Microscale Hickman still

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. 

Hickman Still-Rotary Evaporation Apparatus. A simple microscale rotary evaporator for use in the instructional laboratory consists of a 10-mL round-bottom flask connected to a capped Hickman stOl (side-arm type), which in turn is attached to a water aspirator (with trap) The procedure involves transferring the solution to be concentrated to the preweighed 10-mL flask. The flask is then attached to a Hickman stiH with its top joint sealed with a rubber septum and threaded compression cap. The apparatus is connected by the stiU side arm to the trap-vacuum source with a vacuum hose. lAdth the aspirator on, one shakes the apparatus while warming the flask in the palm of the hand. In this manner, bumping is avoided and evaporation is expedited. The stiU acts as a splash guard. Heat transfer is very effective, and once the flask reaches ambient temperature, the vacuum is released by venting through the trap stopcock. 

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. 

Microscale spinning-band distillation apparatus (Fig. 5.11) can achieve nearly 12 theoretical plates and are simple enough to be used in the instructional laboratory. This stiU has a Teflon band that fits closely inside an insulated glass tube. The Teflon band has spiral grooves which, when the band is spun (1000-1500 rpm), rapidly return condensed vapor to the distillation pot. A powerful extension of this apparatus uses a short spinning band inside a modified Hickman stiU head (see Fig. 3.15). These stills are called Hickman-Hinkle stills 4-cm Hickman-Hinkle columns can have more than 10 theoretical plates. The commercially available 2.5-cm version is rated at 6 theoretical plates. Experiments [3C] and [3D] involve fractional distillation with spinning-band columns. 

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