(E)-2,6-Dibromo-4-{2-[1-(1H,1H,2H,2H-perfluorooctyl)pyridinium-4-yl]ethenyl}phenolate methanol disolvate, a fluoroponytailed solvatochromic dye

The title compound, C$sb 21$H$sb 12$Br$sb 2$F$sb 13$NO$ot$2CH$sb 3$OH, was obtained by condensation of 4-methyl-1-(1it H,1it H,2it H,2it H-perfluorooctyl)pyridinium iodide and 3,5-dibromo-4-hydroxybenzaldehyde, followed by deprotonation. It crystallizes as a methanol disolvate and exhibits short O---H$ots$O hydrogen bonds and a disordered perfluoroalkyl chain [occupancy ratio 0.538(7):0.462(7)]. Significant $--$ stacking interactions are observed between the benzene and pyridine rings of neighbouring molecules along the it b-axis direction.Peer reviewe

Role of intrinsic and extrinsic xylan in softwood kraft pulp fiber networks

Xylan is primarily found in the secondary cell wall of plants providing strength and integrity. To take advantage of the reinforcing effect of xylan in papermaking, it is crucial to understand its role in pulp fibers, as it undergoes substantial changes during pulping. However, the contributions of xylan that is added afterwards (extrinsic) and xylan present after pulping (intrinsic) remain largely unexplored. Here, we partially degraded xylan from refined bleached softwood kraft pulp (BSKP) and adsorbed xylan onto BSKP. Enzymatic degradation of 1 % xylan resulted in an open hand sheet structure, while adsorption of 3 % xylan created a denser fiber network. The mechanical properties improved with adsorbed xylan, but decreased more significantly after enzymatic treatment. We propose that the enhancement in mechanical properties by adsorbed extrinsic xylan is due to increased fiber-fiber bonds and sheet density, while the deterioration in mechanical properties of the enzyme treated pulp is caused by the opposite effect. These findings suggest that xylan is decisive for fiber network strength. However, intrinsic xylan is more critical, and the same properties cannot be achieved by readsorbing xylan onto the fibers. Therefore, pulping parameters should be selected to preserve intrinsic xylan within the fibers to maintain paper strength

Reinvestigating the concurring reactions in early-stage cellulose pyrolysis by solution state NMR spectroscopy

Low temperature pre-treatments increase the char yield during cellulose carbonization. Although this effect is mostly understood on a kinetic basis, the formed chemical structures leave room for scrutiny. In ongoing ambitions to enhance the char yield of bioderived precursors, the thereby occurring chemistry was reinvestigated. A set of isothermal heating protocols ranging from 150° to 250°C was applied to man-made Ioncell® cellulose fibers and to Avicel® PH-101 microcrystalline cellulose. The prepared cellulosic samples were examined by solution state NMR using a tetra-n-butyl phosphonium acetate ([P4444][OAc]): DMSO-d6 (1:4 wt%) electrolyte as dissolving medium. Complementary, IR spectroscopy, size-exclusion chromatography (SEC) and thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) measurements were performed. The NMR spectra evidenced the formation of levoglucosan end capped moieties as being the first and major occurring reaction during low temperature pre-treatments. In contrast to other mechanistic proposals, no signs for carbonyl or alkene functionalities were discernible in the cellulosic material soluble in the NMR electrolyte, even after treatment at 250 °C for several hours. Thermal cross-linking was observed in SEC already at temperatures not known to significantly influence the overall char yield. In the solution state analytics only partial solubility was observed, owing to the formation of a reluctant fraction previously described as “thermostable condensed phase”. This resulted in analytical blind spots and led to discrepancies between NMR results and FTIR spectra in which carbonyl and alkene vibrations were clearly discernible. Those discrepancies might also imply the co-existence of different fractions in the early stages of cellulose pyrolysis.</p

Indirect determination of partial depolymerization reactions in dialdehyde celluloses (DAC) by gel permeation chromatography of their oxime derivatives

