Dimethylacetamide-lithium chloride solvent

Poirier, M. and Charlet, G. (2002) Chitin fractionation and characterization in N, N-dimethylacetamide/ lithium chloride solvent system. Carbohydrate Polymers, 50, 363-370. 

In another oudine, cellulose was complexed with cuprammonium ions (Nicoll and Conaway, 1943). Lately, laboratory-scale isolation has relied on polar aprotic solvents and solvent systems, e.g., dimethylsulfoxide, pyridine, Af,7V-dimethylacetamide-lithium chloride, and l-methyl-2-pyrrolidinone-lithium chloride (Baker et al., 1978 McCormick and Shen, 1982 Seymour et al., 1982 Arnold et al., 1994). These solvents have enabled such homogeneous17 reactions as O- and N-derivatization of cellulose and chitin (Williamson and McCormick, 1994) and selective site chlorination (Ball et al., 1994). Dimethylsulfoxide was the solvent in a homogeneous reaction of cellulose and paraformaldehyde, prior to isolation of purified cellulose (Johnson et al., 1975). In yet another outline, paraformaldehyde enabled superior quality extracts when the parent tissues were presoaked in this solution (Fasihuddin et al., 1988). 

For a specific polymer, critical concentrations and temperatures depend on the solvent. In Fig. 15.42b the concentration condition has already been illustrated on the basis of solution viscosity. Much work has been reported on PpPTA in sulphuric acid and of PpPBA in dimethylacetamide/lithium chloride. Besides, Boerstoel (1998), Boerstoel et al. (2001) and Northolt et al. (2001) studied liquid crystalline solutions of cellulose in phosphoric acid. In Fig. 16.27 a simple example of the phase behaviour of PpPTA in sulphuric acid (see also Chap. 19) is shown (Dobb, 1985). In this figure it is indicated that a direct transition from mesophase to isotropic liquid may exist. This is not necessarily true, however, as it has been found that in some solutions the nematic mesophase and isotropic phase coexist in equilibrium (Collyer, 1996). Such behaviour was found by Aharoni (1980) for a 50/50 copolymer of //-hexyl and n-propylisocyanate in toluene and shown in Fig. 16.28. Clearing temperatures for PpPTA (Twaron or Kevlar , PIPD (or M5), PABI and cellulose in their respective solvents are illustrated in Fig. 16.29. The rigidity of the polymer chains increases in the order of cellulose, PpPTA, PIPD. The very rigid PIPD has a LC phase already at very low concentrations. Even cellulose, which, in principle, is able to freely rotate around the ether bond, forms a LC phase at relatively low concentrations. 

Aqueous salt solutions such as saturated zinc chloride or calcium thiocyanate can dissolve limited amounts of cellulose [131]. Two nonaqueous salt solutions with a lengthy history are ammonium thiocyanate/ammonia and dimethylacetamide/lithium chloride (DMAc/LiCl). Solutions up to about 15% can be prepared with these solvents. DMAc-LiCl has been used for molecular weight determinations of cotton [135] (see Section 1.5.2). 

Essentially we find in the literature just two polymers which have been spun to such fibres. Their preparation is simplicity itself merely requiring the bringing together of 2,5-dimethyl piperazine (XIV) and a bis-isocyanate of the type (XV) (where R = H or CH3) in a suitable solvent such as dimethylacetamide-lithium chloride. The resulting viscous polymer solution may be employed as the spinning dope. 

Still due to the strong cohesion of this material, cellulose is insoluble in most organic solvents. Only some highly polar mixtures such as A, A -dimethylacetamide/ lithium chloride, AT-methylmorpholine/water, Cu(OH)2/ammonia, trifiuoroacetic acid/alkyl chloride, calcium thiocyanate/water, and ammonium thiocyanate/liquid ammonia are solvents of cellulose. In spite of the potential applications of such solutions, they are exploited relatively little due to their high cost. 

The bromination of 4,5-j -dihydrocortisone acetate in buffered acetic acid does not proceed very cleanly (<70%) and, in an attempt to improve this step in the cortisone synthesis, Holysz ° investigated the use of dimethylformamide (DMF) as a solvent for bromination. Improved yields were obtained (although in retrospect the homogeneity and structural assignments of some products seem questionable.) It was also observed that the combination of certain metal halides, particularly lithium chloride and bromide in hot DMF was specially effective in dehydrobromination of 4-bromodihydrocortisone acetate. Other amide solvents such as dimethylacetamide (DMA) and A-formylpiperidine can be used in place of DMF. It became apparent later that this method of dehydrobromination is also prone to produce isomeric unsaturated ketones. When applied to 2,4-dibromo-3-ketones, a substantial amount of the A -isomer is formed. 

The polymerization of aromatic diamines with acid chlorides in solution works well.7 914 35 The basicity of the aromatic diamine is low and acid binding can be achieved with several compounds and even solvents such as TV-methylpyrrolidonc (NMP) and dimethylacetamide (DMAc). The all-para aromatic amide poly(p-phenyleneterephthalamide) can be synthesized in DM Ac.7,9,14 To prevent precipitation of the polymer, a salt such as calcium chloride or lithium chloride can be added. It is also possible to react the acid chloride with a silylated diamine ... 

Dimethylacetamide (DMAc), cellulose solvent (with lithium chloride), 5 384 N, N-Dimethylacetamide (DMAc), 23 703 extractive distillation solvent, 8 802 solvent for cotton, 8 21 N, AA-Dimethylacrylamide (DMA), 20 487 P,P-Dimethyl acrylic acid, physical properties, 5 35t Dimethylallylamine, 2 247... 

Aprotic dipolar solvents such as dimethylacetamide containing about 2.5% of a salt as lithium chloride or calcium chloride... 

Amylopectins. — The effects of acrylamide graft copolymerization on the solution properties of amylopectin have been discussed. Amylopectin has been dyed with DyAmyl-L and used in this form as a substrate for the assay of a-amylase. Amylopectin has been treated with isocyanate derivatives of 4-amino-( 1,1-dimethyl ethyl)-3-(methylthio)-l,2,4-triazin-5(4/f)-one ( metribuzin ) or acid chloride derivatives of 2,4-dichlorophenoxyacetic acid ( 2,4-D ) and 2,2-dichloropropionic acid ( dalapon ), to produce controlled-release polymeric pesticide systems. The solvent system utilized for these reactions, a lithium chloride or bromide salt in AW-dimethylacetamide, allows dissolution of the reactant salt and facilitates analysis of the polymer product by such techniques as i.r., U.V., and n.m.r. spectroscopies and gel permeation chromatography. Derivatives of other naturally occurring polysaccharides, including amylopectin, cellulose, chitin, and dextran, were also prepared. 

McCormick [6] discovered that Af,Af-dimethylacetamide (DMAc) (Figure 10.3) and lithium chloride (LiCl) would dissolve the cellulose. He and his coworkers also observed cholesteric lyotropic mesophases of cellulose in this solvent system [7,8], which formed at cellulose... 

Typically tetramethyl urea or dimethylacetamide are employed as amide solvents. Lithium chloride May be added to stabilise the resulting polymer solution or may be produced in situ by addition of lithium hydroxide or carbonate. The degree of polymerisation can be controlled by adding a chain stopper such as p aminobenzoic acid. ... 

For the direct method special solvent systems are employed without chemical modification of the cellulose chains. Some examples are LiCl/DMAc (lithium chloride/N,N-dimethylacetamide), DMSO/TBAF (dimethyl sulfoxide/tetra-n-butylammonium fluoride). 

The DD is the key property that affects the physical and chemical properties of chitosan, such as solubility, chemical reactivity and biodegradabdity and, consequently their applications. A quick test to differentiate between chitin and chitosan is based on solubdity and nitrogen content. Chitin is soluble in 5% lithium chloride/N,N-dimethylacetamide solvent [LiCI/DMAc] and insoluble in aqueous acetic add while the op>posite is true of chitosan. The nitrogen content in purified samples is less than 7% for chitin and more than 7% for chitosan (Dash et al, 2011 Rinaudo, 2006). 

Nevertheless, ytterbium and erbium incorporation in a porphyrin macrocycle faces certain difficulties. For this purpose highly boiling solvent, long time of heating and use of inert gas are required. In Ref [5] incorporation of erbium and gadolinium in a porphyrin cycle in the medium of dimethylacetamide Boiling point (B.p.) 165°C in a presence of dry lithium chloride is described. 

The amorphous regions can be hydrolysed by acids to create short cellulose nanocrystals [31]. Nevertheless, cellulose is stable in most common organic solvents. It can only be dissolved in strong acidic solutions such as concentrated phosphoric acids and concentrated sulphuric acid [32] or ionic liquids such as Ai-ethylpyridinium [33] and lithium chloride/Ai,Ai-dimethylacetamide [34]. 

The molecular cellulose chains have varying lengths. Measurements of the chain length require that cotton be in solution. Solvents for this purpose include cuprammonium hydroxide solution, phosphoric acid [7664-38-2], nitric acid [7697-37-2], quaternary ammonium bases, cadmium ethylenediamine hydroxide [14874-24-9], cupriethylenediamine hydroxide [111274-71-6] (76), dimethylacetamide [127-19-5]-lithium chloride [7447-41-8] (DMAC—LiCl), and... 

MPD-1 fibers may be obtained by the polymerization of isophthaloyl chloride [99-63-8] and m-phenylenediamine [108-45-2] in dimethylacetamide with 5% lithium chloride (26). The reactants must be very carefully dried since the presence of water would upset the stoichiometry and lead to low molecular weight products. Temperatures in the range of 0 to -40°C are desirable to avoid such side reactions as transamidation by the amide solvent and acylation of m-phenylenediamine by the amide solvent. Both reactions would lead to an imbalance in the stoichiometry and result in forming low molecular weight polymer. Fibers may be either dry spim or wet spim directly from solution. 

Chitin exhibits very ordered, crystalline structure that is stabilized by a high number of intermolecular H-bonds [24]. Chitin exhibits highly hydrophobic character and is insoluble in water and most organic solvents. It is soluble in hexafluoroisopropanal, hexafluoroacetone and chloroalcohols in conduction with aqueous solutions of mineral acids and dimethylacetamide (DMAc) containing 5% lithium chloride (LiCl) [98,99], Upon hydrolysis of chitin with concentrated acids under harsh conditions, a relatively pure amino sugar D glucosamine is produced [96]. 

Solvents known to dissolve chitin are a mixture of formic acid and dichloroacetic acid, a mixture of trichloroacetic acid and dichloroethane, a mixture of dimethylacetamide and lithium chloride, methane sulfonic acid, calcium chloride dihydrate saturated methanol, and 10% sodium hydroxide solution [4], Chitosan is much more soluble than chitin. It dissolves in aqueous solutions of many organic and inorganic acids. 

The features of the traditional reaction have been studied in detail. An important feature of synthesis of the polymer is that the polymer gelatinizes and polycondensation is strongly slowed in formation of Pl A with a logarithmic viscosity of 2.2 dl/g. The reaction can be accelerated by mechanical destruction of the gel, and the molecular weight of the PPTA increases as a result. It has been shown that old or fresh gels made turbid as a result of crystallization of the polymer are not reactive. The M of the polymer can be sharply increased on addition of tertiary amines to the organic solvent (iVA -dimethylacetamide with lithium chloride), which is due to the acceptor-catalytic effect of these products [2. 3]. 

TABLE 10.1. Effea of the Ccmcentration of the Anisotropic Phase on the Properties of PBA Fibers (T iog of Polymer = 2.1 dl/g. Solvent iV -Dimethylacetamide with Lithium Chloride)... 

The most common method for obtaining aramids is the reaction of diamines with dicarboxylic add chlorides in a dipolar aprotic solvent at low temperature. N/f-Dimethylacetamide (DMAc), N-methylpyrrolidinone (NMP) and tetramethylurea (TMU) are the preferred solvents for such polymerizations, giving good polymer solubility and acting as add acceptors. However, as the molecular weight builds up, organic solvents alone are not sufficient to keep aramids in solution. However, addition of lithium chloride and/or caldum chloride to DMAc has been shown to greatly increase polymer solubility. ... 

Although cellulose is not soluble in common organic solvents, a series of special solvents have been found to be able to dissolve celMose. However, only some of them can be used to spin cellulose fibers via direet methods. So far, all these viable direct solvents consist of two components, e.g., N-methylmorpholine-N-oxide/ water (NMMO/HjO), lithium chloride/dimethylacetamide, trifluoroacetic acid/di-chloroethane, calcium thiocyanate/water, ammonia/ammonium thiocyanate, zinc chloride/water, and sodium hydroxide/water. 

Lithium chloride (LiCl)/N,N-dimethylacetamide (DMAc) was employed as a solvent for cellulose by McCormick et al. [83]. Turbak and coworkers were the first to spin cellulose fibers from this solvent system and studied the process extensively [84]. Patel and Gilbert were the first to report the lyotropic mesophase of cellulose in mixtures of trifluoroacetie acid (TFA) and chlorinated alkanes, such as 1,2-dichloroethane and methylene chloride [85]. Other solvents proposed for cellulose include ammonia (NH3)/ammonium thiocyanate (NH4SCN), calcium thiocyanate (Ca(SCN)2)/water, zinc chloride (ZnCl)/water, sodium hydroxide (NaOH)/urea [86], NaOH/thiourea [87, 88], and phosphorie aeid [89, 90]. 

More than 100 polymers, both synthetic and natural, have been successfully electrospun into nanofibers, mostly from polyma solutions, as any polymer may be electrospun into nanofibers, provided that the polymer molecular weight is sufficiently high and the solvent can be evaporated in the time during the jet transit period, over a distance between the spinneret and the collector. Standard polymers successfully electrospun into nanofibers include polyacrylonitrile (PAN), poly(ethylene oxide) (PEO), poly(ethylene terephthalate) (PET), polystyrene (PS), poly(vinyl chloride) (PVC), Nylon 6, PVA, poly(8-caprolactone), Kevlar (poly[p-phenylene terephthalamide]), poly(vinylidene fluoride) (PVDF), polybenzimidazole, polyurethanes (PUs), polycarbonates, polysulfones, poly(vinyl phenol) (PVP), and many others [36,37]. Electrospinning has also been used to produce nanofibers from natural biomacromolecules, including cellulose [either electrospun from cellulose acetate (CA) with subsequent hydrolysis or directly electrospun from cellulose solutions in Af,Af-dimethylacetamide with lithium chloride], collagen and gelatin, modified chitin, chitosan, and DNA. 

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