Sulfation of Hydroxyethyl Cellulose by N(SO3Na)3 and the Anticoagulant Activity of Sulfated Hydroxyethyl Cellulose

Hydroxyethyl cellulose sulfate (HECS) was synthesized by sulfation of hydroxyethyl cellulose with N(SO₃Na)₃, which was manufactured by reaction of sodium bisulfite and sodium nitrite. Barium sulfate nephelometry and light scattering method were used to determine degrees of substitution (DSs) and molecular weights (M_ws), respectively. Sulfate products with DS values from 0.26 to 1.88 and M_w in the range of 12.1–54.8 kDa were obtained at temperatures from 30°C to 80°C. Furthermore, the anticoagulant activity of HECS with different DSs, concentrations, and M_ws was studied. Clotting assays revealed that the introduction of sulfate groups into hydroxyethyl cellulose could improve its anticoagulant activity.     

Direct sulfation of bacterial cellulose with a ClSO3H/DMF complex and structure characterization of the sulfates

Bacterial cellulose (BC) is a form of cellulose synthesized by microorganisms, which has unique structure properties and differs from plant cellulose. Up to now, chemical modification of BC has not been studied widely. This paper aims to prepare sodium bacterial cellulose sulfate (SBS) in N,N‐dimethylformamide (DMF) with a ClSO₃H/DMF complex as the sulfating agent. SBSs with diverse degree of sulfation (DS, 0.04–0.86) were synthesized. The system could change from heterogeneous to homogeneous during the sulfation. Regarding to the DS, the optimal ClSO₃H amount and reaction time were 6 mol/mol anhydroglucose unit and 4 h, respectively. DS increased a little when increasing the temperature, while the yield decreased significantly. SBSs with DS > 0.24 were soluble in deionized water. Carbon nuclear magnetic resonance spectroscopy revealed that the sulfation prefers to take place in the order of C‐6 > C‐2 > C‐3. The X‐ray diffraction profiles indicated that the crystalline structure of BC was destroyed during sulfation. BC has better reactivity than microcrystalline cellulose in both sulfation and depolymerization processes. SBS is a potential biomaterial. However, BC depolymerized obviously in present sulfation, which forbids application of SBS in material. Moisture of the reaction mixture should be removed as completely as possible to guarantee efficient sulfation and decrease depolymerization. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of Sulfation Route and Subsequent Oxidation on Derivatization Degree and Biocompatibility of Cellulose Sulfates

Sulfated cellulose (CS) represents an interesting biopolymer due to bioactivity comparable to heparin. However, use of CS for making surface coatings or hydrogels requires the presence of reactive groups for covalent reactions. Here, an approach is presented to oxidize cellulose sulfates for subsequent cross‐linking reactions with amino groups to form imine bonds. Cellulose is sulfated by direct sulfation or acetosulfation, followed by a M alaprade oxidation. The CS obtained is characterized by elemental analysis and ¹³C‐NMR spectroscopy. The resulting oxidized cellulose sulfates (oxCS) have different degrees of sulfation ranging from 0.79 to 1.13 and oxidation degrees from 0.18 to 0.34, but also different mass average molecular mass (M_W). Toxicity studies are carried out with mouse 3T3 fibroblasts exposed to aqueous solutions of oxCS. The results show that all oxCS are non‐toxic at lower concentrations (0.5 mg mL^?1), but with both increasing degree of oxidation and concentrations, toxic effects are observed particularly for acetosulfated and lesser for direct sulfated oxCS, which is related to a decrease in the M_W of the products. It is concluded that oxCS obtained by direct sulfation with M_W above 70 kDa may represent a biocompatible material for the applications suggested above.     

