Water-Insoluble Crystals

Water-insoluble Crystals. Aqueous solutions of mineral acids, acidic salts and alkalies, and melts of alkalies and salts are the usual dislocation etchants for water-insoluble crystals. However, in order to reveal dislocations in some cases, particularly hard crystals, it is desirable to manipulate etching conditions, such as etchant composition, temperature and time of etching. Low concentrations and low temperatures are generally suitable for revealing dislocations in these crystals by mineral acids (58-60). At high concentrations and elevated temperatures, H SO and H3PO4 often exhibit polishing action. 

It should be pointed out that during the etching of water-insoluble crystals, an insoluble or sparingly-soluble reaction product may deposit on the crystal surface. 

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Folic acid 14 consists of 6-methylpterine, p-aminobenzoic acid and (5)-glutamic acid residues. It belongs to the vitamin B complexes group and has been isolated from spinach leaves. Folic acid is a growth hormone and effective in the treatment of certain types of anaemia. It is important for the metabolism of amino acids, proteins, purines and pyrimidines. Folic acid forms orange, water-insoluble crystals, mp 250°C (dec). Its synthesis is carried out by condensation of 6-hydroxy-2,4,5-triaminopyrimidine, 1,1,3-trichloroacetone and A -(4-aminobenzoyl)-( S)-glutamic acid at pH 4-5 and in the presence of NaHSOs ... 

Carbazole forms water-insoluble crystals of mp 245 °C, bp 355 °C, and occurs in the anthracite fraction of coal tar. 

Folic acid forms orange, water-insoluble crystals, mp 250 °C (dec). Its synthesis is carried out by condensation of 6-hydroxy-2,4,5-triaminopyrimidine, 1,1,3-trichloroacetone, and N-(4-aminobenzoyl)-(S)-glutamic add at pH 4-5 and in the presence of NaHS03... 

Samples having a high water-vapor content should be run in cells with windows made of a water-insoluble crystal. Frequently, wet samples can be run in cells having sodium chloride or even potassium bromide windows, if the partial pressure of the water vapor is kept low and there is no chance of the water condensing on the windows (keeping the cell at an elevated temperature may be required). Even with water-insoluble crystals, condensation of water on the windows should be avoided, as this will give a spectrum of liquid water rather than the spectrum of the sample. A good rule of thumb is avoid the condensation of any material onto the cell windows. 

Mercurous Nitrate. Mercurous nitrate [10415-75-5] Hg2N20 or Hg2(N02)2, is a white monoclinic crystalline compound that is not very soluble in water but hydrolyzes to form a basic, yellow hydrate. This material is, however, soluble in cold, dilute nitric acid, and a solution is used as starting material for other water-insoluble mercurous salts. Mercurous nitrate is difficult to obtain in the pure state directly because some mercuric nitrate formation is almost unavoidable. When mercury is dissolved in hot dilute nitric acid, technical mercurous nitrate crystallizes on cooling. The use of excess mercury is helpful in reducing mercuric content, but an additional separation step is necessary. More concentrated nitric acid solutions should be avoided because these oxidize the mercurous to mercuric salt. Reagent-grade material is obtained by recrystaUization from dilute nitric acid in the presence of excess mercury. 

Ammonia, hydrochloric acid, and sodium perchlorate are mixed and the reaction mixture crystallised in a vacuum-cooled crystalliser. Ammonium perchlorate crystals are centrifuged, reslurried, recentrifuged, and then dried and blended for shipment. Mother Hquor is evaporated to precipitate sodium chloride and the depleted mother Hquor is recycled to the reactor. The AP product made by this method is 99% pure and meets the specifications for propeUant-grade ammonium perchlorate. The impurities are ammonium chloride, sodium perchlorate, ammonium chlorate, and water insolubles. 

Prolonged Action Parenterals Injections. Intramuscular injections have been developed to achieve prolonged therapeutic effects. This can be accompHshed by suspension of dmg particles in oils or flowable gels, from which the dmg slowly diffuses. Aqueous suspensions can also provide such therapeutic response. In these cases, the soHd dmg crystals generally are quite water insoluble and of a controlled particle size and crystallized form. 

The mixed oxidation products are fed to a stiU where the pelargonic and other low boiling acids are removed as overhead while the heavy material, esters and dimer acids, are removed as residue. The side-stream contains predominately azelaic acid along with minor amounts of other dibasic acids and palmitic and stearic acids. The side-stream is then washed with hot water that dissolves the azelaic acid, and separation can then be made from the water-insoluble acids, palmitic and stearic acids. Water is removed from the aqueous solution by evaporators or through crystallization (44,45). 

Phospholipids or similar water-insoluble amphiphilic natural substances aggregate in water to form bilayer liquid crystals which rearrange when exposed to ultrasonic waves to give spherical vesicles. Natural product vesicles are also called liposomes. Liposomes, as well as synthetic bilayer vesicles, can entrap substances in the inner aqueous phase, retain them for extended periods, and release them by physical process. 

Some tablets combine sustained-release and rapid disintegration characteristics. Products such as K-Dur (Key Pharmaceuticals) combine coated potassium chloride crystals in a rapidly releasing tablet. In this particular instance, the crystals are coated with ethylcellulose, a water-insoluble polymer, and are then incorporated into a rapidly disintegrating microcrystalline cellulose (MCC) matrix. The purpose of this tablet is to minimize GI ulceration, commonly encountered by patients treated with potassium chloride. This simple but elegant formulation is an example of a solid dosage form strategy used to achieve clinical goals. 

A surfactant is a surface-active agent that is used to disperse a water-insoluble drug as a colloidal dispersion. Surfactants are used for wetting and to prevent crystal growth in a suspension. Surfactants are used quite extensively in parenteral suspensions for wetting powders and to provide acceptable syringability. They are also used in emulsions and for solubilizing steroids and fat-soluble vitamins. 

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