NIR FT Raman Spectroscopy–a Rapid Analytical Tool for Detecting the Transformation of Cellulose Polymorphs

This is a report of the combined use of NIR FT Raman spectroscopy and X-ray diffraction measurements (WAXS) to investigate the polymorphic transformation of cellulose I into cellulose II. For this reason samples of cellulose I were swelled in different concentrations of NaOH and dissolved in different molten inorganic salts hydrates (LiCl·2ZnCl₂·6H₂O, LiClO₄·3H₂O, LiSCN·2,5H₂O and ZnCl₂·4H₂O). NIR FT Raman spectra of the alkali treated samples were recorded. They characterize the pure modifications cellulose I and II as well as mixtures of the two polymorphic phases. The results of the Raman measurements were confirmed by X-ray scattering. The paper demonstrates that FT Raman vibrational spectroscopy is a powerful, rapid analytical method which may be used to follow the polymorphic transformation of cellulose I into cellulose II.     

Study of cellulose/ethylene diamine/salt systems

To better understand the complex interactions leading to dissolution of cellulose in ethylene diamine (EDA)/salt solvents, studies of interactions in sub systems of solution components and a model system based on cellobiose were conducted. Interaction between EDA and salt cation was investigated through comparison of solvation of K⁺, Na⁺ and Li⁺ in the EDA/H₂O binary solvent system. The least degree of solvation of K⁺ in EDA increased its availability for direct interaction with cellulose. Wide angle X-ray diffraction was utilized to study the interaction between EDA and cellulose. The effect of various solvents on cellulose crystalline polymorph was compared. The results indicated that cellulose was easily accessible to EDA and 1,3-diaminopropane, but was not affected by water or ethanolamine. The effect of salt concentration was investigated using cellobiose as a model compound through HSQC (Heteronuclear Single Quantum Coherence) NMR spectroscopy. Solid state CP/MAS (cross polarization/magic angle spinning) ¹³C NMR spectroscopy was employed to characterize changes in the conformation of the CH₂OH group of cellulose during dissolution. A mechanism scheme of cellulose dissolution in EDA/KSCN systems was proposed based on the information gathered.     

Dissolution of cellobiose in the aqueous solutions of chloride salts: Hofmeister series consideration

The effects of chloride salts on the dissolution of cellobiose in aqueous solution were investigated using calorimetry and ¹H NMR. The dissolution of cellobiose in salt solutions is a typical entropy-driven process. The activity of ZnCl₂ and LiCl hydrated ions is enhanced as the hydration number decreases with increasing temperature. Zn²⁺ and Li⁺ hydrates can interact with the oxygen atoms at the O5 and O6 positions of cellobiose and associate with the Cl^? anions, leading to the breakage of cellobiose hydrogen bonds. We found that the solubility of cellobiose in aqueous solutions is on the order of ZnCl₂ > LiCl > NaCl > H₂O > KCl > NH₄Cl, which is consistent with the Hofmeister series. For the first time, we recognized the specific ionic effects of the Hofmeister series on the dissolution of cellobiose in salt aqueous solutions. This finding is helpful for understanding the dissolving mechanism of cellulose in aqueous solvents with salts and providing fundamental knowledge for finding and designing new cellulose solvents.     

7Li NMR as probe for solvent–cellulose interactions in cellulose dissolution

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.     

Evaluation of molten inorganic salt hydrates as reaction medium for the esterification of cellulose

Molten inorganic salts and salt hydrates are highly efficient solvents for cellulose. The acetylation and deacetylation of the polymer dissolved in this group of cellulose solvents was investigated. The formation of cellulose acetates in molten salts with low water content and low acidity was confirmed by FT-IR-spectroscopy and ¹³C-CP/MAS-NMR spectroscopy. The degree of substitution was investigated by ¹H-NMR measurements after perpropionylation.     

