draft biochem lab

Synthesis of Cyclohexane via Dehydration of Cyclohexanol

Purpose:

The purpose of this lab is to synthesize cyclohexene via an acid-catalyzed dehydration of cyclohexanol with phosphoric acid, in addition to purification of product through fractional distillation and analysis using chemical tests and gas chromatography.

Reaction Scheme:

Experimental Procedure:

The hotplate was turned on upon arrival to around 400℃. Two g of cyclohexanol and .8 mL of 85% phosphoric Acid were placed into a round bottom(rb) flask along with boiling chips.  A fraction distillation apparatus with aluminum foil wrapped around the cylinder containing copper mesh. The mixture was then heated over the aluminum block to fractionally distill at a rate of one drop per second with drops collected in a collection vial.  Once there is a about a 10% of the mixture left in the rb flask, distillation was stopped. After the distillation stopped the contents of the collection vial were moved to a test tube. In the test tube two layer were observed and both layers were mixed using the pipette, then using water to wash. Using the pipette, the lower aqueous layer was removed and placed in waste. Then 1mL of 1M sodium hydroxide was added to the tube and again through washing the liquids were thoroughly mixed and the bottom layer was removed to waste. Then 2 mL of brine were added and the contents of the tube were mixed well via washing and the bottom layer was removed to waste.  

Using a clean pipette, the organic layer was transferred from the test tube to a new clean

collection vial.  Several spheres of CaCl₂ were added in the new collection vial and the contents were gently swirled until the spheres were no longer clumped together, then the vial was left capped and to dry for 5 minutes. The product was then transferred to a preweighed vial using the pipette, leaving the CaCl₂ spheres. Chemical test where then performed on the cyclohexene, then 3 drops of potassium permanganate was added to each tube. After swirling, the cyclohexane remained purple in color, while the cyclohexene formed a pinkish color that turned colorless.  A few drops of the product were left in the vial for the gas chromatography test and IR spectroscopy.