Funnel Hirsch

When only a small quantity of solid material has to be filtered from a liquid, the small conical funnel C, usually known as a Hirsch funnel, is used in order to collect and drain the material on a very small filter-paper (see p. 68). 

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). 

For the HCI salt Do exactly as above except use 6N Hydrochloric Acid. 6N HCI may be produced by diluting 60.4mL of "Muriatic Acid" to lOOmL with distilled water. Evaporate the bubbler solution to dryness then add 15ml of water, lOmL 10% NaOH soln. and heat gently to a boil with constant motion until dense white fumes appear. This will remove the Ammonium Chloride. Remove from heat while stirring as it cools down. Pulverize the dry residue, then reflux with absolute Ethanol for several minutes. Filter the refluxed soln. on a heated Buchner or Hirsch funnel, then distill the alcohol off the filtrate until crystals just begin to form. Allow the soln. to cool naturally to room temperature, then cool further in an ice bath. Filter the solution on a chilled Buchner funnel with suction. The yield of Meth iamine Hydrochloride should be around 55% of the theoretical. 

S-ml. portions of water, and dried over anhydrous sodium sulfate. The solvent is removed on a steam bath in a stream of nitrogen and finally at reduced pressure. The crystalline residue of 0.207 g. (Note 7) is recrystallized in a 10-ml. conical flask from 1 ml. of acetone. When the flask has cooled to room temperature, 0.5 ml. of methanol is added, and the flask is chilled to +2° for 2 hours. The crystals are collected on a tared Hirsch funnel of 40-mm. diameter, washed on the funnel with two 0.5-ml. portions of ice-cold methanol, and dried for 2 hours at 40°/2 mm. The first crop of cholestanyl methyl ether thus obtained forms large colorless glistening plates, m.p. 85.5-86° (Note 8). An additional... 

The mother liquor may be evaporated to dryness and the slightly colored residue recrystallized in a 3-ml. conical flask from 6 drops of 1 1 acetone-methanol. The resulting large plates are easily transferred to a small Hirsch funnel and washed with 5 drops of methanol. This second crop of colorless methyl ether amounts to 0.010 g., m.p. 78.5-79.5°. 

The Buchner and Hirsch funnels, and the filter flasks and tubes, are available with interchangeable ground glass joints (for example, Fig. 2.43(/)). The Buchner funnel is also available with a screw-thread side-arm for easy attachment via a plastic hose connector to the vacuum line (Bibby Science Products). 

Filter off the spent catalyst on a small Hirsch funnel and wash it with a little of the solvent. The damp used catalyst should be transferred immediately to a residues bottle for subsequent recovery (Sections 4.2.54 and 61, pp. 452 and... 

For the suction filtration of small quantities of solid (less than 5g) contained in a small volume of liquid, a small conical Buchner funnel, known as a Hirsch funnel, is employed (see Fig. 2.43(h)) the filtrate is collected either in a small filter flask or in a test tube with side-arm, the arrangement being illustrated in Fig. 2.43(f). A small sintered funnel, or a slit-sieve funnel may also be employed. The procedure for filtration is similar to that already given for the Buchner funnel. 

The goal of vacuum filtration is usually to remove liquids from a solid to obtain a solid that is dry. An aspirator or a vacuum pump is used to provide suction though a rubber tube to a filter trap. The trap is attached to a filter flask (show to the right) by a second rubber tube. The filter flask is an Erlenmeyer flask with a thick wall and a hose barb for the vacuum tube. Filter flasks are used to filter material using a Buchner funnel (shown to the right) or a smaller Hirsch funnel. These porcelain or plastic funnels hold a circular piece of filter paper. A single-hole rubber stopper supports the funnel in the flask while maintaining suction. 

B. Vacuum pump, Hirsch funnel, rubber stopper with a single hole... 

General procedure for recrystallization. Heat a small volume (10-20 mL) of solvent to boiling on a steam bath (or carefully on a hot plate). Place crystals into a test tube (100 X 13 mm) and add the hot solvent (dropwise) until the crystals just dissolve (keep the solution hot, also). Allow the solution to cool to room temperature then cool further in an ice bath. Collect the crystals on a Hirsch funnel by vacuum filtration. Use a trap between the Hirsch funnel set-up and the aspirator (Fig. 31.1). Wash the crystals with 10 drops of ice cold solvent. Allow the crystals to dry by drawing air... 

Figure 31.1 Vacuum filtration with a Hirsch funnel.

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