The coagulation of cellulose from anisotropic solutions in the NH3/NH4SCN solvent system

Coagulation of cellulose has been studied in cellulose/ammonia/ammonium thiocyanate anisotropic solutions. The effect of coagulation variables such as coagulant, bath temperature, and cellulose concentration on the coagulation process is reported. The coagulation rate was measured by microscopic observation of the moving boundary associated with coagulation. Results indicate that the coagulation rate increases with increasing cellulose concentration and bath temperature. Methanol has the highest coagulation power among the coagulants employed. Mass transfer rate difference and equilibrium swelling were also measured. The results on the mass transfer rate differences show that the mass transfer rate of NH₃/NH₄SCN is greater than those of the respective coagulants under all coagulation conditions. The equilibrium swelling decreases with increasing bath temperature and cellulose concentration.     

The solubility of cellulose in liquid ammonia/ammonium thiocyanate solution: The effect of composition and temperature on dissolution and solution properties

The dissolution process and some solution properties of cellulose in mixtures of liquid ammonia (NH₃) and ammonium thiocyanate (NH₄SCN) are discussed. The mole fraction ratio of NH₃, NH₄SCN, and H₂O which dissolve cellulose were determined. The effect of temperature on several solution properties was also examined. The temperature coefficient d In [n]/dT for the limiting viscosity number [n] has a value of ?1.58 × 10^?2 °C^?1. This is considered to be rather large but is, in fact, a common occurrence for almost all cellulose derivatives in solution. The values for the Huggins constant K′ showed no systematic trends with temperature. They did, however, suggest the presence of considerable association of the cellulose in solution. Miscibility results of adding the cellulose solutions to organic liquids are also reported.     

A study on the mechanism of dissolution of the cellulose/NH3/NH4SCN system. I

Ammonia/ammonium thiocyanate (NH₃/NH₄SCN) is an excellent swelling agent and solvent for cellulose, even at a high degree of polymerization. Because polymorphic conversion in cellulose has been a long-standing, perplexing, troublesome problem, we have undertaken to study that mechanism. Solid state CP/MAS ¹³C-NMR and X-ray analysis proved to be very useful analytical techniques for the task. It appears that during temperature cycling, specific cellulosic inter- and intramolecular hydrogen-bonds are broken as polymorphic conversion proceeds sequentially from the polymorph I to III, and finally at total solvation to amorphous. This proceeds correspondingly via transformation of the polymorph conformations of CH₂OH from trans-gauche, “tg,” to gauche-trans, “gt,” to gauche-gauche, “gg.” © 1994 John Wiley & Sons, Inc.     

Lyotropic mesophases of cellulose in the ammonia/ammonium thiocyanate solvent system: Phase relationships

Mesophase formation of the cellulose/NH₃/NH₄SCN system has been studied as a function of system composition at 25°C. Compositions for incipience of mesophase formation and for wholly anisotropic phase formation have been determined and relevant phase diagrams constructed. The biphasic gap narrowed when the solvent composition approached 75.5 weight percent NH₄SCN and as the cellulose concentration decreased. As solvent composition was changed, the minimum cellulose volume fraction for mesophase formation ranged between 0.02 to 0.045.     

Helical concept of the fine structure of cellulose

The helical concept of the fine structure of cellulose as proposed by Manley is discussed. The deuterium exchange experiments with cotton, cotton crystallites, and regenerated cellulose I, in which accessibility was determined by comparing the ratio of the infrared absorbance of the O? D peak to the O? H peak, revealed that the accessibility of cotton linters decreased on acid hydrolysis, whereas it increased on treatment with ethylamine followed by washing with water. This is in contrast to the finding of Manley, who had evaluated the accessibility by a gravimetric D₂O exchange method and had come to the conclusion that acid hydrolysis did not change the accessibility of cellulose and hence cellulose did not contain crystalline and amorphous phases but was all crystalline. On the basis of Manley's protofibril and the accessibility data obtained in this investigation, a concept of the fine structure of cellulose is proposed, in which the role of Manley's protofibril is analogous to the role of individual molecule in the fringe micellar model. This concept explains the properties of cellulose that are otherwise explainable on the currently accepted fringe micellar theory. In addition, it explains the marked shrinkage in the length of cotton and rayon fibers when placed in 16% sodium hydroxide solution.     

