Filtration suction

Isolation of the products is usually carried out by filtration. Suction filtration is faster and preferable to gravity filtration. When pyrophoric noble metal catalysts and Raney nickel are filtered with suction the suction must be stopped before the catalyst on the filter paper becomes dry. Otherwise it can ignite and cause fire. Where feasible centrifugation and decantation should be used for the separation of the catalyst. Sometimes the filtrate contains colloidal catalyst which has passed through the filter paper. Stirring of such filtrate with activated charcoal followed by another filtration usually solves this problem. Evaporation of the filtrate and crystallization or distillation of the residue completes the isolation. 

The sample mixture should contain no strongly retained components and thin-layer chromatography can be used to check this (no trace should remain at the starting point). The sample may be cleaned by adsorptive filtration (suction filter with a coarse stationary phase) or column chromatography if required. This is of special importance in the case of reaction mixtures or samples of natural origin. A guard colunrn is essential if impurities or decomposition in the column cannot be fully ruled out. Losses can be avoided by ensuring that the sample loop is not filled to capacity (see Section 4.6). 

Vakuum vacuum Vakuumdestillation vacuum distillation, reduced-pressure distillation Vakuumeindampfer vacuum concentrator Vakuumfalle vacuum trap vakuumfest vacuum-proof Vakuumfiltration vacuum filtration, suction filtration Vakuumfonnen vacuum forming Vakuumofen vacuum furnace Vakuumpumpe vacuum pump... 

The technique of the filtration of hot solutions has already been described in Section 11,28. The filtration of cold solutions will now be considered this operation is usually carried out when it is desired to separate a crystalline solid from the mother liquor in which it is suspended. When substantial quantities of a solid are to be handled, a Buchner funnel of convenient size is employed. The ordinary Buchner fimnel (Fig. 11,1, 7, a) consists of a cylindrical porcelain funnel carrying a fixed, flat, perforated porcelain plate. It is fitted by means of a rubber stopper or a good cork into the neck of a thick-walled filtering flask (also termed filter flask, Buchner flask or suction flask) (Fig. 11,1, 7, c), which is connected by means of thick-walled rubber tubing (rubber pressure tubing) to a similar flask or safety bottle, and the latter is attached by rubber pressure tubing to a filter pump the safety bottle or trap is essential since a sudden fall in water pressure may result in the water sucking back. The use of suction renders rapid filtration possihle... 

FILTRATION OF SMALL QUANTITIES OF MATERIAL WITH SUCTION... 

The apparatus depicted in Fig. 11,34, 1, intended for advanced students, may be used for the filtration of a small quantity of crystals suspended in a solvent either a Hirsch funnel or a glass funnel with Witt filter plate is employed. The mixture of crystals and mother liquor is filtered as usual through the funnel with suction. Rotation of the three-way tap wifi allow air to enter the filter cylinder, thus permitting the mother liquor to be drawn oflF by opening the lower tap. The mother liquor can then be applied for rinsing out the residual crystals in the vessel, and the mixture is again filtered into the cylinder. When all the crystals have been transferred to the funnel and thoroughly drained, the mother liquor may be transferred to another vessel the crystals may then be washed as already described (Section 11,32). 

Filtration of corrosive liquids with suction. A strongly alkaline or acid suspension is best filtered through a sintered glass funnel. Alternatively, glass wool or asbestos may be plugged into the stem of a glass funnel or supported upon a Witt plate in a glass funnel. 

Pure pyridine may be prepared from technical coal-tar pyridine in the following manner. The technical pyridine is first dried over solid sodium hydroxide, distilled through an efficient fractionating column, and the fraction, b.p. 114 116° collected. Four hundred ml. of the redistilled p)rridine are added to a reagent prepared by dissolving 340 g. of anhydrous zinc chloride in a mixture of 210 ml. of concentrated hydrochloric acid and 1 litre of absolute ethyl alcohol. A crystalline precipitate of an addition compound (probable composition 2C5H5N,ZnCl2,HCl ) separates and some heat is evolved. When cold, this is collected by suction filtration and washed with a little absolute ethyl alcohol. The yield is about 680 g. It is recrystaUised from absolute ethyl alcohol to a constant m.p. (151-8°). The base is liberated by the addition of excess of concentrated... 

In a 1-litre three-necked flask, fitted with a mechanical stirrer, reflux condenser and a thermometer, place 200 g. of iodoform and half of a sodium arsenite solution, prepared from 54-5 g. of A.R. arsenious oxide, 107 g. of A.R. sodium hydroxide and 520 ml. of water. Start the stirrer and heat the flask until the thermometer reads 60-65° maintain the mixture at this temperature during the whole reaction (1). Run in the remainder of the sodium arsenite solution during the course of 15 minutes, and keep the reaction mixture at 60-65° for 1 hour in order to complete the reaction. AUow to cool to about 40-45° (2) and filter with suction from the small amount of solid impurities. Separate the lower layer from the filtrate, dry it with anhydrous calcium chloride, and distil the crude methylene iodide (131 g. this crude product is satisfactory for most purposes) under diminished pressure. Practically all passes over as a light straw-coloured (sometimes brown) liquid at 80°/25 mm. it melts at 6°. Some of the colour may be removed by shaking with silver powder. The small dark residue in the flask solidifies on cooling. 

