Conventional recrystallization

Chemicals. All solvents were purified by distillation in glass apparatus. Standard compounds were supplied commercially and their purity checked by GC. If necessary standards were further purified by distillation in vacuo or by conventional recrystallization. Standard solutions were prepared by dissolving weighed amounts of PAH and chlorinated hydrocarbons in cyclohexane and of aromatic amines in 2-butanone. The standard mixtures were stored at 4 °C in the dark. 

The process can also include a deoiling section ( see Figure 6.11) to make hard wax. The soft wax that is to become foots oil is in the last few layers of the DILCHILL crystal and dissolves when exposed to hot solvent, leaving the low-oil wax to be filtered off. This represents a major energy savings over the conventional recrystallization process, where all the wax must be redissolved. 

The development of a sharp COE texture in the finished strip requires complex control of numerous variables. The conventional commercial process (18) involves hot-rolling a cast ingot at ca 1370°C to a thickness of about 2 mm, annealing at 800—1000°C, and then cold-rolling to a final thickness of 0.27—0.35 mm in two steps of 70 and 50%, respectively, with a recrystallization (800—1000°C) aimeal in between. The cold-roUed strip is decarburized (800°C) to ca 0.003% C in mixtures of wet results in a primary recrystallized stmcture containing grains of the COE... 

The thiazolecarboxylic acid structure (40) was also guessed in a similar way, from tracer experiments. The unknown compound was converted into the thiamine thiazole by heating at 100°C and pH 2. On paper electrophoresis, it migrated as an anion at pH 4. Tracer experiments indicated that it incorporated C-l and C-2 of L-tyrosine, and the sulfur of sulfate. The synthetic acid was prepared by carboxylation of the lithium derivative of the thiamine thiazole, and the derivatives shown in Scheme 19 were obtained by conventional methods. Again, the radioactivity of the unknown, labeled with 35S could not be separated from structure 40, added as carrier, and the molar radioactivity remained constant through several recrystallizations and the derivatizations of Scheme 17. 

The feasibility of synthesizing oxovanadium phthalocyanine (VOPc) from vanadium oxide, dicyanobenzene, and ethylene ycol using the microwave synthesis was investigated by comparing reaction temperatures under the microwave irradiations with the same factors of conventional synthesis. The efficiency of microwave synthesis over the conventional synthesis was illustrated by the yield of crude VOPc. Polymorph of VOPc was obtained ttough the acid-treatment and recrystallization step. The VOPos synthesized in various conditions were characterized hy the means of an X-ray dif actometry (XRD), a scanning electron microscopy (SEM), and a transmission electron Microscopy (TEM). 

The microwave synthesis described in the present paper has proven to be quite eifective due to its intense internal heating, compffl ed to conventional syndesis. The yield of crude VOPc increased with increasing the reaction temperature under both synthetic methods. Fine crystal VOPc was prepared successfiiUy from the crude VOPc obtained by microwave synthesis through the acid-treatment and recrystallization step. 

By the mid-1930s, commercial insulin was being prepared by crystallization from crude porcine or bovine extracts. The crystallized preparation was generally subjected to a recrystallization step in order to further increase the product s purity. Such preparations are termed conventional insulins (Box 8.2). 

Chromatographic or electrophoretic analysis of conventional insulins generally yields three major fractions or bands a, b and c). Fraction a contains high molecular mass material which can be removed from the product by additional recrystallization steps. The major components of fraction b are proinsulin and insulin dimers, while insulin, as well as slightly modified forms of insulin (e.g. arginine-insulin and desamido-insulin), are found in fraction c. 

The conventional preparative routes to anionic, neutral, or cationic complexes of indium start with the metal, which is dissolved in a suitable mineral acid to give a solution from which hydrated salts can be obtained by evaporation. These hydrates react with a variety of neutral or anionic ligands in nonaqueous solvents, and a wide range of indium(III) complexes have been prepared in this manner.1 Alternatively, the direct high-temperature oxidation of the metal by halogens yields the anhydrous trihalides, which are again convenient starting materials in synthetic work. In the former case, the initial oxidation of the metal is followed by isolation, solution reaction, precipitation, and recrystallization. 

In the alkylation reactions of the chiral 3-acyl-2-oxazolidinones, deprotonation to the lithium or sodium enolate is by treatment with lithium diisopropylamide or lithium or sodium hexamethyldisilazanide in tetrahydrofuran at low temperature (usually — 78 °C). The haloalka-ne, usually in excess, is then added to the enolate solution at low temperature (usually — 78 °C) for the sodium enolates and at higher temperatures (between —78 and 0CC) for the lithium enolates. When small, less sterically demanding halides, such as iodomethane, are used the sodium enolate is usually preferred 2 24 and in these cases up to five equivalents2,6- 24,26,27 of the halide are necessary in order to obtain good yields of the alkylation products. Conventional extractive workup provides the crude product as a diastereomeric mixture (d.r. usually > 90 10) which is relatively easy to separate by silica gel chromatography and/or by recrystallization (for crystalline products). Thus, it is possible to obtain one diastereomer in very high diastereomeric purity. 

This reaction changes a racemic form into a mixture of diastereomers. Diastereomers have different b.p., m.p. and solubilities, and can be separated by conventional means, e.g. recrystallization and chromatography. 

