Ketal Formation (Step 1 of 4,4-Diphenyl-3-buten-2-one Preparation) Lab Report PDF

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Lab report on protecting the ketone carbonyl group of ethyl acetoacetate using ethylene glycol in toluene. Includes complete abstract, introduction, results, discussion, conclusion, procedure, references, and pictures of lab notebook & NMR spectra of final product. Part of a multi-step synthesis....

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Ketal Formation (Step 1 in Multistep Synthesis of 4,4-Diphenyl-3-buten-2-one )

California State University, Los Angeles CHEM 2211 28 February 2018

Abstract Protecting groups are one of the essentials in synthesis because it allows certain reactions to take place on a less reactive functional group of a molecule. The ketone carbonyl group of ethyl acetoacetate was protected through the use of an ethylene ketal protecting group by reacting ethyl acetoacetate with ethylene glycol in toluene and under heat. The product resulted in a mixture of 20.89% toluene and 79.11% ethyl acetoacetate ethylene ketal (fructone).

Introduction This lab report documents the results of the first step in the multistep synthesis of 4,4-diphenyl-3-buten-2-one. The first step involves the protection of the ketone carbonyl group of the starting material (ethyl acetoacetate) using an ethylene ketal protecting group because adding a Grignard reagent to the starting material will not provide the desired intermediate for this multistep synthesis.1

A protecting group temporarily masks a reactive part of the molecule in order for another part of the molecule to undergo a reaction; as such, good protecting groups are considered to be easy to add and remove in high yield reactions.2 By protecting the ketone carbonyl group of ethyl acetoacetate, Grignard addition can be done onto the ester instead of the ketone in the next step of the synthesis. The following figure shows the overall reaction of this experiment.

Figure 1. Reacting ethyl acetoacetate with ethylene glycol in toluene and under heat to produce ethyl acetoacetate ethylene ketal (fructone) and water.

+ H2O

+ toluene, heat

Results & Discussion Table 1. Determining weight of final product. FLASK (g)

FLASK + PRODUCT (g)

PRODUCT WEIGHT (g)

92.52

109.50

16.98

Table 2. Determining the limiting reagent. REACTANT

WEIGHT (g)

MOLES (mol)

LIMITING REAGENT

Ethyl acetoacetate

26.028

0.20

Limiting reagent

Ethylene glycol

24.828

0.40

-

By observing the reactants of those in Figure 1, the limiting reagent is determined to be ethyl acetoacetate because after converting weight to moles, there are less moles of ethyl acetoacetate than there are moles of ethylene glycol. The moles limiting reagent will be used in the following equation to determine the final percent yield.

Equation 1. Calculating percent yield of final product. mol f ructone 0 .20 mol ethyl acetoacetate ( 1 mol1 ethyl )( 174.194 g ) = 35. g fructone acetoacetate mol f ructone 16.98 g actual f ructone 35. g theoretical fructone

Figure 2. H1  NMR spectra of final product

· 100% = 49% yield

Equation 2. Calculating weight percent of toluene from mole fraction of toluene. (0.02 · 100)% 0.04 + 0.02 = 33.3% toluene (mole fraction) 92.14 g 3 3.3 mol toluene ( mol ) = 3068.262 g toluene toluene 174.194 g 6 6.7 mol fructone ( mol ) = 11618.7398 g fructone f ructone

100 mol mixture ⇒ 3068.262 g + 11618.7398 g = 14687.0018 g mixture 3068.262 g toluene 14687.0018 g mixture 11618.7398 g fructone 14687.0018 g mixture

= 20.89% weight toluene = 79.11% weight fructone

2 0.89% weight toluene · 1 6.98 g product) = 3.55 g toluene The results show that the product is not as pure as the experiment intended. With this information, the quantities in step two of the synthesis of 4,4-diphenyl-3-buten-2-one must be adjusted as needed to account for any toluene present.

When refluxing the mixture with the Dean-Stark apparatus, the following observations were observed: the liquids separated; as the mixture boiled, the cloudiness of the mixture appeared clearer; the product obtained after cooling, washing, and filtering appeared as a cloudy white. After distilling out the toluene by simple distillation, the liquid appeared as cloudy white as well.

Conclusion The purpose of this experiment was to protect the ketone carbonyl group of ethyl acetoacetate. After following the experimental details, the product resulted in 79.11% fructone and 20.89% toluene. The relatively significant amount of toluene is not ideal but altering the quantities in the next step of the synthesis will help the reaction reach the desired final product. Possible reasons as to why there was still a significant amount of toluene include the fact that while distilling, the appropriate drop rate of one drop per second was not established initially.

Experimental Details A Dean-Stark apparatus was used to reflux a mixture of 100 msL toluene, 25 mL ethyl acetoacetate, 22 mL ethylene glycol, and 0.2174 g toluenesulfonic acid monohydrate for ninety minutes as water collects in the Dean-Stark trap. The resulting mixture was cooled, washed with 20 mL cold 10% sodium hydroxide solution and again with 20 mL water, twice. The solution was gravity filtered with magnesium sulfate. Toluene was removed via simple distillation. The H1 NMR spectrum of the final product was taken for analyzation.

References 1. Chemistry 2211 Organic Chemistry Laboratory II Supplementary Material,  Department of Chemistry and Biochemistry, California State University, Los Angeles, 2016. 2. Hunt, I. Protecting Groups http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch17/ch17-3-4-3.html (accessed Feb 26, 2018).

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