A 13C-NMR spectral study of cellulose and glucopyranose dissolved in the NH3/NH4SCN solvent system

The ¹³C-NMR chemical shifts of a cellulose with a DP_w of 23 dissolved in the NH₃/NH₄SCN solvent system were found to be very similar to those of cellulose dissolved in DMSO (cellulose oligomers), in the LiCl/DMAC system and in the N-methylmorpholine N-oxide/DMSO system. It was concluded from this that cellulose does not react with the NH₃/NH₄SCN solvent. It was found, however, that glucose reacts with the solvent at C-1 to form β-D -glucopyranosy-lamine. Separation of this compound from the solvent resulted in another compound which was determined to be β,β-di-D -glucopyranosylamine. The compounds β-D -glucopyranosylamine, N-acetyl-2,3,4,6-tetra-O-acetyl-β-D -glucopyranosylamine, β,β-di-D -glucopyranosylamine, α,β-di-D -glucopyranosylamine, 2,3,4,6,2′,3′,4′,6′-octa-O-acetyl-α,β-di-D -glucopyranosylamine were all synthesized and the ¹³C-NMR chemical shifts of these compounds are reported. It was also found that for the low-DP cellulose sample which was used the reducing end group existed and had reacted with the solvent to form an amine at C-1.     

Use of ICP and XAS to determine the enhancement of gold phytoextraction by <Emphasis Type="Italic">Chilopsis linearis</Emphasis> using thiocyanate as a complexing agent

Under natural conditions gold has low solubility that reduces its bioavailability, a critical factor for phytoextraction. Researchers have found that phytoextraction can be improved by using synthetic chelating agents. Preliminary studies have shown that desert willow (Chilopsis linearis), a common inhabitant of the Chihuahuan Desert, is able to extract gold from a gold-enriched medium. The objective of the present study was to determine the ability of thiocyanate to enhance the gold-uptake capacity of C. linearis. Seedlings of this plant were exposed to the following hydroponics treatment: (1) 5 mg Au L^–1 (2.5×10^–5 mol L^–1), (2) 5 mg Au L^–1+10^–5 mol L^–1 NH₄SCN, (3) 5 mg Au L^–1+5×10^–5 mol L^–1 NH₄SCN, and (4) 5 mg Au L^–1+10^–4 mol L^–1 NH₄SCN. Each treatment had its respective control. After 2 weeks we determined the effect of the treatment on plant growth and gold content by inductively coupled plasma–optical emission spectroscopy (ICP–OES). No signs of shoot-growth inhibition were observed at any NH₄SCN treatment level. The ICP–OES analysis showed that addition of 10^–4 mol L^–1 NH₄SCN increased the concentration of gold by about 595, 396, and 467% in roots, stems, and leaves, respectively. X-ray absorption spectroscopy (XAS) studies showed that the oxidation state of gold was Au(0) and that gold nanoparticles were formed inside the plants.     

Selective reactivities and accessibilities of the hydroxyl groups in cotton cellulose based on equilibrium data from a reversible chemical reaction

In order to determine the relative equilibrium constants for reactions of the hydroxyl groups at C₂, C₃, and C₆ of the D-glucopyranosyl units, methyl vinyl sulfone was reacted with cellulose dissolved in benzyltrimethylammonium hydroxide. The reaction was carried to constancy in distribution of substituents between the 2–0– and 6–0–positions. The distributions of substituents in the D-glucopyranosyl units were measured by gas-liquid chromatographic analysis of the products from hydrolysis of the modified cellulose. Relative equilibrium constants were then evaluated, assuming complete accessibility of all three types of hydroxyl groups of the cellulose in solution. For determination of the relative accessibilities of the individual types of hydroxyl groups in heterogeneous reactions of cotton cellulose with methyl vinyl sulfone, the reactions were carried to equilibrium distributions in media of various normalities of sodium hydroxide (i.e., media of various swelling strength). The distributions of substituents in the D-glucopyranosyl units were measured. From these values and the ratio of equilibrium constants, the relative accessibilities of the hydroxyl groups at C₂ versus those at C₆ were calculated. Apparent accessibilities of the hydroxyl groups at C₂ are approximately double those at C₆ when the reaction is carried out in 1N sodium hydroxide and about triple those at C₆ when the reaction is carried out in 0.5N sodium hydroxide.     

