Application of Ionic Liquids for the Direct Chemical Characterization
of Waterlogged Archaeological Woods

The three-dimensional network that binds wood lignocellulosic components together makes it practically impossible to dissolve in its native form in conventional molecular solvents. Thus, it is important to find a non-derivatizing solvent that provide efficient dissolution in order to achieve a homogeneous reaction environment and to preserve the native structure of wood. Ionic liquids (ILs) have arisen as such solvent, in fact 1-allyl-3-methylimidazolium chloride ([amim]Cl) can provide a homogeneous reaction medium for wood-based lignocellulosic materials. Highly substituted lignocellulosic esters can be obtained under mild conditions by reacting wood dissolved in ionic liquid with either acetyl chloride or benzoyl chloride in the presence of pyridine. Alternatively, the lignocellulosic material can be phosphytilated by reaction with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane in the presence of pyridine as well. As a result, the functionalized wood develops an enhanced solubility in molecular solvents, allowing for a complete characterization by means of wet techniques, such as spectroscopic (2D-HSQC-NMR and 31P-NMR) and chromatographic (Gel Permeation Chromatography). The only necessary pretreatment was a planetary ball milling that reduces the particle size and makes the material soluble in [amim]Cl after 24 h a 90ºC. These combined techniques permitted a deep chemical characterization and an evaluation of the state of conservation of the archaeological wood samples, with different advantages: i) we avoided time and materials consuming fractions isolation; ii) we reduced the amount of material used (150 mg); iii) we minimized the possible generation of analytical artifacts.

Published papers
• Luca Zoia, Anika Salanti, Marco Orlandi. “Chemical Characterization of Archaeological Wood: Softwood Vasa and Hardwood Riksapplet Case Studies”. Journal of Cultural Heritage, 2015, 16, 4, 428-437.
• Zoia Luca, Salanti Anika, Orlandi Marco. “Application of Ionic Liquids for the Chemical Characterization of Archaeological Woods from Oseberg” 18th ISWFPC International symposium on Wood, Fiber and Pulping Chemistry. Vienna, Austria. September 09-11, 2015. ISBN 978-3-900932-24-4.

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