Precipitation separation

Sulphonamides. Mix together 1 0 g. of the dry acid or 1 - 2 g. of the anhydrous salt with 2 5 g. of phosphorus pentachloride f and heat under a reflux condenser in an oil bath at 150° for 30 minutes. Cool the mixture, add 20 ml. of dry benzene, warm on a steam bath and stir the solid mass well to extract the sulphonyl chloride filter. Add the benzene solution slowly and with stirring to 10 ml. of concentrated ammonia solution. If the sulphonamide precipitates, separate it by filtration if no solid is obtained, evaporate the benzene on a steam bath. Wash the sulphonamide with a little cold water, and recrystallise from water, aqueous ethanol or ethanol to constant m.p. 

Introduce a solution of 100 g. of sodium bisulphite in 200 ml. of water and continue the stirring, preferably for 10 hours with exclusion of air. A thick precipitate separates after a few minutes. Collect the bisulphite compound by suction filtration, wash it with ether until colourless, and then decompose it in a flask with a lukewarm solution of 125 g. of sodium carbonate in 150 ml. of water. Separate the ketone layer, extract the aqueous layer with four 30 ml. portions of ether, dry the combined organic layers over anhydrous magnesium sulphate, remove the ether at atmospheric pressure, and distil the residual oil under reduced pressure from a Qaisen flask with fractionating side arm (Fig. II, 24, 5). Collect the cyclo-heptanone at 64r-65°/12 mm. the yield is 23 g. 

Triiodobeiizoic acid. Dissolve 6-8 g. of 3 5-diiodo-4-aminobenzoic acid in 30 ml. of cold concentrated sulphuric acid, add a large excess (3 0 g.) of powdered sodium nitrite, and allow the mixture to stand at 0° for 2 hours. Treat the cold diazonium solution with a solution of 17 0 g. of potassium iodide in 40 ml. of water a dark red precipitate separates. Warm the mixture on a water bath until the evolution of nitrogen ceases, and remove any residual iodine with a little... 

A number of substances, such as the most commonly used sulfur dioxide, can reduce selenous acid solution to an elemental selenium precipitate. This precipitation separates the selenium from most elements and serves as a basis for gravimetry. In a solution containing both selenous and teUurous acids, the selenium may be quantitatively separated from the latter by performing the reduction in a solution which is 8 to 9.5 W with respect to hydrochloric acid. When selenic acid may also be present, the addition of hydroxylamine hydrochloride is recommended along with the sulfur dioxide. A simple method for the separation and deterrnination of selenium(IV) and molybdenum(VI) in mixtures, based on selective precipitation with potassium thiocarbonate, has been developed (69). 

Freshly distilled cyclohexanone (10.8 g., 0.11 mole) is now added dropwise. The solution becomes colorless and a white precipitate separates. The mixture is heated under reflux overnight, allowed to cool to room temperature, and the prcciiiitate... 

When a precipitate separates from a solution, it is not always perfectly pure it may contain varying amounts of impurities dependent upon the nature of the precipitate and the conditions of precipitation. The contamination of the precipitate by substances which are normally soluble in the mother liquor is termed co-precipitation. We must distinguish between two important types of co-precipitation. The first is concerned with adsorption at the surface of the particles exposed to the solution, and the second relates to the occlusion of foreign substances during the process of crystal growth from the primary particles. 

Altman and King made the first detailed study of this system, using Cr(ril) solutions containing only the monomeric species and Cr(VI) solutions which had been allowed to age. The isotopic method and lead chromate precipitation separation were used to obtain kinetic data at a temperature of 94.8 °C. Over the range of concentrations, Cr(VI) 2.3x10 to 8.4x10 A/, Cr(III) 1.8x10 to... 

It is well established that primary amino-functional groups, particularly aliphatic ones, react instantaneously with isocyanates to form ureas at ambient temperature. Indeed this was observed when 6-aminoethylferrocene (3) and freshly distilled phenylisocyanate were shaken vigorously. A yellow precipitate separated out immediately. Elemental analysis and an IR spectrum of the product indicate this compound to have the structure 6. ... 

