Cellulose acetylation in ionic liquid-molecular solvent mixtures: influence of the biopolymer-induced preferential solvation on its dissolution and reactivity

• Published in: Cellulose (London) Vol. 31; no. 15; pp. 9043 - 9055
• Main Authors: Keppeler, Nicolas, Pires, Paulo A. R., de Freitas, José L. S., Malek, Naved I., Frollini, Elisabete, El Seoud, Omar A.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.10.2024; Springer Nature B.V
• Subjects: Acetylation; Binary mixtures; Bioorganic Chemistry; Biopolymers; Cellulose; Ceramics; Chemistry; Chemistry and Materials Science; Composites; Crystalline cellulose; Dimethyl acetamide; Dimethyl sulfoxide; Dissolution; Glass; Hydrogen bonding; Hydrophobicity; Hydroxyl groups; Ionic liquids; Molecular dynamics; Natural Materials; Organic Chemistry; Original Research; Physical Chemistry; Polymer Sciences; Separation; Solvation; Solvents; Substitution reactions; Sustainable Development; Vinyl acetate; Ionic liquids; Degree of substitution; Molecular solvents; Theoretical calculations; Cellulose acetylation
• DOI: 10.1007/s10570-024-06014-4
• ISSN: 0969-0239

Microcrystalline cellulose was subjected to acetylation by different agents in solvent mixtures, composed of the ionic liquids (ILs) 1-butyl-3-methylimidazolium X (X = acetate, BuMeImAcO; chloride, BuMeImCl), and the molecular solvents (MSs), N , N -dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO). The reactions were carried out under homogeneous conditions using the following acetylation agents: acetic anhydride ((Ac) 2 O), 1-acetyl-3-methylimidazolium acetate (AcMeImAcO), and vinyl acetate (VA). The efficiency of acetylation was judged by the degree of biopolymer substitution, DS. For all binary solvent mixtures, the order of DS was: AcMeImAcO > (Ac) 2 O > VA. For the same acetylating agent, the order of DS was: BuMeImAcO-DMSO > BuMeImAcO-DMAc > BuMeImCl-DMSO. We rationalize this dependence of DS on reaction conditions by considering our experimental data and the results of molecular dynamics simulations (MD). Thus, solvent-induced separation of cellulose chains leads to higher acetylation rates, hence larger DS values. The order of biopolymer dissolution/chain separation is attributed to a combination of hydrogen-bonding of the IL anion with cellulose hydroxyl groups, and biopolymer-solvent hydrophobic interactions. The results of MD simulations showed an additional important point: the compositions of the cellulose solvation layers are different from those of bulk solvent mixtures; they are richer in IL ions; this difference affects the values of DS. Thus, theoretical calculations help in choosing the best solvents for cellulose dissolution/derivatization.