Structural Characterization of 6‐Halo‐6‐Deoxycelluloses by Direct‐Dissolution Solution‐State NMR Spectroscopy

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Abstract
Regioselective modifications of cellulose using activated cellulose derivatives such as 6‐halo‐6‐deoxycelluloses provide a convenient approach for developing sustainable products with properties tailored to specific applications. However, maintaining precise regiochemical control of substituent distribution in 6‐halo‐6‐deoxycelluloses is challenging due to their insolubility in most common solvents and the resulting difficulties in precise structure elucidation by modern instrumental analytical techniques. Herein, an accessible NMR‐based approach toward detailed characterization of 6‐halo‐6‐deoxycelluloses, including the determination of the degrees of substitution at carbon 6 (DS6), is presented. It is shown that the direct‐dissolution cellulose solvent, tetrabutylphosphonium acetate:DMSO‐d6, converts 6‐halo‐6‐deoxycelluloses to 6‐monoacetylcellulose, enabling in situ solution‐state NMR measurements. A range of 1D and 2D NMR experiments is used to demonstrate the quantitivity of the conversion and provide optimum dissolution conditions. In comparison with other NMR‐based derivatization protocols for elucidating the structure of 6‐halo‐6‐deoxycelluloses, the presented approach offers major advantages in terms of accuracy, speed, and simplicity of analysis, and minimal requirements for reagents or NMR instrumentation.
Funding Information
  • European Research Council (755865)

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