Date work performed: 10.18.2012--10.25.2012
Date work submitted: 11.01.2012
The aim of this experiment was to perform a multistep synthesis to form tetraphenylcyclopentadienone. The first step of the reactions was to synthesize benzoin from the condensation of benzaldehyde. A yield of 28.91% benzoin was obtained. The MP of benzoin was 127O-130O C and the IR spectra displayed a carbonyl peak at 3415 cm-1 ,,which represents and OH functional group. The second step of the reaction was to oxidize benzoin to form benzil; this reaction yielded 27.04% benzil. The MP of the benzil was 91O-93O C and the IR spectra revealed no OH functional groups. The last step of the synthesis was a double aldol condensation reaction to form tetraphenylcyclopentadienone; this reaction had a yield of 76.56% and a melting point of 222O-225O C. The IR spectra revealed a ketone carbonyl peak at 1700 cm-1. Introduction:
In this experiment a multistep reaction will be performed in order to synthesize tetraphenycyclopentadienone. The product will be synthesized in three steps, but in the industrial world companies often produce compounds that involve up to twenty steps. Tetraphenycyclopentadienone is produced by synthesizing benzoin through the condensation of benzaldehyde and thiamine being used as a catalyst. In the second step of the reaction, benzoin is oxidized to benzil; nitric acid is used as the oxidizing agent in this step. In the last step of the reaction, a mixture of benzil and 1,3-diphenylacetone undergo a double aldol condensation reaction then a dehydration reaction in order to form tetraphenycyclopentadienone.
* Round bottom flask (RBF)
* Reflux condenser
* Hot plate
* Hirsh Funnel
* Melttemp 2, to measure melting point
* Microlet IR 100, to measure IR
Benzoin Condensation of Benzaldehyde
First 1.20 grams of benzaldehyde was weighed out and put into a RBF containing a magnetic stir bar. Next 225 mg of thiamine was dissolved in 0.67 mL of water and 2.0 mL of 95% ethanol. This mixture was added to the RBF and 3 M NaOH was added drop wise until the solution turned a bright yellow color. If too much 3 M NaOH is added then the solution will turn a dark amber color; in this situation an additional 200 mg of thiamine should be added. The yellow solution was stored in a vial until the next weeks lab, so the mixture would have a suffienct amount of time to react. At the start of the next lab the vial was cooled in an ice bath to achieve complete crystallization. Next, a Hirsch funnel was used to filter the crystals; the crystals were washed three times using a 50:50 mixture of cold ethanol/water and left to dry. Once dry, the product was recrystallized using 95% ethanol. The benzoin obtained (0.370 g) had a percent yield of 28.91% and melting point of 127O-130O C. The IR spectrum displayed a strong carbonyl peak at 2912 cm-1, a small OH peak at3415.24 cm-1 and an alkene group at 1472 cm-1 which represented the conjugated phenyl rings.
Oxidation of Benzoin to Benzil
This reaction was begun by placing all the benzoin that was synthesized in the previous lab into a RBF along with a magnetic stirrer. 1 mL of concentrated nitric acid was added to the RBF; the RBF was then attached to a reflux condenser and submerged into a hot water bath at 100oC for thirty minutes or until no more fumes are observed. A vacuum with a funnel attached to the end was placed on top of the reflux condenser in order to collect any nitrogen oxide fumes that formed. Once the reaction stopped producing fumes, the reaction mixture was left to cool; when the mixture reached room temperature the contents in the RBF where transferred using a Pasteur pipet into a beaker containing 3 mL of water. Additional water was used to rinse out the RBF and it was poured into the beaker in order to insure...