Funding Information: This work was a part of the Academy of Finland's Flagship Programme under Projects No. 318890 and 318891 (Competence Center for Materials Bioeconomy, FinnCERES). The support by the Austrian Biorefinery Center Tulln (ABCT-II) is gratefully acknowledged. The authors thank Muhammad Awais for help in the visualization of the results. Publisher Copyright: © 2023, The Author(s).Owing to a supposed quantitative transformation, oximation of dialdehyde cellulose (DAC) with hydroxylamine hydrochloride is commonly employed in chemical DAC analysis, e.g., for the determination of the degree of oxidation (DO) by titration or elemental analysis. In this study, this modification was utilized for the indirect determination of molecular weight distributions (MWD) by gel permeation chromatography (GPC). The presumably quantitative conversion of aldehyde groups in DAC to the corresponding oxime also breaks up the intermolecular and intramolecular hemiacetal crosslinks, which were associated with solubility issues in the DMAc/LiCl solvent system in previous studies. The limits of the procedure and the material's stability during oximation were investigated. For samples with a DO up to approximately 9% a good applicability was observed, before at higher DO values residual crosslinks led to solubility problems. The oximation/GPC protocol was used to examine the development of the MWD in the early stages of DAC formation under different reaction conditions. The time-dependent partial depolymerization of the polymer backbone was observed. Furthermore, the stability of DAC towards different pH conditions ranging from strongly acidic to strongly alkaline was tested. The depolymerization of DAC in alkaline media occurred with concomitant degradation of aldehyde moieties. In turn, DAC proved to be remarkably stable in acidic and neutral solutions up to a pH of 7.Peer reviewe

Fluoroponytailed Brooker's merocyanines

In this investigation, influences on solution behavior and solvatochromism caused by the attachment of a 1H,1H,2H,2H-perfluorooctyl side chain onto derivatives of the well-known Brooker’s Merocyanine (BM) chromophore are explored. Starting from either 4-picoline or 2-picoline, the corresponding polyfluoroalkylated o- and p-BM have been synthesized in three steps. For all dyes, UV-Vis measurements were conducted in 21 different solvents. An attempted analysis of solvatochromic properties applying linear fits according to Kamlet-Taft parameters turned out to be partially inconclusive and was only feasible for five of the novel dyes after careful examination of their UV-Vis spectra. The observed changes of the spectral characteristics, in combination with the occurrence of either strong hypsochromic or bathochromic shifts, were too significant to be only ascribable to the influence of the solvating medium. Additionally, the maxima of different dyes in different solvents exposed tendencies to converge at specificwavelengths. Taking into account that both, merocyanines as well as fluorosurfactants are known for their formation of supramolecular assemblies, we suggest that aggregation is responsible for the observed phenomena, although controversially disputed in the preliminary literature concerning BM. To underline our proposal, concentration dependent UV-Vis measurements were supplemented.Peer reviewe

Insights into the borohydride reduction of dialdehyde cellulose: the dilemma of competing reduction and β-elimination reactions

Funding Information: Open access funding provided by University of Natural Resources and Life Sciences Vienna (BOKU). The financial support by Business Finland, UPMKymmene Oyj (Finland), the Austrian Biorefinery Center Tulln (ABCT), and the doctoral school “Advanced Biorefineries: Chemistry & Materials” (ABC&M) is gratefully acknowledged. Publisher Copyright: © 2023, The Author(s).Borohydride reduction of dialdehyde cellulose (DAC) is a promising strategy to generate dialcohol cellulose as bio-based alternative to petroleum-based materials. However, the degradation of the polymer backbone according to β-elimination mechanisms limits the practical applications of the reaction. Therefore, we aimed at optimizing the process to suppress degradation reactions by varying reaction time, pH, and reagent stoichiometry. The degree of oxidation (DO) of the DAC intermediates significantly impacts the yields and molecular weights of the isolated dialcohol celluloses, with a “leveling-off” effect at higher DO values. Increasing the amount of sodium borohydride can minimize—but not entirely prevent—chain scissions. Lowering the pH value during reduction slows down the degradation but results in incomplete conversion of the aldehyde functionalities. Our study provides valuable insights into the consequences of side reactions during borohydride reduction of DAC as well as into chemistry and analysis ofthe dialdehyde cellulose/dialcohol cellulose system. Graphical abstract: About a dilemma in cellulose chemistry: Dialcohol cellulose derived by periodate oxidation and subsequent borohydride reduction of cellulose has received increasing attention in the development of sustainable thermoplastic materials. The present study highlights the challenge of suppressing β-elimination and favoring the reduction pathway to optimize reaction conditions and minimize chain degradation.Peer reviewe

