycerol,4 observed including dimethyl isosorbide, 5-O-monomethyl Accepted isosorbide5 and 5-hydroxymethylfurfural,6 has been recognized as isosorbide and 2-O-monomethyl isosorbide due to the different a common and significant approach. These methyl ether products configurations of hydroxyl groups (Scheme 1). Pure dimethyl 25 of considerable interest, by themselves or as key chemical 65 isosorbide, 2-O-monomethyl isosorbide and 5-O-monomethyl intermediates, are extensively applied as green solvents, biofuels isosorbide were sequentially achieved by separating reaction or oxygenated additives, surfactants, and biopolymers.7 Several mixture through silica-gel column chromatography. They were methylating agents with corresponding catalysts have been identified by NMR spectroscopy, data shown in experimental explored for etherification of hydroxyl groups. Highly toxic section. 30 methylating agents, such as dimethyl sulfate and methyl halides, 70 The introduction of different acid catlysts lead to obvious have been commonly used for methylation reaction in the changes in the catalytic results, as shown in Fig. 1. Surprisingly, 8 Advances presence of strong base as catalyst over the past decades. H2SO4 was inert for the etherification reaction with a low Dimethyl carbonate, due to its low toxicity, has been widely conversion of isosorbide (below 1%) under our reaction employed nowadays as a substitute methylating agent catalyzed conditions. However, when ion-exchange resins bearing SO3H 9 35 by base. Nevertheless, considering its molecular structure and 75 groups were employed as catalysts, the isosorbide conversions the reaction pathway, stoichiometric amount of CO2 is inevitably were increased to 6%, 6% and 34%, for Amberlyst-70, RSC formed. Recently, methanol as an alternative agent has been Amberlyst-15 and Nafion-H, respectively. Interestingly, reported to convert hydroxyl compounds to monoethers using heteropolyacids including 12-tungstosilicic acid (H4SiW12O40) 10 acid as catalyst. However, the consecutive etherification of and 12-tungstophosphoric acid (H3PW12O40) exhibited superior 40 hydroxyl groups in polyols with methanol can be prevented by 80 activities with the isosorbide conversions of 80% and 87%, water formed due to equilibrium restrictions.11 Therefore, it is respectively. Furthermore, the mono- and dimethyl ethers of desirable to develop a new environmental benign etherification isosorbide were achieved in excellent total GC yields up to 76% agent which could be efficient and facile for the synthesis of by using H3PW12O40 as catalyst. Noticeably, H3PW12O40 provides methyl ethers from mono- and dihydroxyl compounds. the highest yield of dimethyl isosorbide among the acid catalysts 45 Interestingly, 1,2-dimethoxyethane (DMET), as an important 85 with the same acid amount. Acid strength is correlated with the chemical, holds the potential to serve as an efficient etherification type of acid catalyst. It has been reported that acid strength of agent for the synthesis of methyl ethers because of its relatively these catalysts is in the order H3PW12O40 H4SiW12O40 o 12 13 high boiling point (85 C), low toxicity and easy availability. Nafion-H Amberlyst-15 Amberlyst-70 H2SO4. The acid This journal is © The Royal Society of Chemistry [year] [journal], [year], [vol], 00–00 | 1 RSC Advances Page 2 of 4 strength order of these tested catalysts is consistent with the was consumed rapidly in the initial 30 min, and then slowly order of their activities for the etherification of isosorbide. 35 reduced with further prolonged reaction time. The yields of both Therefore, the acid strength of the catalysts plays a vital role in 5- and 2-O-monomethyl isosorbide ethers increased significantly the etherification of isosorbide with DMET. and reached 29% and 19% in the first 60 min of reaction, respectively. With prolonging reaction time, the yield of 5-O- monomethyl isosorbide decreased apparently while the yield of 2- 40 O-monomethyl isosorbide slightly decreased. Meanwhile, the yield of dimethyl isosorbide was gradually increased with increasing reaction time. A slight decrease in the total yields of isosorbide methyl ethers was noted as reaction time prolonged to 600 min. The different changing trends for isosorbide methyl 45 ethers indicate that the etherification of two hydroxyl groups in isosorbide takes place sequentially, namely via the isosorbide monomethyl ethers towards the formation of dimethyl isosorbide. Additionally, the recyclability of the catalyst, H3PW12O40, was attempted in the same reaction. After reaction, hexane was added 50 into the reaction mixture to recover the catalyst. As shown in Fig. 5 S1 (ESI†), although the isosorbide conversion decreased over Fig. 1 Catalytic performances of different acid catalysts for the etherification reaction of isosorbide with DMET. Reaction conditions: three cycles, yields for monomethyl ethers of isosorbide remained. Isosorbide (2 mmol), acid catalyst (0.077 mmol H+), DMET (43 mmol), The loss in reactivity of the recovered catalyst might be caused o 150 C, 60 min. by leaching of H3PW12O40 in DMET. Manuscript Accepted 10 55 Fig. 2 Effect of acid amount on the etherification reaction of isosorbide Fig. 3 Time course of the etherification reaction of isosorbide with with DMET. Reaction conditions: Isosorbide (2 mmol), DMET (43 DMET catalyzed by H3PW12O40. Reaction conditions: Isosorbide (2 o o mmol), H3PW12O40, 150 C, 60 min. mmol), H3PW12O40 (0.019 mmol), DMET (43 mmol), 150 C. The acid amount is expected to influence etherification of 15 isosorbide with DMET. Detailed study was performed to evaluate the effect of acid amount of H3PW12O40 on its catalytic behaviors (Fig. 2). Both the conversion of isosorbide and the total yields of isosorbide methyl ethers increased with increasing the acid Advances amount of H3PW12O40 from 0.005 to 0.098 mmol. Furthermore, 20 the formation of dimethyl isosrobide increased with an increase in acid amount, while the total formation of monomethyl ethers first increased and then decreased. The total yields of isosorbide RSC methyl ethers were up to 80% including 48% yield of dimethyl isosorbide at the acid amount of 0.098 mmol. Further increasing 25 the acid amount to 0.147 mmol, no more increase was observed in both isosorbide conversion and yields of etherified products. Therefore, the increase in the acid amount of H PW O could 60 Fig. 4 Catalytic results for the etherification reaction of isosorbide