Quantitative 31P Research Articles

Synthesis and Characterization of Bio-oil-Based Self-Curing Epoxy Resin

A novel self-curing epoxy resin was synthesized using bio-oil. Bio-oil was produced by hydrothermal liquefaction of loblolly pine and utilized as a biopolyol in the synthesis of bio-oil-based epoxy resin (BOBER) for the first time. Hydroxyl groups in bio-oil were analyzed by quantitative 31P NMR. It was found that not only does the total hydroxyl number of bio-oil influence the yield and epoxy equivalent weight of BOBER, but also the distribution of hydroxyl groups within bio-oil (aliphatic, phenolic, and acidic OH) played an important role in the determination of the optimum amount of catalyst in the synthesis of BOBER. Differential scanning calorimetry analysis proved the self-curing phenomena of BOBER, and Fourier transform infrared spectroscopy suggested that etherification reaction was the dominate reaction during the self-curing. Glass transition temperature, cross-linking density, and the storage modulus of self-cured BOBER were calculated using a dynamic mechanical analyzer.

Tetraphosphines with tetra(biphenyl)silane and -stannane cores as rigid scaffold linkers for immobilized catalysts

The silane Si(p-C6H4-p-C6H4Br)4 and the stannane Sn(p-C6H4-p-C6H4Br)4 have been synthesized and characterized. For the silane a single crystal X-ray structure has been obtained. Tetralithiation of the silane with nBuLi and quenching with the corresponding chlorophosphines gave the tetraphosphines Si(p-C6H4-p-C6H4PR2)4 with (R = Ph, Cy, iPr, tBu). Tetralithiation of Sn(p-C6H4-p-C6H4Br)4 led to cleavage of the Sn-C bonds. Therefore, Sn(p-C6H4-p-C6H4PPh2)4 was synthesized by Br/Li exchange of p-Br-C6H4-p-C6H4PPh2 with nBuLi and reaction with SnCl4. The silanes have been immobilized on silica by generating three phosphonium groups per molecule that were bound to the surface via strong electrostatic interactions. The remaining phosphine group was subsequently coordinated to Wilkinson's catalyst via ligand exchange. All solids have been characterized by quantitative 31P solid-state NMR spectroscopy. The catalysts, immobilized via the tetraphosphine linker scaffolds with biphenyl spacers, showed high activities and selectivities with respect to the hydrogenation of 1-dodecene. They have been recycled 9 times in a batchwise manner. All immobilized catalysts eventually formed rhodium nanoparticles that retained their catalytic activity even after being exposed to air.

Modelling the kinetics of pyrolysis oil hydrothermal upgrading based on the connectivity of oxygen atoms, quantified by 31P-NMR

In the light of current environmental concerns, pyrolysis of biomass offers a carbon neutral pathway to cheap renewable fuels known collectively as pyrolysis oil (PO). However, crude PO is not immediately usable in the current energy infrastructure and needs to be deoxygenated via upgrading technologies. Upgrading reactions are invariably complex since the chemical components in PO can run into hundreds. Moreover, these components are often very difficult to characterise, posing difficulties towards tracking their chemical reactivity and the overall kinetics as a function of time. To address this problem, the aim of this work is to present a modelling strategy to help researchers predict the kinetics of PO deoxygenation in hot compressed water, under hydrothermal conditions, near to or at the supercritical region. To do this, a trial reaction network superstructure with the maximum degrees of freedom was formulated and evaluated for the deoxygenation of three different Oils. This superstructure was based on the connectivity of an oxygen atom matrix which was quantified based on hydroxy groups by quantitative 31P{H} NMR. The complexity of the large-scale superstructure was subsequently simplified by trimming insignificant arcs; subject to an empirical understanding of the underlying chemistry. By parameter estimations, reaction networks were validated or rejected, depending on whether the computationally simulated data for a given reaction network fits the experimental results. It is anticipated that the development of the disclosed “proof of concept” models could promote the chemical understanding and hence optimization of hydrothermal upgrading technologies.

