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In this lab, you will distill a mixture of cyclohexane and p-xylene. The success of a distillation can be evaluated by collecting temperature and spectroscopic data as the fractions are being separated. A good distillation will produce a temperature vs. fraction graph with a plateau for each compound collected and a steep rise in temperature between fractions and spectroscopic data will show little or no contamination from neighboring fractions.
The most popular method for separating miscible compounds with different boiling points is by simple distillation. The impure liquid is placed in a round-bottom flask and fitted with a distillation head, which is in turn attached to a condenser. The end of the condenser is placed over a collection vessel in which the distillate is collected. The flask is heated, and the liquids will begin to vaporize (the lowest boiling first). The vapor rises through the distillation head and passes into the condenser. In the condenser the vapor is cooled by the running water causing it to condense into the liquid phase and drip into the collection flask. Distillations can be monitored by observing the temperature at the entrance to the condenser; as the apparatus heats up, the vapor from the first component (with the lowest boiling point) will reach the thermometer and enter the condenser while the higher boiling point components condense lower in the apparatus. The temperature will remain constant until all of the first liquid has been removed at which point the temperature will increase and plateau again until the second liquid is distilled away; this pattern will repeat until all liquids have been distilled.
About the author
Brandon English began his career as an intern in the pharmaceutical industry developing new drugs for the treatment of viral diseases. After returning to Penn State he had the opportunity to work in the Weinreb group investigating the total synthesis of biologically active natural products. In 2003, Brandon moved to Colorado State University where he studied the biosynthesis and total synthesis of the plant-derived secologanin alkaloids. During graduate school Brandon had the opportunity to teach at CSU and several local community colleges and his career made an abrupt turn toward teaching. After finishing his Ph.D. and an intense two year teaching position at Colorado College he moved to Red Rocks Community College.