Experiment 6 - Lab PDF

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Samantha Hoffman TA Avi Benitah CH 237-017 4/3/2020 Experiment 6: Synthesis of Triphenylmethanol and Trityl Carbocation Introduction: Students were tasked with preparing phenylmagnesium bromide by adding a solution of bromobenzene in anhydrous diethyl ether to magnesium metal. Then the Grignard that was previously formed, will react with benzophenone to create a white/pink precipitate of triphenylmethanol. The solution is washed with dilute hydrochloric acid, diether, sodium bicarbonate and water remove extra magnesium salts, and other impurities. The final solution was used to prepare a TLC plate and the melting points was found of the sample.

Results: Compound

Initial Melting Point

Final Melting Point

℃ ℃ Crude product 98 122 Crystalized product 130 139 Table 1. Melting Range of the Crystallized Product Compound

Yield Mass (g)

Triphenylmethanol Trityl tetrafluoroborate Table 2. Yield Mass of compounds

2.31 0.70

1. Report the theoretical yield of trityl alcohol based on the amounts of reagents that you used. 20 mmol benzophenone

benzophenone 1 mol triphenylmeth |10001molmmolbenzophenone | 1 mol phenylmagnesiumbromide | 1 mol benzophenone 1 mol phenylmagnesium

Theoretical yield of trityl alcohol = 5.21 g 2. Report your isolated and percent yield of trityl alcohol. Percent yield=

2.31 g yield product X 100 % 5.21 g theoretical yield

= 44.3 % trityl alcohol 3. Report the theoretical yield of trityl tetrafluoroborate.

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1.0 g triphenyl methanol 1 mol triphenyl methanol 1 mol trityl tetrafluoroborate 330.1 g trityl tetrafluorobor 260.3 g triphenyl methanol 1 mol triphenyl methanol 1 mol trityl tetrafluorobora Theoretical yield of trityl tetrafluoroborate = 1.27 g 4. Report the isolated and percent yield of trityl tetrafluoroborate. Percent yield=

0.70 g yield product X 100 % 1.27 g theoretical yield

= 55.1 % 5. Report the melting range of your crude and recrystallized product – see Table 1. 6. Draw the TLC plate using ChemBioDraw you ran on your samples. Report Rf values for each spot you observed (biphenyl, trityl alcohol, and any other spots observed).

Rf Values: Crude Triphenylmethanol: 0.31 and 0.47 Recrystallized Triphenylmethanol: 0.31 Triphenylmethanol Standard: 0.31 Benzophenone: 0.50 Biphenyl: 0.75 Questions: 1. Triphenylmethanol is the white precipitate that is formed when benzophenone is added to the Grignard solution. 2. Acetic anhydride was used as the solvent in the conversion of trityl alcohol to trityl tetrafluoroborate because it helps remove water from the reaction solution. 3. The two substances cannot be concluded to be the same compound based on the TLC analysis because there is a chance that they each have similar properties or substituents that have the same

Rf in propanol. An IR and an NMR test should be run to determine the structure of each compound to determine the similarity. 4. The synthesis of malachite green and crystal violet is shown below.

Discussion: Students produced triphenylmethanol from a Grignard reagent and benzophenone. The yield for the triphenylmethanol was 44.3%, and this can be contributed to errors and difficulties during the formation of the Grignard. It is possible that the glassware was not completely dry and/or that not enough magnesium sulfate was added to remove the water from the solution. If there was water present, then the Grignard would react, and it was return to benzene and magnesium salt of phenol. If this was the case, then the amount of Grignard was low which would cause a low yield of triphenylmethanol. The melting point of trityl alcohol is 164℃ , however, for the crud sample students had a melting range of 98℃ -122℃ . The students crystallized sample had a melting point of 130℃139℃ . The large differences in the melting points can be inferred to be due to impurities in the samples. The student’s TLC plate had one solution noted for each sample, however, the crude triphenylmethanol had two solutions noted. The two solutions noted for the crude sample, implies that there is an impurity in the sample, such as biphenyl. This is consistent with the melting points, since the crude range was much lower than the established, due to the impurity. If the ethyl acetate concentration were to increase, then the Rf values would increase since the samples would carry farther up the plate. This is a result of the different polarities of the solvent and the samples. The IR spectrum of triphenylmethanol and trityl fluoborite have two similar peaks in the 3000-3500 but the rest of the peaks in the 500-1600 range differentiate based on the differences in the compound structures. The IR for triphenylmethanol has the appropriate peaks for the

stretching and bending that is necessary for the structure. This confirms that the appropriate reaction has taken place. It can be concluded that the appropriated reaction took place and the triphenylmethanol was produced. The color of trityl carbocation was yellow. Based on the results, the amino group effects the aromatic rings of the dye to act as chromophores.

Conclusion: Students used bromobenzene and magnesium to create phenylmagnesium bromide, a Grignard reagent. This reagent was reacted with benzophenone to create a white precipitate known as triphenylmethanol. The solution was washed several times to remove impurities, before it was weighed. A TLC plate was completed, and the melting point was determined....