New solvents for cellulose: dimethyl sulfoxide/ammonium fluorides

New solvents based on DMSO in combination with alkylammonium fluorides, in particular TBAF . 3H(2)O and BTMAF . H(2)O, were established as media for homogeneous functionalization of cellulose. Even DMSO in combination with freshly prepared, anhydrous TBAF, obtained by the reaction of tetrabutylammonium cyanide and hexafluorobenzene, dissolves cellulose. In contrast, a mixture of DMSO and tetramethylammonium fluoride does not dissolve cellulose. The solvents were characterized by capillary viscosity, which showed that a cellulose solution of DMSO/BTMAF . H(2)O possesses a lower viscosity at comparable cellulose concentrations compared with DMSO/TBAF . 3H(2)O. The determination of the degree of polymerization of the starting cellulose (microcrystalline cellulose, spruce sulfite pulp, and cotton linters), and of the regenerated samples, shows that degradation of the polymer depends on the dissolution time, temperature and on the ammonium fluoride used. The results of different homogeneous reactions including acylation and carbanilation of cellulose in the solvents were compared with those of the most-commonly-applied solvent N,N-dimethylacetamide/LiCl. The products were characterized by elemental analysis, (1)H- and (13)C NMR spectroscopy (additionally after perpropionylation) and FTIR spectroscopy.     

Rheological properties of solutions of general‐purpose poly(vinyl alcohol) in dimethyl sulfoxide

The characteristic rheological responses of solutions of atactic poly(vinyl alcohol) (PVA) in dimethyl sulfoxide were investigated in terms of the concentration and molecular weight. The syndiotactic dyad content and weight‐average molecular weight of PVA were 52% and 85,000–186,000, respectively. On a modified Cole–Cole plot, the solutions did not give a single master curve with a slope of 2 but gave various curves with slopes of less than 2. Furthermore, the slope slightly decreased with increasing concentration. The deviation from the master curve indicated that the solutions were rheologically heterogeneous, despite optical transparency. Among the PVA solutions, the 14 wt % solutions exhibited very unusual rheological behavior. The loss tangent changed with the shear rate and produced three distinct regions, which indicated a shear‐induced phase transition. With respect to Winter's view on gelation, the 14 wt % solutions underwent a double sol–gel transition as the shear rate increased over the frequency range of 0.05–500 rad/s. However, the molecular weight did not have such noticeable effects on the rheological behavior over the concentration range of 10–14 wt %. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1451–1456, 2004     

Water effect on the gelation behavior of polyacrylonitrile/dimethyl sulfoxide solution

The gelation behavior of polyacrylonitrile (PAN)/dimethyl sulfoxide (DMSO) solution containing different amounts of water has been investigated using various methods. The ternary phase diagram of PAN/DMSO/water system indicated that water enhanced the temperature at which phase separation of PAN/DMSO solution occurred. Intrinsic viscosities [η] of dilute PAN/DMSO solution and PAN/DMSO/water solution at varied temperatures were measured to examine the influence of water on the phase behavior of PAN/DMSO solution. The presence of water in the solution gave rise to elevated critical temperature T_c. The gelation temperature T_g obtained by measuring the loss tangent tan δ at different oscillation frequencies in a cooling process was found to increase with increased water content in the solution. The critical relaxation exponent n value, however, changed little with varied concentration. During the aging process, the gelation rate of PAN/DMSO solution increases with the water level. The n values of the PAN/DMSO solutions with 2 wt% and 4 wt% water were a little larger than that of the solution without water, which may be explained by the turbid gel resulted from phase separation. The n values obtained in the aging process were larger than those obtained in the cooling process for the same three solutions, ascribed to the weaker gel with less cross-linking points formed in long time. Water led to the formation of denser gel structure. The coarser gel surface can also be attributed to the phase separation promoted by water.     

Dilute solution properties of cellulose in LiOH/urea aqueous system

Cellulose was dissolved rapidly in 4.6 wt % LiOH/15 wt % urea aqueous solution and precooled to –10 °C to create a colorless transparent solution. ¹³C‐NMR spectrum proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The result from transmission electron microscope showed a good dispersion of the cellulose molecules in the dilute solution at molecular level. Weight‐average molecular weight (M_w), root mean square radius of gyration (〈s²〉_z^1/2), and intrinsic viscosity ([η]) of cellulose in LiOH/urea aqueous solution were examined with laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 4.6 wt % LiOH/15 wt % urea aqueous solution was established to be [η] = 3.72 × 10^?2 M in the M_w region from 2.7 × 10⁴ to 4.12 × 10⁵. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were given as 6.1 nm, 358 nm^?1, and 20.8, respectively. The experimental data of the molecular parameters of cellulose agreed with the Yamakawa–Fujii theory of the worm‐like chain, indicating that the LiOH/urea aqueous solution was a desirable solvent system of cellulose. The results revealed that the cellulose exists as semistiff‐chains in the LiOH/urea aqueous solution. The cellulose solution was stable during measurement and storage stage. This work provided a new colorless, easy‐to‐prepare, and nontoxic solvent system that can be used with facilities to investigate the chain conformation and molecular weight of cellulose. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3093–3101, 2006     

