Diels Alder Experiment

Topics: Chemistry, Atom, Chemical substance Pages: 11 (1208 words) Published: November 18, 2014
EXPERIMENT
OBJECTIVE
The aim of this experiment is synthesize hexaphenylbenzene via an aldol condensation reaction, followed by a Diels-Alder [4+2] cycloaddtion. This is final step in the multistep synthesis pathway to form hexaphenylbenzene, and uses the products of the previous experiments: benzil and diphenylacetylene REACTION DIAGRAM

TABLE OF REAGENTS

BENZIL
DIBENZYL KETONE
TRITON B
40wt% IN METHANOL (1.79 M)
TRIETHYLENE GLYCOL
TETRAPHENYL-CYCLOPENTA-DIENONE
DIPHENYL ACETYLENE
HEXAPHENYL-BENZENE
FORMULA

EQUIV

MW

DENSITY

VOLUME

MASS

Mmol

MELTING POINT

BOILING POINT
-
-
210 °C
-

PROCEDURE
1 A hot plate with an aluminum block was preheated to 150°C. 2 100mg of benzil and 100mg of dibenzylketone were added to a conical vial with a spin vane and an air condenser. 3 0.5mL of triethylene glycol was added to the vial, and the mixture was stirred on the hot plate until a homogenous mixture was obtained. 4 The heat was turned off and 0.1mL of Triton B was added through the condenser. 5 The vial and its contents were allowed to cool to room temperature, and purple crystals were observed. 6 1.3mL of methanol was added to the vial as it was stirred at room temperature. 7 The vial was then placed in an ice bath for further cooling. 8 The purple crystals were collected and were dried using vacuum filtration with a Buchner funnel. 9 The crystals were washed with ice-cold methanol until the filtrate was a purple-pink color, and were then left under vacuum. 10 The dried crystals were placed in a test tube, and 178 mg of diphenylacetylene and 2mL of silicon oil were added. 11 A clamp was attached to the tube and the contents were heated to a boil over a Bunsen Burner until the solution was a pale pink color. 12 The test tube was allowed to cool to room temperature.

13 6.0mL of hexanes was added to the tube and the mixture was stirred with a spatula. 14 The crystals were collected via vacuum filtration using a Buchner funnel. 15 The residue was washed with 2.0mL of hexanes and 2mL of toluene. 16 The crystals were then allowed to dry under vacuum.

17 The percent yield was calculated.

LIST OF GLASSWARE/ EQUIPMENT
Hot plate
Conical Vial
Pipette, Pipette filler
Beaker
Bunsen burner
Measuring cylinder
Spatula
Stirring rod
Spin vane
Buchner funnel
Ice bath
Aluminum block
MECHANISM

RESULTS AND CALCULATIONS

MELTING POINT:

This is a reasonably high yield, giving the impression that the experiment was carried out efficiently. However, the IR spectrum obtained for the product had a broad and strong OH peak, indicating that water was a significant impurity in the product. Therefore, the high yield is more likely due to the presence of water in the crystals of benzil obtained. In addition, the peaks for the other functional groups had very low transmittances. This also supports that the idea that the benzil formed was impure. This is most likely due to the addition of water to initialize the formation of crystals before, the vial as placed in the ice bath. Water was also used to wash the crystals which would add to the amount of water present if the crystals we not completely dried before the IR spectrum was obtained. In addition, the melting point of the crystals obtained was very wide, with a range of 10°C. This also indicates that the benzil obtain was impure, as the presence of impurities tends to lower the melting point, increase the boiling point, and increase the range in which changes of state take place.

FURTHER DISCUSSION
SOURCES OF ERROR
Some sources of error that may have occurred in this experiment are: 1 Parallax error when measuring volumes from the syringes and...

References: 1 Mohrig, Jerry R. Techniques in organic chemistry. 3rd ed. New York: Freeman, 2003. Print.
2 Perry, Robert H. Perry 's chemical engineers ' handbook. 8th ed. New York [etc.: McGraw-Hill, 1997. Print.
3 Lide, David R. CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data. 75th ed. (1994-95 ed. Boca Raton, FL: CRC Press, 1994. Print.
4 "Structural Biochemistry/Proteins/NMR Spectroscopy - Wikibooks, open books for an open world." Wikibooks. .
5 UW Madison. "C-13 Chemical Shifts." UW Madison - Department of Chemistry. .
6 "Chemical Structure Drawing Search - eMolecules." Chemical Structure Drawing Search - eMolecules.
7 Macaione, Domenic P., and Stanley E. Wentworth. "An Improved Method For The Synthesis Of Benzils From Benzoins." Synthesis 1974.10 (1974): 716-716. Print.
8 “The Catalytic Oxidation of Benzoin to Benzil.” http://chemistry.cos.ucf.edu/redesign/wp-content/uploads/2013/01/Benzil.pdf.
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