Filtering pipet

Fill the filter pipet from another pipet. 

Let the liquid drain out of the filter pipet into your clean vial. Note that you could—could, mind you—put a rubber bulb onto the filter pipet and use the bulb to help push the solution out. Watch out ... 

If you ve compared this outline to the large-scale recrystallization, you ll find that, with one exception—keeping a reservoir of hot solvent ready— the only difference here is the size of the equipment. Test tubes for flasks, filter pipets for funnels with paper, and so on. Because you can easily remove solvent at this scale, adding too much solvent is not quite the time-consuming boiling-off you d have to do at the larger scale. 

When volumes less than about 5 mL must be filtered, there is a danger of losing material on the filter paper, because the paper absorbs a significant volume of liquid. A Pasteur filtering pipet (Sec. 2.5) should be used in such cases. The liquid mixture to be filtered is transferred by pipet into the filtering pipet as shown in Figure 2.51. The plug should be rinsed with about 0.5 mL of solvent to maximize the recovery of the solute. 

Gravity filtration with a Pasteur filtering pipet. 

Completely removing decolorizing carbon by hot filtration (Sec. 2.17) may be difficult if the powdered rather than the pelletized form is used, because the finely divided solid particles may pass through filter paper or the cotton of a Pasteur filtering pipet (Sec. 2.5). If this occurs, the dark particles should be visible in the filtrate. 

Apparatus A 5-mL conical vial or 10-mL round-bottom flask, ice-water bath, Fasteur filter-tip and filtering pipets, tared 5-mL Craig tube, apparatus for heating under reflux, magnetic stirring, and flame/ess heating. 

Allow the mixture to cool to room temperature and then gravity-filter the ethereal solution into a Craig tube, using Pasteur filter-tip and filtering pipets (Fig. 2.51). Use a filter-tip pipet to rinse the reaction vessel with 0.5-1 ml of technical diethyl ether, and use the pipet to transfer the rinsing to the Craig tube. ... 

There are two reasons for placing the cotton plug in the pipet. First, it solves a particular problem with the transfer of volatile liquids via the standard Fhsteur pipet the rapid buildup of back pressure from solvent vapors in the rubber biolb. This pressure quickly tends to force the liquid back out of the pipet and can cause valuable product to drip on the bench top. The cotton plug tends to resist this back pressure and allows much easier control of the solution once it is in the pipet. The time-delay factor becomes particularly important when the Pasteur filter pipet is employed as a microsep-aratory funnel (see the discussion on extraction techniques in Technique 4, p. 67). 

Second, each time a transfer of material is made, the material is automatically filtered. This process effectively removes dust and Unt, which are constant problems when working at the microscale level. A second stage of filtration may be obtained by employing a disposable filter tip on the original Pbsteur filter pipet as described by Rothchild. °... 

Separation. At the microscale level, the two phases are separated with a Pasteur filter pipet (a simple Pasteur pipet can be used in some situations), which acts as a miniature separatory funnel. The separation of the phases is shown in Figure 5.14. 

Figure 5.16 Pasteur filter pipet separation of two immiscible liquid phases the more dense layer contains the product.

Step 3. Transfer the heated solution to the Craig tube by Pasteur filter pipet (see Fig. 3.30) that has been preheated with hot solvent. This transfer automatically filters the solution. A second filtration is often necessary if powdered charcoal has been used to decolorize the solution. 

Concentration of solvent by distillation is straightforward, and the standard routine is described in Technique 2 (page 61). This approach allows for high recovery of volatile solvents and often can be done outside a hood. The Hickman stiU head and the 5- or 10-mL round-bottom flask are useful for this purpose. Distillation should be used primarily for concentration of the chromatographic fraction, followed by fransfer of the concentrate with a Pasteur filter pipet to a vial for final isolation. 

In the next step, disconnect and cool the 3-mL conical vial in an ice water bath for 10 min. frans-l,2-Dibenzoylethylene will crystallize from the concentrated solution. Remove the remaining solvent from the distUlation vial with a Pasteur filter pipet and place the crystals on a porous clay plate to air dry. The melting point of the crystalline material is obtained by the evacuated capillary method and compared with the literature value. 