FT Raman investigation of sodium cellulose sulfate

FT Raman investigation of sodium cellulose sulfates (NaCS) was reported. Different NaCS were prepared by two diverse sulfation methods and their total degrees of substitution (DS) of sulfate groups were determined through either ¹³C-NMR spectroscopy or elemental analysis. Subsequently, these NaCS were characterized with FT Raman spectroscopy. The caused bands through the introduction of the sulfate groups in cellulose chain were explained and assigned. Additionally, a strong linear correlation between the areas under the bands ascribed to the stretching vibrations of C–O–S groups and the total DS of NaCS was presented. A rapid method of quantifying the total DS of NaCS was established. Finally, sodium sulfate (Na₂SO₄), a salt that is very often produced during the sulfation of cellulose, was found to be analyzable even with a weight content of 0.12% in NaCS. The method of quantifying the content of this salt in NaCS was investigated with Raman spectroscopy.     

Effect of sulfuric and phosphoric acid pretreatments on enzymatic hydrolysis of corn stover

The pretreatment of corn stover with H₂SO₄ and H₃PO₄ was investigated. Pretreatments were carried out from 30 to 120 min in a batch reactor at 121°C, with acid concentrations ranging from 0 to 2% (w/v) at a solid concentration of 5% (w/v). Pretreated corn stover was washed with distilled water until the filtrate was adjusted to pH 7.0, followed by surfactant swelling of the cellulosic fraction in a 0–10% (w/v) solution of Tween-80 at room temperature for 12 h. The dilute acid treatment proved to be a very effective method in terms of hemicellulose recovery and cellulose digetibility. Hemicellulose recovery was 62–90%, and enzymatic digestibility of the cellulose that remained in the solid was >80% with 2% (w/v) acid. In all cases studied, the performance of H₂SO₄ pretreatment (hemicellulose recovery and cellulose digestibility) was significantly better than obtained with H₃PO₄. Enzymatic hydrolysis was more effective using surfactant than without it, producing 10–20% more sugar. Furthermore, digestibility was investigated as a function of hemicellulose removal. It was found that digestibility was more directly related to hemicellulose removal than to delignification.     

Thermal stabilization of TEMPO-oxidized cellulose

A partially C6-carboxylated cellulose with carboxylate content of 1.68 mmol/g was prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation of a softwood bleached kraft pulp. Thermogravimetric analyses of the TEMPO-oxidized cellulose (TOC) and its related materials were studied to improve thermal stability of the TOC. Thermal decomposition (T_d) points of the TOC with sodium carboxylate groups, alkali-treated TOC with free carboxyl groups of 0.23 mmol/g and the original cellulose were 222 °C, 264 °C and 275 °C, respectively. Thus, the anhydroglucuronic acid units formed by TEMPO-mediated oxidation of the native wood cellulose and present in the TOC cause the decrease in T_d point by decarbonation during heating process. When carboxyl groups in the TOC were methylated with trimethylsilyl diazomethane (TMSCHN₂), the T_d point increased from 222 °C to 249 °C, and the peak temperature in its derivative thermogravimetric (DTG) curve increased from 273 °C to 313 °C, which was almost equal to that of the original cellulose. Thus, the methyl esterification of carboxyl groups in the TOC is effective in improving thermal stability. When sodium ions present in the TOC as counter ions of carboxylate groups were exchanged to some other metal ions, thermal stability was improved to some extent. Especially, when CaCl₂, Ca(OAc)₂, Ca(NO₃)₂ and CaI₂ solutions were used in the ion-exchange treatments, the peak temperatures in the DTG curves increased to approximately 300 °C. MgCl₂, NiCl₂, SrCl₂ and Sr(OAc)₂ solutions were also effective to some extent in increasing the peak temperatures of DTG curves. Thus, thermal stability of the fibrous TOC can be improved to some extent by methyl esterification of the sodium carboxylate groups present in the original TOC with TMSCHN₂ or ion-exchange treatments with some metal salt solutions.     

Precursor memory effect determining structural properties of sulfated zirconia

Properties of two catalysts tailored in the laboratory conditions by sulfation of commercial Zr-hydroxide and Zr-hydroxide of nitrate origin were compared with those of commercial SO₄-Zr-hydroxide. Equally thermally treated samples in the temperature interval 500–700°C, and having the same amount of sulfur, show different properties indicating memory effect of their solid parent materials. The catalyst obtained by sulfation of commercial Zr-hydroxide differs in amount of residual sulfates upon calcination from other two catalysts. The instability of sulfates in the previous case might be connected to the lowest surface area values of catalyst and the highest fraction of monoclinic phase observed at all applied calcination temperatures.     

