The 3-halotetrahydropyran-2-ols have been found to readily give derivatives of tetrahydrofurfural in aqueous alcohol under weakly basic or acidic conditions. In strongly alkaline solution tetrahydropyran-2,3-diol and its anhydro-polymers were formed. 3,3-Dichlorotetrahydropyran-2-ol and 2,3,3-trichlorotetrahydropyran have been converted by aqueous alkali to viscous sirups which appear to contain 2-hydroxytetrahydropyran-3-one and its tautomers. On oxidation with permanganate these sirups have yielded succinic acid.