Solvent evaporation azeotrope

The latex can be concentrated by different means. One method consists of heating the latex under vacuum conditions to remove excess water and organic solvent by evaporation. In the case of an organic solvent forming azeotrope with water, the final concentration may be higher and the temperature of the treatment can be reduced. Using the concentrating treatment, the polymer content in the latex can be increased to 70% and the water content can be reduced to 2%. 

Oxidation procedure. The reagent is freed from residual water by azeotropic distillation with benzene (CAUTION). The compound to be oxidised is then added and refluxed in benzene (c. 200ml for 0.5-2.0g of compound). At the end of the reaction (determined by t.l.c. monitoring), the solid phase is filtered off and the solvent evaporated. The product is usually highly pure and recrystallisation is unnecessary. With 2,6-dimethylphenol the molar ratio of phenol to silver carbonate is 1 4.4, and the reaction time is half an hour in this case 3,3, 5,5 -tetramethyldiphenoquinone is obtained in 98 per cent yield and has m.p. 217-218 °C. With 2,4,6-trimethylphenol, using the same molar ratio of phenol to oxidant, and a reaction time of 2 hours, 3,3, 5,5 -tetramethylstilbenequinone is obtained in 93 per cent yield and having m.p. 227-228 °C. 

In 1993, a perfluorocarbon was used as a reaction solvent for azeotropic transesterification reactions of carboxylic acid esters. One of the ultimate goals of transesterification is the use of a 1 1 ratio of ester and alcohol. Such a 1 1 transesterification was recently achieved using a fluorous version of the Otera method, which is based on tetraalkyldistannoxane. For example, octanol and ethyl 3-phenylpropionate were added to an FC-72 solution containing fluorous stannoxane [(C6Fi3CH2CH2)2SnO] 15. The mixture was then sealed and heated at 150°C for 16h. When the mixture was cooled, phase separation occurred and octyl 3-phenylpropanoate was obtained by separation and evaporation of the upper layer (Scheme 19). The lower FC-72 layer, which contained the catalyst, was used more than 20 times without any loss in catalytic activity. ... 

Blushing, Gloss, and Flow Properties. When the solvents evaporate from a paint the latter cools. At high atmospheric humidity water droplets condense if the temperature of the paint surface is below the dew point. This water is absorbed and homogeneously distributed in paints that contains solvents that are able to absorb water (e.g., ethanol or glycol ether). If the paint does not contain such solvents the water remains on the surface as a visible white haze (blushing). Blushing disappears if the paint contains solvents that form volatile azeotropes with water (e.g., aromatic hydrocarbons or butanol). 

Water can be removed from the polymerization system by thin-layer evaporation, azeotropic distillation with suitable solvents, under vacuum, or by reaction at elevated temperatures. At higher temperatures, however, side reactions tend to occur. The application of vacuum, particularly at low conversions, may remove volatile reactants as well as the water, which destroys the equivalence in the case of different volatilities of the two reactants. The combination of these events is responsible for the fact that there is a limit in the extent to which the equilibrium can be shifted in the direction of polyester. Other reasons are the partial vapor pressure of the water and, considering the macrokinetics (high melt viscosity), the time required for the diffusion of water from the reaction system. 

Thus, numerous papers have been published in the literature on lipase-catalyzed condensation polymerizations using activated diacids, such as vinyl esters (3,4). Whereas these polymerizations are facile, they are not conunercially viable due to the cost of the activated diacids. The methyl ester has been attempted (X = CH3) however, the reaction tends to be sluggish. The reaction for the carboxylic acid (X = H) is even more sluggish and is only practical with the removal of water through evaporation, azeotropic distillation, or chemical drying (2a,3). Most of these reactions are carried out in non-aqueous media, e.g., in bulk (neat) or in polar aprotic solvents. Recently, much progress has been made on this type of polymerizations (5). 

Sodium di(ethylhexyl)sulfosuccinate (Aerosol-OT) [577-11-7] M 444.6. Dissolved in MeOH and inorganic salts which ppted were filtered off. Water was added and the solution was extracted several times with hexane. The residue was evaporated to one fifth its original volume, benzene was added and azeotropic distillation was continued until no water remained. Solvent was then evaporated. The white solid was crushed and dried in vacuum over P2O5 for 48h [El Seoud and Fendler J Chem Soc, Faraday Trans I 71 452 /9751. 

To a stirred and refluxing solution of 40 parts of benzene and 35 parts of dimethylformamide (both solvents previously dried azeotropically) are added successively 1.6 parts of sodium hydride and 7.7 parts of Ct-(2,4-dichlorophenyl)imidazole-1-ethanol, (coolingon ice is necessary). After the addition is complete, stirring and refluxing is continued for 30 minutes. Then there are added 7.8 parts of 2,6-dichlorobenzyl chloride and the whole is stirred at reflux for another 3 hours. The reaction mixture is poured onto water and the product 1-[2,4-dichloro-/3 (2,6-dichlorobenzyloxy)phenethyl] imidazole, is extracted with benzene. The extract is washed twice with water, dried, filtered and evaporated in vacuo. The bese residue is dissolved in a mixture of acetone and diisopropyl ether and to this solution is added an excess of concentrated nitric acid solution. The precipitated nitrate salt is filtered off and recrystallized from a mixture of methanol and diisopropyl ether, yielding 1-[2,4-dichloro- (2,6-dichlorobenzyl-oxv)phenethyl] imidazole nitrate melting point 179°C. 

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. 

Octahydro-l,l -bi-2-naphthol (1.5g, 5.1 mmol) was placed in a three-necked round-bottomed flask, and dried azeotropically with toluene (3 X 30 mL), and then the solvent was evaporated. 

Dilution of urine with acetonitrile, azeotropic distillation for water removal, evaporation of solvent, redissolution in acetone and derivatization using pentafluorobenzyl bromide. 

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