Galacturonic acid dehydration

The major, monomeric dehydration-product, namely, 2-furaldehyde (27), formed during the reaction results from D-galacturonic acid in yields in the vicinity of 30% of the theoretical.110 This result is in contrast to its production from D-xylose,111 L-ascorbic acid,54 and D-arafotno-hexulosonic acid54 when treated under comparable conditions (3.3 M hydrochloric acid under reflux), these give almost theoretical yields of 27. 

Deoxy- l- threo- hex-4-enuronic acid X dehydration of D-galacturonic acid... 

It is necessary to postulate the existence of a previously unknown, modification reaction of glycosyl nucleotides, that is, deoxygenation at C-4, in order to explain the formation of 4-deoxy-D-arafc//io-hexose, a monosaccharide constituent of Citrobacter lipopolysaccharide.202 4-Deoxy-L-threo-hex-4-enuronic acid, found in Klebsiella K22 polysaccharide,203 may be formed through dehydration of the D-galacturonic acid group or residue, either in the glycosyl nucleotide, or in the polysaccharide. 

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