СОВЕРШЕНСТВОВАНИЕ МЕТОДИКИ ОПРЕДЕЛЕНИЯ ГИДРОКСИЛЬНЫХ ГРУПП ЛИГНИНА МЕТОДОМ ЯМР-СПЕКТРОСКОПИИ

Lignin is one of the most abundant biopolymers and a potential renewable source of valuable aromatic compounds. Concerning this, actual problem is functional composition characterization of the lignin samples and the products of their chemical processing. The subject of research is the modification of 31P NMR analysis of different types of hydroxyl groups in the lignin samples. We proposed the phosphitylation of lignin and the quantitative 31P NMR analysis using nondeuterated solvent in order to decrease the cost of experiment. 31P NMR spectra are registered using deuterated and nondeuterated solvents in order to compare them. It is obtained that the use of nondeuterated solvent in mixture doesn’t influence on the chemical shifts of the 31P NMR spectra and the results of quantitative estimation of the content of different hydroxyl groups in lignin macromolecule. The experiments with lignin model compound confirm the adequacy of chosen approach. The method is approbated on the sample of dioxane lignin of birch and the quantitative analysis of hydroxyl groups content is implemented.

Fractional Precipitation of Wheat Straw Organosolv Lignin: Macroscopic Properties and Structural Insights

Wheat straw organosolv lignin has been thoroughly characterized with respect to bulk material properties, surface properties, and structural characteristics by means of antioxidant assays and determination of the equilibrium constant in water–octanol partitioning, i.e., logP determination, optimized gel permeation chromatography, quantitative 31P NMR spectroscopy, quantitative HSQC measurements, and XPS studies. The material was subsequently fractionally precipitated based on a binary solvent system comprised of n-hexane and acetone to yield four fractions that exhibit distinct molecular mass characteristics, while displaying similar structural characteristics, as revealed by the same set of analysis techniques applied to them. Extensive correlation studies underline the versatility of the obtained fractions as higher quality starting materials for lignin valorization approaches since, for example, glass transition temperatures correlate well with number-average molecular weights, applying the Flory–Fox r...

Effect of Fatty Acid Esterification on the Thermal Properties of Softwood Kraft Lignin

Esterification of kraft lignin inherently addresses its potential for thermoplastic applications either on its own or as a component of polymer blends. In this effort, we have investigated the selectivity of softwood kraft lignin toward esterification via acylation. LignoBoost kraft lignin was esterified with acetyl (C2), octanoyl (C8), lauroyl (C12), and palmitoyl (C16) chlorides at various molar ratios with respect to the total hydroxyls present. Quantitative 31P NMR spectroscopy, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) were used to evaluate the selectivity and efficiency of these reactions on the various hydroxyl groups present. The C8–C16 acyl chlorides showed distinct enhanced reactivity toward the aliphatic hydroxyl groups, whereas C2 acyl chloride was found to react uniformly with any available OH irrespective of their chemical nature. The effects of long chain acylation on the polymer and material properties were also examined using solution viscosit...

Solid-State Quantitative (1)H and (31)P MRI of Cortical Bone in Humans.

Magnetic resonance imaging (MRI) plays a pivotal role for assessment of the musculoskeletal system. It is currently the clinical modality of choice for evaluation of soft tissues including cartilage, ligaments, tendons, muscle, and bone marrow. By comparison, the study of calcified tissue by MRI is still in its infancy. In this article, we review the potential of the modality for assessment of cortical bone properties known to be affected in degenerative bone disease, with focus on parameters related to matrix and mineral densities, and porosity, by means of emerging solid-state (1)H and (31)P MRI techniques. In contrast to soft tissues, the MRI signal in calcified tissues has very short lifetime, on the order of 100μs to a few milliseconds, demanding customized imaging approaches that allow capture of the signal almost immediately after excitation. The technologies described are suited for quantitatively imaging human cortical bone in specimens as well as in vivo in patients on standard clinical imagers, yielding either concentrations in absolute units when measured against a reference standard, or more simply, in the form of surrogate biomarkers. The two major water fractions in cortical bone are those of collagen-bound and pore water occurring at an approximately 3:1 ratio. Collagen-bound water density provides a direct quantitative measure of osteoid density. While at an earlier stage of development, quantification of mineral phosphorus by (31)P MRI yields mineral density and, together with knowledge of matrix density, should allow quantification of the degree of bone mineralization.