Solubility of some lanthanide sulfates in polycomponent systems containing H2SO4

Summary The paper presents data on the solubility of La, Ce, Pr, Nd sulfates in the polycomponent system La₂(SO₄)₃·8H₂O-Ce₂(SO₄)₃·8H₂O-Pr₂(SO₄)₃·8H₂O-Nd₂(SO₄)₃· 8H₂O-H₂SO₄-H₂O (at 25°C and 64°C) as well as in the same polycomponent system but in the presence of CaSO₄·2H₂O. The solubility of the sulfates — ocathydrates of Pr at 25°C and 64°C and of La and Ce at 64°C in tricomponent systemLn ₂(SO₄)₃·8H₂O-H₂SO₄-H₂O are also reported.

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Löslichkeit einiger Lanthanidsulfate in Mehrkomponenten-Systemen mit H₂SO₄

Zusammenfassung Die Arbeit präsentiert Daten für die Löslichkeit von La-, Ce-, Pr- und Nd-Sulfaten in den Vielkomponenten-Systemen La₂(SO₄)₃·8H₂O-Ce₂(SO₄)₃·8H₂O-Pr₂(SO₄)₃·8H₂O-Nd₂(SO₄)₃· 8H₂O-H₂SO₄-H₂O (bei 25°C und 64°C) sowie in den gleichen Systemen, jedoch in Anwesenheit von CaSO₄·2H₂O. Über die Löslichkeit von Sulfatoctahydraten von Pr bei 25°C und 64°C und von La und Ce bei 64°C in den Dreikomponenten-SystemenLn ₂(SO₄)₃·8H₂O-H₂SO₄-H₂O wird auch berichtet.

     

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.     

Effect of wet spinning parameters on the properties of novel cellulosic fibres

Novel cellulose fibres (Biocelsol) were spun by traditional wet spinning technique from the alkaline solution prepared by dissolving enzyme treated pulp directly into aqueous sodium zincate (ZnO/NaOH). The spinning dope contained 6 wt.% of cellulose, 7.8 wt.% of sodium hydroxide (NaOH) and 0.84 wt.% of zinc oxide (ZnO). The fibres were spun into 5% and 15% sulphuric acid (H₂SO₄) baths containing 10% sodium sulphate (Na₂SO₄). The highest fibre tenacity obtained was 1.8 cNdtex⁻¹ with elongation of 15% and titre of 1.4 dtex. Average molecular weights and shape of molecular weight distribution curves of the celluloses from the novel wet spun cellulosic fibre and from the commercial viscose fibre were close to each other.     

Localization of Iα and Iβ phases in algal cellulose revealed by acid treatments

Highly crystalline I-rich type Cladophora cellulose, which had been kept in never-dried condition, was treated in 60wt% sulfuric acid at 100°C, for 1–48h. The cellulose microcrystals thus obtained were analysed by X-ray diffractometry, FT-IR, and transmission electron microscopy. The I component was found to be more degraded than the I component. The cellulose I/I ratios of the samples acid-treated for 0, 24, and 48 h were about 8:2, 6:4, and 4:6, respectively. After the acid treatment, the microcrystals became narrower in width, and very sharp at their ends. These results indicate that the I phase is mostly located at the surface of the microcrystals, which is morphologically more susceptible to the acid treatment.     

Radioselective tritiation of acetailide and para-substituted acetanilides

Acetanilide and para-substituted acetanilides were tritiated by heating with HTO in the presence of RhCl₃.3H₂O as a catalyst in an N,N-dimethylformamide solution at 105–107°C for 18 h. Under such conditions, tritium introduced into the anilide molecules was found at the adjacent ortho positions to the acetamido group with virtually 100% regioselectivity. The substituent effect on the rate of tritiation was observed.     