Ionic and neutral fluorosurfactants containing ferrocene moieties as chromophoric constituents

In two eventually interlinked projects emphasizing on the exploitation of the peculiar properties of ferrocene moieties, as well as fluoroponytails, the two compounds (E)-1-ferrocenyl-2-(1-(1H,1H,2H,2H-perfluorooctyl)-4-pyridiniumyl)ethylene hexafluorophosphate and (4-perfluorooctylphenyl)ferrocene were prepared. Despite the crystallization of polyfluoroalkylated materials is usually very challenging, attempts to grow single-crystals suitable for X-ray determination were successful, allowing for a detailed structural discussion of ferrocene containing fluorosurfactants for the first time. Additionally, a tentative UV–vis study was performed in four solvents. In contrast to the commonplace spectral behavior of (4-perfluorooctylphenyl)ferrocene, different interesting features, including slight solvatochromism, peak-splitting at higher concentrations, as well as the formation of a colored dispersion were detected for the ionic dye (E)-1-ferrocenyl-2-(1-(1H,1H,2H,2H-perfluorooctyl)-4-pyridiniumyl)ethylene hexafluorophosphate.Peer reviewe

Reductive Amination of Dialdehyde Cellulose: Access to Renewable Thermoplastics

Funding Information: We kindly thank Business Finland and UPM-Kymmene Oyj (Finland) for their financial support and UPM-Kymmene Oyj for providing the softwood kraft pulp. We also thank Flavia Fröhlich (IMC University of Applied Sciences, Austria) for her help in preparing the diamine celluloses. The BOKU doctoral school ABC&M and the Austrian Biorefinery Center Tulln (ABCT) are gratefully acknowledged for their support. Publisher Copyright: © 2022 The Authors. Published by American Chemical Society.The reductive amination of dialdehyde cellulose (DAC) with 2-picoline borane was investigated for its applicability in the generation of bioderived thermoplastics. Five primary amines, both aliphatic and aromatic, were introduced to the cellulose backbone. The influences of the side chains on the course of the reaction were examined by various analytical techniques with microcrystalline cellulose as a model compound. The obtained insights were transferred to a 39%-oxidized softwood kraft pulp to study the thermal properties of thereby generated high-molecular-weight thermoplastics. The number-average molecular weights (Mn) of the diamine celluloses, ranging from 60 to 82 kD, were investigated by gel permeation chromatography. The diamine celluloses exhibited glass transition temperatures (Tg) from 71 to 112 °C and were stable at high temperatures. Diamine cellulose generated from aniline and DAC showed the highest conversion, the highest Tg (112 °C), and a narrow molecular weight distribution (Døµ of 1.30).Peer reviewe

A Fluoroponytailed NHC–Silver Complex Formed from Vinyl-imidazolium/AgNO3 under Aqueous– Ammoniacal Conditions

Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.3-(1H,1H,2H,2H-Perfluorooctyl)-1-vinylimidazolium chloride [2126844–17–3], a strong fluorosurfactant with remarkably high solubility in water, was expediently converted into the respective doubly NHC-complexed silver salt with nitrate as counter ion in quantitative yield. Due to its vinyl substituents, [bis(3-(1H,1H,2H,2H-perfluorooctyl)-1-vinylimidazol-2-ylidene)silver(I)] nitrate, Ag(FNHC)2NO3, represents a polymerizable N-heterocyclic carbene transfer reagent, thus potentially offering simple and robust access to coordination polymers with crosslinking metal bridges. The compound was characterized by infrared and NMR spectroscopy, mass spectrometry as well as elemental analysis, and supplemented by X-ray single-crystal structure determination. It crystallizes in the monoclinic crystal system in the space group P21/c. With 173.3◦, the geometry of the Ag-carbene bridge deviates slightly from linearity. The disordered perfluoroalkyl side chains exhibit a helical conformation.Peer reviewe