Crystallization by cooling

The ammonium chloride process, developed by Asahi Glass, is a variation of the basic Solvay process (9—11). It requires the use of soHd sodium chloride but obtains higher sodium conversions (+90%) than does the Solvay process. This is especially important ia Japan, where salt is imported as a soHd. The major difference from the Solvay process is that here the ammonium chloride produced is crystallized by cooling and through the addition of soHd sodium chloride. The resulting mother Hquor is then recycled to dissolve additional sodium chloride. The ammonium chloride is removed for use as rice paddy fertilizer. Ammonia makeup is generally suppHed by an associated synthesis plant. 

Stannic Chloride Pentahydrate. Stannic chloride pentahydrate [10026-06-9] is a white, crystalline, deHquescent soHd that is soluble in water or methanol and stable at 19—56°C. It is used in place of the anhydrous chloride where anhydrous conditions are not mandatory. It is easier to handle than the fuming anhydrous Hquid form. The pentahydrate is prepared by dissolving stannic chloride in hot water, thereby forming the pentahydrate at a temperature above the melting point and crystallizing by cooling. The cake is broken into small lumps for packaging. 

The complex is decomposed by stirring the reaction mixture into a solution prepared from 500 g of ammonium chloride in 2,000 ml of water to which 3 kg of crushed ice have been added. After extraction and washing, the ether is evaporated in vacuo at 40°C. The oily residue is taken up in 500 ml of petroleum ether and left to crystallize by cooling at -20°C. The yellowish crystals formed are dried (309 g) MPi< (Kofler block) 74°C yield 92%. 

The aqueous solution is then concentrated to dryness at an outside temperature of 40° to 45°C and at low pressure. The residue, obtained by drying in a vacuum at 40° to 45°C is triturated in a mortar with ethyl ether and, after filtration, is extracted with 3,400 ml boiling absolute ethanol. The ethanol extract is separated from the undissolved part by filtration, cooled and the product which crystallizes by cooling is filtered and dried at 40°C in a vacuum. In that manner the disodium (4,4 -disulfoxy-diphenyl)-(2-pyridyl)-methane bi-hydrate is obtained, which takes the form of a white solid, according to U.S. Patent 3,528,986. 

Figure 25 shows the time evolution of the difference SAXS intensity which was observed in situ when a PET sample was crystallized by cooling down from... 

Di-p-tolyl ditelluride (typicalprocedure) A solution of hydrazine hydrate (3.2 g, 0.1 mol) in EtOH (20 mL) is added slowly dropwise to a refluxing solution of p-tolylteUurium trichloride (3.25 g, 10 mmol) in EtOH until evolution of N2 ceases. The hot mixture is filtered, and the ditelluride crystallizes by cooling (0.96 g (44% m.p. 52°C). 

Crystallization by Cooling. The ideal solvent is one in which the compound to be obtained in pure crystalline form is insoluble at cold temperatures, but readily soluble at hot temperatures. Also the impurities should either be insoluble or else very soluble and filtered accordingly to remove. In real life operations, this perfect solvent cannot always be found, so the nearest approach to it should be selected. 

The type of vessel employed depends on volatility of the solvent obviously the conical flask already recommended for "crystallization by cooling" is not suitable for spontaneous evaporation, while a beaker or shallow dish is. When the latter type of vessel is used, "crusts" often form on the sides above the surface of the liquid. Such cmsts seldom consist of pure substance so they should be removed carefully with a spatula or spoon before attempting to filter off the crystals. 

For crystallization by cooling, the effects of agitation, impurity concentration, and time after nucleation were examined. The experimental apparatus used was the same as shown schematically in Figure 3 except that acid was not added to the solution. 