The oxysulfenylation of alkenes with dimethyl sulfoxide/oxalyl chloride

A convenient method for the oxysulfenylation of alkenes using dimethyl sulfoxide/oxalyl chloride is described. Cycloalkenes give trans-adducts stereospecifically. The reactions of styrene are highly regioselective for Markovnikov adducts, whereas aliphatic alkenes lead to anti-Markovnikov adducts mainly.     

Preferential solvation of lysozyme by dimethyl sulfoxide in binary solutions of water and dimethyl sulfoxide

To reveal the denaturation mechanism of lysozyme by dimethyl sulfoxide (DMSO), thermal stability of lysozyme and its preferential solvation by DMSO in binary solutions of water and DMSO was studied by differential scanning calorimetry (DSC) and using densities of ternary solutions of water (1), DMSO (2) and lysozyme (3) at 298.15 K. A significant endothermic peak was observed in binary solutions of water and DMSO except for a solution with a mole fraction of DMSO (x ₂) of 0.4. As x ₂ was increased, the thermal denaturation temperature T _m decreased, but significant increases in changes in enthalpy and heat capacity for denaturation, ΔH _cal and ΔC _p, were observed at low x ₂ before decreasing. The obtained amount of preferential solvation of lysozyme by DMSO (∂g ₂/∂g ₃) was about 0.09 g g⁻¹ at low x ₂, indicating that DMSO molecules preferentially solvate lysozyme at low x ₂. In solutions with high x ₂, the amount of preferential solvation (∂g ₂/∂g ₃) decreased to negative values when lysozyme was denatured. These results indicated that DMSO molecules do not interact directly with lysozyme as denaturants such as guanidine hydrochloride and urea do. The DMSO molecules interact indirectly with lysozyme leading to denaturation, probably due to a strong interaction between water and DMSO molecules.     

Thallium-205 NMR spectroscopy. Solvation of the Tl(l) ion in the binary solvent systems water/pyridine,water/dimethyl sulfoxide,and pyridine/dimethyl sulfoxide

Solvation of the Tl⁺ ion in 0.005M solutions of water/pyridine, water/dimethyl sulfoxide, and pyridine/dimethyl sulfoxide was studied with ²⁰⁵ Tl NMR spectroscopy as a function of solvent composition and anion (NO ₃ ^– and ClO ₄ ^t- ). Dimethyl sulfoxide solvated the Tl⁺ ion more strongly than did pyridine, despite the latter's greater electron-donating ability. This was explained in terms of structural effects, which were found to be large for all three binary solvent systems. Ion pairing was evident in the DMSO/pyridine and water/pyridine solvent systems in which the pyridine mole fraction was greater than 0.8.     

Mechanism of the reaction of radicals with peroxides and dimethyl sulfoxide in aqueous solution

The reactions of methyl and methylperoxyl radicals derived from dimethyl sulfoxide (DMSO) with hydrogen peroxide, peroxymonocarbonate (HCO4 (-)), and persulfate were studied. The major reaction observed for the hydroperoxides was the abstraction of the hydrogen atom by the radicals. The radicals interact with a lone pair of electrons on the peroxide to produce methanol and formaldehyde. Furthermore, the results indicate that in RO2H and RO2R', electron-withdrawing groups cause a considerable increase in the reactivity of the peroxides towards the radicals and not only towards nucleophiles. The HO2 (.)/O2 (.-) and CO3 (.-) radicals react with DMSO to produce methyl radicals. Thus, the formation of the (.)CH3 radicals in the presence of DMSO is not proof of the formation of the (.)OH radicals in the system. These reactions must be considered when radical processes, such as in biological and catalytic systems, are studied. Especially, the plausible role of HCO4 (-) ions in biological systems as a source of oxidative stress cannot be overlooked.     

Vapor pressure of dimethyl sulfoxide and water binary system

The total vapor pressures of dimethyl sulfoxide (DMSO) and water mixtures have been measured at 15, 20, 25 and 30°C. The activity coefficients and molar excess Gibbs energies of the system have been calculated. Possible association interaction in the system are discussed.     