Effects of zinc and nickel salts in intumescent flame-retardant polypropylene

Variable amounts of zinc and nickel salts, such as ZnSO₄·7H₂O and NiSO₄·6H₂O, have been incorporated into blends of polypropylene (PP)/ammonium polyphosphate (APP)/dipentaerythritol (DPER) with the aim of studying their effect on intumescent flame retardance (IFR). The PP/IFR/salt composites have been prepared using a twin-screw extruder, and their IFR behaviours have been evaluated through limiting oxygen index (LOI), vertical burning tests (UL-94), and cone calorimeter tests (CONE). The results show that, at an appropriate level, zinc and nickel salts can increase the LOI and decrease the heat release rate (HRR). The composites have been studied with the aid of thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The flame-retardant mechanism of the PP/IFR/salts system is also discussed in terms of catalytic charring. ZnSO₄·7H₂O has been shown to be the most effective among the aforementioned metal salts, which has proved to be strongly associated with its low melting point and the interaction between DPER and SO₄²⁻.     

The behaviour of cellulose in hydrated melts of the composition LiXċn H2O (X=I−, NO3−, CH3COO−, ClO4−)

The dissolution behaviour of cellulose in low temperature molten salts was investigated. Depending on the chosen anions in the melt, cellulose shows different reaction behaviour in different Li⁺containing melts. Dissolution of the polymer was observed in molten LiClO₄3H₂O and molten LiI2H₂O. In the hydrated melts of LiCH₃COO2H₂O and LiNO₃3H₂O a fine distribution of cellulose was stated. Cellulose can be regenerated by cooling the melt and removing the salt by dissolution in water.The structure of the recrystallized product is determined by the used low temperature molten salt.     

Synthesis, spectroscopic characterization, X-ray structure and DFT studies on 4-(2-hydroxyphenyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridin-5-ium chloride hydrate

The title molecular salt, 4-(2-hydroxyphenyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridin-5-ium chloride hydrate (C₁₂H₁₄N₃O⁺·Clˉ·H₂O), was synthesized and characterized by IR-NMR spectroscopy and single-crystal X-ray diffraction. In addition to the molecular geometry from X-ray experiment, the molecular geometry, vibrational frequencies and gauge-independent atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated using the density functional theory (DFT/B3LYP) method with the 6-31++G(d,p) and 6-311++G(d,p) basis sets, and compared with the experimental data. Besides, molecular electrostatic potential (MEP) distribution and non-linear optical properties of the title compound were investigated by theoretical calculations at the B3LYP/6-311++G(d,p) level.     

Oxo-tricyano complexes of molybdenum(IV) with salicylaldehydehydrazone

[Mo(CN)₄O(H₂O)]^2– reacts with hydrazine and salicylaldehyde in aqueous solution to give [Mo(CN)₃O(salhy)]^2– (Hsalhy = salicylaldehydehydrazone), isolated as green (Ph₄P)₂[Mo(CN)₃O(salhy)] · 6H₂O. In CHCl₃, the product converts within seconds into (Ph₄P)₂[Mo(CN)₃O(salhy)] · H₂O · 2CHCl₃ yielding microcrystals having a metallic golden sheen. The complexes were characterised by elemental analysis, t.g. and d.t.a., u.v.–vis. absorption, i.r., ¹H-n.m.r. spectroscopy and by magnetic susceptibility measurements. The visible spectra in various solvents are dominated by the metal-to-ligand charge-transfer bands with absorption maxima linearly dependent on the Reichardt E _T parameter. In halogenated alkanes, the unusual hipsochromic band shift is interpreted in terms of possibile solvent bonding to the metal centre. Cyclic voltammetry indicates that the salt undergoes reversible one electron oxidation with E _1/2 = –0.473 V in DMSO versus ferrocene.     

