Purification by recrystallization

A solution of 6-bromoindole (O.lOmol) in toluene (200 ml) was treated with Pd(PPh3)4 (5mol%) and stirred for 30 min. A solution of 4-fluorophenyl-boronic acid (0.25 M, 0.15 mol) in abs. EtOH was added, followed immediately by sal aq. NaHCOj (10 eq.). The biphasic mixture was refluxed for several hours and then cooled to room temperature. The reaction mixture was poured into sat. aq. NaCl (200 ml) and the layers separated. The aq. layer was extracted with additional EtOAc (200 ml) and the combined organic layers dried (Na2S04), filtered and concentrated in vacuo. The solution was filtered through silica gel using hexane-CHjCl -hexanc for elution and evaporated. Final purification by recrystallization gave the product (19 g, 90%). 

Evaporation to dryness under reduced pressure gives 20.9-22.1 g. (90-95%) of crude product. Purification by recrystallization from 500 ml. of pentane yields 15.5 g. (67%) of p-nitrobenzyl fluoride as colorless needle-shaped crystals, m.p. 36-37 (Note 2). 

A compound whose solubility increases with temperature can be purified by recrystallization. The impure solid is dissolved in a minimum volume of hot water. The hot solution is filtered to remove insoluble impurities, and then the solution is cooled in an ice bath. The solubility of the compound decreases as the temperature drops, causing the substance to precipitate from solution. Soluble impurities usually remain in solution. Purification by recrystallization is not restricted to aqueous solutions. An organic solid can be purified by recrystallization from an appropriate organic solvent. 

Since the alkylation products are usually crystalline, purification by recrystallization provides the pure diastereomers prior to cleavage. Hydride reduction of these purified alkylation products furnishes chiral, nonracemic alcohols 7 with moderate to high ee. Although not yet demonstrated, saponification of the alkylation products should be possible and would not occur in the ring, thereby providing an advantage over the corresponding 3-acyl-2-oxazolidinones (see Section 1.1.1.3.34.2.1.)6. 

In a 500-cc. round-bottomed, three-necked flask fitted with a reflux condenser, dropping funnel, and a mercury-sealed stirrer (Note 1) is placed a solution of 46 g. (0.5 mole) of dry aniline in 125 cc. of pure dry benzene. Stirring is started, and a solution of 42 g. (0.5 mole) of ketene dimer (p. 64) in 75 cc. of pure dry benzene is added dropwise over a period of half an hour. The reaction mixture is then heated under reflux on the steam bath for one hbur. After the major portion of the benzene has been removed by distillation from the steam bath, the remainder is removed under reduced pressure. The residue is dissolved in 500 cc. of hot 50 per cent aqueous alcohol from which the aceto-acetanilide separates on cooling. The mixture is cooled to 0° before filtration. A second crop of crystals can be obtained by adding 250 cc. of water to the mother liquor and cooling again (Note 2). The total yield of product, m.p. 82-83.5°, is 65 g. (74 per cent of the theoretical amount). Further purification by recrystallization from 300 cc. of 50 per cent alcohol yields 55 g. of a product which melts at 84-85°. 

The benzaldehyde derivative 1 (4 mmol), alkyl propiolate 2 (8 mmol), primary amine 3 (4 mmol), and 2 g silica gel were mixed thoroughly in a mortar. Then tlie reaction mixture was transferred to a beaker and irradiated with microwaves for 4 min. The progress of reaction was monitored by TLC. The mixture was extracted widi 3x30 mL CHC13, filtered, and the solvent was removed by a rotary evaporator under reduced pressure. Further purification by recrystallization gave die desired pure products 4. 

The trans- [Rh(PR3)2Cl(CO)] complexes were prepared by treating [RhCl(CO)2]2 under nitrogen in chloroform solution with 2 equiv of tertiary phosphine per rhodium atom. The only side product was carbon monoxide so that purification by recrystallization from ethanol or ethanol-chloroform was relatively simple. The lower-molecular-weight trialkylphosphine and higher-molecular-weight triarylphos-phine complexes were orange, viscous oils the others were cream-colored, low-melting crystalline solids. 

A mixture of the a,(3-unsaturated ketone 1 (0.24 g, 0.001 mol) and 1-isopropyl-piperidin-4-one 2 (0.14 g, 0.001 mol) in methanol saturated with ammonia (2 ml) was sonicated at room temperature for 90 min in a round-bottomed flask equipped with a condenser (Scheme A.21). The reaction mixture was allowed to stand for 2 h at room temperature and was then filtered to give the solid tetrahydropyrimidine products 3 and these were washed with methanol and dried in air. The reaction products were obtained in high purity (more than 98% by lH NMR) and did not require further purification by recrystallization. Melting point 239-240°C. 

