Amino-polystyrene supported hexaethylene glycol-bridged ionic liquid as an efficient heterogeneous catalyst for water-mediated nucleophilic hydroxylation

Abstract

We report a simple and eco-friendly method for producing an amino-polystyrene supported hexaethylene glycol-bridged ionic liquid (APS-HEGBIL) based on the copolymerization of amino-styrene with 1-vinyl imidazolium ionic liquid bearing hexaethylene glycol moieties, and its characterization by several analytical techniques. The resulting APS-HEGBIL catalyst was found to be remarkably efficient at catalyzing the selective nucleophilic hydroxylation of alkyl halides to produce the corresponding alcohols in water, which acted as a solvent and a nucleophilic hydroxide source. The catalyst was easily recycled and maintained its catalytic activity and stability after ten cycles with excellent yields. The main attributes of the catalyst were that it significantly enhanced the nucleophilicity of water during reactions and promoted the rapid conversions of polar and base-sensitive alkyl halide reactants to alcohols in excellent yields. The combination of ionic liquids and polymeric materials afforded quasi-homogeneous catalysts that were recycled by simple filtration and provided environmentally benign means for conducted catalytic procedures.

Fig. 1. Conventional and custom-made ionic liquids. bmim = 1-n-butyl-3-methylimidazolium; hexaEGmim = 1-hexaethylene glycol 3-methylimidazolium; hexaEG-DHIM = hexaethylene glycol-bridged dicationic imidazolium dimesylate.

Scheme 1. Preparation of APS-HEGBIL.

Fig. 2. FT-IR spectra of APS-HEGBIL and HEGBDVIM.

Fig. 3. XPS patterns of (a–c) HEGBDVIM and (d–f) APS-HEGBIL.

Fig. 4. (a) Solid state ¹³C NMR spectrum of APS-HEGBIL. (b) TGA patterns of APS-HEGBIL and HEGBDVIM.

Scheme 2. Comparison of the activity of APS-HEGBIL as a heterogeneous promoter with homogenous custom-made IL promoters.