Dimethylformamide, purification

Other options for the purification of CA include dissolution in hot water, aqueous ammonia, aqueous formaldehyde, or hot dimethylformamide followed by filtration to remove most of the impurities. The CA is recoverable by cooling the aqueous solution (84), acidifying the ammonium hydroxide solution (85), or cooling the dimethylform amide solution with further precipitation of CA by addition of carbon tetrachloride (86). Sodium hydroxide addition precipitates monosodium cyanurate from the formaldehyde solution (87). 

A mixture of 50 g of betamethasone, 50 cc of dimethylformamide, 50 cc of methyl orthobenzoate and 1.5 g of p-toluenesulfonicacid Is heated for 24 hours on oil bath at 105°C while a slow stream of nitrogen is passed through the mixture and the methanol produced as a byproduct of the reaction is distilled off. After addition of 2 cc of pyridine to neutralize the acid catalyst the solvent and the excess of methyl orthobenzoate are almost completely eliminated under vacuum at moderate temperature. The residue Is chromatographed on a column of 1,500 g of neutral aluminum oxide. By elution with ether-petroleum ether 30 g of a crystalline mixture are obtained consisting of the epimeric mixture of 170 ,21 -methyl orthobenzoates. This mixture is dissolved without further purification, in 600 cc of methanol and 240 cc of methanol and 240 cc of aqueous 2 N oxalic acid are added to the solution. The reaction mixture is heated at 40°-50°C on water bath, then concentrated under vacuum. The residue, crystallized from acetone-ether, gives betamethasone 17-benzoate, MP 225°-231°C. 

While water has been used as a solvent more than any other media, nonaqueous solvents [e.g., acetonitrile, propylene carbonate, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or methanol] have also frequently been used. Mixed solvents may also be considered for certain applications. Double-distilled water is adequate for most work in aqueous media. Triple-distilled water is often required when trace (stripping) analysis is concerned. Organic solvents often require drying or purification procedures. These and other solvent-related considerations have been reviewed by Mann (3). 

Soluble support-based synthetic approaches offer the advantages of both homogeneous solution-phase chemistry (high reactivity, ease of analysis) and solid-phase synthesis (large excess of reagents, simple product isolation and purification) [98,99]. As a representative example, PEG, one of the most widely used soluble polymers, has good solubility in most organic solvents (i.e., dichloromethane, acetonitrile, dimethylformamide, and toluene), but it... 

In a similar way, reaction of 2,4-dichloro-l,3,5,6-tetramethylborazine with N,N-dimethylformamide and dimethylamine gives a 36-membered macrocyclic oligoborazine 7 with six borazine rings linked by oxygen bridges (Fig. 2). Again, purification through several vacuum sublimations is necessary and yields are quite low [19]. 

Catalytic incineration has been appHed in the abatement of chlorinated VOC emissions in the pharmaceutical industry. The major compounds in the emission mixture are dichloromethane, perchloroethylene, dimethylformamide, oxitol, and toluene. The incinerator operates normally at 400-500 °C, but when emissions contain perchloroethylene the temperature is increased up to 500-600 °C. The emission mixture also contains water, which pushes the selectivity further toward HCl formation instead of formation of CI2. After oxidation, the product gases are washed with NaOH scrubbers. The purification level of over 99% can be achieved with the incinerator, the activity of which has been shown to be very stable after one year of continuous operation [69-71]. 

The groups of Giacomelli and Taddei have developed a rapid solution-phase protocol for the synthesis of 1,4,5-trisubstituted pyrazole libraries (Scheme 6.194) [356]. The transformations involved the cyclization of a monosubstituted hydrazine with an enamino-/8-ketoester derived from a /8-ketoester and N,N-dimethylformamide dimethyl acetal (DMFDMA). The sites for molecular diversity in this approach are the substituents on the hydrazine (R3) and on the starting j3-keto ester (R1, R2). Subjecting a solution of the /8-keto ester in DMFDMA as solvent to 5 min of microwave irradiation (domestic oven) led to full and clean conversion to the corresponding enamine. After evaporation of the excess DMFDMA, ethanol was added to the crude reaction mixture followed by 1 equivalent of the hydrazine hydrochloride and 1.5 equivalents of triethylamine base. Further microwave irradiation for 8 min provided - after purification by filtration through a short silica gel column - the desired pyrazoles in >90% purity. 

Treatment of the CH-acidic carbonyl compound with 1.5-2.5 equivalents of D M F D EA in N, N-dimethylformamide at 180 °C resulted in full conversion to the enam-ine synthons within 5 min. The enamines were obtained in 53-93% yield (based on LC-MS analysis) and were used without further purification in the next step. 

