Wittig Synthesis of trans-9-(2-phenylethenyl)

Exp 39.1 Wittig Synthesis of trans-9-(2-Phenylethenyl)anthracene 2
Final Steps:
1. Determine the % yield of trans-9-(2-phenylethenyl)anthracene.
2. Determine the mp.
3. Turn in your product in a labeled vial.
Notes:
A. The dropwise addition of 1.5 mL of 50% NaOH should take about 1-2 minutes.
B. The exact amount of water and methylene chloride required for quantitative transfer of the reaction is
not critical. What is important is that the transfer be complete.
C. Normally, organic layers are the upper layer. Halogenated solvents such as methylene chloride are
higher density than water and will be the lower layer.
D. There is no danger of evaporating the product during the evaporation of methylene chloride step, but
be certain to set the sand bath temperature to a moderate temperature sufficient to evaporate the
methylene chloride, which boils at 40°C. Too high a sand bath temperature can cause the Wittig
product to decompose and blacken, especially after the solvent has completely evaporated and the flask
is allowed to become hot.
E. When recrystallizing any compound, always allow the solution to cool slowly on its own in the
beginning. The paper towel and inverted beaker are precautions to help slow down the rate of cooling
and allow fewer nucleating crystals to form at the beginning, which then grow to larger well formed
crystals of high purity and predictable mp. If the solution is cooled too quickly, the solid will “crash”
out of solution sometimes along with impurities into micro sized powder particles of lower quality.
F. The mp is sufficient in this case to confirm the product.
Waste & Clean Up:
1. Into Mr. White: All aqueous washings; organic residues; and acetone rinses of dirty equipment
2. Halogenated Waste: All mixtures of halogenated containing waste, i.e. methylene chloride, CH 2 Cl 2 .
Prep Room Instructions:
For a class of 24 students
1. 9-anthraldehyde 15 g
2. benzyltriphenylphosphonium chloride 25 g
3. 50% NaOH 40 mL
4. stir bars 24
5. anhydrous Na 2 SO 4 bottle
6. pentane 500 mL
7. methylene chloride, CH 2 Cl 2 500 mL
8. 2-propanol 500 mL
9. 42.5 mm filter paper box