Intermolecular Interactions in N,N-Dimethylacetamide without and with LiCl Studied by Infrared Spectroscopy and Quantum Chemical Model Calculations

Abstract

The mixture of LiCl and N, N-dimethylacetamide (DMAc) is an important laboratory-scale solvent for cellulose. However, the mechanism of cellulose dissolution in DMAc/LiCl could not be fully established due to the limited knowledge about the interactions between DMAc and LiCl. To address this issue, we studied neat DMAc and DMAc/LiCl mixtures by ATR FTIR spectroscopy and quantum chemical model calculations. On the basis of the calculations, we newly assigned the bands at 1660 and 1642 cm in the ν(C═O) region of the spectra to DMAc monomeric and dimeric structures. The latter are presumably stabilized by the C-H···O═C weak hydrogen bonds that prevail in both neat DMAc and DMAc/LiCl mixtures. The analysis of the concentrated (7.9 wt % of LiCl) DMAc/LiCl mixture revealed that only about half of DMAc molecules interact directly with LiCl. The resulting average stoichiometry of about 2.8:1 (DMAc:LiCl), indicating the predominance of [(DMAc)-LiCl] and [(DMAc)-LiCl] complexes, was found to be temperature independent. Conversely, the stoichiometry was considerably temperature sensitive for the diluted DMAc/LiCl mixture (2.6 wt % of LiCl), indicating that further DMAc molecules can be incorporated into the primary solvation shell of LiCl at higher temperatures. These results highlight the dynamic character of the DMAc/LiCl system that needs to be considered when studying the cellulose dissolution mechanism.

Cellulose-Based Solid Electrolyte Membranes Through Microwave Assisted Regeneration and Application in Electrochromic Displays

“…Second, it suggests that the interaction between the entrapped solvent and the cellobiose units is different when microwave irradiation is used. The blue shift in this band for CSE can be associated with lower interaction between DMAc and Li + (Zhang et al, 2014;Kotov et al, 2018) and also less interaction between DMAc molecules (Kotov et al, 2018). Both phenomena are coherent with heating promoted by microwave irradiation that reduces solvation of the Li + and stoichiometry of the [(DMAc) x -LiCl] complexes, moving from DMAc dimmers toward DMAc monomers.…”

Neptunium(V) Isothiocyanate Complexes with 4′-Aryl-Substituted 2,2′:6′,2″-Terpyridines and N,N-Dimethylacetamide as Molecular Ligands

“…The range of 3100–3000 cm –1 is typical for valence vibrations ν as (CH) of aromatic rings, which are not sensitive to the presence of substituents. , Vibrations ν as (CH) of methyl groups belonging to coordinated and solvate DMA molecules are manifested by weak bands in the range of 3000–2800 cm –1 . − …”

Molecular‐Scale Design of Cellulose‐Based Functional Materials for Flexible Electronic Devices

“…[47] Compared with the above solvents, novel green solvent systems, such as ionic liquids, alkali/urea, deep-eutectic solvents, and dimethylacetamide (DMAc)/LiCl, are characterized by environmental friendliness, high thermal stability and solubility, and recyclability, so they show great potential for cellulose dissolution and constructing functional materials. [24][25][26][27][48][49][50][51] Due to the strong interactions between the anion/cation of the solvent and the hydroxyl group of cellulose, [52][53][54][55][56][57] the original hydrogen-bonding networks of the cellulose can be easily destroyed through purely physical means. [58][59][60][61][62][63][64] Then, the cellulose can be rapidly and completely dissolved into single molecular chains (Figure 1b,c), which allows the design of materials based on the molecular-scale concept.…”