Swelling and dissolution of cellulose,Part III: plant fibres in aqueous systems

Raw and refined flax, hemp, abaca, sisal, jute and ramie fibres are dipped into N-methylmorpholine N-oxide (NMMO)–water with various contents of water and into hydroxide sodium (NaOH)–water. The swelling and dissolution mechanisms of these plant fibres are similar to those observed for cotton and wood fibres. Disintegration into rod-like fragments, ballooning followed or not by dissolution and homogeneous swelling are all observed as for wood and cotton fibres, depending on the quality of the solvent. Balloons are not typical of wood and cotton and they seem to be present in all plant fibres. Another interesting result is that the helical feature seen on the balloon membrane is not related to the microfibrillar angle. Plant fibres are easier to dissolve than wood and cotton. This is not related to the molar mass of the cellulose chain. Raw plant fibres keeping most its non-cellulosic components do not show the formation of balloons. Patrick Navard is a Member of the European Polysaccharide Network of Excellence (EPNOE)     

Morphology of cellulose objects regenerated from cellulose–N-methylmorpholine N-oxide–water solutions

The precipitation in aqueous media of cellulose from solutions in N-methylmorpholine N-oxide (NMMO) hydrates is an important stage in the process of manufacturing of fibres, films and other cellulose objects. It is responsible for the formation of the structure of the regenerated object and their morphological characteristics significantly influence the properties of the final products. Regeneration of rather large cellulose objects was observed in situ by optical microscopy. It was found that all regenerated objects present an asymmetric structure composed of a dense skin surrounding a sub-layer characterised by the presence of finger-like voids. The porous texture of the cellulose parts between these voids is typical of the one obtained by spinodal decomposition. The morphologies of regenerated cellulose samples are described as a function of various parameters, initial cellulose solutions and composition and temperature of the aqueous regeneration bath. A mechanism of the structure formation during regeneration is proposed. P. Navard is a Member of the European Polysaccharide Network of Excellence (EPNOE), .     

N-Oxides of polychloropyridines.13C NMR study

The effect ofN-oxidation of a series of polychloropyridines on¹³C NMR parameters has been studied. It has been established that inN-oxides of polychloropyridines an electric field through-space effect of theN-oxide group predominates in the shielding of the -carbon atom compared to the other carbon atoms. A linear correlation between¹³C NMR chemical shifts and total charge densities calculated by the MNDO method for the carbon atoms ofN-oxides of polychloropyridines has been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2425–2428, December, 1995.The authors are grateful to V. V. Kolchanov for help in the synthesis of compounds under study.     

Degradation processes in the cellulose/<Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide system studied by HPLC and ESR. Radical formation/recombination kinetics under UV photolysis at 77 K

Degradation processes of N-methylmorpholine-N-oxide monohydrate (NMMO), cellulose and cellulose/NMMO solutions were studied by high performance liquid chromatography (HPLC) and electron spin resonance (ESR) spectroscopy. Kinetics of radical accumulation processes under UV (λ = 248 nm) excimer laser flash photolysis was investigated by ESR at 77 K. Beside radical products of cellulose generated and stabilized at low temperature, radicals in NMMO and cellulose/NMMO solutions were studied for the first time in those systems and attributed to nitroxide type radicals ∼CH₂–NO^•–CH₂∼ and/or ∼CH₂–NO^•–CH₃∼ at the first and methyl ^•CH₃ and formyl ^•CHO radicals at the second step of the photo-induced reaction. Kinetic study of radicals revealed that formation and recombination rates of radical reaction depend on cellulose concentration in cellulose/NMMO solutions and additional ingredients, e.g., Fe(II) and propyl gallate. HPLC measurements showed that the concentrations of ring degradation products, e.g., aminoethanol and acetaldehyde, are determined by the composition of the cellulose/NMMO solution. Results based on HPLC are mainly maintained by ESR that supports the assumption concerning a radical initiated ring-opening of NMMO.     

Oxidation of secondary alcohols byN-methylmorpholine-N-oxide (NMO) catalyzed by atrans-dioxo ruthenium(VI) complex or perruthenate complex: A kinetic study

Thetrans-dioxo ruthenium (VI) complex, [P(C₆H₅)₃C₆H₅CH₂]⁺[Ru(O)₂OAcCl₂] or tetrapropylammonium perruthenate catalyzes the oxidation of secondary alcohols to ketones byN-methylmorpholine-N-oxide (NMO). Kinetic studies showed the formation of a complex between catalyst and substrate (alcohol) as the first step in the mechanism.     