Substitution Patterns of Cellulose Ethers - Influence of the Synthetic Pathway

Commercial cellulose ethers are usually prepared under heterogeneous reaction conditions. In contrast, this contribution also describes the derivatization under homogeneous conditions in N-methylmorpholine-N-oxide monohydrate (NMMNO*H₂O) and under heterogeneous conditions after converting native cellulose to amorphous cellulose. Amorphous cellulose is prepared by dissolving cellulose in NMMNO*H₂O followed by precipitation in different media. The degree of order and the porosity of the regenerated cellulose is significantly influenced by the content of water in the precipitating agent. The differences are described by measurements using wide angle X-ray scattering, solid-state ¹³C-NMR, mercury porosimetry, and water/liquid retention values. Three synthetic pathways (heterogeneous, heterogeneous with amorphous cellulose and homogeneous) are compared regarding the structure-property relationship of the cellulose ethers formed. Carboxymethylation, hydroxyethylation, hydroxypropylation and sulfoethylation are considered in detail. The choice of synthetic pathway has a significant influence on the degree of substitution (DS), the distribution of substituents on the level of the anhydroglucose unit (AGU), solubility behavior, and the viscosity of aqueous solutions. In general an increasing solubility and an increasing viscosity are observed from heterogeneous to heterogeneous with amorphous cellulose to homogeneous reaction conditions. There is a remarkable difference between the heterogeneously produced cellulose ethers with a DS distribution C2 ≥ C6 > C3 and the strictly homogeneous etherification in NMMNO*H₂O/organic solvent systems with a DS distribution of C3 > C2 ≫ C6. This high regioselectivity at the secondary OH-groups of the AGU may be caused by the strong solvation behavior of NMMNO*H₂O and thereby a protecting function at the C6-OH-group.     

The role of salt on cellulose dissolution in ethylene diamine/salt solvent systems

Ethylene diamine (EDA)/salt solvent systems can dissolve cellulose without any pretreatment. A comparison of the electrical conductivity of different salts in EDA was made at 25 °C, and conductivity decreased in the order of KSCN>KI>NaSCN at the same molar concentration. Among the salts tested, potassium thiocyanate (KSCN) was capable of dissolving both high molecular weight (DP>1000) and low molecular weight (DP = 210) cellulose, and this was confirmed by polarized light microscopy. ³⁹K and ¹⁴N NMR experiments were conducted at 70 °C as a function of cellobiose concentration with EDA/KSCN as the solvent. The results showed that the K⁺ ion interacts with cellobiose more than the SCN⁻ ion does. Recovered cellulose was studied by infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). Changes in the FTIR absorption bands at 1,430 and 1,317 cm⁻¹ were associated with a change in the conformation of the C-6CH₂OH group. The changes in positions and/or intensities of absorption bands at 2,900, 1,163, and 8,97cm⁻¹ were related to the breaking of hydrogen bonds in cellulose. X-ray diffraction studies revealed that cellulose, recovered by precipitating cellulose solutions with water, underwent a polymorphic transformation from cellulose I to cellulose II.     

EPR and electronic spectroscopic studies of Keggin type undecatungstophosphocuprate(II) and undecatungstoborocuprate(II)

The coordination of Cu(II) to the Keggin type anions α-undecatungstophosphocuprate(II) and α-undecatungstoborocuprate(II) was investigated in different environments by EPR and electronic spectroscopy. This study has shown that the coordination geometry around Cu(II) in the tetrabutylammonium (TBA) salts, (TBA)₄H_x[XW₁₁CuO₃₉], with X=P or B, is square pyramidal, with copper bound to the five oxygen donor atoms of the polyoxometalate, whereas for the [XW₁₁Cu(H₂O)O₃₉]ⁿ⁻ anion, on the corresponding potassium salt, a tetragonally elongated pseudo-octahedral geometry was found. For the potassium salts, in aqueous solution, six-coordinated copper is the only form found. For the TBA salts, in nonaqueous solvents, we can observe either the presence of only one form (the six-coordinated Cu(II) species, with a solvent molecule bound to copper), or of two forms: the solvent coordinated copper anions and the five-coordinated copper [XW₁₁CuO₃₉]ⁿ⁻ anions.     

