Crystallization and Drying

Certain crystallization conditions, such as temperature, can assist in the control of sticking [18, 40], An increase in both the melting point and sticking point in the SSP process has been observed. The heating associated with a homogenous heat flow should therefore bring the chips to the desired temperature. 

---

To prepare pure anhydrous o-benzoylbenzoic acid, dissolve the air-dried (or the moist) product in about 175 ml. of benzene contained in a 500 ml. round-bottomed flask fitted with a reflux condenser and heat on a water bath. Transfer the benzene solution to a separatory funnel, run oflF any water present, and dry with anhydrous magnesium sulphate. Concentrate the benzene solution to about 75 ml. and add light petroleum, (b.p. 60-80°) to the hot solution until a slight turbidity is produced. Allow to cool spontaneously to room temperature, then cool in ice to about 5°, collect the crystals and dry. The yield of pure, anhydrous o-benzoylbenzoic acid, m.p. 128°, is 32 g. 

Method 2. Place a mixture of 126-5 g. of benzyl chloride, 76 g. of thiourea and loO ml. of rectified spirit in a 500 ml. round-bottomed flask fitted with a reflux condenser. Warm on a water bath. A sudden exothermic reaction soon occurs and aU the thiourea passes into solution. Reflux the resulting yellow solution for 30 minutes and then cool in ice. Filter off the white crystals and dry in the air upon filter paper. Concentrate the filtrate to half its original volume and thus obtain a further small crop of crystals. The yield of crude hydrochloric acid as in Method 1 the m.p. is raised to 150°, although on some occasions the form, m.p. 175°, separates. 

In the second step, KA is further oxidized by nitric acid [7697-37-2] to adipic acid, which is separated, purified usually through crystallization, and dried (see Adipic acid). 

Recryst from H2O or 50% aq EtOH. Alternatively, dissolve ca 3g in cone HCl (lOmL) and evaporate to dryness. Dissolve the residual hydrochloride in the minimum volume of warm H2O and make faintly alkaline with aq NH3. Collect the crystals and dry in a vacuum at 100 . [J Am Chem Soc 56 134 1934.]... 

Diethyl succinate was obtained by the submitters from Eastman Organic Chemicals and used without purification. The checkers obtained the ester from British Drug Houses, Ltd., and distilled it at 100° (11 mm.). In general, it is preferable to distill or crystallize and dry all esters before attempting acyloin condensations. 

Aseptic Crystallization and Dry Powder Filling. Aseptic crystallization is primarily used for manufacture of sterile aqueous suspensions. However, if the physical form of the drug is critical to quality of the final product, better control over physical form can be attained by aseptic crystallization because a large variety of organic solvents can be used to control the crystallization process. In aseptic crystallization, the drug is... 

Nickel sulfate can be produced from either pure or impure sources. The pure source involves the reaction of pure nickel or nickel oxide powder (combined or separately) with sulfuric acid to produce nickel sulfate that is filtered and crystallized to produce a solid product. The impure raw material may be spent industrial liquor that contains a high percentage of nickel sulfate. The impurities in the liquor are precipitated by sequential treatment with oxidizers lime and sulfides can later be filtered out. The treated liquor, which is a pure solution of nickel sulfate, can be packaged in a drum or further crystallized and dried to produce solid nickel sulfate. Nickel sulfate is used mainly in the metal plating industries. Other uses include dyeing and printing of fabrics and production of patina, an alloy of zinc and brass. 

Fig. 1.93. Photograph taken by a cryomicro-scope showing Tc (water, upper left corner, black) and Tr (white ice crystals and dried product (gray), lower right corner (from f 1.112J unpublished).

Filter off the formed crystals and dry them on filter paper. Choose a well formed crystal of the alum, fasten it with the aid of a thin thread or hair to a glass rod and lower it into the mother liquor. Watch how the crystal grows several days. Examine the shape of the chromium potassium alum crystals under a microscope and compare it with that of potassium aluminium alum crystals. What will happen if crystals of potassium aluminium alum are lowered into a saturated solution of chromium potassium alum. 

Et4NBF4 Dissolve 5.3 g of Et4NBr (25 mmol) in 8 ml of water, add 3.6 ml of 48-50% HBF4 ( 26 mmol) to it, and concentrate by heating. Then, dilute it with ethyl ether and filter it to get crude precipitate of Et4NBF4. Recrystallize the precipitate twice from a MeOH-petroleum ether mixture to get pure crystal of Et4NBF4. Before use, powder the crystal and dry at 80-100 °C for several days under vacuum, mp 377-378 °C. 

In crystallizing and drying salts, it must be remembered that the entire operation is usually carried out in the presence of air. The air contains three constituents that are more or less active as chemical reagents, viz., oxygen, carbon dioxide, and water vapor, and in many cases special precautions must be taken to protect the preparation from atmospheric action. Each case will suggest a somewhat different mode of procedure, and a few typical examples will be used to illustrate these. 

The crystals form very slowly, as diffusion brings the reagents into contact. When a sufficient crop has been secured, carefully remove the paraffin, siphon off the solution as well as possible, and lift out the small beakers with their contents. Collect the crystals and dry them on paper. The place where they will form will depend on the relative rates of diffusion of the two ions concerned in the precipitation. 

If the m.p. is not quite satisfactory, dissolve the o-nitroplienol in hot alcohol (or methylated spirit) under reflux, add hot water drop by drop until a cloudiness just appears, and allow to cool spontaneously. Filter off the bright yellow crystals and dry between Alter paper. 

Proteins that remain in whey after removing casein from milk are recovered as whey protein concentrates by precipitation with added polyphosphate or other polyvalent anionic compounds, ultrafiltration, ion exchange adsorption, gel filtration, or a combined acid and heat precipitation process. Whey protein concentrates are also manufactured by a combined process involving electrodialysis, concentration, lactose crystallization, and drying (Richert 1975 Morr 1979 Marshall 1982 Anon. 1982 Muller 1982B). 

---