Carbamoylation of cellulose esters (CE) and investigation of the mixed derivatives obtained with NMR spectroscopy represents a useful analytical tool for the determination of the degree of substitution (DS) and analysis of the distribution of substituents on the level of the anhydroglucose unit (AGU). Especially the carbethoxymethylcarbamoylation and the ethylcarbamoylation of CE combined with 1H NMR spectroscopy are efficient and inexpensive ways to gain information on the over-all DS and partial DS values in position 2, 3, and 6 of the AGU. Complete subsequent phenylcarbamoylation can be achieved even for CE with bulky substituents, e.g., adamantanecarboxylic acid esters. In addition to NMR experiments the carbamoylated CE were studied by HPLC after complete chain degradation. Carbethoxymethylcarbamoylation has turned out to be the most useful tool for this path. Chromatograms comparable to carboxymethylated cellulose (CMC) were obtained, which can be exploited to calculate the mole fractions of the basic building units (un-, mono-, di- and tri-substituted glucoses) of the polymer. Comparison with statistic calculations gave a first hint on the distribution of substituents along the polymer chain. For a commercial cellulose diacetate a statistic pattern of substitution was determined. 相似文献
Periodic and molecular cluster density functional theory calculations were performed on the Iα (001), Iα (021), Iβ (100), and Iβ (110) surfaces of cellulose with and without explicit H2O molecules of hydration. The energy-minimized H-bonding structures, water adsorption energies, vibrational spectra, and 13C NMR chemical shifts are discussed. The H-bonded structures and water adsorption energies (ΔEads) are used to distinguish hydrophobic and hydrophilic cellulose–water interactions. O–H stretching vibrational modes are assigned for hydrated and dry cellulose surfaces. Calculations of the 13C NMR chemical shifts for the C4 and C6 surface atoms demonstrate that these δ13C4 and δ13C6 values can be upfield shifted from the bulk values as observed without rotation of the hydroxymethyl groups from the bulk tg conformation to the gt conformation as previously assumed. 相似文献
Summary: The copper‐catalyzed Huisgen reaction as a typical example of click chemistry was realized with the polysaccharide cellulose for the first time. The generality, selectivity, and the efficiency of click chemistry perfectly fit the requirements of polysaccharide modification, which is demonstrated by the introduction of triazole‐spacer bound functional groups, i.e., carboxylic ester, thiophene, and aniline moieties. Azide moieties introduced into cellulose via the tosyl derivative were simply transferred with ethynyl compounds under Cu(I) catalysis and mild and easily applicable conditions. Hydrolytically stable cellulose derivatives soluble in organic solvents, e.g., DMSO or DMF with DS up to 0.9 are obtained. The triazole substituted cellulose derivatives were characterized by elemental analysis, FTIR, 1H NMR, and 13C NMR spectroscopies and show no impurities or substructures resulting from side reactions.
13C NMR spectra of 24 methyl 2,3-anhydro-4-deoxy-pento and hexopyranosides have been obtained. 1H NMR spectra were also recorded for comparison purposes. The 13C NMR data can be used for differentiation of the stereo-isomeric epoxide configuration. 1H and 13C NMR spectra give some insight, though still of qualitative nature, into conformation of epoxy compounds. 相似文献
The determination of the degree of substitution (DS) of fatty acid cellulose esters with alkyl chain lengths from C8 to C18
was performed by direct transesterification with trimethylsulphonium hydroxide (TMSH) using tert-butyl methyl ether (MTBE) as a solvent. Transesterification was demonstrated to be quantitative at 75 °C in 60 min. The quantification
of the formed fatty acid methyl esters was performed by gas chromatography (GC). After the optimization of the method, long
chain cellulose esters (LCCE) could be analyzed in a wide range of DS. The obtained values were compared to those given by
other existing protocols. LCCE with DS-values in a range of 5 × 10−5 to 3 were analyzed with high accuracy. Reproducibility is weakened for high DS values if the sample has a compact aspect
limiting the accessibility of TMSH to the ester functions. This method can also be suitable for the analysis of mixed cellulose
esters. 相似文献
All-cellulose composites were prepared by partly dissolving microcrystalline cellulose (MCC) in an 8.0 wt% LiCl/DMAc solution,
then regenerating the dissolved portion. Wide-angle X-ray scattering (WAXS) and solid-state 13C NMR spectra were used to characterize molecular packing. The MCC was transformed to relatively slender crystallites of cellulose
I in a matrix of paracrystalline and amorphous cellulose. Paracrystalline cellulose was distinguished from amorphous cellulose
by a displaced and relatively narrow WAXS peak, by a 4 ppm displacement of the C-4 13C NMR peak, and by values of T2(H) closer to those for crystalline cellulose than disordered polysaccharides. Cellulose II was not formed in any of the composites