SNPE, France, produced reduced sensitivity RDX (RS-RDX) by the Woolwich synthesis by employing a proprietary recrystallization process. This RS-RDX displayed reduced sensitivity to shock initiation. Subsequently, some other manufacturers also claimed to produce some form of RDX that exhibits reduced sensitivity to shock compared with the conventional RDX produced by the Bachmann process. EURENCO has also developed a process to mass-manufacture a variety of low sensitive Hexogen (RDX), called I-RDX. 

The particle-size and size-distribution of solid materials produced in industrial processes are not usually those desired for subsequent use of these materials and, as a result comminution and recrystallization operations are carried out. Well known processes for particle size redistribution are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several practical problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, and in recrystallization processes the product is contaminated with solvent, and waste solvent streams are produced. Applying supercritical fluids may overcome the drawbacks of conventional processes. 

Internal latent image is a latent image formed inside the grains. It can be developed by a conventional developer to which is added a silver halide solvent or an agent that promotes recrystallization of the silver halide to allow the developer to make contact with the latent image centers. 

Unless asymmetric induction is complete, it is necessary to remove the undesired enantiomer from the product mixture. Whereas in conventional diastereoselective asymmetric syntheses this removal can typically be readily accomplished by crystallization or chromatography, the separation of enantiomeric products can be problematic. Often, though, with enantio-enriched samples it is possible to recrystallize either the racemate from the pure enantiomer or, preferably, one enantiomer from the other [I2a,16,17], Another very effective method to produce enan-tiopure compounds is by enzymatic resolution of the enantio-enriched product from chiral PTC [16,18]. These methods are illustrated by examples in the alkylation section of this chapter (Chart 10.6). 

Sodium and potassium were distilled into ampoules and stored in the dry box. Lithium and the alkaline earth metals were the best grade available commercially and were used without further purification. Reagent grade sodium iodide was dried at 300°C. in vacuo, recrystallized from anhydrous liquid ammonia, and heated to 200°C. in vacuo prior to use. The recrystallization procedure eliminated the rapid fading of dilute sodium-ammonia solutions containing sodium iodide which had been dried in the conventional manner. 

Melphalan and the racemic analog have been prepared by two general routes (Scheme I). In Approach (A) the amino acid function is protected, and the nitrogen mustard moiety is prepared by conventional methods from aromatic nitro-derivatives. Thus, the ethyl ester of N-phthaloyl-phenylalanine was nitrated and reduced catalytically to amine I. Compound I was reacted with ethylene oxide to form the corresponding bis(2-hydroxyethyl)amino derivative II, which was then treated with phosphorus oxychloride or thionyl chloride. The blocking groups were removed by acidic hydrolysis. Melphalan was precipitated by addition of sodium acetate and was recrystallized from methanol. No racemization was detected [10,28—30]. The hydrochloride was obtained in pure form from the final hydrolysis mixture by partial neutralization to pH 0.5 [31]. Variants of this approach, used for the preparation of the racemic compound, followed the same route via the a-acylamino-a-p-aminobenzyl malonic ester III [10,28—30,32,33] or the hydantoin IV [12]. 

Patent US 4,377,584, issued Mar. 22,1883, and J. Med. Chem., 29, 2298 (1986)). The resulting slurry was cooled to -5-10°C, and 27.6 mL of t-butylamine was added. A solution of ethylmagnesium bromide in THF (122 mL, 2 M) was added maintaining the temperature of the reaction mixture below 10°C. The reaction mixture was heated at reflux for 12 hours and was added to a cold (10°C) solution of 25% ammonium chloride in water. The mixture was warmed to 25°C and allowed to settle. The THF solution was separated and concentrated by atmospheric distillation to 200 mL and the product was crystallized by adding approximately 600 mL of dilute aqueous HCI. The resulting white solid was isolated by filtration and was dried at 70°C under vacuum to give 21.7 g (97% yield) 2-butyl-l-(4-carboxybenzyl)-4-chloroimidazole-5-acetic acid of finasteride. The finasteride can be purified by conventional procedures, e.g. recrystallization from methylene chloride/ethyl acetate or acetic acid/water, melting point 261°C. 

This plant will use the high-pressure Shortened Liquid Phase (SLP) process developed by DSM. Melamine produced with the SLP process has the same quality as melamine produced in the gas phase (or low pressure) process. The new technology is a result of DSM s further development of a process acquired from MCI (Melamine Chemical Industries) in 1997. The SLP process is expected to increase efficiency by 25%. It is also expected to enable the plant to reach a level of cost-effectiveness similar to a 100,000 tonnes/year production facility. The new process requires only 3 or 4 processing steps, in contrast to the 10 steps in conventional processes115,231. The process employs the same raw materials as the low-pressure urea process, but the final melamine recrystallization step is eliminated. The company may be able to make 99% purity melamine without recrystallization114. 

Recrystallization can also be carried out in the same system. The procedures follow closely the conventionally employed vacuum-line filtration techniques The 3.56-g. sample of cobalt-(III) acetylacetonate (0.01 mole) and the 7.86-g. sample of triphenylphosphine (0.03 mole) are placed in flask A then 40 ml. of toluene is distilled into the reactor in vacuo from the vacuum manifold by placing flask A into a Dry Ice-methanol cooling bath (—78°C.). 

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