Principles of Organic Chemistry Laboratory, Department of Chemistry and Biochemistry North Dakota State University, Fargo, ND 58102
The purpose of this experiment was to synthesize tetraphenylcyclopentadienone using a reaction of dibenzyl ketone (1,3-diphenyl-2-propanone) with benzil in the presence of base. The reaction then proceeded with an aldol condensation reaction.5 This product was obtained using extraction (reflux), recrystallization and vacuum filtration to separate the product from the waste.
Figure 1: Experiment Reaction5
Figure 2: Step wise reaction mechanism including aldol condensation reaction5
About 1.55-g of benzil, 1.51-g of dibenzylketone and 12-mL of ethanol were placed in a 50-mL round bottom flask. A magnetic stir bar was also placed in the flask. A condenser was attached to the round bottom flask while the flask was placed in a 70oC hot water bath. The mixture was heated until all solids were dissolved. The temperature of the water bath was then heated to 80oC. A pasture pipet was used to add 2.25-mL of ethanolic potassium hydroxide solution downward through the condenser and into the flask.
The mixture immediately turned purple. The temperature was then raised to 85oC while being stirred for 15 min. The flask was then removed from the water bath and allowed to cool to room temperature. The flask was then placed in an ice bath for 5 minutes to allow crystallization to complete. Using a Buchner funnel, the crystals were collected and washed in three 4-mL increments of 95% ethanol. The tetraphenylcyclopentadienone was then place in an oven for 15 minutes to dry. The final product was then weighed in order to calculate the percentage yield. Using a small amount of the product, the melting point was also determined. 5 Data:
Molecular Weight: (g/mol)
eye and skin irritant
low flash point
ethanolic potassium hydroxide(l)
eye and skin irritant
Table 1: Chemical Data3
Mass of tetraphenylcyclopentadienone
Melting Point Determination
Table 2: Experimental Data
During the experiment it was observed that the dibenzyl ketone was an opaque, colorless, viscous liquid. The benzyl was observed as small, yellow crystals. When the mixture was heated in the water bath the solution started as a transparent, yellow liquid. When the ethanolic potassium hydroxide solution was added the solution turned to a blood red, opaque color then to a deep purple, opaque color. When the tetraphenylcyclopentadienone was collected it had the physical appearance of small, dark purple crystals and the organic liquid waste was dark purple. Discussion:
In this experiment, the goal was to synthesize tetraphenylcyclopentadienone from benzil and dibenzylketone. The reaction proceeded via an aldol condensation reaction, with dehydration giving the purple unsaturated ketone. An aldol reaction takes place when a carbonyl compound enolates with aldehydes and ketones to form a β-hydroxy carbonyl compound. If conditions result in a subsequent dehydration to form the α, β-unsaturated compound, then the reaction is termed Aldol Condensation. This type of reaction is important to this experiment because of its ability to form new carbo-carbon bonds.2
The experiment was successful in terms of the quantity of product produced. While doing the experiment, tetraphenylcyclopentadienone was successfully...
References: 1) Adapted By Kurt Rublein From Introduction To Organic Laboratory Techniques, A Microscale Approach By D. L. Pavia, G. M. Lampman, G. S. Kriz, And R. G. Engel; 7/1/98, 1. R. The Aldol Reaction of Benzaldehyde and Acetophenone. Exp 't 20. 1990.
2) Aldol Condensation. Aldol Condensation, http://www.organic-chemistry.org/namedreactions/aldol-condensation.shtm (accessed Jan 30, 2015).
3) Material Safety Data Sheet. Chemicals and Laboratory Equipment, http://www.sciencelab.com/msds.php?msdsid=9927187 (accessed 2015).
4) Melting Point Determination. Organic Chemistry at CU Boulder, http://orgchem.colorado.edu/technique/procedures/meltingpt/meltingpt.html (accessed Feb 2, 2015).
5) Pavia; Lampman. Tetraphenylcyclopentadienone. In Organic Chemistry Laboratory Manual; Radke, K.; Stolzenberg, G.; Cengage Learning: Mason, OH, 2009; pp. 53-55.
6) Synthesis of tetraphenylcyclopentadienone. Chemical Forums, http://www.chemicalforums.com/index.php?topic=32718.0 (accessed Feb 2, 2015).
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