Syntheses based on anabasine. Preparation and transformations of N-oxides

The oxidation of N-acetyl-and N-benzoylanabasine with the tert-butyl hydroperoxide (TBHP)— MoCl₅ system or MCPBA proceeds selectively at the nitrogen atom of the pyridine ring. The oxidation of N-methylanabasine under similar conditions gives a mixture of stereo-isomeric N-oxides at the piperidine nitrogen atom, their ratio depending on the reagent used. The oxidation of anabasine by TBHP— MoCl₅ or MCPBA is accompanied by dehydrogenation and results in anabaseine N-oxide. The reactions of anabasine and anabaseine pyridine N-oxides with acetic anhydride were investigated. The substituted 1H-3-pyridin-2-ones were prepared. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 322—328, February, 2006.     

Phenazinee di-N-oxide radical cation and its reactions with hydrocarbons

The absorption spectra of phenazine di-N-oxide radical cation (OPO^+·) in dichloromethane were recorded by the spectroelectrochemical method in the range from 300 to 700 nm. The reactions of the electrochemically generated OPO^+· withpara-substituted toluenes, ethylbenzene, and cumene were studied. Using differential cyclic voltammetry, relative rate constants of reactions of OPO^+· with substrates were determined; their correlations with ⁺ para constants of substituents gives p = -2.7, which attests to the nonradical character of the reaction of OPO^+· with RH. This conclusion is confirmed by the study of the effect of O₂ on oxidation of ethylbenzene and cumene.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1992–1998, August, 1996.     

Synthesis and crystal structure ofN,N′-DicyclohexylpiperazineN,N′-dioxide octahydrate

N,N-DicyclohexylpiperazineN,N-dioxide octahydrate, C₁₆H₄₆N₂O₁₀,M _r=426.55, monoclinic, space groupC2/m (No. 12),a=12.961(4),b=11.533(4),c=7.907(1) Å, =98.37(2)^o,V=1169.3(6) ų,Z=2. The structure was solved by the direct method and refined toR=0.045 for 1192 observed MoK reflections. TheN,N-dioxide molecule occupies a site of symmetry 2/m. The piperazine ring takes the chair form with the two N–O bonds oriented axially in atrans configuration. Hydrogen bonding between the water molecules, as well as between theN-oxide groups and water molecules, gives rise to a puckered layer composed of edge-sharing four-membered, five-membered, six-membered, and eight-membered rings. Adjacent layers are cross-linked by theN,N-dicyclohexylpiperazine moieties lying between them, thereby generating a sandwich structure consolidated by covalent and hydrogen bonding. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82062 (8 pages).     

Catalytic silylotropy inN-trimethylsilylpyrazole derivatives

Silylotropy in 4-substitutedN-trimethylsilypyrazoles is studied by dynamic¹H,¹³C, and²⁹Si NMR spectroscopy. The catalytic 1,2-migration of a trimethylsilyl group in 4-halo-N-trimethylsilylpyrazoles was detected. Silylotropy inN-trimethylsilylpyrazoles in the presence of halogens of trimethylhalosilanes is believed to proceed through formation ofN,N-bis(trimethylsilyl)pyrazolium salts, the barrier of silylotropy in pyrazoles being markedly reduced.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 3011–3013, December, 1996.     

Extraction and spectrophotometric determination of titanium(IV) withN 1-hydroxy-N 1,N 2-diphenylbenzamidine and thiocyanate

A precise, reliable, sensitive, and selective method for the determination of titanium(IV) is described. Titanium(IV) reacts withN ¹-hydroxy-N ¹,N ²-diphenylbenzamidine (HDPBA) and thiocyanate to form an orange-coloured mixed-ligand complex of stoichiometry 112 (Ti SCN^– HDPBA). The complex is quantitatively extractable into toluene from 0.05–0.15M hydrochloric acid. The spectrum of the complex exhibits an absorption maximum at 400 nm with a molar absorptivity of 20000M ^–1 cm^–1 and the coloured system obeys Beer's law in the concentration range 0.20–3.0 gml^–1 titanium. The effects of foreign ions and of various experimental parameters have been studied to establish the optimum conditions for the extraction and determination of titanium. The precision of the method has been evaluated and the relative standard deviation has been found to be 0.53%. The method has been successfully applied to the determination of titanium in synthetic matrices corresponding to titanium-containing ores, minerals, and alloys.     