Purpose. This exercise illustrates the general procedures that are used to determine a partition coefficient at the microscale level. Experience in weighing milligram quantities of materials on an electronic balance, the use of automatic delivery pipets for accurately dispensing microUter quantities of liquids, the transfer of microHter volumes of solutions with the Pasteur filter pipet, and the use of a Vortex mixer, are techniques encountered in this experiment. 

Carefully draw the lower methylene chloride layer into a Pasteur filter pipet and transfer it to a 5-mL conical vial containing 100 mg of anhydrous, magnesium sulfate. If the amount of the methylene chloride layer is insufficient to properly transfer into the 5-mL conical vial, carefully add more so that a proper transfer can occur. Once complete, recap the vial. 

Isolation of 9-Fluorenone The Neutral Component. Use a Fhsteur filter pipet to transfer the dried ether solution collected earUer to a tared 10-mL Erlen-meyer flask containing a boiling stone. Rinse the drying agent with an additional 1 mL of ether and combine the ether wash with the anhydrous organic phase. 

Isolation of Product. When the reaction is complete as judged byTLC, use a calibrated Pasteur pipet to add dropwise 1.0 mL of cold dilute hydrochloric acid (0.1 M HQ). Extract the aqueous mixture with three 0.5-mL portions of methylene chloride. Upon each addition of methylene chloride, cap the vial, shake it gently, and then carefully vent it by loosening the cap (a Vortex mixer may be used if available). After the layers have separated, remove the bottom methylene chloride layer using a Fhsteur filter pipet and transfer it to a Fhsteur filter pipet containing about 500 mg of anhydrous sodium sulfate. 

Isolation of Product. When the reaction is complete as judged by TLC, work up the resulting solution using the procedure described in Experiment [5A], Isolation of Product (p. 154), with the exception that 250 mg of sodium sulfate is placed in the Pasteur filter pipet... 

Add decolorizing charcoal pellets (10 mg) to this solution and swirl the mixture gently for several minutes. Use a Pasteur filter pipet to transfer the methylene chloride solution to a second 10-mL Erlenmeyer flask containing a boiling stone (remember to hold the necks of the two flasks close together with the fingers of one hand during the transfer). 

Chlorobenzyl alcohol. Wash the combined methylene chloride extracts with two 0.25-mL portions of saturated sodium bicarbonate solution followed by one 0.5-mL portion of distilled water. Remove the aqueous upper phase (Pasteur filter pipet) used in each washing step and save this combined material in a separate 10-mL Erlenmeyer flask. This material will be discarded at the end of the experiment [see Rule 10 for the Microscale Laboratory, Chapter 1, p. 4.7) Dry the methylene chloride layer over 150 mg of granular anhydrous sodium sulfate (-41). 

Isolation of Product. After removing the reflux condenser and drying tube, remove the spin vane with forceps. Add a boikng stone to the cooled vial and then concentrate the reaction solution to a volume of about 0.25 mL by warming in a sand bath in the hood. Remove the vial from the sand bath and allow the vial to cool. Use a 1.0-mL graduated pipet to add 0.5 mL of diethyl ether and 0.25 mL of 5% sodium bicarbonate solution to the concentrated product mixture. Cap the conical vial and shake gently (or mix on aVortex mixer). Loosen the cap carefully to vent the two-phase mixture. Remove the bottom aqueous layer using a Fhsteur filter pipet and set it aside in a labeled Erlenmeyer flask. Extract the ether phase with three additional 0.25-mL portions of 5% sodium bicarbonate solution. Save the aqueous wash after each extraction (you may combine them with the initial aqueous basic phase in the Erlenmeyer) and do not discard them until you have successfully purified and characterized the ethyl Iaurate. 

Purification and Characterization. Dry and purify the wet, crude ether solution of ethyl Iaurate by column chromatography. In a Pasteur filter pipet, place 500 mg of activated silica gel followed by 500 mg of anhydrous sodium sulfate (- ). Wet the column first with 0.5 mL of methylene chloride and then transfer the crude ether solution of ethyl Iaurate to the column using a Fhsteur filter pipet. Use a tared 5-mL conical vial containing a boiling stone as a collection flask for the column eluant. Rinse the reaction vial with methylene chloride (0.5 mL). Transfer the rinse to the column. Repeat both rinse and transfer with a second aliquot of methylene chloride (0.5 mL). Add an additional 1.0 mL of methylene chloride directly to the column to ensure complete elution of the ester. 

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