Darstellung,Kristallstruktur, Schwingungsspektren und Normalkoordinatenanalyse von [Co(NH3)6][Os(SCN)6]

Synthesis, Crystal Structure, Vibrational Spectra, and Normal Coordinate Analysis of [Co(NH₃)₆][Os(SCN)₆] From the mixture of the linkage isomers [Os(NCS)_n(SCN)_6–n]^3–, n = 0–2, pure [Os(SCN)₆]^3– has been isolated by ion exchange chromatography on diethylaminoethyl cellulose. The X‐ray structure determination on a single crystal of [Co(NH₃)₆][Os(SCN)₆] (trigonal, space group R 3, a = 12.368(2), c = 11.830(2) Å, Z = 3) reveals that the thiocyanate ligands are exclusively S‐coordinated with the Os–S distance of 2.388 Å and the Os–S–C angle of 108.8°. The IR and Raman spectra of (n‐Bu₄N)₃[Os(SCN)₆] are assigned by normal coordinate analysis based on the molecular parameters of the X‐ray determination. The valence force constant f_d(OsS) is 1.42 mdyn/Å.     

Light-scattering studies on solutions of cellulose in the ammonia / ammonium thiocyanate solvent system. II. Quasielastic light-scattering and liquid crystal study

This is the second part of a two–part study of the NH₃NH₄SCN cellulose solvent system. Quasielastic light scattering was used to determine the diffusion coefficients of cellulose in solution and the effective hydrodynamic radius of the dissolved molecules. Additionally, the system was studied using light microscopy to determine the minimum critical volume fraction or liquid crystal formation. Very little change was found in the diffusion coefficients with change in cellulose concentration indicating little interaction between the chains in solution. Values of 7.69 and 2.66 × 10⁸ cm²/s were measured for samples having a degree of polymerization of 153 and 969. The value of the coefficient relating the hydrodynamic volume to the radius of gyration was found to be in the range of 0.33 to 0.53, indicating an extended coil conformation according to the Kirkwood-Riseman theory. The minimum critical volume fractions necessary for liquid crystal formation, υ₂′ were 0.039, 0.038, and 0.048 for the three solvent compositions studied. The values calculated for υ₂′ based on the measured persistence lengths were much larger than the predicted values, indicating strong deviation from theory or possible aggregation in the system.     

Modification of polysulfone membranes 4. Ammonia plasma treatment

The effect of NH₃ and NH₃/Ar plasma on ultrafiltration polysulfone membranes have been studied. Results of contact angle, FTIR-ATR and X-ray photoelectron spectroscopy experiments clearly showed that both plasmas introduced hydrophilic, nitrogen- and oxygen-containing moieties on the polymer surface and that NH₃/Ar plasma was more efficient. That plasma was also more aggressive--signs of strong etching could be seen on the SEM pictures. Redeposition of etched material seemed to take place inside the pores. On the contrary, ammonia plasma was soft and caused cleaning the surface and pores enlargement. Performance of ammonia plasma modified membranes was greatly improved and independent on solution pH. The last observation proved amphoteric character of the surface. NH₃/Ar plasma treatment gave membranes of acidic surface and filtration indices not so good as for ammonia plasma.     

