Azeotrope-soluble extracts

To separate solutions of both liquids and of solids in a liquid (particularly water), two methods usually are considered first (1) vaporization—i.e., evaporation or distillation—to utilize the different relative volatilities of the components, either normally or accentuated by another liquid in azeotropic or extractive distillation and (2) liquid-liquid extraction to take advantage of the relative preferential solubility of one component in an added liquid. 

Total ChCl3 Soluble (Soxhlet) Hexane Soluble Portion of ChCl3 Extract Total Azeotrope Soluble (Soxhlet) Hexane Soluble Portion of Azeotrope Extract... 

The major advantage of the use of two-phase catalysis is the easy separation of the catalyst and product phases. FFowever, the co-miscibility of the product and catalyst phases can be problematic. An example is given by the biphasic aqueous hydro-formylation of ethene to propanal. Firstly, the propanal formed contains water, which has to be removed by distillation. This is difficult, due to formation of azeotropic mixtures. Secondly, a significant proportion of the rhodium catalyst is extracted from the reactor with the products, which prevents its efficient recovery. Nevertheless, the reaction of ethene itself in the water-based Rh-TPPTS system is fast. It is the high solubility of water in the propanal that prevents the application of the aqueous biphasic process [5]. 

The carotenoid extract obtained by extraction of fresh food with a water-soluble solvent contains large amounts of water from the sample. In order to remove the water and solvent, in the case of acetone, carotenoids are transferred to petroleum ether, diethyl ether, or a mixture by adding small portions of the solvent extract and a large amount of water in a separatory funnel. The remaining traces of water can be removed either by addition of anhydrous Na2S04 or ethanol to form the azeotropic mixture. 

Since the cis-diol 2 is very water soluble, a polar solvent such as butanol is required to extract it. Butanol forms an efficient water azeotrope. More conventional solvents may be used for less polar products. 

The solubility of tetracyanoethylene in chlorobenzene apparently increases sharply as the boiling point of the solvent is approached. Thus the crystals should be extracted in boiling chlorobenzene. Chlorobenzene may be conveniently dried by distilling until the distillate no longer runs cloudy (azeotrope, b.p. 90°, 28.4% water). 

Applications of the Karl Fischer method are numerous food stuffs (butter, margarine, powdered milk, sugar, cheese, processed meats, etc.), solvents, paper, gas, petroleum, etc. Before the determination can be made, solid components that are not soluble must either be ground into powders, extracted with anhydrous solvents, eliminated as azeotropes or heated to eliminate water. Problems are encountered with very acidic or basic media that denature reactants and transform ketones and aldehydes into acetals that interfere with the titration. Special reagents must be used in these instances. 

Trimethylborate forms an azeotropic mixture with the excess of methyl alcohol, which boils approximately at 55 °C. To separate the mixture and extract pure trimethylborate, there are several techniques to flush methyl alcohol with sulfuric acid to separate methyl alcohol with the help of calcium chloride, lithium chloride or other alcohol-soluble salts to distil methyl alcohol (in the form of azeotropic mixture with trimethylborate, which boils under a lower temperature than both components) with subsequent extraction of trimethylborate with mineral oil, etc. 

The EA-soluble phase was then extracted with NaHCOa (5% w/w, 10 x 200 mL) and the aqueous layer saved for isolation of the organic acids fraction. The solvent was removed from the remaining EA-soluble fraction, which contained the phenolic and neutrals (P/N) fractions, on a rotoevaporator until no EA distilled over. The EA was not dried prior to evaporation, but rather, water was azeotroped during the distillation. Final water contents of each fraction were 0.5 to 1.0% by weight. 

Table II. Sequential Extraction of Coals with CHCI3 (Soxhlet), CHCI3 Acetone Methanol, 47 30 23, Azeotrope (Soxhlet) and Separation of Hexane Solubles (Wt% maf Coal, Duplicates were Averaged)...

Before extraction, soil and sediment samples may be dried, for example, by freeze-drying — provided that volatile compounds are not to be analyzed — or by mixing with anhydrous sodium sulfate and extraction in a Soxhlet apparatus. It should, however, be noted that it has frequently been found advantageous to add low concentrations of water, and this is consistent with the finding that addition of water to dry soils inhibits sorption of PAHs (Karimi-Lotfabad et al. 1996). If wet samples are to be analyzed directly, acetonitrile, propan-2-ol, or ethanol may be employed first, and these may be valuable in promoting the chemical accessibility of substances sorbed onto components of the matrices the analyte may then be extracted into water-immiscible solvents and the water phase discarded. Alternatively, if the analyte is sufficiently soluble in, for example, benzene, the water may be removed azeotropically in a Dean Stark apparatus and the analyte then extracted with the dry solvent. Analytes may, however, be entrapped in micropores in the soil matrix so that, for example, recovery of even the volatile 1,2-dibromoethane required extraction with methanol at 75°C for 24 h (Sawhney et al. 1988). 

For the more sandy soils with low water content, toluene may be used successfully due to the solubility of toluene in water and the azeotropic mixture of water in toluene. An example of this is the determination of PAH (see ISO 13877). Soxhlet extraction with azeotropic mixtures e.g. acetone n-hexane (60-40% m/m, bp 50°C) may be very useful if a more polar extraction solvent is required. 

Considerable research was carried out in the 1980s using ethanol and isopropanol as oil extraction solvents. Ethanol is unusual because its oil solvating capacity is temperature and moisture-dependent. Oil solubility is relatively low at room temperature and moisture contents above the water alcohol azeotrope. Thus, the moisture content of the flakes must be in equilibrium with the alcohol (e.g., 2% for 95% ethanol and 7% for 91% isopropanol) (Wan Wakelyn, 1997), otherwise the solvency changes. Differences in oil solubility afford inexpensive means of oil separation from the solvent by merely cooling the miscella to separate an oil-rich phase without evaporating the bulk solvent. 

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