Swelling and dissolution of cellulose, Part V: cellulose derivatives fibres in aqueous systems and ionic liquids

The swelling and dissolution mechanisms of several cellulose derivatives (nitrocellulose, cyanoethylcellulose and xanthate fibres) are studied in aqueous systems (N-methylmorpholine-N-oxide—water with various contents of water, hydroxide sodium—water) and in ionic liquids. The results are compared with the five modes describing the swelling and dissolution mechanisms of cotton and wood cellulose fibres. The mechanisms observed for the cellulose derivatives are similar to the ones of cotton and wood fibres. Swelling by ballooning is also seen with cellulose derivatives, showing that this phenomenon is linked to the fibre morphology, which can be kept after undergoing a heterogeneous derivatisation. Patrick Navard and Thomas Heinze—Members of the European Polysaccharide Network of Excellence (EPNOE),     

Cellulose organic solutions: A nuclear magnetic resonance investigation

Four solvents of cellulose have been studied by using ¹³C-NMR spectroscopy. All these solvents, N-methyl morpholine-N-oxide, methylamine, hydrazine, and paraformaldehyde (PF), contained dimethyl sulfoxide (DMSO) as a cosolvent. Oligomers of cellulose of DP = 10 soluble in hot DMSO have been used as model compounds. ¹³C chemical shifts and line shapes show that three of the mentioned solvents are “true solvents” of cellulose. On the other hand, dissolution of cellulose in DMSO-PF system occurs by the formation of a statistical derivative of cellulose. Enriched ¹³C bacterial cellulose on C-1 and C-6 positions have been used to identify the ¹³C positions mainly in DMSO-N-methyl morpholine-N-oxide system. This solvent has been found to be degradative for the macromolecule when the solution is kept at 100°C over a long period. Viscosity measurements show a reduction of the molecular weight in these conditions. Polarimetry indicates that no glucose is present in solution and hence there is a statistical break of the chain. Enriched cellulose solution in DMSO–N-methyl morpholine-N-oxide has been also used for relaxation time (T₁) determination both of the solvent and of the enriched carbons of the polymer. Nuclear Overhauser enhancement (NOE) was found to be 1.8 for C-1 and 2.1 for C-6 showing that relaxation phenomenon is not purely dipolar. T₁ values of 97 and 65 msec are found for C-1 and C-6 of cellulose, in good agreement with the values known for polysaccharides. Determination of T₁ for the different carbon atoms of the solvent DMSO-N-methyl morpholine-N-oxide with and without cellulose shows a large reduction of T₁ for N-methyl morpholine-N-oxide molecule. This denotes a slower molecular motion of this molecule and a preferential interaction with the cellulose macromolecule.     

Effects of ionization on the phase behavior of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-acrylic acid) and poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylacrylamide-co-acrylic acid) in water

Phase transitions of poly(N-isopropylacrylamide-co-acrylic acid) (PiPA-AA) and poly(N,N- diethylacrylamide-co-acrylic acid) (PdEA-AA) in water have been investigated by means of turbidimetry, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The phase transition temperatures (T_p) of these copolymers increase with the degree of ionization () of the acrylic acid (AA) units, which in turn is dependent on the pH of the solutions. Apparent values of pK_a for the AA units, determined from the pH dependencies of T_p, are 4.7 and 5.4 for PiPA-AA and PdEA-AA, respectively. Differences between T_p for PiPA-AA and T_p for PiPA homopolymer (T_p) are +1.5 and –0.2 °C/mol% of AA at =1 and 0, respectively. The values of T_p for PdEA-AA are +2.6 (ionic) and –0.5 (nonionic)°C/mol%, indicating that the incorporated AA units have a larger effect on PdEA than on PiPA. DSC measurements performed with each of these copolymers at different pH values show a linear relationship between T_p and the enthalpy of transition (H). IR measurements of PiPA-AA show that the profiles of IR bands from both iPA and AA units exhibit critical changes at T_p of the copolymer. Heating the solution above T_p leads to shifts of the amide II, C–H stretch, and C–H bend bands from the iPA units toward lower wavenumbers, as well as a shift of the amide I band from the iPA units toward higher wavenumbers. A decrease in the intensity of the symmetric C=O stretch IR band from carboxylate anions (1560 cm^–1), and an increase in the intensity of the C=O stretch band from COOH groups (1705 cm^–1) suggest that a partial protonation of the carboxylate groups (COO^–+H⁺COOH) takes place upon the phase transition.     

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.     