The flask containing the residual yellow oil is fitted with a water trap and condenser, and 120 ml. of benzene is added. The water is then removed by azeotropic distillation (Note 4). When the removal of water is complete, the triphenylarsine oxide is crystallized by cooling the flask in an ice bath for 1.5-2 hours. The light-brown crystals are collected on a Buchner funnel and washed on the funnel with 25 ml. of cold benzene. The crude product weighs 97-98.5 g. (91-93%) and melts at 186-188°. The crude product is transferred to a porcelain dish and triturated with 50 ml. of benzene, collected on a Buchner funnel, pressed as dry as possible, and washed with 25 ml. of cold benzene. After drying in the air, the triphenylarsine oxide amounts to 89-92 g. (84-87%) of white crystals, melting at 189°. 

Hence, to prepare a cone. soln. of ammonium monosulphide, a current of washed hydrogen sulphide is passed into cone, aqua ammonia cooled to 0° until the neutral point is reached. Attempts to obtain crystals by cooling the soln. to —40° were not successful. W. P. Bloxam believes that the soln. so obtained is not really the monosulphide at all, but rather a soln. of a mol. of the complex (NH4)2S.2NH4SH in two mols. of ammonium hydroxide, NH4OH because of (i) its action on cupric sulphate (ii) its failure to yield crystals by cooling, attributed to the solvent action of free ammonia and (iii) because it exhibits no tendency to dissolve sulphur. 

When boric acid is made from colemanite, the ore is ground to a fine powder and stirred vigorously with diluted mother liquor and sulfuric acid at about 90°C. The by-product calcium sulfate [7778-18-9] is removed by settling and filtration, and the boric acid is crystallized by cooling the filtrate. 

V-Vinylpyrrolidone 1 (1.00 g, 9.0 mmol) was spread on cylindric glass rings (Raschig coils) in a 500-mL flask and crystallized by cooling to -40 °C in a vacuum. HBr gas (1 bar) was applied for 2h at that temperature. Excess gas was pumped off to a recipient at -196 °C for further use and the solid reaction product 2 was left at room temperature with repeated evacuation for removal of the liberated HBr. The racemic product 3 was recrystallized from acetone to yield 650 mg (65%) of the pure compound (mp 70-73 °C) that was spectroscopically characterized. 

Liquid rac-1 (500 mg, 2.8 mmol) was crystallized by cooling to -60 °C in a 100-mL flask under vacuum. HC1 gas (1 bar, 4.5 mmol) was let in through a vacuum line. After 15 h at -60 °C the excess gas was pumped off and 600 mg (100%) yellow crystals (73 27 mixture of 2a and 3a) were obtained that melted at room temperature. 2a (mp 65-67 °C) was obtained pure by crystallization from n-hcx-ane, though involving heavy losses. 

Dichlorobenzaldehyde is reacted with methyl acetoacetate in a suitable solvent in the presence of a catalytic amount of acetic acid and piperidine. Water is azeotropically separated off during the reaction. The reaction mixture is extracted in order to remove the catalysts. The solvent is evaporated and methanol is added. The product is crystallized by cooling the solution, isolated by filtration and finally washed with methanol. 

If sodium perchlorate should be manufactured the final solution from the electrolysis is peutralized with soda and boiled down in an evaporator until it contains about 1 300 g NaC104 per litre. The concentrated liquid is filtered and the salt allowed to crystallize by cooling to 30 °C in aluminium crystallizers. Precipitated crystals of sodium perchlorate are separated from the mother liquor in aluminium suction filters, washed with water, centrifuged, dried with hot air and finally ground to powder. 

Determine the appropriate operating temperature for the crystallizer. Figure 10.6 shows the mutual solubility of benzene and naphthalene. Most of the naphthalene can be crystallized by cooling to (i.e., operating the crystallizer at) the eutectic temperature of —3.5°C (25.7°F), where the solubility... 

The double salt with ammonium chloride, (NH4)4Fe(CN)6.NH4Cl. 3H20, is obtained as pale yellow or brown crystals by cooling warm, mixed solutions of ammonium ferrocyanide and ammonium chloride in the presence of sodium cyanide or of acetic acid respectively.11 The anhydrous salt has also been obtained.8... 

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