Incipient crystallization

Begin pulling incipient crystal out of melt at a rate which maintains crystal size and growth. 

The maximum observed rotation for the 2-amino-2-methyl-1-propanol salt of levopimaric acid is [a] n —218°. Methanol and ethanol solutions give the same specific rotations, but methanol is the preferred solvent because the time required to effect solution in ethanol is longer. If pure levopimaric acid, m.p. 151-153°, [a] D —276° is desired, the salt with —210° rotation should be dissolved in 8 parts of boiling methanol, the solution concentrated to the point of incipient crystallization, cooled, and filtered. The yield in this recrystallization is about 70%. 

At Ty, the Gibbs free energy of phase a (i.e., melt) at all compositions is lower than that of mechanical mixture y + y" phase a is then stable over the whole compositional range. At T2, the chemical potential of component 1 in a is identical to the chemical potential of the same component in y . Moreover, the equahty condition is reached at the standard state condition of the pure component T2 is thus the temperature of incipient crystallization of y. At T, the Gibbs free energy of a intersects mechanical mixture y + y" on the component 1-rich side of the diagram and touches it at the condition of pure component 2. Applying the prin-... 

To a stirred methylene chloride solution of 4.62 gm (15 mmoles) of 1-phenyl-2-(diphenylphosphine oxide)hydrazine maintained at —20°C is added over a 10 min period 2.67 gm (15 mmoles) of iV-bromosuccinimide. The solution is allowed to warm to room temperature, and stirring is continued for 10 min. The solids formed are removed by filtration and discarded. The solution is washed in turn with two portions of 5 % aqueous sodium thiosulfate solution, 0.1 N hydrochloric acid, water, dilute aqueous potassium bicarbonate, and again water. The methylene chloride solution is dried over anhydrous sodium sulfate and filtered. The filtrate is evaporated to incipient crystallization at room temperature at reduced pressure yield 4.1 gm (90%), m.p. 105°-106°C. 

The DTA endotherms of the antiplasticized polymers indicate the presence of forces which are broken by the input of thermal energy. Instead of a degree of order or incipient crystallization, it is possible that these forces consist of secondary bonds... 

For recrystallization, a solution of the nitrile in 3-4 ml. of hot methanol per gram was treated with Darco G-60 and filtered on a fluted paper. Distilled water was added to the hot solution until incipient crystallization was observed. In general the final solvent was approximately 90% methanol. 

Results with Ni have shown [589, 590] that the amorphous metal can be more active than the crystalline material, but the small decrease in Tafel slope for the amorphous electrode is outweighed by the higher overpotential at low current densities (Fig. 33). An increase in temperature raises the Tafel slope substantially, presumably on account of the incipient crystallization of Ni. Higher adsorption strength on amorphous Ni is pointed out, while surface diffusion of Had is suggested as the possible r.d.s. 

A 3 per cent solution of hydrazoic acid (synthesis 26A) is neutralized with an aqueous solution of pure potassium hydroxide. The resulting solution of potassium azide is concentrated on the steam bath to incipient crystallization. The solution is then made slightly acid with hydrazoic acid to replace the hydrogen azide lost by hydrolysis. A volume of ethyl alcohol twice that of the solution is added, and the solution is cooled in an ice bath. Since the solubility in alcohol of the alkali and alkaline earth azides is very slight (see table below), precipitation in the form of a white microcrystalline salt takes place readily. From 90 to 95 per cent recovery of the theoretical quantity of potassium azide can be effected. The precipitated azide is filtered on a Buchner funnel and washed with cold absolute alcohol and then with ether. Any traces of adhering solvent may be removed in a vacuum desiccator. In a typical run, 300 ml. of a solution of hydrazoic acid containing 8.5 g. of HN3 was neutralized with potassium hydroxide, and the isolation of potassium azide effected as indicated above. Yield 14.7 g. (91.5 per cent) KN3. 

An 11.1 g (24.1 mmol) portion of the compound 16a,17a-cyclopentylidenedioxy-9a-fluoro-lip,21-dihydroxy-l,4-pregnadiene-3,20-dione is placed in a 250 ml round-bottom flask. A 100 ml portion of pyridine is added and the mixture is stirred to a complete solution. A 5.5 ml (54.6 mmol) portion of acetic anhydride is added dropwise and the mixture is stirred for 2% hours. An 11 ml portion of methanol is added and the mixture is stirred an additional hour. This mixture is concentrated under reduced pressure to about 10 to 15 ml and then poured slowly into a mixture of ice, water and dilute hydrochloric acid. This mixture is stirred and the solid which forms is collected by filtration, washed with water to a neutral pH and air dried yielding 11.5 g. This solid is taken up in hot acetone, treated with activated charcoal and filtered while hot through diatomaceous earth. The filtrate is concentrated on a steam bath while adding n-hexane to the point of incipient crystallization. This mixture is allowed to cool to room temperature. The solid which forms is... 

The heat stabilities of both ovotransferrin and its iron complex were greatly increased under a pressure of 1000 atm. (8). Metal-free ovotransferrin was completely stable under 1000 atm. at 64° C. and pH 8.2 for 7 minutes. At the same temperature and pH the control at atmospheric pressure was completely denatured within five minutes. Temperatures as high as 90° C. for 30 minutes caused no change in iron ovotransferrin at pH 8.2 in 0.05 M sodium bicarbonate under 1000 atm. (37). Dilution of solutions of iron ovotransferrin with an equal volume of one of several different alcohols caused no demonstrable changes after 15 minutes incubation at room temperature while the metal-free ovotransferrins were completely and irreversibly denatured. (Advantage has been taken of this property to prepare crystalline iron ovotransferrin by incipient crystallization in the author s laboratory. Solutions are prepared at room temperature and then are chilled slowly in the refrigerator.)... 

