Studies on Ketoses, 1 Distribution of Furanoid and Pyranoid Tautomers of D‐Fructose in Water, Dimethyl Sulfoxide, and Pyridine via¹H NMR Intensities of Anomeric Hydroxy Groups in [D₆]DMSO

Abstract

In [D,]DMSO the anomeric 2-OH groups of furanoid and pyranoid tautomers O f D-fIUtOSe give distinct. clearly separated singlets, their intensities providing an exact measure of the tautomeric distribution and allowing its determination as a function of temperature and time. Equilibration of tautomers in DMSO being exceedingly slow, this OH-NMR methodology can be applied to detcrmine tautomeric ratios in other solvents, too, by freezing a sample (liquid Nz), dissolution of the resulting ice-matrix in DMSO and rapid recording of the intensities in the low-field OH-region. 'The data obtaincd in this way for aqueous solutions at equilibrium between 0 and 8O'C correlate well with "C NMR-derived values yet are more consistent and considerably more easy to obtain; they cxhibit a clearly linear relationship between equilibrium composition and temperature such that the two fructofuranoses and the a-p-tautomcr increase with temperature on expense of the P-p-form, which at 80°C comprises 550/. at 110°C (i. e. in thc molten state) only 45"h of the tautomers. In pyridinc, the cquilibrium distribution shows a similar linear temperature dependence as does the ratc of equilibration, being nearly nondetectable at 0°C versus essentially instantaneous adaption above 6 0 T , thereby explaining the different outcome of fructose derivatizations in pyridine. (0 VCH Verlagsgesellschaft mbH, D Untersuchungen an

Observation of the keto tautomer of d-fructose in D2O using 1H NMR spectroscopy

“…13,21 These investigations have provided inconsistent results in terms of tautomers identified and relative concentrations of each at equilibrium. 12,13,15,18,19,32 The reasons for this inconsistency have typically been attributed to the shortcomings of the methods used, 12,18,21,30 misreading of results by researchers 18 and the complexity of the mutarotation of fructose. 4,12 …”

“…This relies on the slow tautomeric equilibration in DMSO- d 6 to provide data for the tautomeric composition in water. 18 …”

Mechanism of the dehydration of d-fructose to 5-hydroxymethylfurfural in dimethyl sulfoxide at 150°C: an NMR study

“…The anomeric compositions of D-fructose at 23 °C (room temperature) and 150 °C were determined by the reported method21,22 of integrating the anomeric 2-OH 1 H NMR signals of furanose and pyranose tautomers in the t = 0.0, 1.0 and 3.0 min samples. These results are shown in Table 1.…”

Versatile building blocks from disaccharides: glycosylated 5-hydroxymethylfurfurals

“…30,32 Of the two pathways delineated in Scheme 2, there are no arguments for a preference, as of now. That aqueous solutions of D D-fructose mainly contain the b-pyranoid tautomer (73% at 25°C 33 appears equally important as conversion of the 6-Oblocked glucoses 5-7 to their respective fructoses 8-10 can only proceed through furanose intermediates.…”