Stable complex formation with boric acid in pyrolysis of levoglucosan in acidic media

The influence of boric acid or phenylboronic acid on thermal conversion of levoglucosan in acidic sulfolane was studied. Although levoglucosan was converted to levoglucosenone, furfural and 5-hydroxymethyl furfural (total yield: similar to 40 mol%) at 200 degrees C in sulfolane containing 0.1wt% H2SO4, addition of boric acid enormously lowered the yields of these, and instead caused the formation of a stable complex in more than 70 mol% yield. Thus, boric acid substantially suppressed the acid-catalyzed dehydration and formation of furfurals from levoglucosan through complex formation. From the H-1 NMR spectrum, the chemical structure of this complex was confirmed as alpha-D-glucofuranose cyclic 1,2:3,5-bisborate, which was readily hydrolyzed quantitatively to glucose by the addition of water. Phenylboronic acid also exhibited similar influences. (C) 2008 Elsevier B.V. All rights reserved.