Application of the solvent dimethyl sulfoxide/tetrabutyl-ammonium fluoride trihydrate as reaction medium for the homogeneous acylation of Sisal cellulose

Two types of Sisal cellulose were studied as starting material for homogeneous acylation in the solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF). The native Sisal cellulose investigated contains 14% hemicellulose (mainly composed of xylose) as confirmed by ¹³C-NMR spectroscopy in DMSO-d₆/TBAF and HPLC analysis after complete polymer degradation. Alkali treatment of Sisal cellulose decreases the amount of hemicellulose, the degree of polymerization and the crystallinity. Both Sisal cellulose samples can be dissolved in DMSO/TBAF after treatment at elevated temperature. GPC measurements showed high aggregation in the solution. Different homogeneous acylation reactions using carboxylic acid anhydrides and vinyl esters were carried out, showing a pronounced tendency of the anhydride towards hydrolysis in the solvent. This disadvantage can be diminished by decreasing the amount of the salt hydrate (TBAF trihydrate) or by a distillative removal of the majority of water. A strong interaction of the polymer with the water in the solvent was observed.     

The solvation of the dioxouranium(VI) ion by dimethyl sulfoxide

The species UO₂(DMSO) ₅ ²⁺ is shown from¹H NMR studies to be the predominant dioxouranium(VI) species existing in dilute anhydrous acetonedimethyl sulfoxide (DMSO) solutions, and this result is compared with data reported for the analogous water-acetone-dimethyl sulfoxide system. Complete line-shape analyses of exchange-modified¹H NMR line shapes indicate that the mechanism for DMSO exchange on UO₂(DMSO) ₅ ²⁺ is probably of theD orI _D type. A typical set of rate parameters arek _ex (260°K) =273±14 sec^–1, H ^#=38.9±0.5 kJ-mole^–1, and S ^#=–47.5±1.8 J-^oK^–1-mole^–1 for a solution in which [UO₂(DMSO)₅ ²⁺], [DMSO], and [d ₆ acetone] are, respectively, 0.01155, 0.0875, and 13.00 moles-dm^–3.     

Viscoelastic behavior of polyacrylonitrile/dimethyl sulfoxide concentrated solution with water

The spinnability and polydispersity of polyacrylonitrile/dimethyl sulfoxide (PAN/DMSO)/H₂O spinning solutions with conventional PAN molecular weight and comparative high PAN concentration have been investigated using a cone‐plate rheometer. It is observed from the measurements that, the viscosities of the solutions decreased with the rising of shear rate, and then stabilized to almost the same value, regardless of the PAN concentration. The chain orientation in the fiber formed under constant shear rate cannot be changed considerably even after long relaxation of more than 900s. For dynamic experiments, a steady increase of both G′ and G″ with escalating oscillation frequency was seen for all samples. Higher viscous‐elastic modulus at higher H₂O content was found, too. It is also concluded from the log G′ ? log G″ plot and the gel point that the PAN/DMSO/H₂O system with regular PAN molecular weight behaves very close to a mono‐disperse system, thus very suitable for gel spinning and for preparation of high performance PAN precursor fiber. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1437–1442, 2009     

Thermal hazards and safe scale-up of reactions containing dimethyl sulfoxide

Extensive thermal analysis has shown that DMSO-containing reaction mixtures can be more energetic and decompose at lower temperatures than pure DMSO. Several processes at Merck using DMSO as a solvent were found to have the onset temperatures of decompositions reduced to the point where it became a thermal and operational hazard. The onset temperature depended on the reagents in the reaction mixture and the thermal history of the mixture. The case studies presented in this paper will include discussion on what process hazards were identified, how the process hazards differ from the pure DMSO hazards, and how to scale up these processes safely.     

Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution

A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 10⁴ to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H₂SO₄) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ¹³C NMR, and tensile tests. ¹³C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H₂SO₄ aqueous solution for 5 min exhibited higher mechanical properties than that with other H₂SO₄ concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002     

Determination of pKa values for (E)-2-hydroxy-5-(aryldiazenyl) benzaldehydes in dimethyl sulfoxide: Cyclic voltammetry and density functional theory calculations

The (E)-2-hydroxy-5-(aryldiazenyl) benzaldehydes (azo dyes 1–4 ) were synthesized in high purity. As they are insoluble in water, the usual analytical methods cannot be utilized to determine their pK_a values. Cyclic voltammetry was experimentally used to determine their pKa values in DMSO solvent. In addition, computational methods and a conductor-like screening model (COSMO) were used to calculate the solvent effect. , , K_exchange, and pK_a values were estimated for the azo dyes being studied using the BP86, TPSS, B3LYP, PBE0, TPSSh, and PW6B95 density functionals in def2-TZVP basis sets. The obtained mean absolute deviations (MADs) indicate that the results of BP86, PBE0, and PW6B95 functionals are in good agreement with experimental values.     

