Precipitation acidification

There are several methods to prepare amorphous silica by precipitation acidification of an aqueous solution of sodium silicate [9] or gelification of a silicon alkoxide solution [10]. As we want to use the same method to get the simultaneous coprecipitation of all the ions in the whole composition range, we choose to neutralize, by ammonia, a clear acid solution containing aluminum, phosphate and partially hydrolyzed tetraethylorthosilicate (TEOS). 

Schweizer s reagent The dark blue solution obtained by dissolving Cu(OH)2 in concentrated ammonia solution. Used as a solvent for cellulose, the cellulose is precipitated on acidification. Used in the cuprammonium process for the manufacture of rayon. 

Anhydrous cupric sulphate is white but forms a blue hydrate and a blue aqueous solution. The solution turns yellow when treated with concentrated hydrochloric acid, dark blue with ammonia, and gives a white precipitate and brown solution when treated with potassium iodide. A yellow-brown aqueous solution of ferric chloride becomes paler on acidification with sulphuric or nitric... 

Action of sodium hydroxide. Does not undergo the Cannizzaro reaction. It dissolves in dil. NaOH solution, giving a yellow solution from which the aldehyde is precipitated unchanged on acidification. If heated with cone. NaOH solution, salicylaldehyde slowly undergoes atmospheric oxidation to salicylic acid. 

B) Benzoyl derivatives. Most amino-acids can be benzoyl-ated when their solutions in 10% aqueous sodium hydroxide are shaken with a small excess of benzoyl chloride until a clear solution is obtained (Schotten-Baumann reaction, p. 243). Acidification of the solution then precipitates the benzoyl derivative and the excess of benzoic acid, and the mixture must be filtered off, washed with water, and recrystallised (usually from ethanol) to obtain the pure derivative. (M.ps., p. 555 )... 

The benzoic acid may be separated by steam distillation or by saturating the aqueous mixture of sodium salts with sulphur dioxide whilst maintaining the temperature below 40° the benzoic acid precipitates and can be separated by filtration or extraction with ether. Acidification of the filtrate with hydrochloric acid liberates the pyruvic acid. The pjTuvic acid may be oxidised < lth hydrogen peroxide to the arylacetic acid, for example ... 

Cool the flask in ice, acidify with 10 ml. of cold 1 1-hydro-chloric acid and distil under reduced pressure (water pump) until most of the alcohol is removed. Add water to the residue, extract several times with ether, wash the combined ethereal extracts with N ammonia solution until a test portion gives no precipitate upon acidification. Extract the combined alkahne solutions once with a fresh portion of ether, and add the aqueous solution to an excess of dilute hydrochloric acid the final mixture should still be acidic to Congo red. Collect the crystalhne half-ester by filtration at the pump, wash it with water and dry at 100°. The yield is 14-5 g., m.p. 122-125°. Recrystallise by dissolving in about 40 ml. of warm benzene and adding an equal volume of petroleum ether (b.p. 40- 60°) 13 -5 g. of the colourless half-ester, m.p. 125-126°, are obtained. 

Lead styphnate monohydrate is precipitated as the basic salt from a mixture of solutions of magnesium styphnate and lead acetate followed by conversion to the normal form by acidification using dilute nitric acid (97—99). 

An alternative pretreatment for seawater is acidification of the bicarbonate followed by degasification to remove the carbon dioxide generated. The precipitation step for the seawater process is given by (76) ... 

Merthiolate/T4- )4-< 7 (3), sodium ethyLmercurithiosahcylate, known also as thimersol, is prepared from a 1 1 ratio of ethyhnercuric chloride/7(97-27-. and disodium thiosahcylate ia ethanol. After removal of the sodium chloride by filtration, the free acid is precipitated by acidification with dilute sulfuric acid. Purification is achieved by recrystallization from 95% ethanol, and the product, merthiolate, is obtained by neutralization with a stoichiometric amount of sodium hydroxide. 

These association reactions can be controlled. Acetone or acetonylacetone added to the solution of the polymeric electron acceptor prevents insolubilization, which takes place immediately upon the removal of the ketone. A second method of insolubiUzation control consists of blocking the carboxyl groups with inorganic cations, ie, the formation of the sodium or ammonium salt of poly(acryhc acid). Mixtures of poly(ethylene oxide) solutions with solutions of such salts can be precipitated by acidification. 

The need for low levels of 3-isomer in 2-thiophenecarboxyhc acid [527-72-0] which is produced by oxidation of 2-acetylthiophene [88-15-3] and used in dmg appHcations, has been the driving force to find improved acylation catalysts. The most widely used oxidant is sodium hypochlorite, which produces a quantity of chloroform as by-product, a consequence that detracts from its simplicity. Separation of the phases and acidification of the aqueous phase precipitate the product which is filtered off. Alternative oxidants have included sodium nitrite in acid solution, which has some advantages, but, like the hypochlorite method, also involves very dilute solutions and low throughput volumes. 

Hydrated Stannic Oxide. Hydrated stannic oxide of variable water content is obtained by the hydrolysis of stannates. Acidification of a sodium stannate solution precipitates the hydrate as a flocculent white mass. The colloidal solution, which is obtained by washing the mass free of water-soluble ions and peptization with potassium hydroxide, is stable below 50°C and forms the basis for the patented Tin Sol process for replenishing tin in staimate tin-plating baths. A similar type of solution (Staimasol A and B) is prepared by the direct electrolysis of concentrated potassium staimate solutions (26). 

