Monday, March 16, 2009

Synthesis of Triphenylmethanol

Purpose of this experiment:
The purpose of this experiment was to synthesize triphenylmethanol. Triphenylmethanol is a white crystalline aromatic compound, which produces an intensely yellow color in a strong acidic solution due to formation of carbocation. Grignard reaction technique was used in this synthesis.



Method and procedures:
Into a 3-ml conical vial, 3.80mmol of benzophenone was dissolved in 2.0ml of anhydrous ethyl ether . When the reaction cooled, after the ether stops boiling, the septum cap was removed, and a dry stir bar was dropped into the reaction flask and the cap was replaced afterwards. The stirrer was started. A syringe was used to add about three drops of benzophenone solution at a rate sufficient to keep the reaction mixture boiling gently without external heating.
When the addition was complete, 0.5ml anhydrius ether was used to rinse the vial that contained benzophenone solution. A warm water bath was used to heat the reaction mixture for another ten minutes, while stirring with stir bar still in the solution.
The reaction was then allowed to cool to room temperature. A syringe was used to add 1.0ml of water drop by drop to the reaction flask, and the reaction is allowed to subside. While stirring, 2.0ml of 5% (1.4M) hydrochloric acid was added to the reaction. When all the reaction subsides, and all the white solid dissolved, stirring was stopped.
The reaction was transferred to a centrifuge tube using a small amount of solvent-grade ether, leaving the stirr bar and any undissolved magnesium behind. The solution was shaked gently to mix the layers thoroughly. Emulsion might formed in the solution, but a wooden applicator stick was used to break it up.
The aqueous layer was removed and discarded from the solution circumspectly. The remaining solution was washed with 3ml of 5% aqueous soldium bicarbonate, and then with 3ml of saturated aqueous soldium chloride. The ether solution was then dried with anhydrous magnesium sulfate. Then the ether was evaporated and a solid residue was left behind.
To the solid residue, 2.0ml of hexane was added. A flat-bladed microspatula was used to rub and grind the solid in the solvent for 2-3minutes. The product was collected by vacuum filteration. The product, crude phenylmethanol, was then recrystallized from a 2/1 mixture of hexane with absolute ethanol. Triphenylmethanol crystals was allowed to form (slowly) for about 30minutes.It was dried, weighed and it’s melting point was recorded.
Result:
The final weight of product obtained from the reaction was 0.51grams, and the melting point ranged from 132-140°C. The actual melting point of triphenylmethanol is 164°C.
The percent yield of the product obtained is as follows :
(0.00380mol benzophenone)/1 x (1mol triphenylmethanol)/(1mol benzophenone) = 0.00380mol triphenylmethanol
Theroetical yield : moles of triphenylmethanol x molecular weight of triphenylmethanol
0.00380mol x 260.33g/mol = 0.989grams.
Percent yield = (actual yield)/(theoretical yield) x (100 %)/1
Percent yield = (0.51mol triphenylmethanol)/(0.989mol triphenylmethanol) x (100 %)/1 = 51.57%

Discussion:
The yield obtained from the experiment was 0.51g, which was 51.57% of product expected. The melting point was 132-140°C, which differred from the actual melting point by about 30°C . However, the product obtained exhibited the same properties as the expected compound, triphenylmethanol.
There was a lot of discrepancy from the results of the experiment. Sources of the discrepancy was from a few mistakes in the procedures. While vacuum filterating, some of the product were spilled, and as a reult this decreased the final weight.
Since the method implemented in this experiment required the use of dried equipments in order to avoid contamination of reaction, an error might have resulted from improper use of clean dry equipments as expected.
Another source of error might have been from washing and drying the product. While performing this procedure, part of the organic part of the liquid might have been removed and discarded along with the aqueous layer.This also might have caused the inconsistency in results obtained
Conclusion:
Although a few sources of errors caused a reduced yield of product, the purpose of the experiment, which was to synthesize triphenylmethanol, was achieved through the method and procedure used in this experiment. One way this experiment could be improved is to ensure that the reaction is not been contaminated by water or spilled while heating, stirring or vacuum filterating.

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