studied. The ratio of cellulose to solvent was varied, with greatest consequent transformation observed for c < 15%, where c is the weight of cellulose expressed as % of the total weight of cellulose, LiCl and DMAc. The dissolution time was varied
between 1 h and 48 h, with only small additional changes achieved by extension beyond 4 h. 相似文献
MS and 1H, 13C and 11B NMR results are presented revealing the formation of cyclic seven-membered boronate structures at trans-1,2-diol moieties of carbohydrates providing new opportunities for the activation, protection and analysis of glucopyranose-based oligomers and polymers such as cellulose or starch. ‘Coordination-induced shifts’ in 13C NMR spectra were identified for the esterification by boronic acids of carbohydrates, which can be applied for further studies. 相似文献
Cellulose was dissolved in lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI), and reacted with alkylketene dimers
(AKDs) under non-aqueous and homogeneous conditions to prepare cellulose/AKD β-ketoesters with high degrees of substitution
(DS). Six AKDs synthesized from octanoic, decanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids via their
fatty acid chlorides were used in this study. The cellulose/AKD β-ketoesters obtained were gummy solid at room temperature,
and had DS values ranging from 1.9 to 2.9. Cellulose/fatty acid esters with DS 2.5–2.9 were also prepared as references. 13C-NMR spectra of the cellulose/AKD β-ketoesters showed that cellulose carbons and substituent carbons close to cellulose chains
were restricted in motion and behaved like solid in solutions. In contrast, the cellulose/fatty acid esters did not demonstrate
such anomalous 13C-NMR spectra. The unique 13C-NMR patterns are characteristic for the cellulose/AKD β-ketoesters, which have long and branched alkyl substituents in each
anhydroglucose unit. Size-exclusion chromatography furnished with multi-angle laser light scattering (SEC-MALLS) revealed,
on the other hand, that all cellulose/AKD β-ketoesters and cellulose/fatty acid esters prepared had flexible or random-coil
conformations in tetrahydrofuran (THF). There were no clear differences in conformation or stiffness of cellulose chains between
cellulose/AKD β-ketoesters and cellulose/fatty acid esters. 相似文献
Molten salt hydrates proved to be alternative solvents to cellulose. Toinvestigate the reasons for this dissolving ability, information about thesolvent–cellulose interactions is essential. As well as 13CHR NMR, 7Li NMR was used to obtain further insight into thisproblem.After comparing several molten salt hydrates, the 7Li NMR spectrarevealed a smaller shielding of the lithium cation for not dissolving than fordissolving and swelling cellulose systems. In most solvent systems theshieldingat the 7Li nuclei increases with the cellulose concentration. 2D7Li-1H HOESY NMR was successfully applied to verify thepresence of cellobiose, used as a model compound for cellulose, in the firstco-ordination sphere of the lithium cation. 相似文献
New adamantane carboxylic acid esters of cellulose (adamantoylcelluloses) were synthesized homogeneously inN,N-dimethylacetamide/LiCl using differently activatedcarboxylic acid derivatives. This includes the reaction of cellulose with1-adamantoyl chloride and with adamantane-1-carboxylic acid after insitu activation with p-toluenesulfonyl chlorideand with 1,1-carbonyldiimidazole, which is a new and efficient tool. Thedegree of substitution (DS) has been determined by means of 1H NMRspectroscopy using the perpropionylated adamantoyl cellulose samples. DS valuesas high as 2.1 were achieved. The reaction efficiency was 85% and the DS can becontrolled by the molar ratio and the reaction conditions applied. The reactionoccurs faster at the primary position compared to the secondary ones. Theproducts are soluble in various organic solvents dependent on the DS.Preliminary results of subsequent modifications and properties of theadamantoylcelluloses are discussed as well. 相似文献
Estimation of the substitution distribution for cyanoethyl cellulose was carried out by 1H and 13C NMR spectroscopic analyses after the additional acetylation. Based on the complemental function of cyanoethyl and acetyl substituents, the degree of substitution (DS) of cyanoethyl groups could be calculated from the ratios of the 1H integrated intensities in acetyl methyl ( 1.8–2.1) and cyanoethyl methylene ( 2.6–2.9) protons, and also from the corresponding ratios for acetyl methyl carbon signals ( 19.7–21.3) and cyanoethyl methylene carbon signals ( 17.5–19.0). Good agreement was obtained between the DS values obtained from the NMR spectroscopic analyses and those determined by the conventional nitrogen content method, indicating the validity of the NMR method used. In addition, the NMR method was found to be effective in determining the positional substituent distribution by the quantitative analysis of the three cyan carbon signals ( 118–120). 相似文献
