Room temperature azeotropes

Methyl Vinyl Ketone. Methyl vinyl ketone [78-94-4] (3-buten-2-one) is a colorless Hquid with a pungent odor. It is stable only below 0°C, and readily polymerizes on standing at room temperature. It can be inhibited for storage and transportation by a mixture of acetic or formic acid and hydroquinone or catechol (266). This ketone is completely soluble in water, and forms a binary azeotrope with water (85 MVK 15 H2O vol %) at 75.8°C. 

A colourless, odourless, neutral liquid at room temperature with a high dielectric constant. The amount of water present can be determined directly by Karl Fischer titration GLC and NMR have been used to detect unreacted propionic acid. Commercial material of high quality is available, probably from the condensation of anhydrous methylamine with 50% excess of propionic acid. Rapid heating to 120-140° with stirring favours the reaction by removing water either directly or as the ternary xylene azeotrope. The quality of the distillate improves during the distn. 

While esters do not usually react with enamines and can, in fact, be substituents in the azeotropic preparation of enamines, they can be used in acylation reactions when these involve intramolecular cyclizations. Such reactions have been observed even at room temperature when they lead to the formation of five- and six-membered vinylogous lactams (362). Applications to precursors for azasteroids (40S) and alkaloids (309,406) are key steps in synthetic sequences. 

To a solution of vanillin in toluene is added nitroethane, butylamine and glacial acetic acid. The mixture is refluxed and the water of reaction is steadily azeotropically removed by distillation. After the theoretical amount of water is distilled out, distillation Is continued to remove excess reactants. The last trace of excess reactants is then removed at room temperature under a vacuum. The product is then triturated with a hydrocarbon solvent such as Skellysolve B and is thus obtained in a crystalline state. In general, however, it is preferred to dissolve the residue directly In toluene for use in the next step, without isolating the 1-(2-nitropropen-1-y I )-4-hydroxy-3-methoxy benzene. 

B. 5-Hexynal. To a solution of 5.60 g. (0.050 mole) of 2,3-epoxycyclohexanone in 120 ml. of benzene in a 500-ml. round-bottomed flask is added 10.82 g. (0.051 mole) of trans-1 -amino-2,3 diphenylaziri-dine.2 Initially, after brief swirling at room temperature, the reaction mixture is a colorless, homogeneous solution however it rapidly turns yellow and cloudy due to separation of water. After 2 hours the benzene and water are removed as an azeotrope under reduced pressure on a rotary evaporator with the bath maintained at approximately 30°. The resulting crude mixture of diastereomeric hydrazones weighs 15.4 g. (Note 7) and is subjected directly to the fragmentation reaction (Note 8). 

The limitations of the reaction have not been systematically investigated, but the inherent lability of the aziridines can be expected to become troublesome in the case of epoxyketones which are slow to form hydrazones. The use of acid catalysis is curtailed by the instability of the aziridines, particularly the diphcnylaziridine, in acidic media. Because of their solvolytic lability, the hydrazones are best formed in inert solvents. A procedure proven helpful in some cases is to mix the aziridine and the epoxyketone in anhydrous benzene, and then to remove the benzene on a rotary evaporator at room temperature. Water formed in the reaction is thus removed as the azeotrope. This process is repeated, if necessary, until no carbonyl band remains in the infrared spectrum of the residue. 

Soya oil, 88.6 g, 20.0 g of pentaerythritol, and 0.06 g of lithium hydroxide monohydrate are weighed into a 250-mL three-necked round-bottom flask fitted with a magnetic stirrer, a Dean-Stark separator, and nitrogen inlet and outlet. The reaction mixture is heated to 250°C for 30 min under nitrogen (note a below), then cooled to 200°C. Phthalic anhydride, 34.6 g, 0.70 g of maleic anhydride, and 8.0 g of xylene are added. The reaction mixture is heated to 230°C and the toluene-water azeotrope is removed by distillation. The reaction is stopped when the acid number of reaction medium is lower than 10 (note b below). After cooling to room temperature, 52 g of white spirit is added. 

The flask was filled with the catalyst (50 mg) and anhydrous toluene (4 mL). The mixture was refluxed until 3.5 mL of solvent was recovered. The catalyst was azeotroped twice with toluene (4 mL) and then cooled to room temperature under argon. 

The ethanol-water azeotrope (95%ethanol-5%water) is an example of a minimum boiling azeotrope. Its boiling point is lower than that of the components (Fig. 143). If you ve ever fermented anything and distilled the results in the hopes of obtaining 200 proof (100%) white lightning, you d have to content yourself with getting the azeotropic 190 proof mixture, instead. Fermentation usually stops when the yeast die in their own 15% ethanol solution. At room temperature, this is point A on our phase diagram. When you heat the... 

Room-temperature solution polycondensation is used for the preparation of hexafluoroisopropylidene-unit-containing poly(azomethine)s. At the end of the reaction, the water liberated by the reaction is thoroughly taken off as an azeotrope by vacuum distillation to allow the reaction to go to completion. Among DMF, DMSO, HMPA, NMP, and m-cresol used as reaction solvents, m-cresol yields a polymer with higher reduced viscosity in higher yield. The reaction proceeds rapidly and is essentially completed in 30 min. 

To a vigorously stirred solution of 1,2-diaminoethane (60 g, 65 ml, 0.994 mol) in methanol (100 ml), at 0°C under nitrogen, was added a solution of (G = 0.5) dendri-PAMAM(C02Me)8 [3] (5 g, 0.004 mol) in methanol (20 ml). The addition was controlled such that the temperature did not rise above 40 °C. The mixture was stirred at room temperature for 96 h, after which time no ester groups were detectable by NMR spectroscopy. The methanol was removed by vacuum distillation at < 40 °C, and excess 1,2-diaminoethane was removed by azeotropic distillation using a mixture of toluene and methanol (9 1). The remaining toluene was removed by azeotropic distillation with methanol and... 

TBA-BH4 (Table 11.8) in CH2C12 (400 ml) is azeotropically dried by evaporation of ca. 250 ml of the CH2C12 under reduced pressure. The organic substrate (0.1 mmol) is added under argon and the mixture cooled to 0°C. The haloalkane (0.2 mol) (Table 11.8) is added dropwise and the mixture stirred for 30 min at room temperature. The excess boro-hydride is destroyed by the addition of EtOH (25 ml) and the solution is neutralized with HC1 (20%). The aqueous phase is separated and extracted with CH2C12 (2 x 20 ml). The combined organic solutions are washed with H20 (10 ml), dried (MgS04), and fractionally distilled to yield the reduced product. 

The solvent system 70/30 methylene chloride/ hexafluorolsopropanol has been In use In our laboratory since 1977 as a solvent for poly(ethylene terephthalate) (PET) and other semlcrystalllne polar polymers. Some advantages of this solvent are It provides rapid room temperature solubilization It Is transparent at 254 nm (U.V.) It Is a solvent for polystyrene and It Is a minimum boiling azeotrope. Disadvantages are Its low boiling point (36 C) and the potential safety hazard It represents. The combination of appropriate HPGPC equipment and this solvent system reveals heretofore unrecognized features of the molecular weight distributions of polyesters ... 

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