Thermal decomposition of double rare earth(III) monomethylammonium sulfates with general empirical formula CH3NH3Ln(SO4)2·3H2O (Ln=La-Er and Y)

Double rare earth(III) monomethylammonium sulfates with general empirical formula CH₃NH₃Ln(SO₄)₂·3H₂O (Ln = La-Er and Y) were synthesized and examined by X-ray powder diffraction, TG, DTG and DTA in the temperature range from 25° to 700°C, and chemical analysis. It was found that these compounds are isomorphous and decompose to rare earth sulfate at 700°C.The authors are grateful to the Research Council of Slovenia for financial support of this research.     

Homogeneous methylation of wood pulp cellulose dissolved in LiOH/urea/H2O

Spruce sulphite cellulose (number average degree of polymerization 620) dissolved in an aqueous solution of 8% (w/w) LiOH*H₂O and 12% (w/w) urea was methylated with dimethyl sulphate (DMS). By varying the reaction temperature between 22 and 50 °C, the molar ratio between 9 and 15 mol DMS per mol anhydroglucose unit, and the reaction time from 4 to 24 h, methyl cellulose (MC) with degree of substitution (DS) values in the range of 1.07 and 1.59 was prepared. The chemical structure of MC was analysed by FTIR and ¹H NMR spectroscopy. The turbidity (given in nephelometric turbidity units, NTU) of the aqueous solution of MC reached an optimum of 10 NTU for a product obtained with 12 mol DMS/mol AGU at 50 °C. GPC measurements revealed polymer degradation to a certain extent. The intrinsic viscosity and the Huggins constant k of the MC samples increased with increasing DS value. The MC samples possess k values higher than 0.8, indicating association of the polymer chain. The zero-shear viscosity decreased with increase of both temperature and the amount of methylation agent due to the depolymerization. During the heating/cooling cycle (20-90 °C) of the aqueous solutions of MC, it was observed that samples synthesized at 22 °C with DS values lower than 1.3 did not undergo phase separation in aqueous solution. Phase separation hysteresis with a precipitation temperature up to 80 °C was obtained for aqueous solutions of MC with DS values between 1.07 and 1.66 synthesized at higher temperatures. The functionalization pattern determined by GLC of the corresponding partially methylated glucitol acetates is close to randomness and comparable with those of commercial MC samples.     

New Possibilities of the Acetosulfation of Cellulose

Regioselectively substituted cellulose sulfates in C2/3-, C2/6-, or C6-position of the anhydroglucose unit are accessible by certain synthesis routes. Thereby, products with different properties and various application areas are resulted. Important characteristics of cellulose sulfates regarding their applications are solubility (e.g. in water), rheological behavior, different interaction with low or high molecular cations, thermo reversible gel formation, enzymatic degradability, anticoagulant and antiviral activity. In C6-position substituted cellulose sulfates can be synthesized in principle by acetosulfation. The acetosulfation is a quasi-homogeneous synthesis proceeding under gradually dissolution of the cellulose by using different reactivity of the primary and secondary OH-groups as soon as converting cellulose acetate sulfates. After precipitation of the polymer the acetyl groups are cleaved in alkaline solution. The focus of our study was firstly the investigation of the acetosulfation in different polar aprotic solvents by various sulfating and acetylating agents. In general it should be investigated if C6 substituted cellulose sulfates can be obtained by acetosulfation with different solvents and agents. The products were characterized by ¹³C-NMR and Raman spectroscopy.     

Double sulfates of some rare earths with tetramethylammonium

Double sulfates of rare earths and tetramethylammonium with empirical formula (CH₃)₄NLn(SO₄)₂ · 3H₂O (Ln=Ce, Pr, Nd, Eu, Gd, Tb and Dy) were synthesized and studied by the methods of TG, DTG and DTA in the temperature range from 20 to 500°C, and by X-ray powder diffraction and chemical analysis. Two isostructural groups were obtained: one from Ce to Eu and another from Gd to Dy. It was found that rare earth sulfates are obtained as final products at 500°C. For comparison, TG, DTG and DTA curves of the thermal decomposition of tetramethylammonium sulfate are given.