Cellulosic polysaccharides have increasingly been recognized as a viable substitute for the depleting petro-based feedstock due to numerous modification options for obtaining a plethora of bio-based materials. In this study, cellulose triacetate was synthesized from pure cellulose obtained from the waste lignocellulosic part of date palm (Phoenix dactylifera L.). To achieve a degree of substitution (DS) of the hydroxyl group of 2.9, a heterogeneous acetylation reaction was carried out with acetic anhydride as an acetyl donor. The obtained cellulose ester was compared with a commercially available derivative and characterized using various analytical methods. This cellulose triacetate contains approximately 43.9% acetyl and has a molecular weight of 205,102 g·mol−1. The maximum thermal decomposition temperature of acetate was found to be 380 °C, similar to that of a reference sample. Thus, the synthesized ester derivate can be suitable for fabricating biodegradable and “all cellulose” biocomposite systems. 相似文献
Cold NaOH/urea aqueous dissolved cellulose was studied for the synthesis of benzyl cellulose by etherification with benzyl chloride. By varying the molar ratios of benzyl chloride to OH groups in cellulose (1.5–4.0) and reaction temperatures (65–70 °C), benzyl cellulose with a degree of substitutions (DS) in the range of 0.29–0.54 was successfully prepared under such mild conditions. The incorporation of benzyl groups into cellulose was evidenced by multiple spectroscopies, including FT IR, 1H NMR, 13C NMR, CP/MAS 13C NMR and XRD. In addition, the thermal stability and surface morphology of the benzyl cellulose was also investigated with regard to the degree of substitution. The results indicated that the benzyl cellulose product with a low DS (0.51) in the present study reached the same solubility in many organic solvents as compared to those prepared in heterogeneous media. After benzylation, the sample decomposed at a lower temperature with a wider temperature range, which indicated that the thermal stability of benzyl cellulose was lower than that of the native cellulose. In addition, benzylation resulted in a pronounced reduction in crystallinity as well as a fundamental alteration of morphology of the native cellulose. 相似文献
Cellulose acetate is widely used in films, filters, textiles, lacquer and cosmetic products. Herein we demonstrate the production of cellulose esters under homogeneous conditions using 1,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc]) as solvent. The reagents have been chosen such that the system is recyclable, i.e. by-products are low boiling and easy to remove. It is demonstrated that cellulose acetate can be synthesized with different degree of substitution (DS) values, and that some commonly used acylation regents, like vinyl carboxylates react well without additional base catalyst. Low to high DS values are possible with good recovery of high purity ionic liquid (IL). A linear correlation method of two separate methods, IR and 31P NMR, is proposed to reliably assess the DS of the products. The recyclability of the solvent is demonstrated by acetylating cellulose with isopropenyl acetate to high degree and regeneration into water. After regeneration of cellulose acetate from the IL with addition of water, the residual water was entrained using n-butanol to minimize hydrolysis of [DBNH][OAc], to allow for high recovery and high purity of the ionic liquid. Thus, an overall scheme for batch cellulose acetylation and recovery of [DBNH][OAc] from aqueous solutions is proposed. 相似文献
Optically active 1-fluoroindan-1-carboxylic acid (FICA) was designed and prepared as its methyl ester for determining the absolute configuration of chiral molecules by both 1H and 19F NMR spectroscopies. Enantiomerically pure isomers of FICA methyl esters (FICA Me esters) were obtained by chromatographic separation using HPLC with a Daicel Chiralcel OJ-H column. The absolute configuration of the (+)-FICA Me ester was deduced to be (S) by X-ray crystallographic analysis of the (+)-FICA amide of (R)-α-phenethylamine. Both enantiomers were derived to the diastereomeric esters of chiral secondary alcohols by an ester exchange reaction. In the 1H NMR spectra, the signs of ΔδH (δR ? δS) were consistent on each side of the FICA molecular plane. Therefore, the concept of the modified Mosher’s method could be successfully applied to the FICA-based procedure. Moreover, the consistency in the signs of ΔδF (δR ? δS) values suggests that the FICA method would be reliable in assigning the absolute configurations of secondary alcohols based on 19F NMR spectroscopy. 相似文献
3-Nitrofurazans with different substituents at position 4 were studied by 1H, 13C, and 14N NMR spectroscopy. A correlation between chemical shifts (CS) in the 13C NMR spectra of furazans and benzene with similar substituents was revealed. Increments for a series of new substituents were determined. The 13C and 14N CS values presented can be used as a reliable set of reference data. 相似文献