Contribution of the oxygen extracted from overlithiated layered oxides at high potential to the formation of the interphase

Li-rich (1−x)LiMO2.xLi2MnO3 layered oxides materials have been proposed recently as an attractive alternative to LiCoO2 Their electrochemical performance is greatly improved by charging above the 4.5–4.6 V voltage plateau during the first oxidation. The associated reaction mechanism has been assigned to a transformation from layered to spinel, accompanied a partial oxygen removal process from the surface. Nevertheless, many questions are still unanswered concerning the influence of oxygen extraction and reaction on the chemical composition and evolution of the electrode/electrolyte interphase. Quantitative 7Li, 19F and 31P MAS NMR shows that the partial oxygen extraction at the surface of the electrode material above 4.5 V has a strong influence on the composition/nature of the interphase and exacerbates reactions at the electrode/electrolyte interface. Oxygen reacts as soon as it is extracted from the structure of the positive electrode material to form fluorophosphates in much higher amount in the case of the overlithiated material compared to the stoichiometric material exposed to comparable potentials. The presented study indicates that the release of oxygen from the Li-rich layered oxides greatly influences the electrode/electrolyte interphasial chemistry.

Integrated hot-compressed water and laccase-mediator treatments of Eucalyptus grandis fibers: structural changes of fiber and lignin.

Eucalyptus grandis fibers were treated with hot-compressed water (HCW) and laccase mediator to enhance the fiber characteristics and to produce an active lignin substrate for binderless fiberboard production. The composition, morphology, and crystallinity index (CrI) analysis of fibers showed that the HCW treatment increased the CrI and lignin content of the treated fibers through partial removal of hemicelluloses. Simultaneously, the HCW treatment produced some granules and holes on the surface of the fibers, which possibly facilitated the accessibility of the laccase mediator. Milled wood lignins and enzymatic hydrolysis lignins isolated from the control and treated fibers were comparatively characterized. A reduction of molecular weight was observed, which indicated that a preferential degradation of lignin occurred after exposure to the laccase mediator. Quantitative (13)C, 2D-HSQC and (31)P NMR characterization revealed that the integrated treatment resulted in the cleavage of β-O-4' linkages, removal of G' (oxidized α-ketone) substructures, and an increase in the S/G ratio and free phenolic hydroxyls.

Solvent-free catalyst-free microwave-assisted acylation of lignin

Valorization of lignin into biomaterials requires its good compatibility with the polymeric matrix it is incorporated into. Softwood Kraft lignin was esterified with various anhydrides (acetic, propionic, butyric, methacrylic, maleic) using a solvent-free, catalyst-free, microwave-assisted method. The esterification was fast and efficient (degrees of substitution >90% after 10min). The reaction was worked up using water or ethanol as purification agent. Esterified lignins were characterized by FT-IR, GPC, quantitative 31P NMR and TGA/DSC. NMR analyses indicated that non-cyclic anhydrides reacted with both aliphatic and phenolic OH groups, while maleic anhydride reacted exclusively with aliphatic OH groups. All acylated lignins except the maleated one showed higher thermal stability than the unmodified lignin. Lignins acylated with non-cyclic anhydrides can be applied as green fillers in apolar polyolefins while maleated lignin can serve as metal adsorbent or macroreagent for the synthesis of polyesters or polyamides. We showed in this study that lignin can be modified in a fast and easy way.

Fractionation of five technical lignins by selective extraction in green solvents and characterisation of isolated fractions

Lignins from softwood, hardwood, grass and wheat straw were fractionated by selective extraction at ambient temperature using green solvents like acetone/water solutions of 10, 30, 50, 70 and 90% (v/v) acetone and ethyl acetate. A comparison between the isolated fractions and unfractionated lignins was made in terms of extraction yield, lignin solubility factor, molecular weight distribution and functional group composition. Low molecular weight (LMW) lignin fractions with narrow dispersity are obtained by extraction with ethyl acetate and acetone–water solution containing 30% acetone, with yields depending on the type and the functional group content of lignins. A significant amount (56%) of the organosolv hardwood lignin with low molecular weight (Mw=1868g/mol) and low dispersity was isolated from ethyl acetate. Insoluble fractions with very high molecular weight (Mw between 10 and 17kg/mol) are obtained in low yield from acetone–water solutions with 50, 70 and 90% acetone. LMW lignins are in general less condensed and have lower aliphatic hydroxyl content than parent lignins while the HMW fractions have a higher content of condensed hydroxyls. Principal component analysis on the chemical composition of lignins and isolated fractions determined from 31P NMR data showed the high heterogeneity of the technical lignins. Partial least squares models based on FT-IR spectral data were developed to predict the functional group content determined by quantitative 31P NMR analysis of technical lignins and lignin fractions. This approach can be used to develop simple, rapid and accurate analytical tools to monitor and control the selective fractionation of lignin.

