Hickman stillhead

The volume of distillate in microscale distillations is typically less than 500 xL (0.5 mL), so it is important to minimize the surface area of glass to avoid unnecessary loss of material. This is accomplished by combining the stillhead and collector in a single piece called a Hickman stillhead, which has a reservoir for containing distillate and may have a port to facilitate removal of distillate (Fig. 2.38). 

A Pasteur or filter-tip pipet (Sec. 2.5) is used to remove distillate from the Hickman stillhead. If the head has a port, the pipet can be inserted at this point. If not, the condenser must first be removed and the pipet inserted through the top of the stillhead. Depending on the geometry of the stillhead, it may be necessary to use a Pasteur pipet having a curved tip to allow the tip to reach the bottom of the reservoir. A Bunsen or microburner (Sec. 2.9) may be used to produce the necessary bend. 

Another common method for removing solvent is by simple microscale distillation (Sec. 2.13). Discontinue heating when only a small amount of solvent remains, and do not overheat the stillpot, as your product may decompose if heated too strongly. The stillpot should be cooled to room temperature. Remove the Hickman stillhead and water condenser and insert an air condenser into the vial. Attach a thermometer adapter fitted with a glass tube to the top of the condenser and attach the tube to a vacuum source (Fig. 2.73). If you use a water aspirator, be sure to place... 

Setting Up Transfer 2 mL of impure cyclohexane confaining a nonvolatile dye to a 5-mL conical vial. Equip the vial with a spinvane, the Hickman stillhead, and a condenser as shown in Figure 2.38. Place the apparatus in the heating source and have your instructor check your apparatus before you start heating the vial. 

Elimination and Isoiation Heat the reaction vial in a bath that has been preheated to about 120 °C (bath temperature). The vial should be positioned so that the levels of the top of the bath and of the liquid in the reaction vial are equal. Slowly raise the temperature of the bath as necessary to maintain distillation of the product and continue distilling until about 0.5-0.7 ml of liquid remains in the vial. It should not be necessary to heat the bath higher than about 130-135 C. Dismantle the apparatus, and remove the distillate from the Hickman stillhead using a Pasteur or filter-tip pipet. Transfer the distillate to a dry sample vial or test tube, and add several microspatula-tips full of anhydrous potassium carbonate to neutralize any acid and to dry the distillate. Occasionally swirl the mixture for 5-10 min to hasten drying and add additional portions of anhydrous potassium carbonate if the liquid remains cloudy. 

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. 

Reaction, Work-Up, and Isolation Warm the vial gently until most of the salts have dissolved and then heat the mixture under gentle reflux for 45 min. Equip the vial for simple distillation. Distill the mixture rapidly and collect the distillate water and 1-bromobutane in the Hickman stillhead. Continue the distillation, increasing the temperature of the heating source as necessary until there is about 1.5-2.0 mL remaining in the vial and the distillate is clear. ... 

Decant about one-half of the ethereal solution into a 5-mL conical vial equipped for simple distillation and concentrate the solution to about half its original volume, removing the distillate from the Hickman stillhead as necessary. Allow the solution to cool below the boiling point, add the remainder of the dried ethereal extracts, and again concentrate the solution to about one-half its original volume. Alternatively, use rotary evaporation or other techniques to concentrate the solution. Cool the concentrated solution to room temperature. Once crystallization has begun, further cool the solution in an ice-water bath, and then collect the product 15 by vacuum filtration. Recrystallize it from 50% aqueous ethanol and air-dry the purified product. 

Setting Up Equip the conical vial with a spinvane and add 10 mg of 2-naphtha-lenesulfonic acid and 2.5 mL of toluene. Working at the hood, use two different syringes to measure first 0.35 mL of 3-buten-2-one and then 0.50 mL of 2-methyl-propanal directly into the conical vial. Set up the apparatus for simple distillation. Using a Pasteur pipet, fill the well of the Hickman stillhead with toluene, being careful not to allow any toluene to flow back into the conical vial. 

Robinson Annulation Bring the solution to a brisk reflux with stirring and continue heating under reflux for 2-2.5 h. To remove water from the reaction mixture, it is important that the reflux ring rise into the bulb of the Hickman stillhead. Allow the reaction mixture to cool to room temperature. ... 

Purification (Optionai) Remove the source of heat and dissemble the apparatus. Clean and dry the Hickman stillhead. Reassemble the apparatus for simple distillation, insulating the upper portion of the conical vial and the lower portion... 

With a filter-tip pipet, transfer the dried organic solution into a clean 5.0-mL conical vial, rinse the sodium sulfate with about 0.2 mL of diethyl ether, and add this rinse to the vial. Equip the vial for simple distillation. Remove the solvent by simple distillation withdraw the distillate from the Hickman stillhead as needed. Alternatively, use rotary evaporation or other techniques to concentrate the solution. The final traces of solvents may be removed by attaching the vial to a vacuum source. After the crude solid residue has dried, determine its melting range, which may be wide. ... 

Remove distillate from the Hickman stillhead as necessary and place it in a conical test tube or vial. 

Upon completing the distillation, combine all distillates in the conical vessel. Rinse any solid contained in the Hickman stillhead into the conical vessel with 1-2 mL of dichloromethane and separate the layers. Extract the aqueous layer once with 2 mL of dichloromethane and combine the dichloromethane solutions. Remove the dichloromethane by simple distillation. Alternatively, use rotary evaporation or other techniques to remove the solvent. Recrystallize the residue from methanol in a Craig tube and isolate the product by Craig tube filtration. 

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