Dimethylformamide azeotropic distillation

An alternative process from U.S. Patent 3,635,946 A vigorously stirred reaction mixture consisting of 32.B7 g (0.1 mol) of 5-fluorouracilmercury, 100 ml of dimethylformamide and 50 ml of toluene is dried by azeotropic distillation of toluene. It is then cooled to -40°C in a stream of dry nitrogen, and a solution of 21.3 g (0.2 mol) of 2-chlorofuranidin in 20 ml of dried dimethylformamide is gradually added to the stirred mixture, the temperature being maintained between -40°C and -30°C. After completion of the reaction (which is marked by complete dissolution of the starting 5-fluorouracilmercury) i.e. after about 3 to 4 hours, 60 to 80 ml of the solvent are distilled off in vacuo at a bath temperature not exceeding 35°C ... 

The various side reactions of the chemical cyclodehydration and because of the high cost for solvents, catalyst and cyclodehydration agent, researchers have been looking at more economic ways to manufacture bismaleimides. Efforts have been directed towards a catalytic cyclodehydration process via azeotropic distillation to avoid undesirable byproducts and to achieve improved yield of pure bismaleimide. The use of Lewis add/base salts based on p-toluene sulfonic acid, sulfuric add or trifluoroacetic add and dimethylformamide (DMF), N-methylpyrrolidone (NMP) and acetone as bases provided high yields of high purity bismaleimide (24). In another patent dimethyldialkylammoniummethane... 

The anhydrous acetates of the rare earths have recently been prepared. Moeller et al. [355] obtained them for La, Dy, Ho, Er, Yb and Y by the azeotropic distillation of a mixture of hydrated acetates with N,N -dimethylformamide (DMF) and benzene. In the case of Ce, Pr, Nd, Sm, Eu and Gd the same method gave a monosolvated acetate, M(C2Hs02)3 DMF. However, the anhydrous acetates of Ce, Pr, Nd, Sm, Eu and Gd can be prepared [355] by vacuum desolvation of the monosolvated compounds. A direct desolvation of the acetates in vacuum at —150° C was attempted by Witt and Onstott [389] after dissolution of the rare earth oxides in 50 per cent acetic acid, and anhydrous acetates of definite composition were obtained for La, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y. 

Note. (1) iV,iV-Dimethylformamide is azeotropically distilled from toluene (Section 4.1.26, p. 409). 

A previously prepared sample of 2 (Tinnemans et al., 1984) was dissolved in dimethylformamide and it was attempted to remove water by azeotropic distillation. Compound 2 was recovered unchanged, indicating the presence of coordinated water. The synthesis of compound 2 was carried out to give the correct product and elemental analysis. (Tait et al., 1978). 

Under less vigorous conditions the acyclic monoamide (—amic acid) is formed and this can usually be converted into the cyclic imide by treatment with a mild dehydrating agent such as acetyl or thionyl chloride [77]. Alternatively, the reactants may be refluxed with triethylamine in benzene or toluene and the water formed in the reaction removed by azeotropic distillation [78]. The phthaloyl group has also been introduced into a-amino acids by heating with 0-carbethoxy-thiobenzoic acid in JV,JV-dimethylformamide at 80° [79], or at room temperature with JV-ethoxycarbonylphthalimide in the presence of sodium hydroxide [80]. 

The principal route for production of isoprene monomer outside of the CIS is recovery from ethylene by-product C5 streams. This route is most viable where ethylene is produced from naphtha or gas oil and where several ethylene plants are located in relatively dose proximity to the isoprene plant. Although the yield of isoprene per mass of ethylene is quite low, there is enough ethylene produced to provide a large portion of demand. Because of the presence of -pentane in these streams which azeotropes with isoprene, extractive distillation must be used to recover pure isoprene. Acetonitrile is the most common solvent, but dimethylformamide is also used commercially. 

C under argon. Methanol was removed azeotropically at 56 °C at a fast rate and as the boiling point began to rise, the distillation rate was reduced to 4 drops/min. and heating continued for 15h. The polymer thus prepared precipitated out of cyclohexane. The powdery polymer was crystalline with a melting point (DSC) of 212 °C. It was insoluble in the usual organic solvents such as methylene chloride, chloroform, ether, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, and dimethylsulfoxide. 

Purification. For polymerization, butadiene that is at least 99 mol% pure is required. Although alkynes are the most troublesome impurities, separation of the butadiene from other C4 products is also necessary. Simple fractional distillation is effective for removing the light (C3) and heavy (C5) ends from butadiene, but not for removing the various C4 species because of the closeness of the boiling points to each other and to butadiene. Further complicating purification, butadiene forms azeotropes with re-butane and 2-butene. The most widely used recovery systems are extraction with aqueous cuprous ammonium acetate (CAA) and solvent extractions with furfural, acetonitrile, dimethylformamide, dimethylacetamide, or AT-methylpyrrolidinone (65,66). 

Figure 3.3.21 Extractive distillation of the azeotropic system cyclohexane and benzene at Benzene 1 bar (a) y-x diagram without (dotted line) and with (short-dashed line) addition of50mol.% dimethylformamide (DMF) note that the content of DMF is not counted, that is,xc6H6= 1 —xccHizi (b) typical process configuration. Adapted from Cmehling and Brehm (1996).

Polymer Synthesis. Polyethylene glycol (PEG) 600,1000, and 1500 were obtained from Aldrich Chemical Company and dried by azeotroping with toluene. Molecular weights for the polyethylene glycols were determined from hydroxyl numbers. DieSiylene glycol (DEG) from Fisher Scientific was purified by vacuum distillation over metallic sodium. Hexamethylene diisocyanate (HMDI) from Aldrich Chemical Company was vacuum distilled. Dicyclohexylmethane-4,4 -diisocyanate (DCDI) (Desmodur W) from Mobay Chemical Company was used as received. Dibutyltin bis-(2-ethylhexanoate) from Kodak was stored over phosphorus pentoxide. N,N-dimethylformamide (DMF) from EM Science and 4-methyl-2-pentanone from Aldrich Chemical Company were dried over 3A molecular sieves. 

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