THE FORMATION OF 2-FURALDEHYDE AND FORMIC-ACID FROM PENTOSES IN SLIGHTLY ACIDIC DEUTERIUM-OXIDE STUDIED BY H-1-NMR SPECTROSCOPY

The title reaction at 96 degrees C and pD 1.5, 3.0, or 4.5 was followe d by H-1 NMR spectroscopy. The rate of pentose degradation increased i n the order: arabinose approximate to xylose < ribose < 2-pentuloses. At pD 1.5, the rate of 2-furaldehyde formation increased in the same c ader. Increasing pD strongly accelerated the degradation of the aldose s but slightly retarded that of the ketoses. Increasing pD also retard ed the formation of 2-furaldehyde, particularly from the ketoses, and increased its deuterium content at H-alpha (from 8-25 to 50-83 atom %) and H-3 (from 79-100 to 100 atom %). This is explained by assuming th at 2-furaldehyde had formed mainly via acyclic intermediates, with rev ersible formation of a 3-deoxypentosulose. The formation of:Formic aci d was slow and did not proceed via 2-furaldehyde. As evident from expe riments with 1- or 5-C-13-substituted aldopentoses, the formic acid wa s derived exclusively from the terminal pentose carbons, C-1 being som ewhat more important than C-5.