Funnel filtration systems

Vacuum-filtration system (Kiriyama funnel or equivalent)... 

Assemble a filtration system consisting of a ring stand, a funnel rack (or two small rings), two clean long-stem funnels, and two beakers or flasks to catch the filtrate. Obtain two pieces of Whatman 40 filter paper, fold, and place into the funnels, moistening with a little distilled water so they adhere to the funnel walls (Figure 3.8). Label the funnels to coincide with the labels on your beakers. 

Use of the Hirsch Funnel. The standard filtration system for collecting products purified by recrystallization in the microscale laboratory is vacuum (suction) ffltration with an 11-mm Hirsch funnel. Many reaction products that do not require recrystallization can also be collected directly by vacuum filtration. The Hirsch funnel (Fig.5.23a) is composed of a ceramic cone with a circular flat bed perforated with small holes. The diameter of the bed is covered by a flat piece of filter paper of the same diameter. The funnel is sealed into a filter flask with a Neoprene adapter (Fig. 5.23b). Plastic and glass varieties of this funnel that have a polyethylene or glass frit are now available. It is stfll advisable to use the filter paper disk with these funnels to prevent the frit from clogging or becoming discolored. Regardless of the type of fflter used, always wet the filter paper disk with the solvent being used in the crystallization and then apply the vacuum. This ensures that the filter paper disk is firmly seated on the bed of the filter. 

A. Dispiro[5.1.5.1]telradecane-7,14-dione. Cyclohexanecarbon-yl chloride (Note 1) (30.0 g., 0.205 mole) and 250 ml. of dry benzene are placed in a three-necked, round-bottomed flask equipped with a stirrer, condenser, and dropping funnel. A nitrogen atmosphere is maintained in the system. Dry triethylamine (35.0 g., 0.35 mole) is slowly added, and the mixture is heated under reflux overnight. The amine hydrochloride is then filtered, and the filtrate is washed with dilute hydrochloric acid and with water. Solvent is removed on a steam bath, and the residue is recrystallized from ligroin-ethanol yield 11-13 g. (49-58%), m.p. 161-162°. 

B. Polymeric Urea [Benzene, diethenyl-, polymer with ethenylbenzene, [[[[(1 methylethyl)amino]carbonyt]amino]methyl] deriv.] A 10.0-g. portion of benzylamine polymer beads prepared as in Part A and 125 ml. of tetrahydrofuran (Note 6) are combined in a 300-ml., three-necked, round-bottomed flask equipped with a magnetic stirrer, a dropping funnel, and a condenser fitted with a gas-inlet tube A nitrogen atmosphere is established in the system, and the slurry is stirred while 1.35 g. (0.0159 mole) of isopropyl isocyanate [Propane, 2-isocyanato-] is added. This causes an exothermic reaction, which subsides after about 20 minutes. The mixture is then stirred at room temperature for 22 hours and at reflux for an additional 4 hours. The beads are collected by filtration, washed with 150-ml. portions of tetrahydrofuran (Note 6) and methanol, and dried under reduced pressure over calcium chloride to yield 9.09 g, of the isopropyl urea polymer. 

To a solution of 2,3-butanedione dioxime (23.2 g, 0.2 mole) in 500 mL of boiling 95% ethanol in a 2-L Erlenmeyer flask is added a solution of cobalt(II) nitrate hexahydrate (29.0 g, 0.10 mole) in 500 mL of hot 95% ethanol. The red-brown solution is boiled on a hot plate for 5 minutes and then a solution of sodium bromide (15.8 g, 0.15 mole) in water (20 mL) is added. The brown solution is allowed to cool to 35°. Dimethyl sulfide (11 mL, 0.15 mole) is added, and the resulting solution is stirred vigorously for 8 hours with the flask open to the atmosphere. During the stirring a brown solid precipitates from solution. The solid is collected by suction filtration on a Buchner funnel and washed successively with 200-mL portions of water, ethanol, and diethyl ether. The fine, dark-brown crystals are air dried and dissolved in dichloromethane and the system is filtered. The filtrate is evaporated to give typically 20 g of product (yield is about 50%). Its purity, as it is isolated in the above procedure, is adequate for subsequent procedures of synthesis. The product can be purified further by recrystallization from dichloromethane-hexane. Anal Calcd. for Ci0H2oN404SBrCo C, 27.85 H, 4.68 N, 12.99 Br, 18.53. Found C, 27.61 H, 4.59 N, 13.03 Br, 18.64. 

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