Synthesis and thermochemistry of MgO·3B2O3·3.5H2O

A new magnesium borate MgO·3B₂O₃·3.5H₂O has been synthesized by the method of phase transformation of double salt and characterized by XRD, IR and Raman spectroscopy as well as by TG. The structural formula of this compound was Mg[B₆O₉(OH)₂]·2.5H₂O. The enthalpy of solution of MgO·3B₂O₃·3.5H₂O in approximately 1 mol dm⁻³ HCl was determined. With the incorporation of the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5595.02±4.85) kJ mol⁻¹ of MgO·3B₂O₃3.5H₂O was obtained. Thermodynamic properties of this compound was also calculated by group contribution method.     

Synthesis and Properties of Barium Dihydrogen 1-Hydroxyethane-1,1-diphosphonate Dihydrate

The only compound that crystallizes from aqueous solutions containing 1-hydroxyethane-1,1-di-phosphonic acid (H₄L) and Ba^{2 +} in molar ratios from 3 : 1 to 1 : 3 is BaH₂L·2H₂O. The product was characterized by powder X-ray diffraction, IR spectroscopy, and thermal analysis. The solubility of the compound in water (2.67 mM at 25°C) increases with temperature and with decreasing pH. No double salts M₂ ^IBa(H₂L)₂·nH₂O crystallize from aqueous solutions.     

Synthesis, characterization, and thermochemistry of a new form of 2MgO·3B2O3·17H2O

A new magnesium borate, β-2MgO·3B₂O₃·17H₂O, has been synthesized by the method of phase transformation of double salt and characterized by XRD, IR, and Raman spectroscopy as well as by TG. The structural formula of this compound was Mg[B₃O₃(OH)₅]·6H₂O. The enthalpy of solution of β-2MgO·3B₂O₃·17H₂O in approximately 1 mol dm⁻³ HCl was determined. With the incorporation of the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(10256.39±4.93) kJ mol⁻¹ of β-2MgO·3B₂O₃·17H₂O was obtained. Thermodynamic properties of this compound was also calculated by group contribution method.     

Thermoanalytical investigations on the decomposition of double salts

The melting and decomposition behaviour of the double salts MBr·MgBr2·6H₂O (M=K, NH₄, Rb, Cs) has been investigated in a closed system under dynamic and quasi-isothermal and quasi-isobaric conditions between 20°C and 300°C or 600°C, respectively. DTA heating and cooling cycles illustrate the melting behaviour of the double salts and give information on the melting point of these substances.The thermal decomposition of double salts under quasi-isothermal and quasi-isobaric conditions takes place in the melt (with the exception of RbBr·MgBr2·6H₂O) and under reduced pressure in the solid phase. A double salt of the type MBr·MgBr2·6H₂O is formed as a stable intermediate. The final product of all types of thermal decomposition are basic products with different hydroxide or oxide contents, respectively.

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Zusammenfassung In einem abgeschlossenem System wurde unter dynamischen und quasiisothermen und quasiisobaren Bedingungen im Temperaturbereich zwischen 20°C und 300°C oder 600°C das Schmelz- und Zersetzungsverhalten der Doppelsalze MBrMgBr2·6H₂O (mitM=K, NH₄, Rb, Cs) untersucht. DTA-Heiz- und Kühlzyklen zeigen das Schmelzverhalten der Doppelsalze und geben gleichzeitig Auskunft über den Schmelzpunkt dieser Verbindungen.Die thermische Zersetzung der Doppelsalze unter quasiisothermen und quasiisobaren Bedingungen erfolgt ausgehend von der Schmelze (mit Ausnahme von RbBrMgBr2·6H₂O) und unter vermindertem Druck ausgehend vom Feststoff. Ein Doppelsalz des Typs MBrMgBr2·2H₂O wird als Zwischenprodukt gebildet. Das Endprodukt bei allen Zersetzungstypen sind basische Produkte mit unterschiedlichem Hydroxidoder Oxidgehalt.

