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.     

Studies on the Stabilization of Modified Lyocell Solutions

Additives with functional properties makes the Lyocell process a versatile tool for the creation of new innovative materials beyond the textile sector. Occupying functional groups or active surfaces the additives emphasize the suitability of Lyocell fibers, but simultaneously enhance the complexity of chemical reactions in cellulose/N-methylmorpholine-N-oxide (NMMO) solutions, respectively. Concerning to the concentration acidic ion exchange resins, activated charcoals, carbon black etc. shift the start of decomposition to lower temperatures, decrease the viscosity, enhance the formation of amines as the main degradation products or cause autocatalytic reactions. New routes in stabilization of modified Lyocell solutions applying a polymeric stabilizer system are described. Using calorimetric, UV/VIS, ESR and HPLC analysis the degradation processes and thermal stability of modified Lyocell solutions compared to the unstabilized were studied. Moreover, as kinetic investigations show a distinguished behavior for modified solutions autocatalytic reactions can be suppressed by the stabilizing system. ESR kinetic study of radicals reveals that formation and recombination rates of radical reactions depend on cellulose concentration in Lyocell solutions and additional ingredients.     

Discoloration of cellulose solutions in <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide (Lyocell). Part 1: Studies on model compounds and pulps

N-Methylmorpholine-N-oxide monohydrate (NMMO) is used as solvent for cellulose in the Lyocell process as a modern industrial fiber-making technology. Undesired chemical side reactions and byproduct formation in the system cellulose/NMMO/water are known to cause detrimental effects, such as chromophore formation and discoloration of the resulting fibers. A detailed kinetic study on the influence of carbonyl structures on chromophore formation in NMMO melts was carried out employing UV spectroscopy. Different sugar model compounds, such as reducing or non-reducing sugars, and sugars with additional oxidized functions, were applied. The chromophore formation rate differed widely for various reducing sugar model compounds, with pentoses generally reacting faster than hexoses, and carbohydrates with protected reducing end being largely inert. The effect of carbonyl groups on chromophore generation has been studied further using oligomers and oxidized pulps with different contents of carbonyl groups. As in the case of model compounds, also for the pulps a linear correlation between carbonyl content and chromophore formation rate was established. A distinct effect of hemicelluloses was observed.     

The purification process and side reactions in the N-methylmorpholine-N-oxide (NMMO) recovery system

In the lyocell process, N-methylmorpholine-N-oxide (NMMO) with a high recovery rate is used as a solvent to directly dissolve cellulose, which is of great significance for the realization of industrialization. In this paper, the impurity removal process and side reactions in the NMMO recovery system are introduced. The NMMO recovery system is generally composed of three major processes: air flotation, ion exchange and evaporation. Air flotation and ion exchange are the processes of removing impurities. And evaporation, where side reactions occur, is the process of increasing the concentration of NMMO. In terms of conductivity and colority, organic flocculants are better than inorganic flocculants in the air flotation process which mainly removes undissolved particulate matter, part of hemicelluloses and some colored substances. The ion exchange process mainly removes ionic substances and propyl gallate (PG). Side reactions occur during evaporation, producing colored substances and black particulate matter. Through analysis, it can be known that the production of colored substances is caused by the condensation reaction of N-methylmorpholine (NMM, 1), morpholine (M, 2), 2-Amino-4-methyl-oxazole (3), furfuryl alcohol (4), Morpholinoacetonitrile (5), xylose and NMMO under alkaline and high-temperature conditions, rather than by PG. The black particles are due to thermal degradation of NMMO or NMM or M in the presence of oxygen and iron at high temperatures.

     

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.     

