Abstract
Heteropoly acids were used as catalysts for cyclodehydration of various 1,n-diols. Cyclodehydration of butane-1,4-diol, pentane-1,5-diol and hexane-1,6-diol catalysed by H3PW12O40 gave tetrahydrofuran, tetrahydropyran and oxepane, respectively. Cyclodehydration of diethylene glycol, triethylene glycol, diethylene glycol monomethyl ether and polyethylene glycol 200 catalysed by H3PW12O40 gave 1,4-dioxane. In particular, cyclodehydration of hexane-1,6-diol gave an excellent yield of oxepane (80%). The selectivity exhibited by the H3PW12O40 catalyst was even better than that exhibited by other reported catalyst systems for similar cyclodehydration reactions.
Highlights
Many natural compounds, such as inostamycins, isosorbide and polyether antibiotics, incorporate cyclic ethers as structural subunits and have significant biological activity [1,2,3]
The present paper reports the application of heteropoly acids (HPAs) as solid acid catalysts for cyclodehydration of 1,n-diols to their corresponding cyclic ethers with high yield and selectivity
Mo and W belong to the same group, they displayed different catalytic activities in this reaction; the order of the catalytic activities was in accordance with that of the Brønsted acidity of the HPAs [16]
Summary
Many natural compounds, such as inostamycins, isosorbide and polyether antibiotics, incorporate cyclic ethers as structural subunits and have significant biological activity [1,2,3]. Many of the commonly used synthetic approaches for the formation of cyclic ethers, including cycloaddition and cyclization, involve chlorine chemistry or heavy metals at different levels [6,7]. Cyclization reactions are often conducted under acidic conditions [8,9]. Cyclodehydration of 1,n-diols to cyclic ethers is an industrially important reaction [4]. These reactions are usually carried out using inorganic and organic acids, solid acid catalysts (such as clays), group (IV) metal halides, metallocenes, sulfated zirconia, zeolite or calcium phosphate. There is a strong interest in the use of solid acid catalysts to replace conventional homogeneous catalysts, such as inorganic and organic acids [10].
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