Savale N, Tarasova E, Krasnou I, Kudrjašova M, Rjabovs V, Reile I, Heinmaa I, Krumme A
School of Engineering, Department of Materials and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086, Tallinn, Estonia.
School of Engineering, Department of Materials and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086, Tallinn, Estonia.
Carbohydr Res. 2024 Mar;537:109047. doi: 10.1016/j.carres.2024.109047. Epub 2024 Feb 10.
Cellulose palmitates (CPs) were synthesized with varying degrees of substitution (DS) via a catalyst-free, homogeneous transesterification of cellulose in a novel superbase ionic liquid (SB-IL) system, specifically 5-methyl-1,5,7-triaza-bicyclo[4.3.0]non-6-enium acetate [mTBNH][OAc], combined with dimethyl sulfoxide (DMSO) as a co-solvent, using vinyl palmitate as the acylating agent. We examined the influence of reaction temperature, reaction time, and the molar ratio of vinyl palmitate to anhydroglucose unit (AGU) on the DS, which ranged from 0.5 to 2.3 under the given conditions. Notably, the reaction order of the three hydroxy groups was C6-OH > C2-OH > C3-OH. To elucidate the chemical structure of CPs and confirm the transesterification process, various spectroscopic techniques including H nuclear magnetic resonance (NMR), C NMR, heteronuclear single quantum correlation (HSQC), and solid-state NMR were employed. Higher reaction temperatures and extended reaction times led to a decrease in the DS of CPs, potentially due to the degradation of some of the involved chemicals during the transesterification process. We also investigated the stability of the pure ionic liquid (IL) and the IL + DMSO solvent system at elevated temperatures by heating them at 100 °C for 5 h, confirming their chemical integrity through H NMR analysis. Additionally, we assessed the compatibility between the solvent system and cellulose by subjecting a mixture of cellulose and the solvent system to 100 °C for 5 h. To compare the structures of untreated cellulose and regenerated cellulose, Fourier transform infrared (FT-IR) spectroscopy was employed. Furthermore, we determined the molar mass of both untreated cellulose and regenerated cellulose, as well as CPs synthesized at higher reaction temperatures and longer durations, using intrinsic viscosity measurements. Lastly, we examined the solubility properties of CPs.
通过在新型超强碱离子液体（SB - IL）体系中，具体为5 - 甲基 - 1,5,7 - 三氮杂双环[4.3.0]壬 - 6 - 烯鎓乙酸盐[mTBNH][OAc]，与作为共溶剂的二甲基亚砜（DMSO）相结合，以棕榈酸乙烯酯作为酰化剂，通过无催化剂的纤维素均相酯交换反应合成了不同取代度（DS）的纤维素棕榈酸酯（CPs）。我们研究了反应温度、反应时间以及棕榈酸乙烯酯与脱水葡萄糖单元（AGU）的摩尔比对取代度的影响，在给定条件下取代度范围为0.5至2.3。值得注意的是，三个羟基的反应活性顺序为C6 - OH > C2 - OH > C3 - OH。为了阐明CPs的化学结构并确认酯交换过程，采用了多种光谱技术，包括氢核磁共振（NMR）、碳核磁共振、异核单量子关联（HSQC）和固体核磁共振。较高的反应温度和延长的反应时间导致CPs的取代度降低，这可能是由于酯交换过程中一些相关化学物质的降解所致。我们还通过在100℃下加热5小时来研究纯离子液体（IL）和IL + DMSO溶剂体系在高温下的稳定性，通过氢核磁共振分析确认它们的化学完整性。此外，我们通过将纤维素和溶剂体系的混合物在100℃下处理5小时来评估溶剂体系与纤维素之间的相容性。为了比较未处理纤维素和再生纤维素的结构，采用了傅里叶变换红外（FT - IR）光谱。此外，我们使用特性粘度测量法测定了未处理纤维素、再生纤维素以及在较高反应温度和较长反应时间下合成的CPs的摩尔质量。最后，我们研究了CPs的溶解性。