Thermal and rheological characterization of cellulose spinning dopes modified with nanosilica and antibacterial agents

The present study concerns cellulose spinning solutions prepared with the use of the organic solvent N‐methylmorpholine‐N‐oxide (NMMO). These solutions were modified with two types of antibacterial agents: an inorganic agent zirconium‐silver phosphate (Alphasan®) and an organic one Triclosan (Irgasan® DP300). Such spinning solutions allow to obtain antibacterial fibers of the Lyocell type. A nanomodifier, colloidal silica (Ludox SM 30®), was also incorporated into the spinning solutions as an additional component to increase the antibacterial activity of fibers. The effect of the compounds incorporated into the spinning solutions on their rheological and thermal properties was assessed by means of the oscillatory method and differential scanning calorimetry (DSC), respectively. The incorporation of nanosilica exerts a clear influence on the rheological properties of spinning solutions, whereas this effect is negligible in the simultaneous presence of nanosilica and antibacterial agents. The results of thermal measurements show that nanosilica affects the crystallization of the solutions examined. Depending on the type of antibacterial agent, nanosilica brings about either a delay or acceleration of the crystallization of the modified solutions. The effect of nanosilica can be explained in terms of interactions between hydroxyl groups occurring on the surface of silica nanoparticles and NMMO molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

Phase diagram of the ternary system NMMO/water/cellulose

The phase diagram of the system N-methylmorpholine-N-oxide(NMMO)/H₂O/cellulose has been measured at 80 °C by establishing a solubility map (observation of the mixtures under the microscope), by the analysis of coexisting phases and determining the critical point. These experiments manifest a continuous reduction of the two phase area existing for the subsystem H₂O/cellulose upon the addition of NMMO, where a weight fraction of NMMO in the mixed solvent exceeding 75 wt% is required for Solucell 400 to reach the critical composition. The critical cellulose concentration is only 0.34 wt%, i.e., more than an order of magnitude lower than for the solutions of typical vinyl polymers in mixed solvents. All experimental observations can be well modeled on the basis of composition dependent binary interaction parameters by means of recently established mixing rules. For the subsystems H₂O/cellulose and NMMO/water the corresponding data are known from independent earlier measurements. The adjustment of two parameters to the ternary phase diagram was required to obtain this information for NMMO/cellulose, the third binary subsystem.     

Cellulose solutions in N-methylmorpholine-N-oxide (NMMO) – degradation processes and stabilizers

Efficient stabilization of cellulose solutions in NMMO(1) against side reactions and their harmful effects meansprevention of both homolytic and heterolytic side reactions, which is mainlyaccomplished by trapping radicals, formaldehyde, andN-(methylene)iminium ions (5). Whileradical trapping is commonly reflected by the antioxidativeefficiency, the effectivity against heterolyticdegradationin the Lyocell dope can be expressed by the newly introduced termformaldehyde trapping capacity (FTC). Propyl gallate (PG,4), the most widely applied Lyocell stabilizer nowadays, actsas a phenolic antioxidant, and is finally oxidized to a deeply colored, highlyconjugated chromophore (11) via ellagicacid (10). It was demonstrated that 4 is alsoa quencher of formaldehyde and N-(methylene)iminium ions,both in organic solutions of NMMO and in Lyocell dope. The processes of radicaltrapping and scavenging of HCHO/5 are competitive in the caseof propyl gallate. A novel oxa-chromanol derivative, PBD (14),was designed as stabilizer for Lyocell solutions. In analogy to propyl gallate,PBD acts as a scavenger of all three dangerous species, namely HCHO,5 and radicals. Upon oxidation by radical species, PBDreleasesacetaldehyde which acts as a very efficient HCHO trap. Thus, in contrast topropyl gallate, radical trapping and HCHO trapping are not competitive. Boththeantioxidative efficiency and the capacity to trap HCHO and 5are higher for PBD as compared to propyl gallate. In preliminary stabilizertesting, mixtures of PBD and PG proved to be especially effective.     

Discoloration of cellulose solutions in <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide (Lyocell). Part 2: Isolation and identification of chromophores

The Lyocell process is a modern green industrial fiber-making technology, which employs N-methylmorpholine-N-oxide monohydrate (NMMO) to directly dissolve cellulose. One problem in Lyocell processing is the discoloration of the spinning dope due to chemical side reactions. Two different methods were elaborated to isolate chromophores, which are present in minute amounts only, from Lyocell fibers, the first one using hydrogen chloride in alcoholic solution, the second one employing boron trifluoride – acetic acid complex. Several chromophores were unambiguously identified by a combination of analytical techniques and comparison to authentic samples. Carbohydrate condensation products, such as catechols, were shown to dominate in early phases of chromophore formation. In later stages, these initial chromophores undergo further condensation reactions with degradation products of NMMO and NMMO itself, leading to nitrogen-containing heterocycles and quinoid products, among others. The incorporation of nitrogen into the chromophores and thus the participation of the solvent in chromophore formation were proven.     

