Supersaturated aqueous solutions

In this method a supersaturated aqueous solution of the racemate is inoculated with a crystal of one enantiomer of any other isomorphous crystal of a foreign substance, when this form of the isomer is precipitated. The resolution of glutamic acid by inoculation is now an industrial process. 

According to Equation 48 calcite should precipitate from waters having a Mg/Ca ratio below a certain value, while dolomite should precipitate from waters having a Mg/Ca ratio above that critical value. This rule is obeyed under conditions of precipitation from very slightly supersaturated aqueous solutions like those occurring in certain areas of the ocean. Ocean water is close to equilibrium with both calcite and dolomite (53). 

The experimental procedure was as follows. One litre of supersaturated aqueous solution was prepared, of which 0.8 was poured Into the crystallizer. After a constant temperature (of 298.2 K) was attained, the solution concentration was determined, and a seed crystal (0.59-0.71 mm) was put Into the solution and was allowed to grow for either 600 or 900 s. The crystal was then taken out of the crystallizer and put Into a 50 ml beaker In which a small quantity of alcohol was placed. The crystal was removed from the beaker and dried In the air for a few mlnltes, then Its weight and surface area were measured. The same crystal was again placed Into the crystallizer and allowed to resume growth. 

Soluble 1 in 300 of cold water, 1 in 20 of boiling water, 1 in about 60 of ethanol, and 1 in about 330 of chloroform very slightly soluble in ether soluble in glacial acetic acid. Phenazopyridine hydrochloride readily forms supersaturated aqueous solutions which deposit slowly on storage. 

Partitation chromatography and countercurrent distribution procedures were used for purification and crystallization of lincomycin hydrochloride (7 ). Anhydrous lincomycin hydrochloride is hygroscopic, consequently different crystal forms have been observed due to the degree of hydration. Crystallization of lincomycin hydrochloride from concentrated and supersaturated aqueous solution gave 70 - 90 inn size crystals (11). 

The reactor is a cylinder made of stainless steel (Fig. 1) (its length is 36 cm and its inner diameter is 10 cm). At the upper part it is connected to a vapor pressure reserve (4.5 L) containing a small amount of an ammonium sulfate supersaturated aqueous solution. This solution provides an 81% relative humidity atmosphere between toe temperature of 293 and 303 K. The vapor pressure reserve, connected to an exhaust valve, allows control of vapor pressure in the reacting area. The reactor, toe temperature of which is regulated at 398 K or 423 1 K, contains a sample holder with six specimens symmetrically disposed around toe axis. The sample holder is composed by two stainless steel disks (92... 

FIGURE 8.21 Phase diagram for the system Na02-Al203-H20 at four different temperatures. The precipitation of Gibbsite, Bayerite, Boehmite, and alumina from supersaturated aqueous solutions is dependent on the temperature. (From Wefers, K. and Misra, C., Report 19, Alcoa Laboratories, 1987, 44. With permission.)... 

Figure 1.26 Diffusion coefficients in aqueous KCl solutions at 25 °C (solution age = 24 h) in the metastable region, (Reproduced from Y.C. Chang and A.S. Myerson (1985), The Diffusivity of Potassium Chloride and Sodium Chloride in Concentrated, Saturated, and Supersaturated Aqueous Solutions, AIChE 7. 31, pp. 890 894. Used by permission of the American Institute of Chemical Engineers. 1985 AIChE.)...

When a supersaturated aqueous solution of this compound was left to stand at room temperature, spontaneous resolution took place... 

The use of selective seeding as a method for separating solutes in solutions supersaturated with two salts was proposed by Rousseau and O Dell (1980). Supersaturated aqueous solutions of potassium sulphate together with either potassium chloride or dichromate were seeded with one of the solutes to cause secondary nucleation of that substance. After recovering the developed crystals by filtration, the filtrate was seeded with the second solute to complete the separation. 

Melikhov, I.V. and Kelebeev, A.S. (1979) Coagulative growth of barium sulphate crystals from a strongly supersaturated aqueous solution. Soviet Physics Crystallography, 24, 239-241. 

Micelles with platelet or rod-like shapes were obtained in supersaturated aqueous solution containing a surfactant and an aromahc compound. In particular, chiral surfactants are known to produce enantiomeric precipitahon, while most of the others give symmetric micelles [45-47]. 

Prymak, O., Sokolova, V., Peitsch, T., Epple, M. he crystallization of fluoroapatite dumbbells fixrm supersaturated aqueous solution. Cryst. Growth Des. 6, 498 (2006)... 

Tran, T-T F. Lenzi, "Methods of estimating the water activity of supersaturated aqueous solutions". Can. J. Chem. Eng., v52, pp798-802 (1974)... 

Silica can be deposited molecularly from supersaturated aqueous solution. Supersaturation can be brought about by one of the following processes ... 

It was recognized by Pasteur, that the enantiomers of racemic tartaric acid can be sep>arted by induced crystallization, if the supersaturated aqueous solution of its sodium-ammonium salt was seeded with the crystals of a pure enantiomer. In this case significant amount of the pure enantiomer could be find in the solid phase and a mixture of enantiomers remaind in the saturated solution in which the other enatiomer was in excess. That other enantiomer... 

Omar, W., Al-Sayed, S., Sultan, A. and Ulrich, J. (2008) Growth rate of single acetaminophen crystals in supersaturated aqueous solution under different operating conditions. 43, 22-27. 

Rate-determining mechanism depends also on saturation index and pH. Rate-determining step for precipitation of salt minerals such as BaS04 from supersaturated aqueous solution is volume diffusion in aqueous solution, but surface reaction controls the precipitation when degree of supersaturation is small (Nielsen 1958). 

The most stable form is a-lactose monohydrate, C12H22O11 H2O. Lactose crystallizes in this form from a supersaturated aqueous solution at T < 93.5 °C. The crystals may have a prism-or pyramid-like form, depending on conditions. Vacuum drying at T > 100 °C yields a hygroscopic a-anhydride. Crystallization from aqueous solutions above 93.5 °C provides water-free P-lactose (P-anhydride, cf. Formula 10.10). Rapid drying of a lactose solution, as in milk powder production, gives a hygroscopic and amorphous equilibrium mixture of a- and P-lactose. 

The existence of uncharged ionic pairs, M HSO (M = Na, K, NH4), in supersaturated aqueous solution droplets was demonstrated by Fung and Tang [59]. Interestingly, close to the crystallization point, no evidence of free anion was found (i.e., the supersaturated solution is formed solely by ionic pairs eventually monohydrated). The main bisulfate Raman band (S—O symmetric stretching) moves from 1048 cm in solution to 1033 cm (supersaturated NaHSOJ, 1027 cm (supersaturated KHSO4), or 1020 cm (supersaturated NH4HSO4). 

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