Solvent method powder mixture preparation

Raman often is evaluated as an alternative to an existing high performance liquid chromatography (HPLC) method because of its potential to be noninvasive, fast, simple to perform, and solvent-free. Raman was compared to HPLC for the determination of ticlopidine-hydrochloride (TCL) [43], risperidone [44] in film-coated tablets, and medroxyprogesterone acetate (MPA) in 150-mg/mL suspensions (DepoProvera, Pfizer) [45] it was found to have numerous advantages and performance suitable to replace HPLC. In an off-line laboratory study, the relative standard deviation of the measurement of the composition of powder mixtures of two sulfonamides, sulfathiazole and sulfanilamide, was reduced from 10-20% to less than 4% by employing a reusable, easily prepared rotating sample cell [46]. 

Metal borides are generally prepared by the direct reaction of the elanents at high temperatures or by the reduction of metal oxides or halides. Thus, reduction of mixtures of BjOj and metal oxides by carbothermic reaction yields metal borides. Reaction of metal oxides with boron or with a mixture of carbon and boron carbide is another route. Some metal borides are prepared by fused salt electrolysis (e.g. TaBj). Borides of IVA-VIIA elements as well as ternary borides have been reviewed by Nowomy [1], The method employed to prepare TiB starting with TiCl is interesting [2], TiCl and BCI3 react with sodium in a nonpolar solvent (e.g. heptane) to produce an amorphous precursor powder along with NaCl. NaCl is distilled off and the precursor crystallized at relatively low temperatures (-970 K). 

The solvent method is preferably used for mixtures with very unfavourable mixing ratios (<5 mg active substance). This method (see Sect. 4.5.1) needs careful testing and validation. For some active substances the solvent method has been developed (Table 4.4). If the substance is not listed, the powder mixture can only be prepared following the low dose method. 

Liposphere formulations are prepared by solvent or melt processes. In the melt method, the active agent is dissolved or dispersed in the melted solid carrier (i.e., tristearin or polycaprolactone) and a hot buffer solution is added at once, along with the phospholipid powder. The hot mixture is homogenized for about 2 to 5 min, using a homogenizer or ultrasound probe, after which a uniform emulsion is obtained. The milky formulation is then rapidly cooled down to about 20°C by immersing the formulation flask in a dry ice-acetone bath, while homogenization is continued to yield a uniform dispersion of lipospheres. 

Method B (general procedure)7 To an NaHTe solution, prepared from tellurium powder (1.27 g, 10 mmol) and NaBH4 (0.9 g, 24 mmol) in absolute EtOH (25 mL), is added the 2-haloethyl ester (10 mmol) in EtOH (5 mL). (The reaction takes place instantaneously for 2-bromoethyl esters at room temperature.) The mixture is stirred for 1 h, then acidified with dilute HCl, extracted with ether and the organic phase dried and evaporated. The residue is recrystalUzed from appropriate solvents to give pure carboxylic acids. 

The following procedure is an operatively simple route for the synthesis of bromotrimethylsilane on a preparative laboratory scale from reagents that are readily accessible and inexpensive. This could be a method of choice in some laboratories despite the fact that bromotrimethylsilane is now commercially available (Petrach Systems, Aldrich, or Alpha). Moreover, the procedure also serves as a suitable method for the synthesis of azidotrimethylsilane and isocyanatotrimethylsilane, and is specially useful for the preparation of cyanotrimethylsilane. Thus a mixture of triphenylphosphine dibromide, hexamethyldisiloxane, and a catalytic amount of powdered metal zinc in 1,2-dichlorobenzene is heated under reflux to produce bromotrimethylsilane in nearly quantitative yield, which is simultaneously distilled over a suspension of the corresponding pseudohalogenoacid salt in N, /V-dimethylformamide as solvent.6... 

When prepared by chemical methods, y-sulphur is frequently accompanied by an apparently amorphous powder which is readily soluble in carbon disulphide. This has been regarded, by some investigators, as a definite form of sulphur and given the name soluble amorphous sulphur 2 in reality, however, it consists of minute spheroidal crystals of rhombic sulphur possibly together with nacreous sulphur.3 Another so-called modification of amorphous sulphur, described 4 as soluble in carbon disulphide but becoming insoluble on evaporation of the solvent, is probably no distinct form, but only a mixture of y-sulphur with finely divided crystalline sulphur. 

Another method of preparation is as follows 1 33 parts of fluorescein are dissolved in 5 parts of ether and treated with 25 parts of selenium chloride in the same solvent. A yellowish-red precipitate separates, and after long stirring at the ordinary temperature the ether is distilled off. The residue is stirred with water, the mixture filtered and the residue now dissolved in sodium hydroxide. After further filtration the filtrate is treated with hydrochloric acid, which precipitates seleno-fluorescei n. Further purification is effected by solution in alkali and reprecipitation. A reddish-brown powder is obtained, soluble with fluorescence in alcohol, but insoluble in water. In concentrated sulphuric acid it dissolves to give an orange solution. Its alkali salts are very soluble in wrater, giving red solutions. This process may also be applied to phthalins, which are obtained by the reduction of phthaleins and their halogen derivatives. If the selenium chloride is replaced by the oxychloride similar products are obtained.2 In place of the phthalins specified in the patents quoted, their O-acetyl compounds or O-acetyl compounds of the phthaleins may be used in indifferent solvents. The products are different from those obtained by the action of selenium on fluoresceins in aqueous alkali solutions.3... 

The second successful dense smokeless powder was the ballistite which was invented by Alfred Nobel.6 This was a stiff gelatinous mixture of nitroglycerin and soluble nitrocellulose in proportions varying between 1 to 2 and 2 to 1, prepared with the use of a solvent which was later removed and recovered. Nobel appears to have been led to the invention by thinking about celluloid, for the patent specification states that the substitution of almost all the camphor in celluloid by nitroglycerin yields a material which is suitable for use as a propellant. In the method of manufacture first proposed, camphor was dissolved in nitroglycerin, benzene was added, and then dry, pulped, soluble nitrocellulose the mixture was kneaded, the benzene was allowed to evaporate, and the material was rolled between warm rollers... 

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