2,5-Dimethylfuran (DMFu): An Internal Standard for the “Traceless” Quantitation of Unknown Samples via1H NMR

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Abstract
The use of 2,5-dimethylfuran (DMFu) as an internal standard for the quantitation of unknown samples by 1H NMR is described. DMFu was selected based upon its low chemical reactivity, good solubility in standard NMR solvents, appropriate volatility (bp 92 °C), and the chemical shifts of its two singlets (5.80 and 2.20 ppm). In particular, the widely separated singlets of DMFu offer two advantages over more traditional “single peak” internal standards (e.g., hexamethyldisiloxane): (1) they reduce the possibility for overlap between analyte and internal standard signals; and (2) they enable the chemist to assess the accuracy of integration (and ergo, the quantitation) by calculating the ratio of the two singlets and comparing the observed ratio to the theoretical value. Our experiments have shown that the precision of the ratio of DMFu singlets strongly correlates to the precision of sample quantitation, an observation which greatly simplifies the assessment of the quality of the quantitation. Utilizing this technique, we have developed straightforward conditions for 1H NMR experiments which consistently provide quantitative results with less than 5.0% error.