Crystals needle-like

The following is an alternative method of purifying the crude aspirin. Dissolve the solid in about 30 ml. of hot alcohol and pour the solution into about 75 ml. of warm water if a sohd separates at this point, warm the mixture until solution is complete and then allow the clear solution to cool slowly. Beautiful needle-like crystals will separate. The yield is 13 g. The air-dried crude product may also be recrystallised from benzene or from ether - light petroleum (b.p. 40-60°). 

When pure needle-like crystals of -aminobenzoyl chloride are polymerized in a high temperature, nonsolvent process, or alow temperature, slurry process, polymer is obtained which maintains the needle-like appearance of monomer. PBA of inherent viscosity, 4.1 dL/g, has been obtained in a hexane slurry with pyridine as the acid acceptor. Therefore PBA of fiber-forming molecular weight can be prepared in the soHd state. 

Strontium bromide [10476-81 -0] SrBr2, forms white, needle-like crystals, which are very soluble in water (222.5 g in 100 mL water at 100°C) and soluble in alcohol. The anhydrous salt has a specific gravity of 4.216 and a melting point of 643°C. 

Solubilities of PETN in 60—95% nitric acid in the temp range of 0—50° were determined by Camera Mauro (Ref 63), and in 20—100% nitric acid at 23-25° by Aubertein (Ref 11) Nearly equi-dimensional PETN crystals rather than the usual needle-like crystals can be obtained by slow cooling of a 40% soln of PETN in boiling EtOAc (Ref 12)... 

Sulfates typically are found as a hard, dense, white deposit (occasionally in a thin, needle-like crystal form) of anhydrite (CaS04). 

The crystal compositions vary, depending on the transport agent used, from TiB,4,y (Ij) and TiBj <,4 (TeCl4). At process temperatures > 1000°C and with I2, the transport direction is reversed. Crystals grow in the cold zone of the tube, but only microscopic needle-like crystals are obtained. ... 

Microstructure is also affected by water content. The 1 16 mortar contained hexagonal plates, while the 1 8 mortar had an ellipsoidal morphology. The 1 5 mortar when prepared at — 5 °C developed striking, well-formed, needle-like crystals (Figure 6.9). 

Each needle-like crystal of p-FeOOH is known to consist of a bundle of much thinner suhcrystals. 

NH4)HC03/H20/Et20 at 0°C, which gave 90-95% yields of the solid silanols (68). Diarylsilanediols (X — C6H4)2Si(OH)2 (X = H, p-F, or p-Cl) have been prepared as needle-like crystals by hydrolysis of the corresponding chlorosilanes under similar conditions (69). 

Various drugs are known to exist in different polymorphic forms (e.g., cortisone and prednisolone). The rate of conversion from a metastable into the stable form is an important criteria to be considered with respect to the shelf life of a pharmaceutical product. Polymorphic changes have also been observed during the manufacture of steroid suspensions. When steroid powders are subjected to dry heat sterilization, subsequent rehydration of anhydrous steroid in the presence of an aqueous vehicle results in the formation of large, needle-like crystals. A similar effect may be... 

Accelerated aging and crystal transformation rates have also been traced to high residual moisture content. Ando et al. studied the effect of moisture content on the crystallization of anhydrous theophylline in tablets [9]. Their results also indicate that anhydrous materials convert to hydrates at high levels of relative humidity. In addition, if hygroscopic materials (e.g., polyethylene glycol 6000) are also contained in the formulation, needle-like crystals form at the tablet surface and significantly reduce the release rate of the theophylline. 

I [Tc8(/i-Br)8Br4]Br 2H20 Black oblong needle-like crystals with a square cross-section and intensive metallic lustree. Insoluble in hot HBr (concentr.). Grinding yields black powder. 

VI [(CH 3)4N] 3 [Tc6( -Br)6Br6]Br 2 Black-brown plate- and needle-like crystals. Soluble in hot HBr (concentr.), forming black-brown solutions. Grinding yields brown powder with a violet tinge... 

IX [H30 H20)3]2[Tc6 3-Br)5Br6]. 4H20 Black with brown tinged needle-like crystals very soluble in HBr (concentr.), alcohol and other polar solvents, forming brown solutions. Grinding yields brown powder. 

X [Fe(C5H5)2]2 [Tc8(/i-Br)8Br4JBr2 Black fine needle-like crystals with metallic lustre. Insoluble in orgaic and inorganic solvents but does not decompose. Grinding yields amorphous black powder. 

There are two basic crystallisation forms for sulphur - monoclinic and rhombic. Rhombic is the most stable form, at least up to 96 °C the other types revert to this stable form at a rate dependant upon temperature. When sulphur solidifies from the molten state (melting point 114 °C) the crystalline form which occurs is monoclinic (needle-like crystal structure). Below 96 °C, the monoclinic form becomes metastable and changes into the rhombic form. 

B. 4-Phenyl-5-anilino-l,2,3-triazole. Six grams (0.025 mole) of 1,4-diphenyl-5-amino-l,2,3-triazole is dissolved in 20 g. of dry pyridine (distilled from solid sodium hydroxide) and heated under reflux for 24 hours (Note 6). The reaction mixture (Note 7) is poured into 11. of ice water. The product separates as a slightly yellowish milky oil which is converted to white needle-like crystals by stirring the mixture and scratching the beaker with a glass rod. The product is collected by suction filtration, washed with water, suction-dried, and recrystallized from aqueous ethanol (Note 8). The yield is 5.5-5.6 g. (92-93%) of fine white needle-like crystals, m.p. 167-169° (Note 9), soluble in hot water and ether, but difficultly soluble in benzene. 

Physical state White solid with needle-like crystals. Produced by chlorination of molten phenol. Technical-grade material is dark gray to brown... 

As observed on a Mettler Hot Stage FP 52 with FP5 controller, the sample appeared as birefringent needle-like crystals which melted from 115-117°C. The sample did not recrystallize from the melt (5). 

I ve included 2532 (Benzoic acid, 2-acetamido) to show that you sometimes get a bonus. Here nd(aa) means you get needle-like crystals from acetic acid. Acetic acid (aa) is the recrystallization solvent (see Chapter 10, Recrystallization ), and you don t have to find it on your own. Thus, pa ye nd (al) means that pale yellow needles are obtained when you recrystallize the compound from ethanol. 

In the case of FAPPO, where two modifications are mixed, such a direct refinement was not possible. As given in Fig. 7, modification I exhibits platelets (0.5 x 2 pm) while modification II forms needle-like crystals of about 0.1 pm width. 

Figure 7 Platelets of modification I (top, left hand side) and needle-like crystal of modification II (bottom, left hand side). Experimental (middle) and kinematical calculated...

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