Abstract
The efficient O-acetylation of monosaccharides and cellulose is demonstrated using a Lewis acidic ionic liquid based on choline chloride and zinc chloride.
Highlights
The application of ionic liquids as environmentally benign reaction solvents for synthesis and catalysis has received extensive recent attention.[1,2,3,4] In this regard we have developed ionic liquids based on the cheap and readily available components choline chloride (ChCl; HOCH2CH2N(Me)3?Cl) and zinc chloride as alternatives to the more commonly employed alkyl imidazolium-aluminium chloride mixtures.[5]
To test the efficacy of Lewis acidic ChCl-based mixtures for the acetylation of carbohydrates the compounds 1–4 were reacted with acetic anhydride in the ionic liquid for 3 h at 90 uC (Scheme 1).{ Substrates 1–4 were completely soluble under the reaction conditions and the mixtures were worked up by the addition of water followed by extraction with ethyl acetate to give in each case only the per-O-acetylated product 1a–4a
It can be seen that the [ChCl][ZnCl2]2 ionic liquid can be successfully employed as both solvent and catalyst for the acetylation of simple monosaccharides
Summary
The application of ionic liquids as environmentally benign reaction solvents for synthesis and catalysis has received extensive recent attention.[1,2,3,4] In this regard we have developed ionic liquids based on the cheap and readily available components choline chloride (ChCl; HOCH2CH2N(Me)3?Cl) and zinc chloride as alternatives to the more commonly employed alkyl imidazolium-aluminium chloride mixtures.[5]. To test the efficacy of Lewis acidic ChCl-based mixtures for the acetylation of carbohydrates the compounds 1–4 were reacted with acetic anhydride in the ionic liquid for 3 h at 90 uC (Scheme 1).{ Substrates 1–4 were completely soluble under the reaction conditions and the mixtures were worked up by the addition of water followed by extraction with ethyl acetate to give in each case only the per-O-acetylated product 1a–4a.
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