Sample Reagents Environment Chemical suppression or Elimination Masking agents Precipitation Separation Extraction Volatilization Chromatography Alternate analytical technique... 

Behaviour towards Alkalis.—Add a few drops of sodium hydroxide solution to the aqueous solution of a basic triphenylmethane dye. For a short time the colour remains unchanged, but soon fades and at the same time a faintly coloured flocculent precipitate separates. In all cases this is the carbinol to which repeated reference has already been made when pure it is colourless. In the case of crystal violet the carbinol is [(CHg N.CgHJjCOH. 

Precipitation by ethanol in the cold was used effectively by J.Mellanby in 1908 to obtain diptheria antitoxin two years later Hardy and Gardiner reported the precipitation of plasma proteins by cold ethanol or acetone. The resulting proteins remained soluble in water, i.e. they were not denatured, and subsequent estimation of protein as nitrogen was helped by the use of nitrogen-free precipitants. Separations using organic solvents were considerably extended by Edsall,... 

Solvent extraction Solvent extraction Absorption/ precipitation Separate unsaturated oils Gas oil, reformate, distillate High-octane gasoline... 

The 20/80 PHBA/diol ratio oligomer was soluble in MIBK. The 30/70, 60/40, 50/50 and 40/60 oligomers form stable, milky dispersions in MIBK. For example, a roughly 12% "solution" of the 40/60 diol was slightly milky, yet it readily passed through fine filter paper (Whatman 42). A 70% dispersion of this oligomer in MIBK retained its milky appearance for more than one year. No precipitate separated. 

The concentrated sodium ethoxide solution must be kept hot throughout the process otherwise a voluminous precipitate separates and the mixture congeals. 

Monammino-aurous Chloride, [Au(NIIs)]Cl.—When aurous chloride is dissolved in an aqueous solution of ammonia and the mixture acidified with hydrochloric acid a white crystalline precipitate separates the precipitate is unstable and cannot therefore be completely dried.3... 

From this salt the bromide, [Cr en2pn]Br3.3H20, is prepared by decomposing it with concentrated aqueous hydrobromie acid. A finely crystalline precipitate separates, which is recrystallised from water and alcohol in glistening yellow clusters. 

Dihydrazino - nickel Chloride, [Ni(N2H4)2]Cl2, is produced by mixing a hot aqueous solution of nickel chloride with 50 per cent, hydrazine hydrate, when a bluish-white precipitate separates which is washed with water and dried in vacuo. The substance is a bluish-white powder which is soluble in ammonia and in dilute acids.1... 

Tetrammino-iridous Chloride, [Ir(NH3)4]Cl2, is obtained by boiling diehloro-dianimino-iridium with excess of ammonia. On cooling a yellowish-white precipitate separates, which is decomposed with evolution of ammonia on boiling with water.1... 

Dichloro-tetrammino-iridium Chloride, [Ir(NH3)4Cl2]Cl.H20, is produced when dinitrito-tetrammino-iridium chloride is heated with ammonium chloride and concentrated hydrochloric acid for several hours. A yellow liquid is obtained, from which on evaporation a yellow crystalline precipitate separates containing the chloro-compound mixed with ammonium chloride. This is collected, dissolved in warm water, filtered, and allowed to crystallise on the addition of hydrochloric acid. It separates in yellow needles and prisms which are impure, but are purified on further reerystallisation from warm water containing acid. It loses water on heating, and finally leaves a residue of iridium. Concentrated hydrochloric acid does not attack the salt. 

Gis-dichloro-diammino-platinum, [Pt(NH3)2Cl2], was first prepared by Peyronne.2 It is easily formed by adding ammonia to a cold solution of platinous chloride in hydrochloric acid, when a greenish-yellow voluminous precipitate separates. This is boiled with water and filtered hot, when, on cooling the filtrate, the substance crystallises in yellow microscopic needles. It is sparingly soluble in water, and is more pure yellow than the isomeric trans-compound. Both cis- and fraws-dichloro-diammino-platinum are obtained on heating tetrammino-platinous chloride with hydrochloric acid. 

---