Effect of the Molecular Structure of Acylating Agents on the Regioselectivity of Cellulosic Hydroxyl Groups in Ionic Liquid

Abstract

Homogeneous functionalization of cellulose with chloroacetyl chloride (CAC), 2-bromoisobutyryl bromide (BrBiB), and 2-chloro-2-phenylacetyl chloride (CPAC) was performed in ionic liquid to evaluate the effect of the molecular structure of the reagents on the reactivity of the cellulosic hydroxyl groups. The results showed that the reaction was very selective for the less hindered C6-OH group, but the substitution of the secondary OH group still occurred, which indicated that the acylation of cellulose was only partly regioselective. The reaction extent and regioselectivity of the cellulosic hydroxyl groups partly depended on the molecular structure of the acylating agents. The reaction rate of the CAC was much faster than the relatively bulky BrBiB and CPAC, but the bulky acylating agents showed a higher C6-OH selectivity. Moreover, the BrBiB was less reactive than the CPAC, although they showed the same regioselectivity for the three hydroxyl groups. The acylation decreased the thermal stability of the cellulose, which decreased further as the bulk of the substituted groups increased.

Highly porous regenerated cellulose hydrogel and aerogel prepared from hydrothermal synthesized cellulose carbamate

“…Therefore, derivatization reactions target primarily substitutions of OH- groups in C6, C2 and C3 of cellulose. The relative substituent distribution among C2, C3 and C6 position are relying on the reaction condition [ 26 ].…”

“…The isocyanic acid will possibly react on C6 of AGU as shown in Fig 1B because C6 is a primary hydroxyl group which is highly accessible compares to C2 and C3 which is secondary hydroxyl group. In homogeneous conditions of cellulose solvent, the OH group in C6 is most reactive as it possesses lower steric hindrance as compares to secondary OH groups in C2 and C3 positions [ 26 ]. This has been confirmed by nuclear magnetic resonance testing in Klemm et al [ 5 ] report, as the resonances of C6 (62–65 ppm) was decreased with the introduction of urea in the cellulose treatment.…”

Cellulose-Based Thermoplastics and Elastomers via Controlled Radical Polymerization

“…As shown in Figure 1, the macroinitiators, cellulose 2-bromopropionate (Cell-Bp), cellulose 2-bromoisobutyrylate (Cell-BiB), and cellulose chloroacetyl (Cell-ClAc) can be synthesized by reacting cellulose with 2-bromopropiomyl bromide, 2-bromoisobutyryl bromide, and chloroacetyl chloride in 1-allyl-3-methylimidazolium chloride (AMIMCl), 1-allyl-3-methylimidazolium chloride (BMIMCl) or DMAc/LiCl solution [32][33][34][35][36][37] under homogeneous conditions. The solubility of cellulose-based macroinitiator is strongly related to the DS of acylation, which can be adjusted by the molar ratio of acylating agent/AGU and reaction time [35,[38][39][40]. Therefore, it is flexible and convenient to prepare cellulose graft copolymers with controlled grafting density.…”

Application of a Low-Cost Cellulose-Based Bioadsorbent for the Effective Recovery of Terbium Ions from Aqueous Solutions

“…It is worth to mention here, that the OH group on C6 in cellulose is a primary carbon, and is being considered the most reactive, and the one presenting less steric hindrance compared to OH groups located on C2 and C3, which are secondary carbons. Therefore, most reactions are more likely to occur through C6 [45,46]. Figure 6 shows the C1s, O1s and N1s XPS spectra for the CRS sample.…”