Precipitation from gas-saturated solutions

ASES aerosol solvent extraction system, GAS gas antisolvent precipitation, PGSS precipitation from gas-saturated solutions, RESS Rapid expansion of supercritical solutions, SAS supercritical... 

Additional Exercises Lead chromate, PbC rO, calcium phosphate, Ca3(PC>4)2 ferrous oxalate, Fe(C2C>4) sodium chloride, NaCl, precipitated from a saturated solution by HC1 gas, Richards and Wells, Revision of the atomic weights of sodium and chlorine, J. Am. Chem. Soc., 27, 459 (1905). 

Micronization with supercritical fluids - Crystallization - Rapid expansion - Gas anti-solvent Recrystallization - Precipitation with compressed anti-solvent - Solution-enhanced dispersion - Particles from gas-saturated solutions 80 - 300 fine particles and powders from various products and of designed properties... 

Toluenesulfonic acid [6192-52-5] M 190,2, m 38 (anhydrous), m 105-107 (monohydrate), pK 1.55. Purify the acid by precipitation from a saturated solution at 0° by introducing HCl gas. It can also be crystallised from cone HCl, then crystallised from dilute HCl (charcoal) to remove benzenesulfonic acid. It has been crystallised from EtOH/water. Dry it in a vacuum desiccator over solid KOH and CaCl2. p-... 

Different precipitation processes based on supercritical carbon dioxide have been proposed in which CO2 performs different functions as solvent, in the rapid expansion of supercritical solutions (RESS) process, as antisolvent, in the supercritical antisolvent (SAS) process, or as solute, in the particles from gas saturated solutions (PGSS) process. 

Some examples of commercial active component production and production of substances with defined and uniform particle sizes (organic and inorganic materials) realized on pilot plant by using the RESS are given in Table 24.8. Other processes were also tested for synthesis of the particles with uniform size distribution as well as production of particles with specific structure (gas antisolvent recrystallization, GASR precipitation with a compressed antisolvent, PCA solution enhanced dispersion of solids, SEDS particles from gas-saturated solutions, PGSS) as shown in Table 24.9. All these processes are of special interest in pharmaceutical industry and in the production of different polymers. 

Both the nucleation of supercritical anti-solvent bubbles in a polymer+organic solvent-rich phase in the supercritical anti-solvent process (SAS) (or, equivalently, precipitation with a compressed antisolvent PCA) (e.g., [76]) and the nucleation of bubbles of a dissolved supercritical fluid from a saturated and nozzle-expanded solution containing a solute to be precipitated, in the formation of particles from gas-saturated solutions (PGSS) [77] are bubble nucleation problems, to which the above ideas apply. In the latter case, the nucleation of bubbles occurs simultaneously with that of solid particles within the bulk supersaturated solution. 

Homogeneous precipitation of particles from gas-saturated solutions (particle generation from saturated solutions (PGSS)). Applications are the powder production from molten polymers or fat compounds [46]. 

Equimolecular quantities of 4-butylaminobenzoic acid and the hydrochloride of p-dimethylaminoethanol are suspended in 10 times their joint weight of toluene. The mixture is saturated with hydrochloric acid gas and heated in an oil bath at about 150°C while a current of hydrochloric acid, gas is slowly passed through the mixture so that toluene slowly distils. Along with toluene the water produced by the esterification distils. After heating for about 10 hours the mixture is cooled and water is added until the salt is dissolved. The layer of toluene is separated and the ester base precipitated from the aqueous solution by means of a solution of sodium carbonate. By dissolving the base in ether, drying the ether solution separated over potassium carbonate and adding alcoholic hydrochloric acid, to the solution until it is neutral to litmus, the monohydrochloride is obtained in the form of a colorless crystalline powder which, when recrystallized from alcohol, melts at 147-148°C. 

Several tetrammino-derivatives of gold salts have been prepared. When dilute ehloraurie acid saturated with ammonium nitrate is added to a cold saturated solution of ammonium nitrate and the mixture treated with ammonia gas at ordinary temperature, a precipitate of fetrammino-auric nitrate, [Au(NH3)4](N03)3, is obtained. Tctrammino-aurie nitrate is soluble in water and may be crystallised from warm water. It may be precipitated from solution by the addition of any soluble nitrate, but with potassium, sodium, or ammonium nitrate it forms double salts. Thus, potassium nitrate if added to a concentrated solution of tetrammino-auric nitrate forms the compound [Au (NH 3).,] (NO 3)j.KNO. j, which crystallises from solution in needles. 

Hexammino-nickel Chloride, [Ni(NH3)6]Cl2.—Nickel chloride absorbs ammonia gas at ordinary temperature. Rise in temperature occurs and increase in volume. The hexammine is best prepared, however, from an aqueous solution of the salt, as when prepared from the dry salt and ammonia gas it is exceedingly bulky. Aqueous ammonia is added to a solution of pure nickel chloride until the nickel hydroxide first precipitated is almost dissolved. The liquid is filtered and a saturated aqueous solution of ammonium chloride containing ammonia added, and air drawn through the liquid. On the addition of a further quantity of ammonium chloride a precipitate forms, which is collected, washed with ammonium chloride and ammonia, and finally with alcohol containing ammonia. 

To 6.75 g (0.0225 mole) of 4-amino-2-chloro-5-(methylsulfamyl) benzenesulfonamide in 45 ml of dimethylformamide is added 4.86 g (0.03 mole) of dimethyl allylmercaptoacetal followed by 1.5 ml ethyl acetate saturated with hydrogen chloride gas. The solution is refluxed for 1.5 hours, cooled and added dropwise with stirring to ice/water. The resulting precipitate is filtered, dried and recrystallized from isopropanol. The recrystallization gave 4.0 g of 2-methyl-3-allylthiomethyl-6-chloro-7-sulfamyl-3,4-dihydro-l,2,4-benzothiadiazine-1,1-dioxide M.P. 168.5-170°C. 

Ethylenebis( e/ /-phosphine)palladium(0) complexes are air-sensitive but can be kept for months, when dry and pure, under inert gas in a refrigerator. They are soluble in organic solvents like benzene and toluene palladium may precipitate from the solutions, especially that of the triphenylphosphine complex, unless they are saturated with ethylene. Therefore, the complexes may be crystallized from toluene-diethyl ether mixtures saturated with ethylene. 

Solubility equilibria resemble the equilibria between volatile liquids (or solids) and their vapors in a closed container. In both cases, particles from a condensed phase tend to escape and spread through a larger, but limited, volume. In both cases, equilibrium is a dynamic compromise in which the rate of escape of particles from the condensed phase is equal to their rate of return. In a vaporization-condensation equilibrium, we assumed that the vapor above the condensed phase was an ideal gas. The analogous starting assumption for a dissolution-precipitation reaction is that the solution above the undissolved solid is an ideal solution. A solution in which sufficient solute has been dissolved to establish a dissolution-precipitation equilibrium between the solid substance and its dissolved form is called a saturated solution. 

Sulfide ion forms precipitates with heavy metal cations that have solubility products that vary from 10 ° to 10 °° or smaller. In addition, the concentration of S can be varied over a range of about 0.1 M to 10 M by controlling the pH of a saturated solution of hydrogen sulfide. These two properties make possible a number of useful cation separations. To illustrate the use of hydrogen sulfide to separate cations based on pH control, consider the precipitation of the divalent cation M from a solution that is kept saturated with hydrogen sulfide by bubbling the gas continuously through the solution. The important equilibria in this solution are ... 

---