Tetraphenylcyclopentadienone Synthesis Essay

CHEM 3125 Experiment 4: Multistep synthesis of tetraphenylcyclopentadienone

Overall Synthesis:

CHEMICALS: wk 1: thiamine hydrochloride (1 g/student), 95% ethanol (8 mls/ student), 2M NaOH (5 mls/student), benzaldehyde (4 mls/student) wk 2: 95% ethanol (30 mls/student) wk 3: acetic acid (6 mls/student), ammonium nitrate (1 g/student), 0.1g/ml cupric acetate (1.5 mls/student), dichloromethane (6 mls/ student), 30% acetone in heptanes (3 mls/student), 95% ethanol (20 mls/student) wk 4: 1,3 diphenylacetone (0.5 g/student), triethylene glycol (5 mls/student), 40% benzyltrimethylammonium hydroxide/methanol (0.5 mls/student)

Part A: Thiamine catalyzed condensation benzoin condensation of benzaldehyde

Procedure:

(Week 1)
Dissolve
Prepare a TLC chamber by cutting a large circle of filter paper in half and placing it in a beaker. Add ~ 6 mL of methylene chloride (or 30% acetone in heptanes-needs to be fresh, otherwise acetone will evaporate) and cover the beaker with a watchglass. For each TLC run, you will need a silica gel plate and two clean capillary tubes for spotting the plate.

Draw a horizontal line near the bottom of each TLC plate (the line must be higher than the level of solvent in the TLC chamber). Draw three dots distributed along the line, (1 = benzoin, 2 = benzoin + reaction mixture, 3 = reaction mixture). Use a capillary tube to draw up a stock solution of benzoin and touch the capillary tube to the plate on the first two dots to spot the plate.

After 30 min at reflux, remove the heating mantle from the RB flask so that the reaction stops boiling. Disconnect the condenser and draw up some of the reaction mixture in a fresh capillary. Reattach the condenser and spot the second and third dots on the plate. Resume heating at reflux and carefully place the plate into the TLC chamber. Place a watch glass on top to prevent evaporation of the methylene
After isolating the crystals, allow them to dry on a watchglass for a couple days.

Determine the mass and mp of the recrystallized benzil and obtain an IR spectrum.

Part C: Base-catalyzed aldol condensation of benzil and 1,3-diphenylacetone

(Week 4)
Add 0.50 g of 1,3-diphenylacetone, 0.50 g of benzil and 5 mL of triethylene glycol to a 50 mL round bottom flask. Add a stir bar and heat the mixture at setting 4-5 on heating manual for ~ 10-15 min (will not reflux boiling point too high). The benzil should dissolve during this time. Remove the heating mantle and add ~0.5 mL of a 40% benzyltrimethylammonium hydroxide/methanol solution to the hot reaction with constant stirring.

Allow the reaction to cool to room temperature. As the solution cools dark-colored crystals should appear. Cooling may be accelerated by placing the flask under a stream of cold water (Note: you are NOT adding any water to the inside of the flask). Add 10 mL of cold methanol with stirring and cool the resulting mixture in an ice bath for 5-10 min. Collect the product by vacuum filtration and wash the crystals with a little cold methanol. Allow the crystals to dry on a watchglass for a couple days.

Determine the mass and mp of the