This highly exothermic reaction often has an induction period the end of which is characterized by a rapid temperature rise dependent on the amount of dibromide already added. At the first sign of reaction (watch the thermometer closely), addition of dibromide should be stopped and should be resumed only after the temperature has stopped rising. Careful purification of the dimethylformamide appears to minimize the induction period. 

Dimethylformamide (DMF), dioxane, piperidine, methylene chloride, acetonitrile, trimethyl orthoformate (TMOF), sodium borohydride, diisopropylcarbodiimide, and trifluoroacetic acid (TFA) were purchased from Aldrich Chemical Company, Inc. and used without further purification. All of the diversity reagents were purchased from Aldrich except for Fmoc-glycine-OH, which was purchased from Novabiochem. 

The submitters used ethyl formate, 97%, available from Janssen Chimica, without further purification. Dimethylformamide (DMF) can be used instead of ethyl formate with the same operating conditions. The checkers used ethyl formate (99%), available from Aldrich Chemical Company, Inc., without further purification. 

Baker reagent grade dimethylformamide was used without further purification. 

Tributyl amine, palladium acetate, triphenyl phosphine from Fluka AG and N,N-dimethylformamide and formic acid from Farmitalia Carlo Erba Chemicals were used without further purification. 

In one study of the effects of additives,9 it was found that on electrochemical oxidation of rubrene, emission was seen in dimethylforma-mide, but not in acetonitrile. When water, n-butylamine, triethylamine, or dimethylformamide was added to the rubrene solution in acetonitrile, emission could be detected on simply generating the rubrene cation.9 This seems to imply that this emission involves some donor or donor function present in all but the uncontaminated acetonitrile system. The solvent is not the only source of impurity. Rubrene, which has been most extensively employed for these emission studies, is usually found in an impure condition. Because of its relative insolubility and its tendency to undergo reaction when subjected to certain purification procedures, and because the impurities are electroinactive and have relatively weak ultraviolet absorptions, their presence has apparently been overlooked, They became evident, however, when quantitative spectroscopic work was attempted.70 It was found, for example, that the molar extinction coefficient of rubrene in benzene at 528 mjj. rose from 11,344 in an apparently pure commercial sample to 11,980 (> 5% increase) after repeated further recrystallizations. In addition, weak absorption bands at 287 and 367 m, previously present in rubrene spectra, disappeared. 

Technical-grade dimethylformamide is stirred over anhydrous cupric sulfate, filtered, and distilled under reduced pressure. The submitters used reagent-grade dimethylformamide without purification. 

Eluent solution (DMF +0.1M LiBr) for GPC analysis was prepared with HPLC grade dimethylformamide (Burdick and Jackson) and lithium bromide (Fisher Scientific Co.), which were used without further purification. 

Exposures to dimethylformamide occur during its production and during the production of inks, adhesives, resins, fibres, pharmaceuticals, synthetic leather, and its use as a purification or separation solvent in organic synthesis. It has been detected in ambient air and water. 

Chemicals and Standard Solutions. Cyclohexanone, cyclohexanol, 1,3,5-trichlorobenzene, 1,2,4-trichlorobenzene, phenol, 4-methylphenol, 4-chloro-phenol, 1,2,3,4-tetrahydroisoquinoline, 1-chlorohexane, 1-chlorododecane, and 1-chlorooctadecane were obtained from Aldrich. Acetone, tetrahydrofuran, ethyl acetate, toluene, dimethyl sulfoxide, and methanol were obtained from J. T. Baker. Distilled-in-glass isooctane, methylene chloride, ethyl ether, and pentane were obtained from Burdick and Jackson. Analytical standard kits from Analabs provided methyl ethyl ketone, isopropyl alcohol, ethanol, methyl isobutyl ketone, tetrachloroethylene, dodecane, dimethylformamide, 1,2-dichlorobenzene, 1-octanol, nitrobenzene, 2,4-dichlorophenol, and 2,5-dichlorophenol. All chemicals obtained from the vendors were of the highest purity available and were used without further purification. High-purity water... 

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 dimethylformamide. Dimethylacetamide, furfural, and... 

To improve the purification by adsorption TLC and to reduce the separation of positional isomers by RP-HPLC, Bandi and Ansari (51) reduced the polarity of the hydroxyl groups forming ferf-butyldimethylsiloxy derivatives of PNB esters of monohydroxy fatty acids (PNB-TBDMS-OHFA) (with terr-butyldimethylimidazole in dimethylformamide). 

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