Buchner filtration

The water pump is another example of the Bernoulli effect, and is an everyday piece of equipment in most laboratories, for example being used during Buchner filtration. It comprises a piece of rubber tubing to connect the flask to be evacuated to a pump. Inside the pump, a rapid flow of water past one end of a small aperture inside the head decreases the pressure of the adjacent gas, so the pressure inside the pump soon decreases. 

Remove the resin by Buchner filtration, wash it with distilled water (30 mL) and evaporate the combined filtrates to a gum. 

Filter the white precipitate using a Buchner filtration apparatus and discard the precipitate. Concentrate the remaining clear solution to approximately 50 mL using a rotary evaporator. Precipitate the product from the concentrate by drop-wise addition into the vortex walls of rapidly stirred cold diethyl ether (250 mL). Filter the white precipitate from the solvent using a Buchner filtration apparatus. Dissolve the precipitate in toluene (50 mL) and repeat the precipitation process. Filter the white precipitate again and dry under vacuum to remove all traces of solvent. The final product should be stored under dry nitrogen in the dark. Yields >90% are usual. 

Recrystalllzatlon is used to purify a product. Many chemicai preparations give dirty products in which the product is contaminated with, for exampie, excess reactants or products from side reactions. A soivent is found that dissoives the desired product when the soivent is hot, but the product is not soiubie when the soivent is cold. This choice of solvent is the difficult part and involves some trial and error experiments. The impure product is dissolved in the minimum of the hot solvent and the hot solution is filtered very quickly to remove insoluble impurities before the mixture cools down - Buchner filtration (using warm apparatus) is useful here. The filtered solution is allowed to cool and the product crystallizes out. Any soluble impurities (since they are present at low concentration) tend to remain in solution and the desired product crystallizes out in a more pure form. If the product is required to be very pure, several recrystallizations may be necessary. 

A similar technique was demonstrated by Wang et al They also fabricated buckypaper but incorporated an epoxy-hardener blend by Buchner filtration. To reduce the viscosity, the blend was mixed with acetone. Very good infiltration was observed throughout the paper. The epoxy was cured by hot pressing 3-5 stacked sheets together at 177 °C to form a thick composite film. 

Cool the flask to 0°C, stand for 2 h, and then collect the precipitate by Buchner filtration through a filter paper, with suction. Wash the solid three times with ice-cold water (3x12 mL). Dry the solid overnight in a beaker. The octenylboronic acid obtained can be used for the coupling reaction without further purification (5.63 g, 90%). 

However, using an appropriate surfactant in water can be cheaper than using DMF and NMP, which also exhibit the disadvantage of high boiling points. The most common surfactants are sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulphate (SDS). Aqueous dispersion of SWNTs in the presence of the water-soluble perylene derivatives has also been reported. After the nanotubes are dispersed in a solvent, the buckypaper can usually be fabricated by a simple Buchner filtration[22]. 

This type of filtration is almost invariably performed with the aid of a Buchner flask and funnel, by means of which a rapid and almost complete separation can be obtained. The Buchner flask A (Fig. 4) consists of a simple thick-walled conical flask with a short side-arm for connection to a water-pump. Into the neck of the flask is fitted the Buchner funnel B which consists usually of a cylindrical porcelain funnel, the bed of which is pierced by a... 

The filtration of crystals is carried outusing a small conical Buchner funnel (C, Fig. 4, p. 10) or a funnel of similar design but having a sintered filtration plate. Alternatively an ordinary conical funnel in which is placed a circular perforated plate can be used. 

Add 5 g. of potassium hydrogen tartrate and 5 g. of antimony trioxide (each being finely powdered) to 30 ml. of water contained in a small flask, and boil the mixture under a reflux water-condenser for 15 minutes. Then filter hot, using a Buchner funnel and flask which have been preheated by the filtration of some boiling distilled water. Pour the clear filtrate into a beaker and allow to cool. Potassium antimonyl tartrate separates as colourless crystals. Filter, drain and dry. Yield, 5 g. The product can be recrystallised from hot water, but this is usually not necessary. 

Dissolve 5 g. of aniline hydrochloride in 120 ml. of hot water contained in a 200 ml. conical flask and then add 4 g. of potassium cyanate. Heat the solution on a water-bath for 30 minutes, adding about 1-2 g. of animal charcoal towards the end of the heating if a slight turbidity has developed. Now bring the solution quickly to the boil over a gauze, and filter it at the pump, using a Buchner funnel and flask which have been preheated by the filtration of some boiling distilled water. The clear... 

When the ij hours boiling is complete, preheat a Buchner funnel and flask by pouring some boiling water through the funnel with the filter-paper already in position, and then quickly filter the boiling solution. Transfer the filtrate to a beaker to cool, and then wash the insoluble residue of diphenylurea on the filter twice with hot water, and drain thoroughly. Cool the filtrate in ice-water the monophenylurea separates as colourless needles. Filter at the pump and drain well. Recrystallise the crude product from boiling water, as in the previous preparation. Yield of monophenylurea, 2 5-3 g. m.p. 147°. 

The insoluble residue of diphenylurea from the original filtration is chemically almost pure. It may be recrystallised from hot rectified spirit or ethanol, a process which will be necessary if the material contains fragments of porcelain. When using either of these solvents, however, the hot solution should be filtered at the pump using a small Buchner funnel and flask which again have been preheated by the filtration of some of the hot solvent, as the solution when cooled rapidly deposits the diphenylurea. iSym-Diphenylurea (or carbanilide) is thus obtained as fine colourless crystals, m.p. 237° yield, 1-1 5 S ... 

For purification, transfer the acid to a 150 ml. flask containing 60 ml. of water, boil the mixture under reflux, and then add acetic acid in 5 ml. portions down the condenser until almost all the solid has dissolved avoid an excess of acetic acid by ensuring that the solvent action of each addition is complete before the next portion is added. A small suspension of insoluble impurity may remain. Add 2 g. of animal charcoal, boil the solution again for 10-15 minutes, and then filter it through a preheated Buchner funnel. Cool and stir the filtrate, which will deposit pale cream-coloured crystals of the acid. Collect as before and if necessary repeat the recrystallisation. Yield of pure acid, 9 g. m.p. 227-229°. 

Allow the reddish-yellow solution to cool to about 40° and then filter off at the pump the polyene which has separated this filtration should be performed as rapidly as possible to avoid contamination with lead acetate, and a Buchner funnel of not less than 6 cm. diameter should therefore be used to avoid clogging the filter. Wash the crude production the filter with... 

Recrystallise the remaining half of the crude anthraquinone from boiling acetic acid, using animal charcoal filter the hot solution through a Buchner funnel which has been preheated by the filtration of some of the boiling solvent, as the anthraquinone crystallises rapidly as the solution cools. Cool the filtrate in cold water and then filter at the pump, drain, wash with methylated spirit and dry. Yield, 4-5 g. 

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