Fluorenene to Fluoronone
The goal of the first part of this experiment was to achieve a 50-50 conversion of fluorene to Fluorenone. In order to achieve the goal of the experiment fluorene was oxidized to Fluorenone. The hydroxide ions from the sodium hydroxide in the presence of Stark’s catalyst would be able to de-protonate the acidic fluorene protons. This would result in the formation of a carbanion which attacks the oxygen from the air resulting in the formation of a hydroperoxide and eventually a ketone (after removal of water).
Since the goal was to have a mixture of 50% fluorene conversion, Thin Layer Chromatography (TLC) was carried out several times to assess the rate of the reaction. In order to separate the aqueous composites from the solution extraction was carried out where the product was washed several times with Toluene and HCl and NaCl. In order to dry the excess water and obtain a ketone calcium chloride was used as a drying agent. The data obtained from TLC showed that the Rf value for the starting material was on a range of 0. 68-0. 75. The Product obtained had varied concentrations of the fluorene and Fluorenone.
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The average Rf value obtained for the product was 0. 205. Through this data, it can be concluded that the ketone (Fluorenone) was more polar that fluorene. This data is theoretically correct as well since ketons are supposed to be more polar than alkenes due to the presence of C=O bond. However, TLC data showed that the conversion of fluorene was not achieved to a 50-50 level but had proceeded even further, almost to a point where none of the fluorene remained in the solution. This was determined because in the last TLC slide the presence of Fluorenone was little (the dots size was smaller than it should have been).
This error served as a basis for more errors in the second part of the experiment. Reason for this error was that the TLC was not carried out sooner than it should have been due to which the rate of reaction was inaccurately monitored. Also the stirrer was left on even during the course of the TLC. This would have also lead to a higher conversion of the reagent. In order to avoid this error, the reaction with air should have been stopped completely, while taking TLC. The mass of the product obtained in the end was about 6. 26 grams. The theoretical yield should have been 0. g. However, the theoretical yield holds true if and only if the reaction went to a 100% completion and contained no impurities.
The goal of the second part of the experiment was to separate the fluorene and Fluorenone mixture by the method of column chromatography. Column chromatography was used in this part of the experiment as a separation technique since it permits the sample to be collected whereas TLC only allows the product to be separated and not collected. In the experiment TLC was also used to monitor the effectiveness of the separation.
Hence, in preparation of the column, glass fiber was first filled into the column followed by sand, after which 3” alumina was filled into the column. Alumina would help retain the more polar ketone longer and would elute the alkene first. A mixture of hexanes was added in order to tighten the alumina column after which the excess hexanes were removed. Next, the sample was added followed by some and hexanes. Hexanes were constantly added and TLC was carried out to check if the resulting solution (which was removed from the column) contained any product.
Once the TLC showed no traces of the product the solvent was switched to elude the ketone. Hexanes dissolve the reagent fluorene which is less polar and it is removed from the sample. After all the fluorene was removed, MTBE (methyl-tert-butyl-ether) was used as the solvent to remove the Fluorenone from the sample. The same procedure was carried out as in case of the hexanes until TLC showed no traces of the product. Once the product was obtained in a mixture of the solvent and product, the solution was boiled In order to obtain only the product (ether has a lower boiling point than ketone).
Melting point of the product was taken in order to check the purity of the product. When the hexanes were used to remove the starting material from the sample, no spots appeared at all in the TLC plate for about 35 trials of the solution. The TLC plate remained blank showing proof of no compound other than the hexane itself. This error was expected since in the first part of the experiment, oxidation of fluoreneto Fluorenone was supposed to be done to a 50-50 level. As mentioned earlier, the oxidation had carried out longer than expected and hence the sample contained little or none of the fluorene.
Thus, no value of Rf were obtained for the fluorenein the experiment. When the solvent was switched to MTBE, the Fluorenone was removed almost instantly. The Rf, for the last the slide that contained Fluorenone was 0. 11 and 0. 21 which falls within the range as earlier, indicating that the product obtained was indeed the ketone expected. To ensure the claim, melting point of the sample was taken. The melting point for the sample was 85°C which is very close to the theoretical melting point of Fluorenone which is about 83 °C.
Since the melting point was off by about 1. °C it is assumed that some sources of error was obtained in the experiment. Since there was very little of the alkene in the sample, and none of it eluded out, it may have been stuck in the stationary phase. Hence when the ketone passed through the stationary phase it may have gotten contaminated leading to the error. Also all of the MTBE may not have evaporated out leading to some scope of error in the melting point of the product. There may have been some human error in determining the exact temperature at which the product began melting.
The first part of the experiment showed significant error which affected the second part of the experiment as well. However, the goal of the experiment was to synthesize and separate fluorene from Fluorenone for which a good separation was obtained as can be concluded through the melting point. Even though the method did not go as planned, the purity of the final product was good. Questions: 1) (4 pts) a. What is the oxidizing agent in the conversion of fluoreneto fluorenone?
What is the function of the Aliquat catalyst? c. Which compound, fluoreneor fluorenone has the highest R¬f? Is it the most polar or nonpolar? d. Would changing to a more polar elution solvent increase or decrease Rf? a) The oxidizing agent in the conversion of fluorene to Fluorenone was oxygen in the air which was aided by a phase-transfer catalyst. b) The function of the Aliquat catalyst is to help the hydroxide ion move into the organic layer and where the hydroxide removes one of the fluorene protons.
The Stark’s catalyst is a phase-transfer catalyst meaning it helps the migration of a reactant from one phase to another (here, OH- transfers from aqueous phase to organic). c) In this reaction Fluorenone has the lower Rf meaning it is more polar. Hence, Fluorene has higher Rf and lower polarity. This is due to the presence of C=O bond in the ketone (Fluorenone). d) Changing to a more polar elution would increase the Rf of the product. 2) (3 pts) Predict the order of elution of a mixture of triphenylmethanol, biphenyl, benzoic acid and methyl benzoate from an alumina chromatographic column.
Ans: The compound that would elute first would be biphenyl, followed by methyl benzoate, triphenylmethanol, and finally benzoic acid. 3) (1 pts) What might possibly result if you used a column of alumina that was 5 cm instead of ten? Ans: If 5cm of the alumina is used instead of a 10cm alumina column the result obtained as the product would be purer than what was obtained experimentally. This is because as the eluent runs through the column some of it tends to naturally bind to the alumina surface.
When more alumina is used the more eluent binds to the column and hence more product is lost. 4) (2pts) Consult the chart on the following page. In what range would you expect a new peak to appear if your oxidation is successful. Identify this peak on your IR; indicate the bond it represents. Also indicate the peaks for the C-H of an aromatic ring.