The Structures of the Oxidation Products formed by Hologenation of Furfural in Water The oxidation products formed on halogenating furfural in water are cis/trans-2,5-dihydroxy-2-(dihydroxymethyl)-2,5-dihydrofuran ( 5) and cis/trans-2,6-dihydroxy-2 H-pyran-3 (6H)-one ( 6) as shown by 1H- and 13C-NMR.-spectroscopy. A new, simple high-yield preparation of 5- and 6- solutions is described, in which sodium bromate is used as the oxidizing agent.