An investigation of the Blue Bottle Experiment, a well-known lecture demonstration reaction involving the dye-catalyzed air oxidation of a reducing sugar in alkaline solution, has delineated the sequence of reactions leading to the bleaching of the dye, the regeneration of color, and so forth. Enolization of the sugar is proposed as a key step in the sequence. The first-order rate constant for this step was found to be ∼2.3 × 10–3 min–1 with respect to total sugar concentration under the conditions used (0.184 M glucose, pH 13.3, 25 °C). Measurements with an oxygen-sensing electrode on Blue-Bottle mixtures containing varying quantities of methylene blue indicated that in a usual demonstration the rate of O2 consumption is ∼60% of the enolization rate. Small samples of the organic oxidation product were isolated and found by chromatographic and NMR-spectroscopic examination to consist primarily of the 5-carbon sugar acid arabinonic acid.Keywords: Analytical Chemistry; Carbohydrates; Catalysis; Graduate Education/Research; Mechanisms of Reactions; Oxidation/Reduction; Problem Solving/Decision Making; Upper-Division Undergraduate;

The physiologically active, gel-forming fraction of the alkali-extractable polysaccharides of Plantago ovata Forsk seed husk (psyllium seed) and some derived partial hydrolysis products were studied by compositional and methylation analysis and NMR spectroscopy. Resolving the conflicting claims of previous investigators, the material was found to be a neutral arabinoxylan (arabinose 22.6%, xylose 74.6%, molar basis; only traces of other sugars). With about 35% of nonreducing terminal residues, the polysaccharide is highly branched. The data are compatible with a structure consisting of a densely substituted main chain of β-(1 → 4)-linked d-xylopyranosyl residues, some carrying single xylopyranosyl side chains at position 2, others bearing, at position 3, trisaccharide branches having the sequence l-Araf-α-(1 → 3)-d-Xylp-β-(1 → 3)-l-Araf. The presence of this sequence is supported by methylation and NMR data, and by the isolation of the disaccharide 3-O-β-d-xylopyranosyl-l-arabinose as a product of partial acid hydrolysis of the polysaccharide.The physiologically active component of psyllium husk is shown to be a highly branched, neutral arabinoxylan with the suggested partial structures: