Dimethylacetamide solvents

Figure 5. SEC calibration curves random-coil vs. rigid-rod (8) (SEC column set of several pore sizes, N,N-dimethylacetamide solvent at 80°C)...

Miyamoto et al. [ 164,165] conducted homogeneous acetylation of cellulose in a 10% LiCl-dimethylacetamide solvent. The 6-OH group was about twice as reactive as the 2-OH group for DS up to 1.2, and the factor was reduced to 1.4 for higher DS samples. 

The initial number average molecular weights (Mn) for the poly-(amic-acids) were between 10,000 and 20,000, and no attempt was made to optimize them. Dimethylacetamide solvent was distilled from calcium hydride under vacuum and stored under nitrogen. The resin solutions were stored also under nitrogen. The water content of the solvent was measured with a Porapak Q column in a Hewlett Packard 5750 gas chromatograph. Unless otherwise stated, the water concentration in the solvent remained below 0.05 vol %. Mn was determined from osmotic pressure measurements on a Hewlett Packard-Mechrolab 502 osmometer using ArRo Lab gel cellophane 600D membranes. 

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). 

Although many problems associated with solvent reactivity are listed in the literature [18], the absence of any literature information on a specific compatibility question cannot be taken to imply that a problem does not exist. This was illustrated by a major explosion and fire in 1990 which was caused by a previously unknown reaction whereby the dimethylacetamide solvent reacted with water, forming acetic acid which reduced the stability of the reaction mass [19]. 

Onogi et al. (2012) carried out reaction of methyl (lR,2S,4R,5R)-2-amino-4,5-di-bromocyclohexanecarboxylate in presence of K COj and dimethylacetamide solvent (DMA) at 60°C for 0.5 h to give unstable intermediate methyl (lS,2R,4S,5R)-7-aza-5-bromo-bicyclo[2.2.1]heptane-2-carboxylate via intermolecular cycloamination, which further reacts at 140°C for 1.5 h to form methyl (lS,2R,4S,5S)-7-aza-5-hy-droxy-bicyclo[2.2.1]heptane-2-carboxylate as final product under microwave irradiation. In this acyloxylation reaction, imusual endo-selectivity occurs due to 7-az-abicyclo[2.2.1]heptane skeleton. 

Dimeihylamine, C2H7N, (CH3)2NH. Colourless, inflammable liquid with an ammoniacal odour, mp -96" C, b.p. 7°C. Occurs naturally in herring brine. Prepared in the laboratory by treating nitrosodimetbyl-aniline with a hot solution of sodium hydroxide. Dimethylamine is largely used in the manufacture of other chemicals. These include the solvents dimethylacetamide and dimethyl-formamide, the rocket propellant unsym-metrical dimethylhydrazine, surface-active agents, herbicides, fungicides and rubber accelerators. 

Resin and Polymer Solvent. Dimethylacetamide is an exceUent solvent for synthetic and natural resins. It readily dissolves vinyl polymers, acrylates, ceUulose derivatives, styrene polymers, and linear polyesters. Because of its high polarity, DMAC has been found particularly useful as a solvent for polyacrylonitrile, its copolymers, and interpolymers. Copolymers containing at least 85% acrylonitrile dissolve ia DMAC to form solutions suitable for the production of films and yams (9). DMAC is reportedly an exceUent solvent for the copolymers of acrylonitrile and vinyl formate (10), vinylpyridine (11), or aUyl glycidyl ether (12). 

Crystallization and Purification Solvent. Dimethylacetamide is useful ia the purification by crystallization of aromatic dicarboxyHc acids such as terephthahc acid [100-21-0] and/vcarboxyphenylacetic acid [501-89-3]. These acids are not soluble ia the more common solvents. DMAC and dibasic acids form crystalline complexes containing two moles of the solvent for each mole of acid (16). Microcrystalline hydrocortisone acetate [50-03-3] having low settling rate is prepared by crystallization from an aqueous DMAC solution (17). 

The water of hydration of these complexes can be replaced with other coordinating solvents. For example, the ethanol and methanol solvates were made by dissolving the hydrates in triethyl and trimethyl orthoformate, respectively (81,82). The acetic acid solvates are made by treating the hydrates with acetic anhydride (83). Conductivity and visible spectra, where appHcable, of the Co, Ni, Zn, and Cu fluoroborates in A/A/-dimethylacetamide (L) showed that all metal ions were present as the MLg cations (84). Solvated fluoroborate complexes of, Fe +, Co +, , Cu +, and in diethyl... 

Separation and Purification. Separation and purification of butadiene from other components is dominated commercially by the extractive distillation process. The most commonly used solvents are acetonitrile and dimethylformarnide. Dimethylacetamide, furfural, and... 

Cellulose dissolved in suitable solvents, however, can be acetylated in a totally homogeneous manner, and several such methods have been suggested. Treatment in dimethyl sulfoxide (DMSO) with paraformaldehyde gives a soluble methylol derivative that reacts with glacial acetic acid, acetic anhydride, or acetyl chloride to form the acetate (63). The maximum degree of substitution obtained by this method is 2.0 some oxidation also occurs. Similarly, cellulose can be acetylated in solution with dimethylacetamide—paraformaldehyde and dimethylformamide-paraformaldehyde with a potassium acetate catalyst (64) to provide an almost quantitative yield of hydroxymethylceUulose acetate. 

For convenience of application it is usual to utilise the two-stage preparation shown above. Initially the soluble polymer (I) is formed which is then converted into the insoluble thermally stable polyimide (II) Figure 18.35). Suitable solvents for the high molecular weight prepolymer (I) include dimethylformamide and dimethylacetamide. 

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. 

However, these methods suffer from their sensitivity to the punty of the solvent Addition of one equivalent of zinc dust and use of dimethylacetamide make the reaction much more reproducible [41] (equation 41) (Table 15)... 

Uses of Methylamines. Dimethylamine is the most widely used of the three amines. Excess methanol and recycling monomethylamine increases the yield of dimethylamine. The main use of dimethylamine is the synthesis of dimethylformamide and dimethylacetamide, which are solvents for acrylic and polyurethane fibers. 

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 ... 

The last method for the preparation of 2-quinolones described in this chapter relies on a intramolecular Heck cyclization starting from heteroaryl-amides (Table 2) [57]. These are synthesized either from commercially available pyrrole- and thiophene-2-carboxylic acids (a, Table 2) or thiophene-and furan-3-carboxylic acids (b, Table 2) in three steps. The Heck cyclization is conventionally performed with W,Ar-dimethylacetamide (DMA) as solvent, KOAc as base and Pd(PPh3)4 as catalyst for 24 h at 120 °C resulting in the coupled products in 56-89% yields. As discussed in Sect. 3.4, transition metal-catalyzed reactions often benefit from microwave irradiation [58-61], and so is the case also for this intramolecular reaction. In fact, derivatives with an aryl iodide were successfully coupled by conventional methods, whereas the heteroarylbromides 18 and 19, shown in Table 2, could only be coupled in satisfying yields by using MAOS (Table 2). 

The electrochemical reduction of Sg in aprotic solvents like DMSO [87, 91, 92], DMF [92, 93], dimethylacetamide [94], acetonitrile [95], or methanol [95] yields primarily Sg ions which then equilibrate with other dianions and radical anions like 83 and others see Eqs. (4)-(8). In a second reduction step tetrasulfide ions are formed ... 

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