Naphtolc Acid (4). 1 and pyndine 2 were heated on a water bath for a short time The product was dissolved in ElOH and precipitated with EtjO Recrystalhzation from 10 volumes ol water affoided pure a-naphthacyl pyndinium bromide 3 A solution of 3 (0 5 g IS mmol) m waler (40 mL), EtOH (12 mL) and 10 N NaOH (2 ml) after healing for 12 min on a waler bath, gave on acidification and extraction with EtzO 4 mp 160-162°C... 

Oden, S., "The Acidification of Air and Precipitation and Its Consequences in the Natural Environment." Ecology Committee, Bulletin No. 1, Swedish National Science Research Council, Stockholm, 1967. 

According to the submitter, acidification of the combined sodium bicarbonate washings with 10% hydrochloric acid yields a colorless precipitate of 6,7-dimethoxy-3-methylindene-2-car-boxylic acid, which is collected by filtration, washed, and dried yield, 3.4-3.Q g. (14-16%) m.p. 216-218°. 

If no precautions are observed, the reaction mixture rapidly darkens after acidification when exposed to air. The sulfur dioxide generated upon acidification of the sodium bisulfite largely prevents this discoloration however, the precipitated product should be collected without delay of more than a few hours. The sulfur dioxide used in the wash water also protects the product. 

Alternatively, Te or Te02 can be oxidized by Cr03/HN03 or by 30% H2O2 under reflux. Acidification of a tellurate with an appropriate precipitating acid offers a further convenient route ... 

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

The oxide (p. 1209), chalcogenides (p. 1210) and halides (p. 1211) have already been described. Of them, the only ionic compound is HgF2 but other compounds in which there is appreciable charge separation are the hydrated salts of strong oxoacids, e.g. the nitrate, perchlorate, and sulfate. In aqueous solution such salts are extensively hydrolysed (HgO is only very weakly basic) and they require acidification to prevent the formation of polynuclear hydroxo-bridged species or the precipitation of basic salts such as Hg(OH)(N03) which contains infinite zigzag chains ... 

The acetone was removed by evaporation in vacuo, and about 750 ml of water were added to dissolve the resulting residue. The solution was filtered. The potassium salt of N-p-ace-tylphenylsuifonyl-N -cyclohexylurea formed in the above reaction, being water-soluble, passed into the filtrate. Acidification of the filtrate with 6 N aqueous hydrochloric acid caused the precipitation of N-p-acetylphenylsulfonyl-N -cyclohexylurea which was collected by filtration. Recrystallization of the filter cake from 90% aqueous ethanol yielded purified N-p-acetylphenylsulfonyl-N -cyclohexylurea melting at about 188°-190°C. 

A solution of 163 g (0.1 mol) of 2-amino-5-chloroben2oxazole in 200 ml of 1 N HCI is refluxed until precipitation is complete. The resulting solid is collected by filtration, dissolved in 200 ml of 1 N NaOH and the solution extracted with 50 ml of ether. Acidification of the alkaline solution gives a precipitate which is purified by crystallization from acetone to give 2-hydroxy-5-chlorobenzoxazole melting at 191° to 191.5°C. 

This material is then dissolved in pyridine. Benzenesulfonylchloride is added and the resulting mixture is heated two hours to 60°C. It is then poured into 300 ml water. The precipitate formed thereby Is filtered off and dissolved in dilute ammonium hydroxide. The solution is purified with charcoal, and filtered. The filtrate is acidifed with acetic acid to give glymidine. 

B) A solution of (SM) (330 mg) in trifluoroacetic acid (7 ml) was kept under nitrogen at room temperature for 15 minutes. Ether (100 ml) was added and the precipitate was filtered, washed thoroughly with ether and dried. This material (300 mg) was added in portions to concentrated sulfuric acid (18 ml) cooled at -20°C with vigorous stirring. After 15 minutes a solution of potassium bisulfate in concentrated sulfuric acid (408 mg in 3 ml) was added. The reaction mixture was stirred for 75 minutes at -15°Cand then stored at -7°Cfor 285 minutes. The sulfuric acid solution was poured into cold ether (400 ml) precipitate was filtered, washed with cold ether, and suspended in cold water. Complete solution was then achieved by careful addition of 2N sodium hydroxide. Acidification with N hydrochloric acid led to the precipitation of the desired octapeptide sulfate ester. Yield 200 mg. 

By heating the diacetyl compound with sodium hydroxide solution partial saponification of the acetyl groups takes place. 25.6 grams of diacetyl compound are heated to boiling for some hours with 100 cc of 2 N sodium hydroxide solution. The precipitate produced by acidification of the solution with acetic acid is filtered off and treated with dilute sodium carbonate solution. The 4-aminobenzene-sulfonacetylamide passes into solution while the simultaneously formed 4-acetylaminobenzene-sulfonamide remains undissolved. It is filtered with suction and the filtrate again acidified with acetic acid. The 4-aminobenzene-sulfon-acetamide separates out and is recrystallized from water. It forms colorless lustrous rhombic crystals Of MP 1B1°C. 

The precipitate obtained by acidification with dilute hydrochloric acid is dissolved in an equivalent quantity of dilute ammonia solution (about 1 20), again treated with animal charcoal and reprecipitated with dilute hydrochloric acid. In this manner N-4-methyl-benzenesulfonyl-N -n-butyl-urea is obtained in analytically pure form in a yield of 70 to 80% of theory. It melts at 125° to 127°C (with decomposition). 

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