Abstract
A novel protocol for a mild, controlled and selective methylation of lignin phenolic OH groups with trimethylphosphate has been developed.
Highlights
Lignins are renewable polyphenols abundantly found in all vascular plants and constitute the main feedstock of biobased aromatic structures
Methylation is probably one of the oldest chemical reactions that was employed by lignin chemists. It was already described in the early stages of the study of the lignin chemical structure by Brauns in 1939.5 Methylation served as a chemical tool to characterize the structure of lignin, mainly by comparing the samples before and after methylation, for instance to quantify phenolic hydroxyl (Ph-OH) and carboxylic (COOH) groups.[6,7]
We describe for the first time the use of trimethyl phosphate (TMP) to methylate various lignins in a precisely controlled manner, leaving the aliphatic OH (Al-OH) groups largely unaffected (Scheme 1)
Summary
Lignins are renewable polyphenols abundantly found in all vascular plants and constitute the main feedstock of biobased aromatic structures. They are more and more seen as a potential source of aromatic building blocks in chemistry and polymer science. The use of lignins in polymer or materials science mainly requires preliminary chemical modifications.[3,4] Methylation is probably one of the oldest chemical reactions that was employed by lignin chemists. The methylation of lignins has been shown to increase their thermal stability by limiting condensation crosslinking reactions, potentially facilitating their thermomechanical processing for incorporation into polymer materials.[16]
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