Aldose-ketose interconversion in pyridine in the presence of aluminium oxide.
The reaction rate of the Lobry de Bruyn-Alberda van Ekenstein transformation of aldoses to ketoses in boiling pyridine was strongly increased by the addition of aluminium oxide. In addition to aldose-ketose transformation, 2-epimers of the starting aldoses and 3-epimers of the primarily produced ketoses were formed to some extent, as reported also when these reactions are carried out without aluminium oxide. The relative amounts of the primary ketose and the starting aldose in the reaction mixtures may be explained on the basis of their stability, predicted from reported free energy calculations. Isomerisation of ketoses to aldoses was much slower than the reverse reaction. The relative free energies are also in these cases important, the very stable xylo-2-hexulose gave only 7% and 6% of the aldoses gulose and idose, respectively, after boiling for 7h in pyridine in the presence of aluminium oxide.
Ekeberg
Dag
D
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, Norway.
Morgenlie
Svein
S
Stenstrøm
Yngve
Y
D000447:Aldehydes; D000537:Aluminum Oxide / Q000737:chemistry; D007536:Isomerism; D007661:Ketoses; D007700:Kinetics; D011725:Pyridines / Q000737:chemistry*; D013816:Thermodynamics
D000447:Aldehydes; D007661:Ketoses; D011725:Pyridines; D000537:Aluminum Oxide; C023666:pyridine