Crystallization, completion

Crystallization was carried out by the rapid cooling method in ethanol (EtOH) solutions. Various amounts of Me-est and Pr-est crystals were dissolved in ethanol at 323 K. After the crystals completely dissolved, the solution was rapidly cooled to 298 K to perform the crystallization. The slurry was sampled at constant intervals and filtered to separate the crystals from the solution. The concentration of the solution was measured by a UV spectroscopic method. After drying the separated crystal, the crystal stmcture was examined by powder X-ray diffraction (XRD) using the RINT2200 (Rigaku). The crystal stractures were analyzed with a single crystal, by a Rigaku R-AXIS with Cu-Ka radiation. 

By considering the extreme case of a crystal completely covered by a layer of foreign atoms, we have already seen in Sec. III,B that, if chemisorption involves the formation of localized electron pair bonds, some interesting interaction effects are to be expected. In this section, we approach the problem from the other extreme by considering just two atoms chemisorbed on a crystal surface. If the localized level formed by the interaction does not lie too far below the normal crystal band (or any surface band), the wave function for the localized level is damped only slowly in the crystal. Therefore, two chemisorbed atoms will be in interaction at distances when the interaction between the isolated atoms would be entirely negligible. To investigate this effect, we take the simplest model which may be expected to yield useful results 11). The crystal is represented by a straight... 

C/80 Torr into a receiver chilled with dry ice and XIcO . This was combined with the trap contents (10 mL) to give the crude product. Rcdistillation gave the pure product yield 9.05 g (47%) bp 104 C. On storage at - 80DC, it crystallized completely. 

S-lactone (Note 1) is added slowly with vigorous stirring. During the addition, the temperature should be kept below 65°. After an hour in the ice bath, the solution is kept at room temperature for 24 hours and is then poured into 1 1. of water and stirred until the hydrolysis of the acetic anhydride is complete (about an hour). The mixture is placed in a refrigerator until the product crystallizes completely (Note 2). The crude material is removed by filtration and washed with a small amount of ice water. The 2,3,4,6-tetra-O-acetyl-D-gluconic acid monohydrate thus obtained melts at 113-117°. The yield is 79-84 g. (74-79%). 

A suspension of the material in 600 ml. of concentrated hydrochloric acid is stirred mechanically in a 3-1. beaker which is set in an ice-salt bath. A solution of 46 g. of sodium nitrite in 150 ml. of water in a 250-ml. dropping funnel fixed with its stem below the surface of the suspension is added slowly while the temperature of the mixture is kept at 4-5° (Note 7). After the addition is completed (in approximately 80 minutes), stirring in the ice-salt bath is continued for 1 hour to crystallize completely the stan-nichloride of the diazonium salt. The reddish brown salt is filtered on a sintered glass funnel (Note 6). 

Disodium dihydrogen hypophosphate hexahydrate is a stable, colorless, crystalline compound. It loses its water of crystallization completely at 110°. The solubility of the hydrate is 2.0 g./lOO ml. of water at 25°. Solutions of the compound are quite stable, but upon heating or the addition of acids, hypophosphate tends to disproportionate to phos-... 

The density of the crystal was estimated by flotation in benzene/ chloroform mixtures. It is recognized that the value is not very accurate and is almost certainly lower than the true value because of the difficulty of freezing the crystal completely from the viscous mother liquor. However, the method is sufficient to confirm the number of molecules per unit cell [8]. 

The mineral acids dissolve the crystals completely. When ignited in air, ferric oxide is obtained, as also when the crystals are fused with an alkali carbonate. Double salts formed by union with the fluorides of the alkali and certain other metals have been described.3 These may be termed... 

The term crystal habit is often used to describe the relative sizes of the faces of a crystal. Crystal habit is readily modified by conditions of nucleation and growth, and it is rather difficult to prepare ciystals with all faces of the same form equally developed (M2). Small amounts of soluble impurities, especially dyes, which may be adsorbed selectively on the different faces of a crystal, cause these faces to be suppressed in favor of others. This can alter the external geometry of a crystal completely, except for its interfacial angles. Many examples of crystal habit modification are reported in the literature (B8), and in some commercial... 

Finally, a partly crystalline polymer (polymers never crystallize completely) have regions of order and disorder that have different densities and refractive indices, leading to an internal scattering of light that makes the material appear opaque. The degree of optical clarity will vary with crystallinity. If the polymer does not absorb light in the visible part of the spectrum, then one would expect it to be optically clear if it were 100%... 

Macromolecular crystallinity differs in three important ways from low-molecular weight molecular crystallinity polymers never crystallize completely, the unit cells are always smaller than the macromolecule, i.e. the crystal lattice is formed by the subunits rather than by the whole molecule and a long polymer chain can thread through different crystallites. Complete crystallization is impeded because of the structural polydispersity and the topological constraints resulting from the fact that... 

PROP Cubic white-yellow, deliq crystals. Completely dissoc in vapor phase to SeCL + CI2. Hydrolyzes in moist air to H2Se03 + HCl. Mp 300° (subl 170-196°), bp decomp 288°, vap press 1 mm 74°, d 2.6. Decomp in water and moist air. Insol in liquid bromine decomp by dry ammonia. Mod sol in nonpolar org solvs. 

Fig. 11-1. Voluine-temperaluie relations for a glass-forming polymer and a material that crystallizes completely on cooling. is a melting point, and and T are glass transition temperatures of an uncrystallized tnaterial that is cooled quickly and slowly, respectively.

A mixture of DAMN (2.0 g, 18.5 mmol) and triethyl orthoformate (2.74 g, 18.5 mmol) in dioxane (31.5 ml) is healed in a flask fitted with a short Vigreux column, distillation head, condenser and receiver. Ethanol mixed with dioxane is removed continuously until the temperature at the distillation head reaches 90°C ( 17ml, 10 min). The clear brown solution remaining is allowed to cool overnight before the addition of hexane (16 ml), which precipitates dark brown crystals. Complete precipitation is ensured by the addition of further hexane. The filtered solid is dissolved in the minimum volume of hot diethyl ether, filtered to remove a dark brown solid impurity, then cooled to give (27) as white needles (2.55 g, 84%), m.p. 132.5°C (dec.). 

Seal the plate with parafilm or an adhesive film to avoid liquid evaporation and incubate overnight at RT until the formazan crystals completely dissolve. 

In the first test (ASTM D-2386, IP 16), a measured fuel sample is placed in a jacketed sample tube also holding a thermometer and a stirrer. The tube is placed in a vacuum flask containing the cooling medium. Various coolants used are acetone, methyl alcohol, ethyl alcohol, or isopropyl alcohol, solid carbon dioxide, or liquid nitrogen. As the sample cools, it is continuously stirred. The temperature at which the hydrocarbon crystals appear is recorded. The jacketed sample is removed from the coolant and allowed to warm, under continuous stirring. The temperature at which the crystals completely disappear is recorded. 

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