Grignard Addition to Ester to Synthesize Ketal-Alcohol 2 (Step 2 in Multistep Synthesis of 4,4-Diphenyl-3-buten-2-one) Lab Report PDF

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Lab report on how Phenylmagnesium bromide is used to reduce the ester group in the fructone molecule in order to synthesize 2-(2-methyl-1,3-dioxolan-2-yl)-1,1-diphenylethanol which was then purified by recrystallization from petroleum ether. Includes complete abstract, introduction, results, discuss...

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Grignard Addition to Ester to Synthesize 2-(2-Methyl-1,3-dioxolan-2-yl)-1,1-diphenylethanol (Step 2 in Multistep Synthesis of 4,4-Diphenyl-3-buten-2-one)

California State University, Los Angeles CHEM 2211 4 March 2018

Abstract Phenylmagnesium bromide is used to reduce the ester group in the fructone molecule in order to synthesize 2-(2-methyl-1,3-dioxolan-2-yl)-1,1-diphenylethanol which was then purified by recrystallization from petroleum ether. The product resulted in 2.44 grams of spiked and translucent white crystals.

Introduction This lab report documents the results of the second step in the multistep synthesis of 4,4-diphenyl-3-buten-2-one. The second step involves the reduction of the ester in fructone via Grignard reaction.1 The addition of an organomagnesium halide to a ketone forms a tertiary alcohol.2 Phenylmagnesium bromide is important to the synthesis of 2-(2-methyl-1,3-dioxolan-2yl)-1,1-diphenylethanol from fructone because the final product in this multistep synthesis requires two phenyl groups in the molecule.

Figure 1. Grignard Addition to Ester Mechanism

Results & Discussion Equation 1. Calculating volume of bromobenzene and amount of reactant. g mL = 17. mL bromobenzene 0.16 mol bromobenzene ( 157.01 )( 1.474 g) mol g 0 .07 mol f ructone ( 174,196 ) = 12.19 g f ructone mol

After combing the anhydrous ether, magnesium, and bromobenzene to synthesize the Grignard reagent, bubbles rose to the surface and the mixture gradually turned brown and cloudy. After adding the Grignard reagent to fructone that has been dissolved in anhydrous ether, the precipitate that formed was a very light peachy white color that floated on the surface of the liquid until eventually collecting at the bottom of the flask. As the reaction occurred very slowly, it became harder to mix with a glass stirring rod. The substance was extremely viscous and very hard to combine altogether. After dissolving the new product in petroleum ether for recrystallization, the liquid was dried in magnesium sulfate; here, its appearance went from a cloudy yellow liquid to a clear yellow liquid. The final product in this part of the multistep synthesis weighed in at 2.44 grams of spiky, translucent white crystals. 0.07 moles of fructone, 0.15 moles of magnesium, and 0.16 moles of bromobenzene was used for the experiment; therefore, the limiting reagent is determined to be fructone. With this information, the percent yield of 2-(2-methyl-1,3-dioxolan-2-yl)-1,1-diphenylethanol after purification by recrystallization is found in Equation 2.

Equation 2. Calculating percent yield of final product. −2−yl)−1,1−diphenylethanol 283.34 g 0 .07 mol f ructone ( 1 mol 2−(2−methyl−1,3−1 dioxolan )( mol ) = 20. g final product mol f ructone 2.44 g actual product 20. g theoretical product

· 100% = 12.2% yield Conclusion

The purpose of this experiment was to reduce the ester group in fructone via Grignard reaction in order to synthesize a tertiary alcohol. After following the experimental details, the product resulted in 2.44 grams of what is assumed to be translucent, purified 2-(2-methyl-1,3dioxolan-2-yl)-1,1-diphenylethanol crystals.

Experimental Details The glassware for the Grignard reaction was cleaned and dried a week before the experiment to ensure proper preparation. The drying tube was filled with drierite drying agent. 3.58 g of ground magnesium turnings and 20 mL of anhydrous ether were poured into the three-neck round bottom flask. 60 mL of anhydrous ether was poured into the addition funnel. 5 mL of bromobenzene was poured into the flask and 12 mL were poured into the addition funnel. As the Grignard reaction took place, 10 mL of anhydrous ether was introduced to the condenser. The bromobenzene and anhydrous ether mixture was added to the reaction dropwise over a period of 30 minutes. 12.19 g of fructone was added to the addition funnel in order for it to add to the reaction in a dropwise fashion. The product was mixed, corked, and dried until the next lab period. The crude product was washed with water, dried using magnesium sulfate, rinsed with ether, evaporated using a rotary evaporator, vacuum filtered, then purified by recrystallization from petroleum ether. The final product was weighed and stored for the next experiment in the

multistep synthesis.

References 1. Chemistry 2211 Organic Chemistry Laboratory II Supplementary Material,  Department of Chemistry and Biochemistry, California State University, Los Angeles, 2016. 2. Grignard Reaction http://www.organic-chemistry.org/namedreactions/grignard-reaction.shtm (accessed Apr 2, 2018).

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