Solid precipitates

Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

Thallium I) iodide. Til yellow or red solid precipitated from aqueous solution. 

Cadmiumdl) sulphide, CdS, is a canary-yellow solid, precipitated by addition of hydrogen sulphide (or sulphide ion) to an acid solution... 

If no solid precipitate is obtained but the solution becomes cloudy, a low-melting or liquid phenol is indicated this will, of course, be revealed also by the characteristic phenolic odour. Transfer to a separating-funnel and extract with an equal volume of ether. Separate and dry with anhydrous sodium sulphate. Distil off the ether and identify the residue. 

If no solid precipitate is obtained, an oil or an oily suspension, may be produced. Allow to stand, and then, if possible, separate the oil directly in a separating Tunnel and dry with solid KOH. If the volume of the oil is too small for such separation, extract with ether and then separate the ethereal solution, dry as before, filter, and distil off the ether. Distil the amine (if considered necessary) and identify. 

The above product (24 g, 0.067 mol) was dissolved in 90 10 dioxane-water (300 ml) and sodium borohydride (92.5 g, 0.067 mol) was added. The mixture was refluxed for 4h. The cooled solution was poured into 0.1 N HCl (1.11). A solid precipitated and was collected by filtration, dried and recrystallized from ether hexane to give 6,7-dibromo-4-methoxyindole (18.5 g, 90%). 

Ethyl 2-nitro-3-(5-benzyloxyindoT3-yl)propanoate (3.7 g, 0.01 mol) was dissolved in abs. ethanol (50 ml) and hydrogenated over PtO catalyst (EOg) until H2 uptake ceased (about 1.75 h). The solution was purged with nitrogen and 20% aq. NaOH solution (4.0 g) w as added. A hydrogen atmosphere was re-established and the hydrolysis was allowed to proceed overnight. The solution was diluted with water (20 ml) and filtered. The pH of the filtrate was adjusted to 6 with HOAc and heated to provide a solid precipitate. The mixture was cooled and filtered to provide 5-benzyloxytryptophan (2.64 g). 

Cloth Blinding Continuous filters, except for precoats, generally use some type of medium to effect the separation of the solid and filtrate phases. Since the medium is in contact with the process solids, there is always the danger, and almost invariably the ac tual occurrence, of medium blinding. The term blinding refers to blockage of the fabric itself, either by the wedging of process solids or by solids precipitated in and around the yarn. 

The following procedure is described in U.S. Patent 3,475,407. A solution of 50 g of lincomycin hydrochloride, 120 g of triphenylphosphine, and 500 ml of acetonitrile in a 3 liter flask equipped with a stirrer was cooled in an ice bath and 500 ml of carbon tetrachloride was added in one portion. The reaction mixture was then stirred for 18 hours without addition of ice to the cooling bath. The reaction was evaporated to dryness under vacuum on a 50° to 60°C water bath, yielding a clear, pale yellow viscous oil. An equal volume of water was added and the mixture shaken until all of the oil was dissolved. The resulting suspension of white solid (03PO) was filtered through a sintered glass mat and discarded. The filtrate was adjusted to pH 11 by addition of 6N aqueous sodium hydroxide. A solid precipitated. 

The catalyst was removed by filtration. The filtrate was diluted to about 18 liters, and was acidified with 15 ml concentrated hydrochloric acid. With vigorous stirring, 1,152 ml N KICI2 solution were run into the diluted filtrate over a period of about 20 to 30 minutes. A solid precipitate was formed, and was filtered off after about six hours. The sol id material was washed with water, with sodium bisulfite solution, and again with water. It was dissolved in aqueous ammonium hydroxide solution, the solution was filtered, and the filtrate was acidified with concentrated hydrochloric acid containing a small amount of sodium bisulfite. After a short time, the precipitate formed was filtered with suction, washed with water, and dried. 

A solution of 192 g 3-acetylamino-2,4,6-triiodophenol, sodium (0.35 mol) in 350 ml di-methylacetamide, was mixed with 107.5 g 3-(2-iodoethoxy)-2-ethylpropionic acid ethyl ester (0.35 mol) at 90°C with stirring over a period of about 20 to 30 minutes. Stirring was continued while the mixture was held at 95°C to 100°C for 16 hours. The solvent was then removed by distillation in a vacuum, and the residue was poured into 4,000 ml water. The solid precipitate formed was recovered and washed with water, dilute sodium carbonate solution, dilute sodium bisulfite solution, and again with much water. The ethyl ester was obtained in a yield of 220 g (90%). When recrystallized from 75% aqueous ethanol, it melted at 80°C to 86°C. 

To a slightly warm suspension of 3-acetoxy-7-chloro-5-(o-chlorophenyl)-1 3-dihydro-2H-1,4-benzodiazepin-2-one thus obtained was added 4N sodium hydroxide solution with stirring. All the solid dissolved and soon a thick white solid precipitated out. The solid was filtered, washed well with water and recrystallized from ethanol. The product was isolated as a solvate with 1 mol of ethanol. When heated it loses the ethanol of solvation and melts at 166°C to 168 C. 

To a suspension of 3.4 g of 3-acetoxy-7-chloro-1,3-dihydro-5-(o-chlorophenyl)-2H-1,4-benzodiazepin-2-one in 80 ml of alcohol was added 6 ml of 4 N sodium hydroxide. After complete solution had taken place a solid precipitated that redissolved upon the addition of 80 ml of water. The solution was acidified with acetic acid to give white crystals. After recrystallization from alcohol the compound melted at192°Cto 194°C. 