A novel polymeric stabilizing system for modified lyocell solutions

A novel polymeric stabilizer consisting of iminodiacetic acid sodium salt (ISDB) and benzyl amine (BSDB) covalently bound to a styrene/divinyl benzene copolymer were studied. Calorimetric, spectroscopic, rheological, and high performance liquid chromatography analysis revealed distinctive improvements of the thermal stability of modified Lyocell solutions compared to the unstabilized solution and to that with conventional NaOH/propyl gallate stabilizer. Segregation processes of the system cellulose/N‐methylmorpholine‐N‐oxide and autocatalytic reactions caused by carboxyl group‐containing additives are suppressed by ISDB/BSDB. Concerning to surface‐active additives, enhanced thermal stability is only received for a weakly reactive charcoal. In the case of nanoscaled carbon black modifier, autocatalytic reactions indicated by isoperibolic measures are prevented by the new polymeric stabilizer system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1702–1713, 2006     

Possibilities for the Physical Modification of Cellulose Shapes Using Ionic Liquids

Summary: Functional cellulose shapes offer valuable properties for innovative application potentials in textile and medical products. Thereby excellent textile physiological properties of cellulose are allowed to be connected with novel application characteristics like bioactivity, electrical conductivity, heat storage or ability to adsorb liquids or gases. A very advantageous way to modify the properties of fibres, films or textile structures is to introduce particular additives via the Lyocell process. Regard to technical applications, functional additives will be able to incorporate themselves in the shape matrix and, in the case of using N-methylmorpholine-N-oxide monohydrate (NMMO) as solvent, implicate massive technological difficulties and deterioration of properties of the spinning dope. Beside a couple of limiting moments, ionic liquids (ILs) offer as direct solvents an excellent chance for physical modification of cellulose shapes. In contrast to NMMO, they exhibit a significantly higher thermal stability as well as a higher chemical resistance. ILs exhibit most widely a better dissolving capability for a number of different polymers. First results of the development of adsorber materials as well as novel bioactive fibres will be discussed and fibre characteristics will be given.     

Morphology of polysaccharide blend fibers shaped from NaOH, <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide and 1-ethyl-3-methylimidazolium acetate

The aim of this study was to find newly structured biopolymer blends bearing those adjustable features able to produce innovative materials. Apart from cellulose derivatives (cellulose carbamate and carboxymethyl cellulose), mannans (guar gum, locust bean gum, and tragacanth gum), xylan, starch (cationized), ι-carrageenan, and xanthan were chosen as blend polysaccharides for cellulose as matrix. In order to study their integration into the cellulose skeleton, fibers were shaped from three different solvents: NaOH by a special wet-spinning process, as well as N-methylmorpholine-N-oxide (NMMO) and 1-ethyl-3-methylimidazolium acetate (EMIMac) via Lyocell technology. The structure and morphologies of the fibers were analyzed by X-ray wide-angle scattering and atomic force microscopy. Hydrophilic/hydrophobic properties were determined by means of a contact angle, as well as moisture content and water retention values, while the surface properties throughout zeta-potential measurements. Being very different processes, the wet spinning in NaOH solution and the dry–wet spinning are deeply impacted by the types of solvent and polysaccharide. The X-ray results for NMMO fibers revealed the highest orientation compared with EMIMac having the lowest orientation of NaOH fibrous types. AFM images also show the lowest surface roughnesses for NMMO and EMIMac fibers. The moisture content and water retention values support these trends, while the water contact angle results show insignificant differences between the samples from EMIMac and NaOH, even though the values calculated for NMMO fibers were the lowest.     

