Salt-out

SNG Substitute natural gas. soaps Sodium and potassium salts of fatty acids, particularly stearic, palmitic and oleic acids. Animal and vegetable oils and fats, from which soaps are prepared, consist essentially of the glyceryl esters of these acids. In soap manufacture the oil or fat is heated with dilute NaOH (less frequently KOH) solution in large vats. When hydrolysis is complete the soap is salted out , or precipitated from solution by addition of NaCl. The soap is then treated, as required, with perfumes, etc. and made into tablets. 

The crude acetonitrile contains as impurity chiefly acetic acid, arising from the action of phosphoric acid on the acetamide. Therefore add to the nitrile about half its volume of water, and then add powdered dry potassium carbonate until the well-shaken mixture is saturated. The potassium carbonate neutralises any acetic acid present, and at the same time salts out the otherwise water-soluble nitrile as a separate upper layer. Allow to stand for 20 minutes with further occasional shaking. Now decant the mixed liquids into a separating-funnel, run off the lower carbonate layer as completely as possible, and then pour off the acetonitrile into a 25 ml, distilling-flask into which about 3-4 g. of phosphorus pentoxide have been placed immediately before. Fit a thermometer and water-condenser to the flask and distil the acetonitrile slowly, collecting the fraction of b.p. 79-82°. Yield 9 5 g. (12 ml.). 

Or altcrmtiTclr add powdered sodium chloride w ith stirring in order to salt out" the araiuc, and then run off the lower aqiieous layer. 

The constant K is termed the distribution or partition coefficient. As a very rough approximation the distribution coefficient may be assumed equal to the ratio of the solubilities in the two solvents. Organic compounds are usually relatively more soluble in organic solvents than in water, hence they may be extracted from aqueous solutions. If electrolytes, e.g., sodium chloride, are added to the aqueous solution, the solubility of the organic substance is lowered, i.e., it will be salted out this will assist the extraction of the organic compound. 

In the isolation of organic compounds from aqueous solutions, use is frequently made of the fact that the solubility of many organic substances in water is considerably decreased by the presence of dissolved inorganic salts (sodium chloride, calcium chloride, ammonium sulphate, etc.). This is the so-called salting-out effect. A further advantage is that the solubility of partially miscible organic solvents, such as ether, is considerably less in the salt solution, thus reducing the loss of solvent in extractions. 

Divide the saturated solution of n-butyl alcohol in water into three approximately equal parts. Treat these respectively with about 2-5 g. of sodium chloride, potassium carbonate and sodium hydroxide, and shake each until the soli have dissolved. Observe the effect of these compounds upon the solubility of n-butanol in water. These results illustrate the phenomenon of salting out of organic compounds, t.e., the decrease of solubility of organic compounds in water when the solution is saturated with an inorganic compound. The alcohol layer which separates is actually a saturated solution of water in n-butyl alcohol. 

The experimental procedure to be followed depends upon the products of hydrolysis. If the alcohol and aldehyde are both soluble in water, the reaction product is divided into two parts. One portion is used for the characterisation of the aldehyde by the preparation of a suitable derivative e.g., the 2 4-dinitrophenylhydrazone, semicarbazone or di-medone compound—see Sections 111,70 and 111,74). The other portion is employed for the preparation of a 3 5-dinitrobenzoate, etc. (see Section 111,27) it is advisable first to concentrate the alcohol by dis tillation or to attempt to salt out the alcohol by the addition of solid potassium carbonate. If one of the hydrolysis products is insoluble in the reaction mixture, it is separated and characterised. If both the aldehyde and the alcohol are insoluble, they are removed from the aqueous layer separation is generally most simply effected with sodium bisulphite solution (compare Section Ill,74),but fractional distillation may sometimes be employed. 

The functions of the potassium carbonate are (a) to neutralise the acetic acid arising from the action of the phosphoric acid upon the acetamide, and (6) to salt out the otherwise soluble methyl cyanide as an upper layer. 

Treat the combined distiUates of b.p. 195-260° with anhydrous potassium carbonate to neutralise the Uttle formic acid present and to salt out the allyl alcohol. Distil the latter through a fractionating column and collect the fraction of b.p, up to 99° separately this weighs 210 g, and consists of 70 per cent, allyl alcohol. To obtain anli5 dious allyl alcohol, use either of the following procedures —... 

Separate the ketone layer from the water, and redistil the lattCT rmtil about one third of the material has passed over. Remove the ketone after salting out any dissolved ketone with potassium carbonate (5). Wash the combined ketone fractions four times with one third the volume of 35-40 per cent, calcium chloride solution in order to remove the alcohol. Dry over 15 g. of anhydrous calcium chloride it is best to shake in a separatory funnel with 1-2 g. of the anhydrous calcium chloride, remove the saturated solution of calcium chloride as formed, and then allow to stand over 10 g. of calcium chloride in a dry flask. Filter and distil. Collect the methyl n-butyl ketone at 126-128°. The yield is 71 g. 

