Fluted filter paper gravity filtration

C. 3-n-Heplyl-5-cyanocytosine. In a 250-ml. Erlenmeyer flask are placed 33.8 g. (0.145 mole) of 3-w-heptylureidomethylenemalononitrile and 70 ml. of methanol then 8.5 g. (0.16 mole) of sodium methoxide (Note 6) is added carefully in small portions (Note 7). The resulting solution is allowed to stand at room temperature for 3 days in the stoppered flask. The contents of the flask are dissolved in 300 ml. of cold water in an 800-ml. beaker, and the solution is stirred as 11 ml. of glacial acetic acid is added. The precipitated solid is collected by suction filtration on a Buchner funnel and washed with three 40-ml. portions of distilled water. The undried product is dissolved in 600 ml. of hot ethyl alcohol then the solution is filtered into a 1-1. flask by gravity through a fluted filter paper, concentrated on the steam bath to 200 ml., and cooled in the refrigerator for 4 hours. The 3-w-heptyl-5-cyanocytosine crystallizes in white needles, melts at 192-197° (Note 8), and amounts to 29.7-31.1 g. (88-92%) (Note 9). 

Set up the gravity filtration and filter off the carbon. It is especially important to wash off any product caught on the charcoal, and it is really hard to see anything here. You should take advantage of fluted filter paper. It should give a more efficient filtration. 

Filter the chloroform-silica gel suspension under gravity through a fluted filter paper, and wash the silica with chloroform (5 mL). Removal of the solvent from the filtrate on a rotary evaporator leaves an oil which... 

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). 

FIG. 2 Gravity filtration of hot solution through fluted filter paper. 

Why is a fluted filter paper used in gravity filtration ... 

Extraction and Isoiation Heat the mixture under gentle reflux for approximately 0.5 h. Allow the contents of the flask to cool to room temperature. Filter the mixture by gravity filtration through a fluted filter paper into the 25-mL round-bottom flask (Fig. 2.50), rinsing any residue remaining in the 50-mL flask onto the filter paper with an additional 2-4 mL of diethyl ether. 

One simple method of crystallizing organic compounds is to find a solvent where the material is soluble when hot but insoluble when cold. A classic example of this method is benzoic acid, which is soluble in hot, but not in cold, water. Insoluble impurities are removed by hot gravity filtration the hot solution is filtered through a fluted filter paper into a heated flask (Figure 5.1). The flask into which the material is filtered needs to contain some hot solvent, so that the funnel and the flask are kept warm, and crystals do not form prematurely. The filter paper is fluted to maximize its surface area and to minimize the contact with the cooler funnel. This technique works well when any impurities are insoluble in the hot solution or soluble in the solvent at any temperature. 

B. Tetracycmoethylene. A mixture of 254 g. (0.25 mole) of the dibromomalononitrile-potassium bromide salt and 1 1. of dry benzene is placed in a 2-1. three-necked flask fitted with a sealed mechanical stirrer and a reflux condenser. The stirrer is started (Note 6), and 100 g. (1.57 g.-atoms) of precipitated copper powder (Note 7) is added. The mixture is heated at reflux with constant stirring for 10-16 hours. The benzene layer becomes progressively deeper yellow as the reaction proceeds. At the end of the reaction period, the hot mixture is filtered by gravity, using a fluted paper. Most of the heavy solid is easily retained in the flask and is heated under reflux with 300 ml. of dry benzene, with stirring, for 30 minutes. Filtration of the hot mixture is carried out as before. Two 25-ml. portions of hot benzene are used to wash the precipitate and are decanted through the filter. 

If filtration by gravity through a fluted paper fails to remove the last traces of charcoal, the filtrate should be refiltered by suction through a thin mat of filter aid such as Super cel. 

Five grams of starch-g-polyacrylamide was dispersed in 333 ml of water and the mixture was heated for 4.5 hr at 95-100°C. The cooled dispersion was then treated with ultrasound, as described for starch-g-PAN in DMSO. The resulting solution was gravity-filtered through fluted Whatman 54 paper, and the filtrate was freeze-dried to give 4.4 g of polymer. To give a denser, more compact product, which might more closely resemble soluble starch-g-PAN, the freeze-dried polymer was dispersed in 20 ml of water, and the polymer was precipitated from the thick paste by addition of ethanol. The polymer was separated by filtration, washed with ethanol, and vacuum dried at 60°C. 

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