A solution of 3.1 g of (2-benzoyl-4-chlorophenyl-carbamoylmethyl)carbamic acid benzyl ester in 30 cc of 20% hydrobromic acid in glacial acetic acid was stirred for 45 minutes at room temperature. On addition of 175 cc of anhydrous ether, a gummy solid precipitated. After several minutes the ether solution was decanted. The resultant 5-chloro-2-gly-cylaminobenzophenone was not isolated, but about 155 cc of ether was added to the residue and after chilling in an ice bath, 10% sodium hydroxide was added until the mixture was alkaline. The ether layer was then separated, washed twice with water and dried over sodium sulfate. After filtration, the ether solution was concentrated to dryness in vacuo. The residue was crystallized from benzene to yield 7-chloro-5-phenyl-3H-1,4-benzodiazepin-2(1 H)-one. 

The resulting solution is poured into ice acidified with dilute hydrochloric acid. A white solid precipitates which Is extracted into ether. The ether phase is washed with a saturated solution of sodium chloride and dried over anhydrous magnesium sulfate. The solvent is evaporated and a white solid, 5-(p-toluoyl)-1 -methylpvrrole-2-acetic acid is obtained which is recrystal-lized twice from isopropanol, melting point 155°C to 157°C. 

Ethyl S-(p-chlorobenzoyl)-3-carboxy-1,4-dimethylpyrrole-2-acetate A suspension of 2.0 g of 5-(p-chiorobenzoyl)-3acetic acid in 20 ml of 0.5% ethanol ic hydrogen chloride is heated under reflux. The solid gradually dissolves. After 40 minutes a white crystalline solid precipitates. The solution is cooled and the solid product, ethyl 5-(p-chlorobenzoyl)-3[Pg.1603]

The less soluble solid precipitates first the more soluble solid stays in solution. 

If sodium hydroxide is added too rapidly some solid precipitates which does not redissolve. 

Increasing the pH to 10-11 (in the case of Nb - HF solution - pH = 8) reduced the Nb205 concentration in the solutions to 0.5-0.3 g/l and the solid precipitate was identified as a pure amorphous substance, which after thermal treatment was identified as niobium oxide. 

In a 500-cc. round-bottomed, three-necked flask provided with a thermometer, dropping funnel, a liquid-sealed stirrer, and calcium chloride tube are placed 16.8 g. (0.2 mole) of thiophene (Org. Syn. 12, 72), 15.6 g. (0.2 mole) of acetyl chloride, and 200 cc. of dry benzene. The solution is cooled to o°, and 52 g. (23 cc., 0.2 mole) of freshly distilled stannic chloride is added dropwise, with efficient stirring, during the course of about forty minutes. The reaction mixture assumes a purple color when the first drops of stannic chloride are added, and soon a purple solid precipitates. 

It is advisable to distil the solvent one day, store the residue overnight under nitrogen at 0°, and distil the product the next morning to allow ample time for the following Grignard reaction. On standing at room temperature a white solid precipitates. 

B. (Z)-l-Iodo-l-heptene.2 A solution of 8.52 g of (112 mmol) of borane-dimethylsulfide complex (Note 13) in 100 mL of ether is added to a flame-dried, three-necked, 300-mL, round-bottomed flask equipped with stirbar, temperature probe, and N2 inlet. The solution is cooled to 5°C with an ice-bath. Cyclohexene (18.4 g, 224 mmol) (Note 14) is then added by syringe over 10 min while keeping the temperature below 15°C. The mixture is stirred at 5°C for 15 min. A white solid precipitates either towards the end of the addition or during the subsequent stirring period. The reaction mixture is allowed to warm to room temperature and is stirred for 1 hr. The non-homogeneous solution is cooled to 2-3°C... 

FIGURE G.4 Precipitation occurs when an insoluble substance is formed. Here lead(ll) iodide, Pbh, which is an insoluble yellow solid, precipitates when we mix solutions of lead(ll) nitrate, Pb(NO,h, and potassium iodide, Kl. 

M.13 When aqueous solutions of calcium nitrate and phosphoric acid are mixed, a white solid precipitates, (a) What is the formula of the solid (b) How many grams of the solid can be formed from 206 g of calcium nitrate and 150. g of phosphoric acid ... 

If we were to conduct a second solubility experiment in which solutions of KI and NaN03 were mixed, we would find that no precipitate forms. This demonstrates that K and NO3 ions do not form a solid precipitate, so the bright yellow precipitate must be lead(II) iodide, Pbl2. As the two salt solutions mix, cations and r anions combine to produce lead(II) iodide, which precipitates from the solution. On standing, the yellow precipitate settles, leaving a colorless solution that contains potassium cations and nitrate anions. The molecular blowups in Figure depict these solutions at the molecular level. 

Solid solutions generally form in one of two ways, both of which involve forming the solid flxim the liquid phase. One way is to heat the solid solvent until it melts, add the solutes into the molten material, and then cool the melt until it solidifies. Solid solutions of one metal in another, such as brass and steel, are prepared in this way. A second method is to dissolve the solid solvent and solutes in an appropriate liquid, then cool or evaporate the liquid until a solid precipitates. Solid solutions of organic substances can form in this manner. 

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