Evaluation of chemical processing impact on E. globulus wood lignin and comparison with bark lignin

In this work a comprehensive characterization of different Eucalyptus globulus lignins was performed in order to evaluate the influence of the industrial process on its structure: LOrg – lignin produced by organosolv process, LKraft – lignin isolated from black liquor (obtained by kraft process) and further purified, taking LEgwood – lignin produced by wood mild acidolysis, as representative of wood lignin. Lignin from bark, LEgbark, also isolated by mild acidolysis, was characterized and compared with LEgwood. Besides the contaminants content (inorganic material plus carbohydrates – 1–3%), lignins structure were studied with reference to yields obtained by nitrobenzene oxidation (NO), and with reference to functional groups and typical structures/linkages by quantitative 13C, 1H and 31P nuclear magnetic resonance (NMR). NO yield order was found to be LKraft (21%)<LOrg (26%)<LEgwood (31%)≈LEgbark (33%), demonstrating that the industrial processing, particularly the kraft one, induced unfavorable changes for a valorization route involving production of functionalized aldehydes by depolymerization. The main changes were the increase of degree of condensation (DC), cleavage of β-aryl ether linkages, and demethoxylation, in particular for the lignin resulting from the kraft process. The NO yield was successful correlated with DC and Syringyl/Guaiacyl (S/G) ratio from 31P NMR and also a good correlation was obtained between β-aryl ether content and DC, clearly ascertaining the structural features related with the potential of the E. globulus lignin as source of functionalized aldehydes. LEgwood and LEgbark have similar structures, whilst the presence of p-hydroxyphenyl (H) detected in the bark lignin leads to a S:G:H (73:23:4) different from wood lignin (80:20:0). The overall results showed that organosolv or a mild delignification process would be a preferable process to obtain lignin from E. globulus wood or bark for production of functionalized aldehydes.

Quantitative 31P NMR analysis of solid wood offers an insight into the acetylation of its components

As a solid substrate, wood and its components are almost invariably examined via spectroscopic or indirect methods of analysis. Unlike earlier approaches, in this effort we dissolve pulverized wood in ionic liquid and then directly derive its functional group contents by quantitative 31P NMR. As such, this novel analytical methodology is thoroughly examined and an insight into the detailed way acetylation proceeds on solid wood and its components is provided as a function of wood density and within its various anatomical features. As anticipated, the efficiency of acetylation was found to be greater within low density wood than in high density wood. The lignin, the cellulose and the hemicelluloses of the low density wood was found to be acetylated nearly twice as fast with remarkable differences in their quantitative degree of acetylation amongst them. This direct analytical data validates the applied methodology and confirms, for the first time, that the order of acetylation in solid wood is lignin>hemicellulose>cellulose and no reactivity differences exist between early wood and late wood.

Esterification of organosolv lignin under supercritical conditions

An organosolv lignin, extracted in organic acid media, named Biolignin™, was acetylated with acetic anhydride in supercritical carbon dioxide (scCO2). The effect of moisture and specific surface of lignin sample, temperature (50, 80, 100, 150°C), reaction time and the use of a catalyst have been studied using analytical techniques such as FT-IR, quantitative 31P NMR and Differential Scanning Calorimetry (DSC).The reaction appeared to be more efficient when a dried organosolv lignin was used (97% Dry Matter) and with a specific surface of 0.645m2/g. The highest degree of substitution of acetylated samples was obtained after 1h of reaction at a temperature of 100°C (180bar) and in the presence of pyridine as a catalyst.When compared with conventionally acetylated lignin (using a solvent medium), it appeared that supercritical conditions allowed a higher yield of acetylation and a decrease of the glass transition temperature of the lignin.