Die Ammonolyse von (NH4)2GeF6. Darstellung und Struktur von NH4[Ge(NH3)F5]

Ammonolysis Reaction of (NH₄)₂GeF₆. Synthesis and Structure of NH₄[Ge(NH₃)F₅] (NH₄)₂GeF₆ reacts with ammonia to yield NH₄[Ge(NH₃)F₅] at 280°C. The reaction path was elucidated by in situ time and temperature resolved X-ray powder diffraction. NH₄[Ge(NH₃)F₅] crystallizes isostructurally to NH₄[Si(NH₃)F₅] in the tetragonal space group P4/n (No. 85) with lattice constants a = 619.41(1) pm and c = 724.70(1) pm. The germanium atom is coordinated by five fluorine atoms and the nitrogen atom of the ammonia molecule. The ammonium cation is located on the Wyckoff position (2 a) in P4/n. The crystal structure is stabilized by extensive hydrogen bonding.     

Darstellung und Kristallstruktur von Tetraphenylphosphonium-Hexathiocyanatorhodat(III), [P(C6H5)4]3[Rh(SCN)6]

Preparation and Crystal Structure of Tetraphenylphosphonium Hexathiocyanatorhodate(III), [P(C₆H₅)₄]₃[Rh(SCN)₆] By treatment of RhCl₃ · n H₂O with KSCN in water a mixture of the linkage isomers [Rh(NCS)_n(SCN)_6–n]^3?, n = 0–2 is formed which is separated by ion exchange chromatography on diethylaminoethyl cellulose. The X-ray structure determination on a single crystal of [P(C₆H₅)₄]₃[Rh(SCN)₆] (monoclinic, space group C1c1, a = 13.620(5), b = 22.929(13), c = 22.899(9) Å, β = 98.55(3)°, Z = 4) confirms the coordination of all ligands via S with the middle Rh? S distance of 2.372 Å and Rh? S? C angles of 109°. The SCN groups are nearly linear with 175° and averaged bondlengths S? C 1.63 and C? N 1.14 Å. The crystal lattice is build up by layers of complex anions and voluminous cations with no specific interactions but which are closely connected by thiocyanate ligands and phenyl rings.     

Absorption of ammonia on tantalum hydroxide synthesized by a hydrofluoric acid method

Ammonia is strongly absorbed on tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ complexes. FTIR analysis of tantalum hydroxide shows a characteristic peak around 1,400 cm⁻¹, attributed to NH₄ ⁺. TG and FTIR analyses show that the NH₄ ⁺ decomposes at about 500 °C. The correct chemical formula of tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ is thus TaO _x (OH)_5-x (NH₄) _x . This conclusion is also confirmed by TG and FTIR analysis of tantalum hydroxide treated with various concentrations of inorganic acid at room temperature. The NH₄ ⁺ in tantalum hydroxide can be exchanged completely in aqueous HNO₃ solution, and the weight loss of the resulting sample is ended at about 415 °C by TG analysis. The NH₄ ⁺ can also be exchanged completely with aqueous H₂SO₄ solution; however, SO₄ ²⁻ is weakly absorbed on the tantalum hydroxide. Finally, the NH₄ ⁺ can be exchanged partially with aqueous H₃PO₄ solution; however, PO₄ ³⁻ is strongly absorbed on the tantalum hydroxide.     

Polymorphism in [Co(SCN)4(ppz-H)2] (ppz,piperazine)

A one-pot reaction of [Co(NO₃)₂ · 6H₂O and piperazine] with NH₄SCN/NaSCN in water–methanol (1:1) solvent leads to two polymorphs of [Co(SCN)₄(ppz-H)₂] (ppz, piperazine) (I and II). X-ray crystal structure reveals both have same space group but the differences in the alignment of pendant SCN⁻ leads to two polymorphs. In I, trifurcated N–H?S hydrogen bonding plays a prominent role in crystal packing leading to S?S interactions between SCN fragments but in II, no such trifurcation arises and thereby the crystal packing occurs through hydrogen bonding interactions only leading to a distinctly different network topology. TG/DSC and FT-IR study reveal they are enantiotropically related.     