Suspend 0 25 g. of 2 4-dinitrophenylhydrazine in 5 ml. of methanol and add 0-4 0-5 ml. of concentrated sulphuric acid cautiously. FUter the warm solution and add a solution of 0 1-0-2 g. of the carbonyl compound in a small volume of methanol or of ether. If no sohd separate within 10 minutes, dUute the solution carefuUy with 2N sulphuric acid. CoUect the solid by suction filtration and wash it with a little methanol. RecrystaUise the derivative from alcohol, dUute alcohol, alcohol with ethyl acetate or chloroform or acetone, acetic acid, dioxan, nitromethane, nitrobenzene or xylene. 

Furfuryl acetate. Reflux a mixture of 39 2 g. (34-8 ml.) of redistilled furfuryl alcohol, 48 g. of glacial acetic acid, 150 ml. of benzene and 20 g. of Zeo-Karb 225/H in a 500 ml. bolt-head flask, using the apparatus described under iaoPropyl Lactate. After 3 hours, when the rate of collection of water in the water separator is extremely slow, allow to cool, separate the resin by suction filtration, and wash it with three 15 ml. portions of benzene. Remove the benzene, etc., from the combined filtrate and washings under reduced pressure (water pump) and then collect the crude ester at 74-90°/10 mm. a small sohd residue remains in the flask. Redistil the crude ester from a Claisen flask with fractionating side arm pure furfuryl acetate passes over at 79-80°/17 mm. The yield is 14 -5 g. 

Mix together in a 250 ml. flask carrying a reflux condenser and a calcium chloride drying tube 25 g. (32 ml.) of freshly-distilled acetaldehyde with a solution of 59-5 g. of dry, powdered malonic acid (Section 111,157) in 67 g. (68-5 ml.) of dry pyridine to which 0-5 ml. of piperidine has been added. Leave in an ice chest or refrigerator for 24 hours. Warm the mixture on a steam bath until the evolution of carbon dioxide ceases. Cool in ice, add 60 ml. of 1 1 sulphuric acid (by volume) and leave in the ice bath for 3-4 hours. Collect the crude crotonic acid (ca. 27 g.) which has separated by suction filtration. Extract the mother liquor with three 25 ml. portions of ether, dry the ethereal extract, and evaporate the ether the residual crude acid weighs 6 g. Recrystallise from light petroleum, b.p. 60-80° the yield of erude crotonic acid, m.p. 72°, is 20 g. 

Procedure 2. Follow Procedure 1 except that no solvent is employed. Pour the s3Tupy reaction mixture on to crushed ice, remove the resulting aryl sulphonyl chloride and/or sulphone, if a sohd, by filtration with suction and, if a hquid, by means of a small separatory funnel or dropper, and wash with water. 

Benzylatnine. Warm an alcoholic suspension of 118-5 g. of finely-powdered benzyl phthalimide with 25 g. of 100 per cent, hydrazine hydrate (CAUTION corrosive liquid) a white, gelatinous precipitate is produced rapidly. Decompose the latter (when its formation appears complete) by heating with excess of hydrochloric acid on a steam bath. Collect the phthalyl hydrazide which separates by suction filtration, and wash it with a little water. Concentrate the filtrate by distillation to remove alcohol, cool, filter from the small amount of precipitated phthalyl hydrazide, render alkaline with excess of sodium hydroxide solution, and extract the liberated benzylamine with ether. Dry the ethereal solution with potassium hydroxide pellets, remove the solvent (compare Fig. //, 13, 4) on a water bath and finally distil the residue. Collect the benzylamine at 185-187° the 3ueld is 50 g. 

Add 25 g. of finely-powdered, dry acetanilide to 25 ml. of glacial acetic acid contained in a 500 ml. beaker introduce into the well-stirred mixture 92 g. (50 ml.) of concentrated sulphuric acid. The mixture becomes warm and a clear solution results. Surround the beaker with a freezing mixture of ice and salt, and stir the solution mechanically. Support a separatory funnel, containing a cold mixture of 15 -5 g. (11 ml.) of concentrated nitric acid and 12 -5 g. (7 ml.) of concentrated sulphuric acid, over the beaker. When the temperature of the solution falls to 0-2°, run in the acid mixture gradually while the temperature is maintained below 10°. After all the mixed acid has been added, remove the beaker from the freezing mixture, and allow it to stand at room temperature for 1 hour. Pour the reaction mixture on to 250 g. of crushed ice (or into 500 ml. of cold water), whereby the crude nitroacetanilide is at once precipitated. Allow to stand for 15 minutes, filter with suction on a Buchner funnel, wash it thoroughly with cold water until free from acids (test the wash water), and drain well. Recrystallise the pale yellow product from alcohol or methylated spirit (see Section IV,12 for experimental details), filter at the pump, wash with a httle cold alcohol, and dry in the air upon filter paper. [The yellow o-nitroacetanihde remains in the filtrate.] The yield of p-nitroacetanihde, a colourless crystalline sohd of m.p. 214°, is 20 g. 

Difluorodiphenyl. Bis-diazotise a solution of 46 g. of benzidine (Section IV,88) in 150 ml. of concentrated hydrochloric acid and 150 ml. of water by means of a solution of 35 g. of sodium nitrite in 60 ml. of water add about 200 g. of crushed ice during the process (compare p-Fbtorotoluene above). Filter the solution and add it to a filtered solution of 85 g. of sodium borofluoride in 150 ml. of water. Stir for several minutes, collect the precipitated bis-diazonium borofluoride by suction filtration, wash with 5 ml. of ice-cold water, and dry at 90-100°. Place the dry salt in a flask fitted with an air condenser, immerse the flask in an oil bath, and slowly raise the temperature to 150° (Fume Cupboard ). When decomposition of the salt is complete, steam distil the mixture collect the 4 4 difluoro-diphenyl which passes over and recrystallise it from ethanol. The yield is 21 g., m.p. 92-93°. 

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