Double crystallization behavior in dry-jet wet spinning of cellulose/N-methylmorpholine-N-oxide hydrate solutions

The structure and resultant mechanical properties of fibers in the dry-jet wet spinning process of cellulose solutions in N-methylmorpholine-N-oxide (NMMO) hydrates were investigated in terms of molecular weight of cellulose, concentration, and hydration number (n) of NMMO hydrate. The value of n had an effect on the crystallization behavior of the cellulose solution system, which influenced the resultant fiber structure. Increasing cellulose concentration and decreasing the value of n retarded crystallization because of the increased interactions between cellulose and NMMO hydrate. Reducing the value of n from 1 to 0.72 produced more highly oriented cellulose fibers. However, incorporating n-propyl gallate, an antioxidant, had little effect on the fiber structure. When n=0.72 a double crystallization behavior was observed in the fiber spinning process irrespective of molecular weight of cellulose and concentration over the experimental ranges examined. It should be noted that such a double crystallization took place in the absence of foreign additives. The double crystallization behavior was more noticeable when the aspect ratio of spinning nozzle was greater. The double layer structure had a positive effect on the mechanical strength.     

Mechanism of nitration of nitrogen-containing heterocyclic <Emphasis Type="Italic">N</Emphasis>-acetonyl derivatives. General approach to the synthesis of <Emphasis Type="Italic">N</Emphasis>-dinitromethylazoles

A general synthetic procedure for the synthesis of N-dinitromethyl derivatives of nitrogen-containing heterocycles has been developed. The procedure includes the destructive nitration of heterocyclic N-acetonyl derivatives of tetrazoles, 1,2,4- and 1,2,3-triazoles, pyrazoles, imidazoles and their bicyclic analogs, as well as imides of carboxylic and sulfonic acids and substituted hydrazines with mixtures of sulfuric and nitric acids. The kinetic study of the reaction mechanism was performed using UV and NMR spectroscopy. It was found that the NO₂ groups were sequentially introduced into the methylene fragment by the addition of the nitronium ion to multiple bonds of intermediate enols followed by hydrolysis of the acetyl moiety. The rate and direction of the enolization (due to the CH₂ and CH₃ groups) of the N-acetonyl compounds in sulfuric acid solutions were determined by the study of the deuterium exchange kinetics. The synthesis of the N-dinitromethyl compounds is complicated by side reactions, such as the decomposition of intermediate α-nitroketone, the nitration of the methyl group in the acetonyl moiety, and the nitration of the dinitromethyl products to trinitromethyl derivatives.     

Synthesis and physiological activity of trialkyl phosphorothioates and trialkyl phosphorodithioates containing fragments of N-acylated amino acids

A series of S-[N-acyl-N-(alkoxycarbonylalkyl)aminomethyl] O,O-dialkyl phosphorothioates and -dithioates were prepared by the reactions of the corresponding alkali salts of dialkyl phosphorothioates or dialkyl phosphorodithioates with esters of N-acyl-N-(chloromethyl)glycine or N-acyl-N-(chloromethyl)--alanine and by the reactions of dialkylphosphorothioic or dialkylphosphorodithioic acids with N-acylated amino acids or their esters and paraformaldehyde in the presence of gaseous HCl. Some of the resulting compounds proved to be active permethrine synergists.     

Formation of cyclic acylphosphoramidates in mass spectra of N‐monoalkyloxyphosphoryl amino acids using electrospray ionization tandem mass spectrometry

The fragmentation reactions of N‐monoalkyloxyphosphoryl amino acids (N‐MAP‐AAs) were studied by electrospray ionization tandem mass spectrometry (ESI‐MS). The sodiated cyclic acylphosphoramidates (CAPAs) were formed through a characteristic pentacoordinate phosphate participated rearrangement reaction in the positive‐ion ESI‐MS/MS and HR‐MS/MS of N‐MAP‐AAs, in which the fragmentation patterns were clearly different from those observed in the corresponding ESI‐MS/MS of N‐dialkyloxyphosphoryl amino acids/peptides and N‐phosphono amino acids. The formation of CAPAs depended on the chemical structures of N‐terminal phosphoryl groups, such as alkyloxy group, negative charge and alkali metal ion. A possible integrated rearrangement mechanism for both P‐N to P‐O phosphoryl group migration and formation of CAPAs was proposed. The fragmentation patterns of CAPAs as novel intermediates in gas phase were also investigated. In addition, it was found that the formation of α‐amino acid CAPAs was more favorable than β‐ or γ‐CAPAs in gas phase, which was consistent with previous solution‐phase experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