Understanding the chemical transformations of lignin during ionic liquid pretreatment

Unveiling the fundamental chemistry of lignin under ionic liquid (IL) pretreatment will facilitate the understanding of biomass recalcitrance involved in pretreatment processes. To examine in greater detail the chemical transformations of lignin under different IL pretreatment conditions without competing reactions from plant polysaccharides, the IL pretreatment of the isolated poplar alkaline lignin (hardwood lignin) under varying IL pretreatment conditions (i.e., 110–170 °C, 1–16 hours) was performed in an appropriate manner. The structural transformations of the lignin have been investigated by elemental analysis, 2D-HSQC spectra, quantitative 13C-NMR spectra, 31P NMR, and GPC analysis. Results revealed that a decrease of aliphatic OH and an increase in phenolic hydroxyl groups occurred in lignin as the pretreatment proceeded. The increased phenolic OH was mainly as a result of cleavage of β-O-4′ linkages, while the reduced aliphatic OH is probably attributed to the dehydration reaction. The cleavage of β-O-4′ linkages, degradation of β–β′ and β-5′ linkages obviously happened at high temperatures and resulted in the decrease of molecular weights. In addition, IL pretreatment selectively degraded the G-type lignin fractions and the condensation reaction took place more easily at S units than G units. Moreover, the demethoxylation preferentially occurred in G units, especially at higher temperatures. It is believed that investigating the fundamental chemistry of lignin during IL pretreatments would be beneficial to optimize and control the pretreatment process.

Direct Evidence for Intermolecular Oxidative Addition of σ(SiSi) Bonds to Gold

Oxidative addition plays a major role in transition-metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl3, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative 31P and 29Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(SiSi) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(SiSi) bonds to gold and open promising perspectives for the development of new gold-catalyzed redox transformations.

Direct Evidence for Intermolecular Oxidative Addition of σ(SiSi) Bonds to Gold

Oxidative addition plays a major role in transition-metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl3, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative (31)P and (29)Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(Si-Si) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(Si-Si) bonds to gold and open promising perspectives for the development of new gold-catalyzed redox transformations.

Tannin Structural Elucidation and Quantitative 31P NMR Analysis. 2. Hydrolyzable Tannins and Proanthocyanidins

An unprecedented analytical method that allows simultaneous structural and quantitative characterization of all functional groups present in tannins is reported. In situ labeling of all labile H groups (aliphatic and phenolic hydroxyls and carboxylic acids) with a phosphorus-containing reagent (Cl-TMDP) followed by quantitative ³¹P NMR acquisition constitutes a novel fast and reliable analytical tool for the analysis of tannins and proanthocyanidins with significant implications for the fields of food and feed analyses, tannery, and the development of natural polyphenolics containing products.

Kraft Lignin Chain Extension Chemistry via Propargylation, Oxidative Coupling, and Claisen Rearrangement

Despite its aromatic and polymeric nature, the heterogeneous, stochastic, and reactive characteristics of softwood kraft lignin seriously limit its potential for thermoplastic applications. Our continuing efforts toward creating thermoplastic lignin polymers are now focused at exploring propargylation derivatization chemistry and its potential as a versatile novel route for the eventual utilization of technical lignins with a significant amount of molecular control. To do this, we initially report the systematic propargylation of softwood kraft lignin. The synthesized derivatives were extensively characterized with thermal methods (DSC, TGA), (1)H, (13)C, and quantitative (31)P NMR and IR spectroscopies. Further on, we explore the versatile nature of the lignin pendant propargyl groups by demonstrating two distinct chain extension chemistries; the solution-based, copper-mediated, oxidative coupling and the thermally induced, solid-state, Claissen rearrangement polymerization chemistries. Overall, we show that it is possible to modulate the reactivity of softwood kraft lignin via a combination of methylation and chain extension providing a rational means for the creation of higher molecular weight polymers with the potential for thermoplastic materials and carbon fibers with the desired control of structure-property relations.

Comparison of hydrogenolysis with thioacidolysis for lignin structural analysis

Abstract Mild hydrogenolysis has been compared with thioacidolysis as a method for degrading lignins in situ and in isolated form before analysis by gas chromatography/mass spectrometry and quantitative 31P nuclear magnetic resonance (NMR) spectroscopy. Both degradation methods gave similar levels of β-aryl ether-linked phenylpropane units that were released as monomers. Degradation by hydrogenolysis generally gave lower levels of total phenylpropane units when analyzed by 31P NMR, especially in the case of lignins with high levels of condensed units. Overall, these results indicate that mild hydrogenolysis could offer an alternative to thioacidolysis for probing lignin structure.