Experiment 5: Wittig Reaction

Topics: Wittig reaction, Chemistry, Filter Pages: 2 (374 words) Published: March 31, 2014


Experiment 5: Wittig Reaction

Purpose
The purpose of this experiment is to synthesize trans-9-(2-phenylethenyl) anthracene using a wittig reagent formed by reacting phosphonium chloride with base.

Experimental

In a reaction tube, (0.200g) benzyltriphenyl phosphonium chloride, (0.115g) anthraaldehyde, and (.6ml) dichloromethane (DCM) is mixed together with a stir bar. We stirred the mixture rapidly and added (0.26ml) of a 50% NaOH solution dropwise. The mixture was stirred for 20-30 minutes. We added (1.5ml) DCM and (1.5ml) water, and the tube was shaken until the layers separated. The water layer was removed. This step was repeated and the water was removed again. CaCl2 pellets were added to DCM solution until it longer clumped. The solution was filtered to separted the CaCl2 pellets from DCM. DCM was used to wash pellets before filtering. To the solid in bottom of flask, (3ml) of propanol was added, heated and cooled. Filteration was tried once more to gain crystals. Due to nonexistent crystals a melting point could not be performed.

Observations:
We noticed after adding propanol our solution became very orange and cloudy. After heating it the solution was a clear golden color. We chilled the solution in ice and attained no crystals. After repeatedly heating and cooling, we saw our solution go from cloudy to clear over and over. After filtering one more time the color of orange stained the filter paper but no crystals.

Data
Melting Point: expected: 131- 132 C

Conclusion
We concluded if this experiment had gone the way expected we would have a melting point of 131-132 C. We believe this error was due to excessive amount of DCM prior to filtering when we tried to get all of the solution out of the reaction tube. We believe we had too small of a volume to attain crystals. We may have also disturbed the crystals too much, and they could not form...
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