Solvation Accounts for the Counterintuitive Nucleophilicity Ordering of Peroxide Anions

The nucleophilic reactivities (N , s _N) of peroxide anions (generated from aromatic and aliphatic peroxy acids or alkyl hydroperoxides) were investigated by following the kinetics of their reactions with a series of benzhydrylium ions (Ar₂CH⁺) in alkaline aqueous solutions at 20 °C. The second‐order rate constants revealed that deprotonated peroxy acids (RCO₃⁻), although they are the considerably weaker Brønsted bases, react much faster than anions of aliphatic hydroperoxides (ROO⁻). Substitution of the rate constants of their reactions with benzhydrylium ions into the linear free energy relationship lg k =s _N(N +E ) furnished nucleophilicity parameters (N , s _N) of peroxide anions, which were successfully applied to predict the rates of Weitz–Scheffer epoxidations. DFT calculations with inclusion of solvent effects by means of the Integral Equation Formalism version of the Polarizable Continuum Model were performed to rationalize the observed reactivities.     

Photoredox-Catalyzed Decarboxylative Bromination,Chlorination and Thiocyanation Using Inorganic Salts

Decarboxylative halogenation reactions of alkyl carboxylic acids are highly valuable reactions for the synthesis of structurally diverse alkyl halides. However, many reported protocols rely on stoichiometric strong oxidants or highly electrophilic halogenating agents. Herein, we describe visible-light photoredox-catalyzed decarboxylative halogenation reactions of N-hydroxyphthalimide-activated carboxylic acids that avoid stoichiometric oxidants and use inexpensive inorganic halide salts as the halogenating agents. Bromination with lithium bromide proceeds under simple, transition-metal-free conditions using an organic photoredox catalyst and no other additives, whereas dual photoredox-copper catalysis is required for chlorination with lithium chloride. The mild conditions display excellent functional-group tolerance, which is demonstrated through the transformation of a diverse range of structurally complex carboxylic acid containing natural products into the corresponding alkyl bromides and chlorides. In addition, we show the generality of the dual photoredox-copper-catalyzed decarboxylative functionalization with inorganic salts by extension to thiocyanation with potassium thiocyanide, which was applied to the synthesis of complex alkyl thiocyanates.     

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), .     

Effect of Chloride Ions on the Behavior of Saccharin, N-Methylsaccharin, and 2-Butyne-1,4-diol during Electrodeposition of Nickel from Acid Electrolytes

Rates of transformation of organic additives (saccharin, N-methylsaccharin, 2-butyne-1,4-diol) and accumulation of products of their cathodic reactions are studied during nickel electrodeposition from the chloride and Watts electrolytes. A large concentration of chloride ions accelerates the saccharine and N-methylsaccharin consumption due accelerated synthesis of o-toluenesulfamide, N-methyl-o-toluenesulfamide, and N-methylbenzylsultam, thus facilitating adsorption of additives on the nickel cathode via the carbonyl group. An inhibition of adsorption via the sulfonyl group is accompanied by a decrease in the accumulation of corresponding benzamides. An increase in the concentration of chloride ions in electrolytes containing 2-butyne-1,4-diol promotes accumulation of 2-buten-1,4-diol and inhibits hydrogenation of the double bond to a saturated bond. Differences in the behavior of the additives are due to (i) competition of chloride ions with the additives in the electrolyte or with their electroreduction products during adsorption on the nickel cathode, (ii) a change in the deposit potential, and (iii) a change in the concentration of inclusions in the deposits, which determine the catalytic activity of the cathode.