Synthesis of highly water-soluble cyclodextrin sulfonates by addition of hydrogen sulfite to cyclodextrin allyl ethers

Highly water-soluble cyclodextrin sulfonates were synthesised by the addition of hydrogen sulfite to allyl ethers of α- and β-cyclodextrin (α- and β-CD). The allyl derivatives were obtained by etherification of β-CD with allyl bromide or 1-allyloxy-2,3-epoxypropane. In this way, it was possible to isolate 2I-O-allyl-β-CD, 2I-O-(3-allyloxy-2-hydroxypropyl)-β-CD and 6I-O-(3-allyloxy-2-hydroxypropyl)-β-CD after column chromatography. Statistically polysubstituted (3-allyloxy-2-hydroxypropyl)-ethers of α- and β-CD were also synthesised. The subsequent addition of HSO3 − to the terminal CC double bonds was complete after 3 h at 120–140 °C. The allyl groups were converted to propylsulfonic acid groups. Sulfinic acids were formed as side products. The resulting cyclodextrin sulfonates are highly water soluble and able to solubilize hydrophobic guest molecules, such as naphthalene.