Recrystallization gravity filtration

The key to successful gravity filtration is the fluted filter paper. A fluted filter paper decreases the area of contact between the filter paper and the funnel, thus allowing rapid filtration. If you use traditional cone-folded filter paper, note that all sides of the paper are touching the sides of the funnel and on half the filter paper the liquid has to pass through three thicknesses of paper, all of which slow the rate of filtration. Slow filtration can lead to disaster in hot filtration during recrystallization (p. 100). 

Extremely wet solids (solid floating in water). Set up a gravity filtration (see Chapter 13, Recrystallization ) and filter the liquid off of the solid. Remove the filter paper cone with your solid product, open it up, and leave it to dry. Or remove the solid and dry it on fresh filter paper as above. Use lots of care, though. You don t want filter paper fibers trapped in your solid. 

Filtering charcoal - never attempt to remove finely divided charcoal, used in decolourization during recrystallization or as a catalyst support, by suction filtration. It is a very fine powder and will always leak into the filtrate. Filter off charcoal by gravity filtration. 

A calcium chloride drying tube is used to protect the contents of the flask from atmospheric moisture, and the reaction mixture is stirred for 18h. Subsequently, 50 mL of methanol is added to the brown mixture, which is stirred for an additional 45 min. The mixture is concentrated to 50 mL by rotary evaporation using an aspirator and a protecting trap, and a solution of 8.2 g (0.05 mol) of ammonium hexafluorophosphate in 40 mL of methanol is added by gravity filtration. The mixture is stirred for 45 min, and the yellow solid that precipitates is collected by suction filtration, washed with a little cold methanol, and dried in vacuo over P Oio- Recrystallization may be effected from acetonitrile-methanol if desired, although the product IX is sufficiently pure for the following reaction. Yield 13.4g (79%). 

Discard the grayish solid obtained by gravity filtration in the container for nonhaz-ardous solids. Pour the diethyl ether obtained by distillation in a container for non-halogenated organic liquids. Flush the filtrate from the recrystallization and the aqueous layer containing aluminum salts down the drain. 

The filtrates are washed in a separatory funnel with 200 ml of saturated aqueous sodium chloride, twice with 200-ml portions of distilled water, and dried over anhydrous calcium chloride. The salt is removed by gravity filtration, and the benzene is stripped from the filtrate by means of a vacuum pump and a warm water (40°-45°C) bath. The residue, a white solid, is mixed with petroleum ether and filtered. The crude product weighs 111 gm (theoretical yield 139 gm) and melts at 48°-53°C. The product is dissolved in 700 ml of petroleum ether-benzene (1 1) solution, stirred with about 5 gm of activated charcoal, filtered, and cooled. About 25 ml of petroleum ether is added. The recrystallized material is filtered and dried in a vacuum over at room temperature. Final yield is 36 gm (m.p. 60 -63°C). 

Filtration and recrystallization run hand in hand. When a product precipitates, it must be collected. Filtration is the most common method of collecting precipitated products. The two methods of filtration include gravity, and vacuum. Vacuum filtration is the most common method of filtering in the lab, and it is also the fastest. 

The product (0.5 g) is recrystallized by stirring it with acetonitrile (20 mL) for 5 min (or until product has dissolved) and then is gravity-filtered (Whatman no. 1 paper). The filtrate is warmed to about 65°, and water (about 5 mL) is added while the solution is kept warm. Crystals usually appear upon addition of the water, and then the solution is allowed to cool to room temperature and evaporate for 24 hr. Approximate yield is 0.45 g. Anal. Calcd. for C50H48N6O8B2Fe C, 63.99 H, 5.16 N, 8.96. Found C, 63.43 H, 5.12 N, 9.04. 

The heating is discontinued after 24 hours, and the excess sodium metal is removed mechanically. After removal of the sodium, 20 ml. of methanol and then 50 ml. of water are added. The tetrahydrofuran and methanol are removed by vacuum rotary evaporation. The remaining aqueous solution is neutralized and gravity-filtered. The filtrate is treated with a saturated solution of cesium or tetramethylammonium chloride. The crude cesium salt is recrystallized as white plates from hot water in 80% yield based on the C-(trimethyIamine)carbaundec-aborane(12). The tetramethylammonium salt is recrystallized from methanol-acetone. 

A 11.46-g (30.00mmol) quantity of bis(l,2-ethanediamine)platinum(II) chloride (Alfa) is dissolved in a minimal amount of water in a SOO-mL Erlenmeyer flask. [The bis(l,2-ethanediamine)platinum(II) chloride must first have been carefully recrystallized twice to insure its purity. Recrystallization is best accomplished by dissolving the solid in SOmL of water, gravity filtering, and allowing the filtrate to evaporate slowly. Pure [Pt(en)2]Cl2 gives a colorless (not brown or yellow) solution when dissolved in water. Impure [Pt(en)2]Cl2 drastically lowers the yield of this procedure.] A 200-mL volume of concentrated HCl is added, and the solution is heated to 89 °C for 7 h. The solution must not be boiled. The reaction mixture is allowed to cool to room temperature, then it is chilled in an ice-water bath. The solid that forms is collected by vacuum filtration, and the filtrate is set aside for platinum recovery. The solid is then washed with lOOmL of water acidified with five drops of concentrated HCl. The product dissolves in this washing, and some insoluble yellow by-product, which is [Pt(en)Cl2], remains on the paper. This second filtrate is treated with 200 mL of concentrated HCl at room temperature, which precipitates the pure product. Yield 4.65 g (30%). 

The hot solution from step 5 is then filtered under gravity, to remove any undissolved sodium chloride, and cooled in ice. The white crystals of the deuterated sodium p-toluene sulphonate sodium salt are collected by filtration using a Buchnerfunnel and the product is recrystallized from hot water and dried in a vacuum oven at 100°C... 

The complex is collected on a medium-porosity sintered glass funnel by initially allowing the solution to filter under gravity, then finally under vacuum. The filtrate may be saved for recovery of the triflic acid as NaCFjSOj. The complex may be purified by boiling in chloroform as described in Section A. However, the complexes may not be recrystallized from acetonitrile, since the triflato ligands are readily substituted by acetonitrile molecules. 

Switzerland) (TEED, 0.76 g, 4.4 mmole) is added with a syringe. A yellow precipitate immediately forms and the suspension is stirred 10 minutes. The product is collected on a Buchner funnel by suction filtration, washed with a 1-mL portion of cold methanol, and dried in vacuo. This crude material, containing potassium chloride, weighs 1.98 g. For purification purposes, the crude product is quickly dissolved in 5 mL cold dichloromethane and gravity filtered. (Recrystallization should be performed as rapidly as possible in order to avoid decomposition in solution.) Upon addition of methanol (5 mL) and evaporative concentration of the orange solution to 5 mL, fine yellow-orange needles form. (The checkers found it necessary to concentrate the solution by evaporation to 2.5 mL. A yield of 70% was obtained.) The crystals (1.28 g) are collected on a Buchner funnel, washed with a 1-mL portion of cold methanol, and dried in vacuo. Additional product (0.21 g) may be obtained by further evaporation of the mother liquor. The total yield amounts to 1.49 g (80%). 

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