The high sodium ion concentration results in facile crystallisation of the sodium salt. This process of salting out with common salt may be used for recrystallisation, but sodium benzenesulphonate (and salts of other acids of comparable molecular weight) is so very soluble in water that the solution must be almost saturated with sodium chloride and consequently the product is likely to be contaminated with it. In such a case a pure product may be obtained by crystallisation from, or Soxhlet extraction with, absolute alcohol the sul-phonate is slightly soluble but the inorganic salts are almost insoluble. Very small amounts of sulphones are formed as by-products, but since these are insoluble in water, they separate when the reaction mixture is poured into water ... 

An alternative method of purification, well adapted for large scale practice, is as follows. Dissolve the crude sulphapyridine in 1-05 mols of 30 per cent. u>/v sodium hydroxide, salt out the sodium derivative with excess of sodium chloride,... 

Step 4. The steam-volatile neutral compounds. The solution (containing water-soluble neutral compounds obtained in Step 1 is usually very dilute. It is advisable to concentrate it by distillation until about one-third to one-half of the original volume is collected as distillate the process may be repeated if necessary and the progress of the concentration may be followed by determination of the densities of the distillates. It is frequently possible to salt out the neutral components from the concentrated distillate by saturating it with solid potassium carbonate. If a layer of neutral compound makes its appearance, remove it. Treat this upper layer (which usually contains much water) with solid anhydrous potassium carbonate if another aqueous layer forms, separate the upper organic layer and add more anhydrous potassium carbonate to it. Identify the neutral compound. 

Some neutral compounds (e.g., methyl alcohol) cannot be salted out with potassium carbonate distillation of the saturated aqueous potassium carbonate solution frequently yields the organic compound in a comparatively pure state, or at least in sufllciently concentrated a form to enable certain derivatives to be prepared. 

Sa.lts Salting out metal chlorides from aqueous solutions by the common ion effect upon addition of HCl is utilized in many practical apphcations. Typical data for ferrous chloride [13478-10-9] FeCl2, potassium chloride [7447-40-7] KCl, and NaCl are shown in Table 9. The properties of the FeCl2-HCL-H2 0 system are important to the steel-pickling industry (see Metal SURFACE TREATMENTS Steel). Other metal chlorides that are salted out by the addition of hydrogen chloride to aqueous solutions include those of magnesium, strontium, and barium. 

Metal chlorides which are not readily salted out by hydrochloric acid can require high concentrations of HCl for precipitation. This property is used to recover hydrogen chloride from azeotropic mixtures. A typical example is the calcium chloride [10043-52-4] addition used to breakup the HCl—H2O azeotrope and permit recovery of HCl gas by distillation (see Distillation, azeotropic and extractive). 

The extent of extraction can be increased by a salting out effect. The selectivity of TBP is very poor compared with HDEHP and it is only useful for light rare-earth separation however, organic phase loadings or REO higher than 100 g/L can easily be achieved. There are a large number of TBP manufacturers in Japan, the United States, and Europe. 

In the production of sodium 3-hydroxy-2,7-naphthaIenedisulfonate/7Jj5 -j5 -J7 (R-salt) (38), 2-naphthol is stirred with excess 98 wt % sulfuric acid at 60°C, sodium sulfate is added, and the mixture is stirred and heated for 36 h at 105—122°C (77). The charge is diluted with water and salted out with ca 15 wt % sodium chloride at 60°C to give R-salt in 68% yield. 

Eor salt-out, add solute which reduces effective solubihty of component to be crystallised (salt having common ion is usual choice) salting-out compound should be cheap, as may be difficult to recover. 

Fast Color Salts. In order to simplify the work of the dyer, diazonium salts, in the form of stable dry powders, were introduced under the name of fast color salts. When dissolved in water they react like ordinary diazo compounds. These diazonium salts, derived from amines, free from solubilizing groups, are prepared by the usual method and are salted out from the solutions as the sulfates, the metallic double salts, or the aromatic sulfonates. The isolated diazonium salt is sold in admixture with anhydrous salts such as sodium sulfate or magnesium sulfate. 

Salting-out crystalli tion operates through the addition of a nonsolvent to the magma ia a crystallizer. The selection of the nonsolvent is based on the effect of the solvent on solubiHty, cost, properties that affect handling, iateraction with product requirements, and ease of recovery. The effect of a dding a nonsolvent can be quite complex as it iacreases the volume required for a given residence time and may produce a highly nonideal mixture of solvent, nonsolvent, and solute from which the solvent is difficult to separate. 

Arylalkylsulfones ate important intermediates obtained by alkylation of arylsulfinic acids. The latter ate obtained by reduction of the corresponding sulfonyl chloride. This reduction process is simple and of general appHcation involving the addition of the isolated sulfonyl chloride paste to excess aqueous sodium sulfite followed by salting-out the product and isolation. With mote rigorous reduction conditions, such as zinc/acid, sulfonyl chlorides ate reduced through to aryknercaptans, eg, 2-mercaptonaphthalene is manufactured from naphthalene-2-sulfonyl chloride. 

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