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

Wittig Synthesis of trans-9-(2-Phenylethenyl)anthracene
(Used as the photosensitizer in Chemiluminescence)
Last update: 22 August 2005
Dr. Glenn Nomura
Reference:
Williamson, Macroscale and Microscale Organic Experiments, 4 th edition, Houghton Mifflin: New York, 2003,
Experiment 39.1, (1 X) macroscale Synthesis of trans-9-(2-phenylethenyl)anthracene, p. 481
Equation:
CHO
Cl -
(C 6 H 5 ) 3 PH 2 C
50% NaOH
CH 2 Cl 2
H
H
9-anthraldehyde
C 15 H 10 O, 206.24
mp 104-105 o C
benzyltriphenylphosphonium chloride
C 6 H 5 CH 2 P(C 6 H 5 ) 3 Cl, 388.88
trans-9-(2-phenylethenyl)anthraldehyde
C 22 H 16 , 280.37
mp 131-132 o C
Materials:
1. 9-anthraldehyde, 0.57 g (0.00276 mol)
2. benzyltriphenylphosphonium chloride, 0.97 g (0.00249 mol)
3. 50% NaOH, 1.3 mL
Procedure:
Synthesis of trans-9-(2-phenylethenyl)anthracene
This reaction should be performed in the hood.
Into a 50 mL Erlenmeyer flask equipped with a stir bar is weighed 0.57 g (0.00276 mol) of 9-anthraldehyde, and
0.97 g (0.00249 mol) of benzyltriphenylphosphonium chloride, and 5 mL of methylene chloride, CH 2 Cl 2 . To this is
added with stirring at room temperature 1.5 mL of 50% NaOH solution dropwise from a Pasteur pipet (Note A).
Continue to stir for 30 minutes; then transfer the contents of the flask to a separatory funnel (pour liquids through a
funnel at the top of the separatory funnel) using about 10 mL of water and 10 mL of methylene chloride, CH 2 Cl 2
(Note B). Shake the mixture, drain the lower methylene chloride layer (Note C), and extract the aqueous layer
again with 5 mL of methylene chloride. Dry the combined methylene chloride layers with anhydrous Na 2 SO 4 .
Decant the methylene chloride to a clean dry 50 mL Erlenmeyer flask, being careful to leave the Na 2 SO 4 behind.
Use additional methylene chloride to complete the transfer. In the hood, evaporate the methylene chloride (bp
40°C) to dryness on a sand bath (Note D). A brownish-yellow solid should result at this point.
Recrystallization of trans-9-(2-phenylethenyl)anthracene While the flask is still warm, add 15 mL of
2-propanol (isopropyl alcohol) to the 50 mL Erlenmeyer flask above. Warm the flask in the sand bath to dissolve
the solid (remember to keep the flask covered with foil or cotton). Place the flask on a paper towel and place an
inverted beaker over the flask to protect it from cold drafts (Note E). Distinct yellow platelets should crystallize in
about 15 minutes. Filter the crystals on a Buchner funnel set up at your bench (remember to clamp the filter flask on
a ring stand to prevent tipping and breakage). Recycle the isopropyl alcohol filtrate from the filter flask to complete
the transfer of crystals onto the Buchner funnel. Rinse the crystals one last time with fresh cold isopropyl alcohol to
clean the outer surface of the crystals. Air dry the crystals on filter paper, determine the yield and mp, and turn in
the final product (Note F).
- A UV light is available in the lab for examining the isopropyl filtrate – IT GLOWS! -

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