First example of the formation of bipolar spiro σ-complexes from 6-bromo-5,7-dinitrobenzo[e]-1,2,3,4-tetrazine 1,3-di-N-oxide

The reactions of 3,5,7-trimethyltropolone and 2-(N-benzylamino)tropone with 6-bromo-5,7-dinitrobenzo[e]-1,2,3,4-tetrazine 1,3-di-N-oxide afforded novel bipolar spiro -complexes. The kinetic and activation parameters of the R,S-enantiotopomerization of a chiral spiro -complex of 2-(N-benzylamino)tropone were determined using dynamic ¹H NMR spectroscopy.     

Interaction and Scale of Mixing in Cellulose Acetate/Poly(<Emphasis Type="Italic">N</Emphasis>-vinyl Pyrrolidone-co-vinyl Acetate) Blends

Binary blends and pseudo complexes of cellulose acetate (CA) with vinyl polymers containing N-vinyl pyrrolidone (VP) units, poly(N-vinyl pyrrolidone) (PVP) and poly(N-vinyl pyrrolidone-co-vinyl acetate) [P(VP-co-VAc)], were prepared, respectively, by casting from mixed polymer solutions in N,N-dimethylformamide as good solvent and by spontaneous co-precipitation from solutions in tetrahydrofuran as comparatively poor solvent. The scale of miscibility and intermolecular interaction were examined for the blends and complexes by solid-state ¹³C-NMR spectroscopy. It was revealed that the formation of complexes was due to a higher frequency of hydrogen-bonding interactions between the residual hydroxyl groups of CA and the carbonyl groups of VP residues in the vinyl polymer component. From measurements of CP/MAS spectra and proton spin-lattice relaxation times (T_1ρ^H) in the NMR study, the existence of the hydrogen-bonding interaction was also confirmed for the miscible blends and the homogeneity of the mixing was estimated to be substantially on a scale within a few nanometers.     

Conformational studies of poly(N5-Ω-hydroxyalkyl-L-glutamine)s in reversed micelles

The molecular conformations of poly(N⁵-dihydroxyethylaminopropyl-L-glutamine) and poly(N⁵-dihydroxyethyl-L-glutamine) were investigated in reversed micelles of AOT as well as in aqueous solutions. Both poly(-amino acid)s assume disordered structures in pure water. The conformation of poly(N⁵-dihydroxyethylaminopropyl-L-glutamine) transits into-helix in the reversed micelles as the molar ratio of water to AOT (w₀=[H₂O]/[AOT]) becomes smaller. A similar conformational transition was also observed in aqueous solutions when a certain amount of AOT was added. Under these conditions, however, poly(N⁵-dihydroxyethyl-L-glutamine) did not undergo a conformational transition into-helix.     

Characterization of Autocatalytic Reactions in Modified Cellulose/NMMO Solutions by Thermal Analysis and UV/VIS Spectroscopy

The thermal stability of cellulose/N-methylmorpholine-N-oxide (NMMO) solutions were investigated using UV/VIS spectrometry with a temperature programming cuvette and caloric measurements by means of the Systag calorimeter RADEX (mini-autoclave). Both analytical methods allow to characterize the influences of stabilizers and additives. With the temporal course of the optical density, temperature and pressure thermal runaway reactions with gas evolution and accumulation of chromophoric degradation products were recognized. Kinetic model calculations compared with UV/VIS measurements demonstrate the existence of autocatalytic reactions in cellulose/NMMO solutions. Varying the heating rate autocatalysis can be proved by dynamic caloric measurements as well.     

Molecular Dipole Moment and Interaction Dipole Moment in 2-N-Substituted Amino-3(or 5)-methyl-4-nitropyridines and Their N-Oxides

The dipole moments of 2-alkylaminoand 2-alkylnitramino-3(or 5)-methyl-4-nitropyridines and their N-oxides have been measured, as well as calculated, using vectorial summation of the group moments and by ab initio method. The estimated interaction dipole moments, _int, have been discussed in terms of the electronic and steric effects and intramolecular hydrogen bonding. Introduction of the NHCH₃ group to position 2 in 4-nitropyridine strengthens the conjugation between the nitro group and ring nitrogen. The lack of such strengthening in 4-nitropyridine-N-oxides is explained as being due to formation of intramolecular hydrogen bond between the N-oxide group and the hydrogen of alkylamino group. Introduction of the nitramino group does not lead to marked modification of the charge distribution in a molecule. This fact may be explained by much weaker electron-donating ability of this group in comparison with the alkylamino group.     

Effect of Aprotic Solvents on Intermolecular Interaction of Cellulose Macromolecule with N-Methylmorpholine N-Oxide Monohydrate

The influence of aprotic cosolvents dimethyl sulfoxide, dimethylformamide, and dimethylacetamide on interaction of N-methylmorpholine N-oxide with cellulose was studied.