Craig tube filtration

Apparatus A 5-mL conical vial, 1-mL graduated pipet, apparatus for heating under reflux, magnetic stirring, vacuum filtration, Craig tube filtration, and flameless heating. 

Apparatus Glass apparatus from the microscale experimental procedure of Section 19.2, 3-mL conical vial, two screw-cap centrifuge tubes, 1-mL plastic syringe, Pasteur pipet with 0.5- and 1.0-mL calibration marks, ice-water bath, and apparatus for magnetic stirring, simple distillation, vacuum filtration, Craig tube filtration, and fiameless heating. 

A one-piece filtration apparatus, as shown in Fig. 4.12a is very useful for small scale filtration of solutions prior to recrystallization. It is often used in conjunction with a Craig tube (Fig. 4.12b, see Chapter 11 for more detail). A sintered funnel (Fig. 4.13) for filtration under inert atmosphere is also useful (see Chapter 6 for more details). 

Remove the apparatus from the bath, wipe the bulb to remove oil or water, and quickly filter the hot solution into a clean receiver by pressurizing the vessel using hand bellows or an inert gas line. Filtering under pressure in this way avoids the problem of unwanted crystallization, and reduces transfer losses. The hot solution can be filtered into a small conical flask, but on a scale of lOOmg or less, a Craig tube (Fig. 11.2) gives better recovery because it allows the crystals to be recovered without another filtration. 

Isolating The Crystals Craig Tube Filtration Centrifuging the Craig Tube... 

Filtration is a technique used for two main purposes. The first is to remove solid impurities from a liquid. The second is to collect a desired solid from the solution from which it was precipitated or crystallized. Several different kinds of filtration are commonly used two general methods include gravity filtration and vacuum (or suction) filtration. Two techniques specific to the microscale laboratory are filtration with a filter-tip pipette and filtration with a Craig tube. The various filtration techniques and their applications are summarized in Table 8.1. These techniques are discussed in more detail in the following sections. 

Collect crystals by vacuum filtration using a Hirsch funnel or by centrifugation using a Craig tube. 

Apparatus A 10-mm x 75-mm test tube, a calibrated Pasteur pipet and Pasteur filtering and filter-tip pipets, apparatus for Craig tube filtration and flameless heating. 

Why is a Craig tube filtration ineffective for removing finely divided particles from a solution ... 

Cool the Hydroxide Extract in an ice-water bath and. with stirring, add concentrated hydrochloric acid dropwise with a Pasteur pipet until the solution is distinctly acidic to pHydrion paper. Allow the acidified solution to remain in the bath to complete the crystallization. Then isolate the benzoic acid by Craig tube filtration (Fig. 2.55). Rinse the solid back into the Craig tube, with 0.5 ml of cold water, stir the mixture briefly, and repeat the filtration. Transfer the benzoic acid to a watchglass, cover it with a piece of filter paper, and allow the product to air-dry until the next laboratory period. After drying, put the isolated solid in a dry. fared vial. 

Complete crystallization by cooling the Craig tube in an ice-water bath for an additional 15 min. and then isolate the product by Craig tube filtration (Fig. 2.55). Carefully disassemble the Craig tube, scrape any crystalline material clinging to the glass or Teflon plug into the tube, and air-dry the product. 

Bromination and isolation Measure 1 mL of freshly prepared 1 M bromine in dichloromethane directly from the dispenser into the vial. Swirl the vial gently during the addition to mix the contents. After the addition of the bromine solution to the vial is complete, loosely screw a cap onto the vial and stir the mixture for 15 min. Isolate the product by vacuum filtration using a Hirsch funnel. Wash the product with several drops of cold dichloromethane until it is white. Transfer the product to a watchglass or a piece of filter or weighing paper and allow it to air-dry. Using a Craig tube, recrystallize the product from xylenes. 

Apparatus Water bath and apparatus for Craig tube filtration. 

Equip the Craig tube for filtration, isolate the crystalline product by centrifugation. and transfer it to a piece of filter or weighing paper for air-drying. Recrystallize the diacid from water. 

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