Structural identification of isomeric O-trimethylsilyl derivatives of some hexuronic acids

The structures of the isomeric products obtained on trimethylsilylation of naturally occurring hexuronic acids and their sodium salts and lactones have been established by the application of n.m.r. (for anomeric configuration) and mass spectrometry (for ring size). The equilibria of some of the hexuronic acids in methyl sulphoxide involved a larger proportion of furanoid forms than those in water or pyridine. The proportion of furanoses was also increased by the addition of hexamethyldisilazane. Kinetic evidence indicated that two molecules of each hexuronic acid interacted autocatalytically during mutarotation.