Kristallstruktur von (Me4N)3[Ir(SCN)6], Schwingungsspektrum und Normalkoordinatenanalyse

Crystal Structure of (Me₄N)₃[Ir(SCN)₆], Vibrational Spectra and Normal Coordinate Analysis From a mixture of the linkage isomers [Ir(NCS)_n(SCN)_6–n]^3–, n = 0–2, pure [Ir(SCN)₆]^3– has been isolated by ion exchange chromatography on diethylaminoethyl cellulose. The X-ray structure determination on a single crystal of (Me₄N)₃[Ir(SCN)₆] (trigonal, space group R3, a = 14.838(2), c = 23.827(1) Å, Z = 6) reveals the presence of two crystallographically independent complex anions which C_3i symmetry correlates with the cation/anion ratio 3 : 1. The thiocyanate ligands are exclusively S-coordinated with the average Ir–S distance of 2.384 Å and the Ir–S–C angle of 106.4°. The torsion angles S–Ir–S–C are 17.5 and 42.1°. The IR and Raman spectra of the (n-Bu₄N) salt are assigned by normal coordinate analysis based on the molecular parameters of the X-ray determination. The valence force constant f_d(IrS) is 1.57 mdyn/Å.     

Crystal structure of diammine(malonato)palladium(II)

Diammine(malonato)palladium(II) is synthesized by the reaction of [Pd(NH₃)₄](NO₃)₂ with malonic acid, and its crystal structure is determined by single crystal X-ray diffraction. Distorted coordination square of the Pd(II) atom is formed by two N atoms of two ammonia molecules and two O atoms of bidentate malonate ligand. The average Pd-N and Pd-O distances are 2.018(7) ? and 2.014(2) ?, respectively. The molecules are stacked in such a way that the planes of coordination squares are parallel with the Pd...Pd distances between the nearest neighbors in a stack of 4.039 ?.     

A simple strategy to prepare graphene oxide modified by ammonia gas catalysts for Knoevenagel condensation

A facile and simple strategy to prepare ammonia gas-modified graphene oxide (GO) catalysts was successfully established by gas–solid acid–base reaction at room temperature. The catalytic performances of ammonia gas-modified GO samples were examined in Knoevenagel condensation. The samples were characterized by X-ray diffraction, Fourier transform infra-red spectroscopy, X-ray photoelectron spectroscopy, atomic force microscope, NH₃ temperature-programmed desorption and elemental analysis. The results indicated that the excellent performances of the ammonia gas-modified GO samples in Knoevenagel condensation should be ascribed to the formation of ammonium ions (NH₄ ⁺) by the reaction between ammonia gas and the carboxyl groups located on the edge of the GO.     

Crystal Structure of the Complex of 1,2-Bis[2-(o-hydroxyphenoxy)ethoxy]ethane with Ammonium Thiocyanate

The complex of the podand 1'2-bis[2-(o-hydroxyphenoxy)ethoxy]ethane (L) with ammoniumthiocyanate, [NH₄(SCN)L], was prepared, studied by single crystal X-ray diffraction. This is a host-guestcomplex; in its molecule the podand L is wrapped around the NH ₄ ⁺ cation, which forms hydrogen bondswith all the six oxygen atoms of the podand and one hydrogen bond with the sulfur atom of the SCN^- anion. The geometric parameters (bond lengths, bond angles, torsion angles, etc.) of the molecule of [NH₄(SCN)L] and packing of the molecules in the crystal were determined. The molecules are linked into infinite polymeric chains by intermolecular hydrogen bonds O-H···NCS.     

Determination of sulfides in synthesis and isomerization systems by reversed-phase ion-pair chromatography with a mobile phase containing tetramethylene oxide as organic modifier

Summary A reversed-phase ionpair chromatographic method with tetramethylene oxide as organic modifier has been developed for the simultaneous separation and detection of the sulfides NH₂CSNH₂, (NH₄)₂CS₃, (NH₄)₂S, and NH₄SCN. The optimized separation conditions were determined by means of a U₇ (7⁶) uniform design experiment, and tetramethylene oxide played an important role in adjusting the retention behavior of (NH₄)₂S and NH₄SCN. The linearity of the calibration plots for the four components was investigated; correlation coefficients were from 0.9989–0.9999. The proposed method was successfully applied to the determination of NH₂CSNH₂, (NH₄)₂CS₃, (NH₄)₂S, and NH₄SCN in synthesis and isomerization samples.