The mother liquor may be separated from the produet by distillation however, this leads to discoloration of the silicon tetraacetate. For this reason, purification by recrystallization is preferable. When the procedure given here is applied to the preparation of organoacetoxysilanes, distillation is usually necessary. In this case, the acetyl chloride is removed at atmospheric pressure, and the excess acetic anhydride and product are separated by fractional distillation under reduced pressure. 

Werner1 resolved the tris(ethylenediamine)rhodium(III) ion both with sodium-3-nitro-(+)-camphor and with (+)-tartrate as resolving agents. Both methods, however, suffer from disadvantages. The solubility of the diastereoisomer (—)D-[Rh(en) 3] - (3-nitro-(-(-)-camphor)3 precipitated by the first method is so low that purification by recrystallization is impossible. On the other hand, the solubilities of the diastereoisomeric chloride (-b)-tartrates used in the second method are of the same order of magnitude, so that the solution has to be seeded with a crystal of (—)D-[Rh(en)3] Cl (+)-tart -aq. The (+)D form of the chloride (+)-tartrate is not obtained in an optically pure condition. Furthermore, the yields of both methods are low because of the many operations needed for obtaining the stereoisomers of the chloride. By the present method (—)D-[Rh(en)3] + is precipitated as the double salt Li (—)D-[Rh(en)3] (+)-tart 2-3H20, which is purified before conversion to the chloride. The (-bichloride is precipitated from the mother liquor by the addition of hydrochloric acid and ethanol. 

Marcasites in reference to how it is prepared. (Marcasites are the sulfide ores.) The vitriols are easily soluble in water so their purification by recrystallization is easy. 

New method of purification by recrystallization from alcohol. Willstatter and Pfannenstiel, Ber. 59B, 1870 (1926). 

When the reaction mixture was warmed to room temperature (4 hr - stirring after removal of cooling bath) before quenching with aqueous ammonium chloride solution, 7-indolinecarboxaldehyde (9.8-10.1 g, 44-46%) was obtained directly after silica gel column chromatography (Si02, 750 g, toluene elution).3 However, the product was contaminated by small amounts of impurities, and attempted purification by recrystallization (ether-pentane) caused considerable loss of the main product. 

This experiment will introduce you to some techniques of chemical synthesis based on acid-base reactions, purification by recrystallization, and brief characterization by melting point. Also on the characterization side, you will investigate the absorption of polarized light by matter. A liquid crystal is a state of matter neither liquid nor crystal but a state in-between. Liquid crystals are often called mesophases after the Greek mesos for middle. Normally when a crystal melts it forms an ordinary liquid phase. However, a substance which exhibits liquid crystalline behavior melts at least twice, first into the liquid crystalline or mesophase, and second, into the ordinary liquid. 

The checker has submitted the following method of purification by recrystallization To the crude product (which crystallizes to a stiff mush at 25°) is added a small amount of heptane to make a nearly saturated solution at 25°. This solution is cooled to 0° to effect crystallization and is filtered. The filtrate is then cooled to —20°, whereupon a second crop of crystals is obtained. This procedure is repeated until the Dry Ice-acetone temperature is reached or until no further crystallization takes place. The crystal crops are combined and recrystallized in a similar manner to give white granular crystals which melt at 45 to 47°. The yield is 13.6 g. (58%). 

Recrystallization is designed to remove all these types of impurity and provide a pure produet suitable for melting point measurement. Purification by recrystallization is based on the theory of saturated solutions (p. 50) and a suitable recrystallization solvent is one in which the chemical to be purified is insoluble in the cold solvent and soluble in the hot solvent. 

This technique separates the components of chemical mixtures by using the dissimilar solubility properties of the components of the mixture in different solvents. Extraction is used mainly to purify a reaction product partially before final purification by recrystallization (p. 92) or distillation (p. 107). The two common types of extraction process used in the laboratory are ... 

Desirable crystal morphology can be obtained during purification by recrystallization Prevention of habit transformation... 

Purification by Recrystallization Most impurities can be removed by the process of recrystallization. Recrystallization involves several steps that you should commit to memory ... 

Anal Calcd. for C12H36P4ClIr ([Ir(PMe3)4] Cl) C, 27.09 H, 6.82. Found C, 27.45 H, 6.70. The reactivity of this complex with polar organic solvents that dissolve it hampers purification by recrystallization. 

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