Ethanol/water/toluene mixture, azeotropes

At this time 270 ml. of toluene is added to the mixture and the condenser is changed for distillation. An azeotropic mixture of ethanol, toluene, and water is distilled at 75-78° with the bath at 105-110°. When the temperature begins to drop (Note 1), 525 ml. of commercial absolute ethanol is added and the mixture is again heated under reflux for 12-16 hours (Note 2). Again 270 ml. of toluene is added, and the azeotropic mixture is distilled until the vapor temperature falls to 68°. After the residue is cooled, the system is evacuated to 25-35 mm. and the remaining ethanol and toluene are distilled. 

By the reaction of concentrated solutions of nickel acetate and Hacac in an ethanol-water mixture the bis-aqua adduct [Ni(acac)2(H20)2] is obtained. An improved synthesis of the same compound has been devised starting from NiO(OH) which was reduced with Hacac at room temperature.1549 The green anhydrous Ni(acac)2 derivative is obtained by azeotropic distillation with toluene of the aqua complex or by its sublimation in vacuo. 

The mechanism for purification of recovered solvent depends on the nature of the material collected and the purity required. Where steam is used with water-immiscible solvents (e.g. toluene), purification can be done by simple decantation, but for water-soluble solvents, distillation is needed. Where water forms an azeotrope with the solvent (e.g. ethyl acetate) further complexity and cost is added to separate the mixture. With nitrogen desorption, purification can be simpler, but with mixed solvents which form azeotropes (e.g. ethyl acetate and ethanol) separation is still very difficult and costly. In this case, the cost of equipment needed to distil and purify the solvent can be higher than that for the recovery unit. 

Extractive distillation can be generally used to separate close boiling liquids or azeotropes, which cannot be separated through conventional distillation process. A solvent is introduced into the distillation column to alter the relative volatility of the feed components, and to avoid the formation of azeotropes. The extracted less volatile components leave from the bottom, whereas more volatile components come out as top products in pure form. Extractive distillation can replace conventional distillation or extraction processes resulting in improved separations, reduced capital investment and energy consumption. Industrially, extractive distillation can be implemented for binary separations resolving the close boiling mixtures, namely m-xylene/ o-xylene, methyl-cyclohexane/toluene, propylene/propane, 1-butane/1,3-butadiene, and azeotropic mixtures such as iso propylether/acetone, ethyl acetate/ethanol/water, MTBE/ethanol, etc. 

Place 146 g (1 mol) of adipic acid, 360 ml (285 g, 6.2 mol) of absolute ethanol, 180 ml of toluene and 1.5 g of concentrated sulphuric acid in a 1-litre round-bottomed flask, attach a short fractionating column connected to a downward condenser and heat in an oil bath at 115°C. When the acid has dissolved, an azeotropic mixture of alcohol, toluene and water commences to distil at 75 °C the temperature of the oil bath may then be lowered to 100-... 

The residue was subjected to azeotropic operation with toluene two times, and ether was added to the residue. The precipitate derived from trioxane was removed by filtration and washed with ether, and the combined ethereal solutions were concentrated under reduced pressure. The residue was dissolved in ethyl acetate, and the solution was washed with water and aqueous saturated solution of sodium chloride, was dried, and was concentrated to give 4 g of an oily material. The oily material was dissolved in 20 ml of methanol and to the solution was added 20 ml of aqueous 1 N solution of sodium hydroxide, and the mixture was stirred for 14 hours at room temperature. After removal of methanol under reduced pressure, water was added to the mixture, and this solution was acidified to pH 3 with aqueous 2 N hydrochloric acid. The mixture was extracted five times with ethyl acetate, and the ethyl acetate extract was dried and concentrated to give 3.5 g of crude crystals. After addition of ethanol to the crude crystals, the crude crystals were filtered. The filtrate was concentrated, and to the residue was added ethanol and ethyl acetate, and precipitate was collected by filtration. The combined amount of the crude crystals was 1.6 g. After the combined crude crystals were methylated with diazomethane, the reaction product was dissolved in 20 ml of ethyl acetate. To this solution was added 1.5 g of sodium acetate and 300 mg of 10% palladium-carbon, and the mixture was stirred for 2 hours under hydrogen. Then, the reaction product was filtered, and after addition of aqueous saturated solution of sodium hydrogen carbonate to the filtrate, the mixture was extracted two times with ethyl acetate. The extract was washed with an aqueous saturated solution of sodium chloride, dried, and concentrated to give 1.3 g of crude crystals. The crude crystals were recrystallized from ethyl acetate to yield 765 mg of the title compound (melting point 134-135°C, yield 43%). 

Typical mixtures that can be separated by a process such as this include mixtures of close-boiling aromatics and paraffins using ethanol or methanol as entrainers. The aromatics such as toluene form the higher-boiling azeotrope while the alcohol and the paraffins form the lower-boiling azeotrope. Water is used to remove the alcohol from the azeotropes by extraction. Finally, the alcohol must be separated from the water and recycled. From this standpoint, methanol is preferred over ethanol because the latter forms an azeotrope with water, thus complicating the ethanol recovery. 

In a fortunate case, distillation aimed at purification may also result in the drying of the solvent. Distillation may be particularly effective in the removal of moisture if azeotropic mixtures with low boiling points are formed. For instance, the first step in the dehydration of ethanol is distillation after the addition of benzene, when water is removed in the volatile ternary azeotrope. Other solvents may also be dehydrated by distillation, e.g., benzene, chloroform, carbon tetrachloride, ethylene dichloride, heptane, hexane, toluene and xylene. In distillations with the aim of dehydration, the apparatus must be fitted with moisture traps (containing calcium chloride, silica gel or some other drying agent). It must be borne in mind that many anhydrous organic solvents are hygroscopic. 

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