Saturation of the aqueous phase

Occasionally when aqueous solutions, and particularly suspensions, are extracted with an organic solvent very unpleasant emulsions make a clean separation impossible. The most effective way of avoiding this difficulty is to mix the liquids carefully. Further remedies are creation of a vacuum in the separating funnel, addition of a few drops of alcohol, saturation of the aqueous phase with common salt,. . . and patience. 

Three primary photochemical reactions contribute to the overall mechanism of methanol degradation depending strongly on the special reaction conditions, i.e. on the initial concentration of methanol and on molecular oxygen saturation of the aqueous phase ... 

In addition, saturation of the aqueous phase with NaCl lowers the solubility of R2S3, which is then more rapidly extracted into the organic phase. ... 

A subsequent study showed that at a given aqueous saturation, the permeability of the aqueous phase was the same whether or not foam was present (53). Foam decreased aqueous permeabilities by increasing the saturation of trapped gas (thus decreasing the saturation of the aqueous phase). The reduction of aqueous permeability was found to last during the passage of many (10 to 25) pore volumes of surfactant-free water. 

Saturation of the Aqueous Phase With Calcite or Dolomite. Tables similar to Table III for the degree of saturation of calcite, CaC03, and for dolomite, CaMg(C03)2, were calculated, and the results were quantitatively represented by the equation... 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

Transfer the residue derived from Section 6.1.1 or 6.1.2 into a 200-mL separatory funnel with 80 mL of water and add 5 g of sodium chloride. Adjust the pH of the aqueous phase to 6-8 with saturated aqueous sodium hydrogencarbonate solution. Extract the aqueous phase successively with 50 and 30 mL of dichloromethane by shaking the funnel with a mechanical shaker for 5 min. Combine the dichloromethane extracts and dry with anhydrous sodium sulfate. Transfer the extracts into a 100-mL round-bottom flask and concentrate the extracts to near dryness by rotary evaporation. Dissolve the residue in 2 mL of n-hexane. 

Discard the supernatant and resuspend the pellet in 650 1 RNase-free water. Add an equal volume of water-saturated phenol chloroform (5 1), pH 5.2. Vortex vigorously and spin at top speed for 5 min at room temperature. Take 500 pi of the aqueous phase into a new microtube tube. 

Since the solubility of octanol in water is only 0.0045M (9), the molar volume of the aqueous phase saturated with purg octanol can be approximated by the molar volume of pure water (V = V ). 

Comparing these results with the half-equilibration time of the aqueous phase, tm (see table above) we conclude that the aqueous concentration reaches its saturation value well before the exchange process switches from the boundary-layer-controlled to the NAPL-diffusion-controlled regime. Thus, diffusive transport of the diesel components from the interior of the NAPL to the boundary never controls the transfer process. Consequently, the simplex box model described in answer (a) is adequate. 

The heavier chlorocyclohexanone layer is separated and combined with three 150-ml. ether extracts of the aqueous phase, and washed with 150 ml. of water and then with 200 ml. of saturated sodium chloride solution. After filtration (gravity) through anhydrous sodium sulfate the ether is removed and the residue vacuum-distilled in a modified Claisen flask. The fraction (300-340 g.) boiling below 100° at 10 mm. (Note 5) is collected (Note 6). This material is then fractionated carefully under reduced pressure by means of a 42-in. modified Vigreux column (heated) with a total condensation variable takeoff head (Note 7). The yield of 2-chlorocyclohexanone boiling at 90-91°/14-15 mm. is 240-265 g. (61-66%) (Notes 8 and 9). 

It has been found satisfactory to continue the extraction for 30 minutes after the volume of the aqueous phase no longer decreases visibly. Saturated aqueous sodium bicarbonate washes may be used to effect removal of the acetic acid from ether solutions of alkyl quinones. The cascade distribution apparatus devised by Kies and Davis4 is useful for this purpose. As halo-genated quinones have been found to be unstable to bicarbonate, the acetic acid must be removed before oxidation of the corresponding aminophenols. 

Later work by Lin et al. overcame this problem by bubbling SC-C02 through a vessel containing TBP upstream of the extraction vessel43 Using this approach, super-saturation of the fluid phase by the extractant was avoided and a supercritical phase containing ca. 11% (on a molar basis)44 of TBP was consistently obtained (at 60°C and 120 atm pressure). This TBP-saturated C02 was then employed to extract uranyl and thorium ions from nitric acid solutions of various concentrations. The extraction of both ions increased with rising aqueous acidity, consistent with the extraction reactions observed in conventional systems (e.g., TBP-dodecane), such as that shown here for uranium ... 

Solubility normally is measured by bringing an excess amount of a pure chemical phase into contact with water at a specified temperature, so that equilibrium is achieved and the aqueous phase concentration reaches a maximum value. It follows that the fugacities or partial pressures exerted by the chemical in these phases are equal. Assuming that the pure chemical phase properties are unaffected by water, the pure phase will exert its vapor pressure Ps (Pa) corresponding to the prevailing temperature. The superscript S denotes saturation. In the aqueous phase, the fugacity can be expressed using Raoult s Law with an activity coefficient y ... 

After evaporation of the ether, a negligible residue remains, which is also different from the indications in the art. The pH-value of the aqueous phase is set to about 14 by saturating it with potash. The aqueous phase is repeatedly extracted with diethyl ether. The mixed ether extracts are evaporated to dryness, the remaining galanthamine-containing residue is dissolved in acetone (50 ml). In contrast to the art, there is no precipitate. 350 ml acetone is replenished, 200 g aluminum oxide is added, and stirring is effected for 45 min. The aluminum oxide is filtered off and washed twice with 100 ml acetone each time. The mixed acetone solutions are evaporated to dryness. 1.3 g of an oily residue is obtained which is examined by means of HPLC. 

The combined aqueous layers of several runs are saturated with potassium hydroxide by adding KOH pellets with cooling. DDB separates on top of the aqueous phase and is extracted with ether. Distillation leads to —90% recovery (bp 42-43°C/0.05 mm). 

Thomlinson [12] was the first chromatographer to note that the classical electrostatic ion-pair concept did not hold for bulky lipophilic IPRs he also emphasized that in the region between the mobile and stationary phases, the dielectric constant of the medium is far lower than that of the aqueous phase. It is now clear that water-enforced pairing effects [13] include hydrophobic attraction between hydrophobic moieties of the pairing ions and dielectric saturation actually the water-enforced pairing effects were demonstrated to be more important than electrostatic attraction even in a water-methanol system [14],... 

Enhanced oil recovery always deals with two or more fluids. By implication these fluids are conjugate phases in equilibrium with each other, although Chapter 6 shows that nonequilibrium mixing can sometimes be important when surfactants are used. When one considers the role of the critical micelle concentration (CMC) in CO2 mobility control, it is the CMC of the aqueous phase saturated with CO2 that is important. As illustrated in Figure 10, this CMC may be much lower than the CMC of C02 free surfactant solutions (R. S. Schechter, University of Texas, personal communication, October 26, 1987). 

---