An EXAFS spectroscopic, large-angle X-ray scattering, and crystallographic study of hexahydrated, dimethyl sulfoxide and pyridine 1-oxide hexasolvated mercury(II) ions

The structure of the solvated mercury(II) ion in water and dimethyl sulfoxide has been studied by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) techniques. The distribution of the Hg-O distances is unusually wide and asymmetric in both solvents. In aqueous solution, hexahydrated [Hg(OH(2))(6)](2+) ions in a distorted octahedral configuration, with the centroid of the Hg-O distance at 2.38(1) A, are surrounded by a diffuse second hydration sphere with HgO(II) distances of 4.20(2) A. In dimethyl sulfoxide, the six Hg-O and HgS distances of the hexasolvated [Hg{OS(CH(3))(2)}(6)](2+) complex are centered around 2.38(1) and 3.45(2) A, respectively. The crystal structure of hexakis(pyridine 1-oxide)mercury(II) perchlorate has been redetermined. The space group R(-)3 implies six equal Hg-O distances of 2.3416(7) A for the [Hg(ONC(5)H(5))(6)](2+) complex at 100 K. However, EXAFS studies of this compound, and of the solids hexaaquamercury(II) perchlorate and hexakis(dimethyl sulfoxide)mercury(II) trifluoromethanesulfonate, also with six equidistant Hg-O bonds according to crystallographic results, reveal in all cases strongly asymmetric Hg-O distance distributions. Vibronic coupling of valence states in a so-called pseudo-Jahn-Teller effect probably induces the distorted configurations.     

Structure and properties of novel fibers spun from cellulose in NaOH/thiourea aqueous solution

Cellulose was dissolved rapidly in a NaOH/thiourea aqueous solution (9.5:4.5 in wt.-%) to prepare a transparent cellulose solution, which was employed, for the first time, to spin a new class of regenerated cellulose fibers by wet spinning. The structure and mechanical properties of the resulting cellulose fibers were characterized, and compared with those of commercially available viscose rayon, cuprammonium rayon and Lyocell fibers. The results from wide angle X-ray diffraction and CP/MAS 13C NMR indicated that the novel cellulose fibers have a structure typical for a family II cellulose and possessed relatively high degrees of crystallinity. Scanning electron microscopy (SEM) and optical microscopy images revealed that the cross-section of the fibers is circular, similar to natural silk. The new fibers have higher molecular weights and better mechanical properties than those of viscose rayon. This low-cost technology is simple, different from the polluting viscose process. The dissolution and regeneration of the cellulose in the NaOH/thiourea aqueous solutions were a physical process and a sol-gel transition rather than a chemical reaction, leading to the smoothness and luster of the fibers. This work provides a potential application in the field of functional fiber manufacturing.     

Hydrogels prepared from unsubstituted cellulose in NaOH/urea aqueous solution

Novel cellulose hydrogels were synthesized through a "one-step" method from cellulose, which was dissolved directly in NaOH/urea aqueous solution, by using epichlorohydrin as crosslinker. Structure and properties of the hydrogels were characterized by using SEM, NMR, and water absorption testing. The hydrogels are fully transparent and display macroporous inner structure. The equilibrium swelling ratios of the hydrogels in distilled water at 25 degrees C are in the range from 30 to 60 g H(2)O/g dry hydrogel. Moreover, the reswelling water uptake of the hydrogels could be achieved to more than 70% compared with their initial swelling states. This work provided a simple and fast method for preparing eco-friendly hydrogels from unsubstituted cellulose.     

Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry

Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a ¹³C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10^?2 weight‐average molecular weight (M_w)^0.815 (mL g^?1) in the M_w region from 3.2 × 10⁴ to 12.9 × 10⁴. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were 6.0 nm, 350 nm^?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004     

Rheology and gelation of cellulose/ammonia/ammonium thiocyanate solutions

Liquid crystalline solutions of cellulose in an ammonia/ammonium thiocyanate solvent will form thermoreversible gels at temperatures below 30°C. These gels are of interest both for processing the cellulose/ammonia/ammonium thiocyanate system and because they have an unusual structure, containing neither crystalline nor covalently bonded crosslinks. Although these gels contain neither crystalline nor covalently bonded crosslinks, the dynamic rheological behavior of the system at the gel point was found to be the same as for gels with covalent or crystalline crosslinks with a loss tangent, tan δ, independent of frequency. The kinetics of the gelation process was monitored via dynamic elastic modulus, G′. All samples revealed an exponential increase in G′ with time during gelation, very different from that observed in covalently bonded or crystalline crosslinked systems. Measurements of the loss tangent enabled precise determination of the gelation time for these systems as a function of cellulose concentration and temperature. We found the gel time to be inversely related to cellulose concentration and directly related to temperature. The strong dependence of gel time on these parameters offers a windows of spinnability that can be tailored for processing high modulus cellulose fibers. © 1996 John Wiley & Sons, Inc.