Crystals suitable for x-ray structure determination were grown slowly ( 1 hr) from dichloromethane by the gradual addition of methanol until incipient crystallization. Under these conditions the crystals obtained contained one molecule of dichloromethane per molecule of 1. The dichloromethane of crystallization was lost upon standing in air or by drying in a vacuum (vide supra). The solvated crystals of 1 were... 

The procedure described in Sec. D for the preparation of dibromotetrakis(ethanol)nickel(II) is followed. The anhydrous ethanol solution is evaporated to the stage of incipient crystallization at the boiling point and then diluted with 1 1. of peroxide-free anhydrous 1,2-dimethoxyethane. The resulting salmon-pink complex is collected under nitrogen in a Schlenk frit of 1-1. capacity, rinsed successively with anhydrous 1,2-dimethoxyethane and then pentane and dried in a current of nitrogen at 23° and 20 cm. Hg. The yield is nearly quantitative. f Anal. Calcd. for C4H10Br2O2Ni C, 15.57 H, 3.27 Br, 51.78 Ni, 19.02. Found C, 15.01 H, 3.43 Br, 52.15 Ni, 18.80. 

Piasta et al. (P60) described the thermal eflfects on the cement paste. Below 500°C, major effects include carbonation and coarsening of the pore structure. Decomposition of CH at 450-550°C, and of CaCOj above 600 C, yield CaO, which rehydrates on cooling. The resulting expansion may disrupt a concrete that has withstood a fire without actual disintegration (L6). Above 500°C, the pore structure continues to coarsen, and incipient crystallization of P-C2S occurs. Extensive carbonation occurs in fire-damaged buildings that have been left standing for a few years (H71). 

Nickel (II) cyanide readily dissolves in cone aq KCN. Evaporation of the solution to incipient crystallization, followed by cooling, produces large well-formed yellow crystals of K2[Ni(CN)4]-H20, from which the anhydrous salt is obtained by heating in vacuo at 100 105"C Salts of other cations are usually obtained from the soluble potassium salt by metathesis with precipitation. 

Potassium hexachlororhodate(III) 1-hydrate may be obtained by chlorination of a mixture of powdered rhodium and potassium chloride, followed by crystallization from the reaction mixture solution in the presence of excess potassium chloride. It may also be prepared by reaction of sodium hexachlororhodate(III) solution with concentrated potassium chloride solution, followed by evaporation to incipient crystallization. Both of these methods are reported to yield potassium pentachloroaquorhodate(III) if potassium chloride is not present in excess. - Anhydrous potassium hexachlororhodate(III) is obtained by heating potassium hexachlororhodate(III) 1-hydrate at 100 to 120°. ... 

Precipitation reactions tend to be sluggish if nucleation is very slow. At the scale of individual grains, cements are not distributed uniformly throughout the available pore spaces, but tend to be spatially localized. Cements are localized on pre-existing surfaces, probably because surface area and surface composition affect nucleation rates. Incipient crystals nucleated on a surface have a smaller total surface area than free crystals of the same volume in the pore fluid, leading to a free energy difference that favors nucleation on a substrate (heterogeneous nucleation, e.g., Kirkpatrick, 1981). In the absence of a suitable... 

Crystallization.— To crystallize a soluble compound out of its solution, the solution is evaporated, not too rapidly, to incipient crystallization, the hot solution filtered and the clear filtrate allowed to cool. By slow cooling from incipient crystallization large crystals are usually obtained, while evaporation of the solution beyond incipient crystallization, followed by rapid cooling, usually yields a more abundant product of purer and finer crystals. After cooling, the crystalline... 

This compound is obtained by the procedure for Section 9-A, using sodium (1.38 g, 60 mmole), 1,1-dimethylethanethiol (6.68 mL, 60 mmole), iron(III) chloride (2.43 g, 15 mmole), elemental sulfur (0.48 g, 15 mmole), and tetra-methylammonium bromide (1.54 g, 10 mmole) 2.2-2.6 g (70-80%) of the crude material is obtained if, after filtration into tetramethylammonium bromide, the reaction solution is allowed to stand at -5° overnight. Black needle-like crystals of the monoacetonitrile adduct can be obtained by adding ethyl acetate to a filtered solution of the compound in warm (45-50°) acetonitrile to incipient crystallization, followed by slow cooling and standing overnight at ca. -5°. Yield 40-50%. 

A procedure similar to that described for Section 9-A may be used to prepare this compound from lithium (0.28 g, 40 mmole), benzenethiol (4.1 mL, 40 mmole), iron(III) chloride (1.62 g, 10 mmole), selenium powder (0.79 g, 10 mmole), and tetrabutylammonium iodide (2.77 g, 7.5 mmole). The black precipitate should be collected by filtration, washed copiously with methanol, and dried in vacuo. This solid can be recrystallized by dissolution in the minimum volume of acetonitrile at 45°, adding methanol to incipient crystallization at this temperature and allowing the solution to cool slowly to room temperature before leaving it overnight at ca. -5°. The compound (2.9 g, 80%) crystallizes as large, black prisms. 

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