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Zusammenfassung Doppelsulfate von Seltenerden und Tetramethylammonium der empirischen Formel (CH₃)₄NLn(SO₄)₂ · 3H₂O mit Ln=Ce, Pr, Nd, Eu, Gd, Tb und Dy wurden synthetisiert und im Temperaturbereich 20–500°C mittels TG, DTG und DTA, weiterhin mittels Röntgenpulverdiffraktion und chemischer Analyse untersucht. Es wurden zwei isostrukturelle Gruppen erhalten, die eine von Ce bis Eu, die andere von Gd bis Dy. Man fand, daß man bei 500°C als Endprodukt die Seltenerdensulfate erhält. Zum Vergleich wurden die TG-, DTG- und DTA-Kurven der thermischen Zersetzung von Tetramethylammoniumsulfat gegeben.

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Financial support by the Research Council of Slovenia is gratefully acknowledged.     

Sulfation of Polysaccharides using Monomethyl Sulfate

ABSTRACT

The polysaccharides, curdlan, starch and dextran were sulfated when heated in DMSO with sodium methyl sulfate and a catalytic amount of H₂SO₄ or with pyridinium methyl sulfate. Use of diminished pressure and anhydrous CaSO₄ as a desiccant improved the degree of sulfation and recovery. Under conditions using sodium methyl sulfate, H₂SO₄ and CaSO₄ in vacuo, sulfation at O-6 was predominant in the cases of curdlan and starch, while sulfation at O-2 and O-3 was preferential in the case of dextran.     

Heterogeneous aspects of acid hydrolysis of α-cellulose

Hydrolysis of α-cellulose by H₂SO₄ is a heterogeneous reaction. As such the reaction is influenced by physical factors. The hydrolysis reaction is therefore controlled not only by the reaction conditions (acid concentration and temperature) but also by the physical state of the cellulose. As evidence of this, the reaction rates measured at the high-temperature region (above 200°C) exhibited a sudden change in apparent activation energy at a certain temperature, deviating from Arrhenius law. Furthermore, α-cellulose, once it was dissolved into concentrated H₂SO₄ and reprecipitated, showed a reaction rate two orders of magnitude higher than that of untreated cellulose, about the same magnitude as cornstarch. The α-cellulose when treated with a varying level of H₂SO₄ underwent an abrupt change in physical structure (fibrous form to gelatinous form) at about 65% H₂SO₄. The sudden shift of physical structure and reaction pattern in response to acid concentration and temperature indicates that the main factor causing the change in cellulose structure is disruption of hydrogen bonding. Finding effective means of disrupting hydrogen bonding before or during the hydrolysis reaction may lead to a novel biomass saccharification process.     

Direct formation of cyclic sulfates utilising hypervalent iodine species and sulfur trioxide adducts

PhIO reacts with SO₃·DMF at 0°C to form an active sulfating reagent; subsequent addition of alkenes results in the direct formation of cyclic sulfates in moderate to good yield (35-75%). Terminal, 1,1-disubstituted and cyclopentenes participate in the reaction which is technically very straightforward to carry out.     

SN2-Selective allylic substitution of chiral γ-aryl substituted allylic picolinates with alkynylcopper reagents

Substitution of γ-aryl secondary allylic picolinates with alkynyl copper reagents was studied. The copper reagent, prepared from TMSCCMgBr and CuBr·Me₂S in 2:1, was subjected to substitution of the picolinate derived from (E)-3-phenyl-1-methyl-2-propenyl alcohol at 0 °C for 1 h in THF to produce a mixture of α- and γ-products and the alcohol in 67:20:13, while the reagent in 3 or 4:1 ratio gave the α-product with 90-91% selectivity. On the contrary, reaction in CH₂Cl₂-THF (6-8:1) at 0 °C for 1 h furnished the α-product with 99% regioselectivity. The effect of CH₂Cl₂ was also demonstrated with eight more examples. Furthermore, 99% inversion was determined by transformation to the literature compound and by chiral HPLC.