Microscale conical vial

I ve put drawings of microscale equipment I ve had occasion to use in this section, along with some discussion ofthe 0-ring seals, conical vials, drying tubes, and so on. I ve put full descriptions of certain microscale apparatus with the operations they re used in. So Craig tubes show up with recrystallization the Hickman still is with distillation. 

In a famous microscale manual, you re told how to make one of these seals between an air condenser and a conical vial from the top down. In sum ... 

The conical vial (Fig. 34) is the round-bottom flask of the microscale set, with considerably more hardware. When your glassware kit is brand new, every vial has a plastic cap, O-ring, and plastic disk to match. After one semester, every vial needs this stuff. When you check-in, make sure that every conical vial has a cap that fits and that you have at least one O-ring for each and a plastic disk that just fits inside this cap. 

Unless the samples are analyzed by gas chromatography immediately after the distillation, it is essential that the samples be stored in leak-proof vials. We have found that GC-MS vials work much better for this purpose than conical vials found in microscale glassware kits. 

When the distillation is complete, transfer the distillate to a tared 3-mL conical vial with a Pasteur pipette and weigh it to determine the percentage yield. Determine a microscale boiling point (Technique 13, Section 13.2) for your product. 

Microscale Methods. A simple means of evaporating a solvent is to place a conical vial in a warm water bath or a warm sand bath. The heat from the water bath or sand bath will warm the solvent to a temperature where it can evaporate within a short time. The heat from the water bath or sand bath can be adjusted to provide the best rate of evaporation, but the liquid should not be allowed to boil vigorously. The evaporation rate can be increased by allowing a stream of dry air or nitrogen to be directed into the vial (Figure 7.17A). The moving gas stream will sweep the vapors from the vial and accelerate the evaporation. As an alternative, a vacuum can be applied above the vial to draw away solvent vapors (Figure 7.17B and 7.17C). 

A convenient water bath suitable for microscale methods can be constructed by placing the aluminum collars, which are generally used with aluminum heating blocks into a 150-mL beaker (Figure 7.17A). In some cases, it may be necessary to round off the sharp edges of the collars with a file in order to allow them to fit properly into the beaker. Held by the aluminum collars, the conical vial will stand securely in the beaker. This assembly can be filled with water and placed on a hot plate for use in the evaporation of small amounts of solvent. 

In microscale work, the apparatus with the round-bottom flask can be modified by replacing the round-bottom flask with a conical vial. The glass tubing is connected by vacuum tubing to either an aspirator or a vacuum pump. A convenient alternative, using a side arm test tube, is also shown in Figure 11.8B. With either apparatus, install a water trap when an aspirator is used. 

The 5-mL conical vial is the most useful piece of equipment for carrying out extractions on a microscale level. In this section, we consider the method for removing the lower layer. A concrete example would be the extraction of a desired product from an aqueous layer using methylene chloride d = 1.33 g/mL) as the extraction solvent. Methods for removal of the upper layer are discussed in the next section. 

To dry a large amount of organic liquid (greater than about 5 mL), follow the same four steps just described for the "Microscale Drying Procedure." The main differences are that an Erlenmeyer flask is used rather than a test tube or conical vial and more drying agent will be required. The size of the Erlenmeyer flask is not critical, but it s best that the flask not be filled more than half full with the solution being dried. 

An aluminum block is a convenient accessory used in conjimction with hot plates for reactions being performed in a microscale apparatus. The block has indentations of various sizes and shapes to accommodate conical vials and flasks (Fig. 2.26). There may also be a receptacle for inserting the bulb of a glass thermometer or the base of... 

Commercial sublimation adapters such as those shown in Figure 2.59 are available for microscale work. A Winston adapter is normally used with a sublimation chamber such as a 3- or 5-mL conical vial (Fig. 2.59a), whereas adjustable adapters may be used with 5- or 10-mL round-bottom flasks (Fig. 2.59b). In both cases a cold-finger that may be connected to a vacuum source is fitted to the chamber containing the substance to be sublimed, and the connection is secured with a standard-taper joint that is often accompanied by an O-ring and threaded collar (Fig. 2.59). The cold-finger can be filled with ice or dry ice. The advantage of using... 

The volumes of solvent are too small to use separatory funnels for extractions when reactions are conducted on a microscale level. In these instances, conical vials may be employed for volumes up to about 4 mL, and screw-cap centrifuge tubes may be used for volumes up to approximately 10 mL (Fig. 2.63). To avoid accidental spills, place the conical vial or centrifuge tube in a small beaker when you are not handhng it. 

Setting Up Place a spinvane in the conical vial. Using a calibrated Pasteur pipet, add 1 mL of cyclohexanol and 0.5 mL of 9 AT sulfuric acid to the vial. Thoroughly mix the contents by briefly stirring or swirling the liquid for a few seconds. Equip the vial for microscale distillation and circulate cold water through the condenser. 

Distillation Using a filter-tip pipet. transfer the dried organic layer into a clean 5-mL conical vial equipped with a stirbar. Attach the vial to a Hickman stillhead equipped with a water-cooled condenser (Fig. 2.38) and perform a microscale distillation. The first fraction should contain solvent and unchanged 1-hexene and should distill at a bath temperature below 110 °C. Remove this fraction from the still, and collect a second fraction, using a bath temperature of 165 °C. This fraction should mainly consist of the desired product. Transfer this distillate to a fared screw-cap vial. 

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. 

One of the most versatile pieces of glassware contained in the microscale organic glassware kit is the conical reaction vial. This vial is used as a vessel in which organic reactions are performed. It may serve as a storage container. It is also used for extractions (see Technique 12). A reaction vial is shown in Figure 3. 

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