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Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60^th birthday     

Reactivity of dissolving pulps modified by TEMPO-mediated oxidation

The reactivity of dissolving pulps towards derivatization or dissolution is a crucial quality parameter and is mainly determined by the accessibility of the hydroxyl groups. When dissolving pulps are produced from paper-grade pulps by cold caustic extraction (CCE), their reactivity is often inferior as compared to commercial prehydrolysis kraft dissolving pulps. It was hypothesized that pulp reactivity can be enhanced by the introduction of small amounts of substituents to facilitate interchain accessibility. In this study, CCE-treated Eucalyptus globulus kraft paper pulp was subjected to TEMPO-mediated oxidation to initiate partial oxidation of the C₆-hydroxyl groups to carboxyl groups. The effect of this pulp modification on the reactivity towards xanthation and the subsequent dissolution in diluted aqueous alkali solution (viscose process) as well as the dissolution in complexing and non-complexing solvents, respectively, was thoroughly examined. The results revealed that the oxidized pulps rich in C₆-carboxylate groups impeded the xanthation reaction obviously because of the reduced availability of hydroxyl groups. When N-methylmorpholine-N-oxide monohydrate was used as a direct solvent, a very high content of C₆-carboxylate groups was found to reduce the solubility of the pulp fibers as less hydrogen bonds can be formed with NMMO·H₂O. In the case of dissolution in the complexing solvent cupriethylenediamine, the dissolution mechanism of cellulose was not deteriorated by the high content of C₆-carboxylate groups. Instead, the oxidation procedure increased the hydrophilic character and the swelling capacity of the outer cell wall layers allowed homogeneous dissolution.     

Copper(II) oxalate and oxamate complexes

Reaction of Cu^II salts with phenanthroline and oxalate (ox) or oxamate (oxm) gives [Cu(phen)(ox)(H₂O)] · H₂O or [Cu(phen)(oxm)(H₂O)] · H₂O complexes while direct treatment of Cu^II salts with oxalate or oxamate gives [NH₄]₂[Cu(ox)₂] and [Cu(oxm)₂(H₂O)₂] respectively. The X-ray structures of one example of each system, aquo-oxamato-phenanthroline-copper(II)-dihydrate and the polymeric ammonium-bis(aquo)-tetraoxalato-dicopper(II)-dihydrate, are reported.     

A New Route to 1,2,3-Propanetrithiol

A new procedure was developed for preparing 1,2,3-propanetrithiol from available initial compounds. 1,2,3-Trichloroethane reacts with sodium disulfide prepared by dissolving sulfur in the system NaOH-N₂H₄ · H₂O-H₂O to give a disulfide dendrimeric polymer, thiokol, in almost quantitative yield. This polymer is subjected to reductive cleavage with an alkaline solution of hydrazine hydrate, which is followed by acidification with HCl. The yield of 1,2,3-propanetrithiol exceeds 60%. The synthesis can be performed as a one-pot procedure.     

Integrated In Situ Characterization of a Molten Salt Catalyst Surface: Evidence of Sodium Peroxide and Hydroxyl Radical Formation

Sodium‐based catalysts (such as Na₂WO₄) were proposed to selectively catalyze OH radical formation from H₂O and O₂ at high temperatures. This reaction may proceed on molten salt state surfaces owing to the lower melting point of the used Na salts compared to the reaction temperature. This study provides direct evidence of the molten salt state of Na₂WO₄, which can form OH radicals, using in situ techniques including X‐ray diffraction (XRD), scanning transmission electron microscopy (STEM), laser induced fluorescence (LIF) spectrometry, and ambient‐pressure X‐ray photoelectron spectroscopy (AP‐XPS). As a result, Na₂O₂ species, which were hypothesized to be responsible for the formation of OH radicals, have been identified on the outer surfaces at temperatures of ≥800 °C, and these species are useful for various gas‐phase hydrocarbon reactions, including the selective transformation of methane to ethane.