Lab Report EXP1 Friedel Crafts Acylation PDF

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Lab Report of Javier Mocassay - Friedel Crafts Acylation Lab 1...

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Experiment 1: Friedel Crafts Acylation Organic Chemistry Lab 2125.04 University of Texas at Rio Grande Valley Fall 2019 Dr. Javier Macossay Mia Ruiz, Hector Pena

Mia Ruiz CHEM 2125.04 Dr. Macossay OBJECTIVE: To perform Friedel Craft’s acylation, an electrophilic aromatic substitution, of anisole and acetic anhydride to produce 4-methoxyacetophenone. To understand the mechanism of Friedel Craft’s acylation, predict the products, and identify the roles of other factors in the reaction such as the substituents and the catalysts. To practice laboratory techniques while maintaining safety protocol. INTRODUCTION: Charles Friedel and Charles Mason Crafts created a method of adding an alkyl or acyl group to a benzene ring via electrophilic aromatic substitution reaction. (Beran) In the reactions the attacks are made by an electrophilic carbocation. (Beran) These are known as Friedel Crafts alkylation and acylation reactions. (Beran) The acylation reaction is significant and more advantageous than alkylation because it places only one acyl substituent from an acyl halide onto an aromatic hydrocarbon without rearrangement due to it’s deactivation or electronwithdrawing nature. (Beran) Deactivating substituents are meta directing. (Beran)

Image: (Beran) On the other hand, an Friedel Crafts alkylation reaction may yield a polyalkylated product after possibly having had multiple electrophilic attacks. (Beran) This is due to alkyl being of high energy as an electron-donating, or activating, substituent. (Beran) These are the limitations of alkylation. Activating substituents are ortho-para directing. (Beran)

Image: (Beran) The mechanism of acylation of a benzene is the same general one that will be followed in this experiment. The acyl halide will react with a Lewis acid and form a complex. (Hunt) The halide will be lost to the Lewis acid and form an acylium ion, which is electrophilic. (Hunt) The pi electrons from the benzene ring will exhibit nucleophilicity and attack the electrophilic carbocation forming a carbocation intermediate and breaking the ring. (Hunt) The proton of the 2

Mia Ruiz CHEM 2125.04 Dr. Macossay same carbon as the acyl group will be removed and reform the double carbon bond, bringing the ring together again. (Hunt) There will be an acid products as well as an acylated product. (Hunt) The catalyst reforms to the same structure it was when it was added. Any drying agents are not used to form the products either.

Image: (Beran) PROCEDURE: A reflux apparatus was assembled primarily using a condenser, Claisen adapter, and round-bottom flask and was connected to a water aspirator. An ice bath was prepared in a 100-mL beaker. A measured .55g of anisole was added to the flask with a boiling chip and 5mL of dichloromethane. A measured 1.45 g of anhydrous AlCl3 was quickly added to the flask and place in the ice bath. Using a Pasteur pipet, 12 drops of acetic anhydride were added drop by drop into the flask with periodic mixing. Then, the water aspiration was turned on. In a 400-ml beaker, 300-ml of hot water were placed. The water was heated with periodic temperature checks until it reached 45-50 degrees C. 5g of ice were placed into a 50-mL beaker under a fume hood. When it was witnessed that gas formation from the reaction had ceased, the mixture was poured over the ice. The flask was rinsed with 2mL of dichloromethane and added to the ice. There was still plenty of product in the flask so it was rinsed again with another .1 mL of dichloromethane and added to the ice. When the ice melted the mixture was added to a separation funnel. Once the two layer separated the bottom inorganic layer was poured out and appropriately disposed of. The remaining organic layer was transferred to a small graduated cylinder which .5 g of anhydrous MgSO4 was added for drying. The cylinder was swirled for approximately 5 minutes. The product was weighed and recorded. DATA: Substance

Quantity

Molar Mass (g/mol)

Experimental amounts

Density (g/mL)

Anisole

.55 g

108.1 g/mol

.553 g

.995 g/mL

Dichloromethane

5.0 mL

84.9 g/mol

5.10 mL

1.325 g/mL

Aluminum Chloride

1.45 g

133.3 g/mol

1.452 g

Acetic Anhydride

.6 mL

102.1 g/mol

.6 mL

1.082 g/mL

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Mia Ruiz CHEM 2125.04 Dr. Macossay 4-methoxyacetophenone

150.2 g/mol

1.062 g

Melting Point Ranges (TINITIAL - TFINAL) Substance 4-methoxyacetophenone

Literature

Experimental

38-39 C

2-methoxyacetophenone

CALCULATIONS: Important calculations for this experiment: 

Moles of Anisole: Theoretical: theoretical quantity of anisole / molecular weight of anisole = theoretical moles of anisole o .55 g anisole / 108.1 g/mol anisole = 5.09x10^-3 moles of anisole o .55 g / 108.1 g/mol = 5.09x10^-3 mols Experimental: molar mass of anisole / experimental quantity of anisole = experimental moles of anisole o .553 g anisole / 108.1 g/mol anisole = 5.11x10^-3 moles of anisole o .553 g / 108.1 g/mol = 5.11x10^-3 mols



Moles of Acetic Anhydride: (use density) Theoretical: (density in g/mL of acetic anhydride / molar mass of acetic anhydride) x volume of acetic anhydride in mL = theoretical moles of acetic anhydride o (.6 mL acetic anhydride x 1.082 g/mL acetic anhydride) =.65 g acetic anhydride .65 g acetic anhydride / 102.1 g/mol acetic anhydride = 6.37x10^-3 o (.6 ml x 1.082) / 102.1 g/mol = 6.37x10^-3 mols Experimental: 12 drops were used as an approximation of .6 mL of acetic anhydride and thus the experimental value is approximately equal to the theoretical.



Theoretical yield in 1:1 stoichiometry ("Limiting Reagents And Percent Yield"): moles of limiting reactant x molar mass of product o 5.11x10^-3 moles of anisole x 150.2 g/mol of 4-methoxyacetophenone = .77 g of 4methoxyacetophenone o 5.11x10^-3 mols x 150.2 g/mol = .77 g



Percent yield: (actual yield / theoretical yield) x 100 = % yield o (1.062 g of 4-methoxyacetophenone / .77 moles of 4-methoxyacetophenone) x 100 = 138% yield o (1.062 g / .77 g) x 100 = 138% yield 4

Mia Ruiz CHEM 2125.04 Dr. Macossay

CONCLUSION: We performed Friedel Crafts acylation of anisole with acetic anhydride to form 4-methoxyacetophenone. This occurs by substituting an acyl substituent from acetic anhydride onto the benzene ring of anisole. During the experiment we also explored laboratory techniques and methods. Based on the calculated theoretical yield, we obtained too much end product as our product weighing 1.062 grams gave us a percent yield of 138%. This indicates that the end product we produced is not pure 4-methoxyacetophenone. This is likely due to error in measuring the reagents before use. It is also likely there was a water contamination as we had to wash a graduated cylinder. It may not have been dried properly. This is an example of improper laboratory technique. I am not exactly sure how 4-methoxyacetopheno is para when acyl groups, like the one from acetic anhydride, are electron withdrawing and meta directing. I will investigate further as it is clear my understanding of the reaction is complete. Ultimately, the experiment was unsuccessful and had a very poor percent yield. POST LAB QUESTIONS: 1. What mass of 4-methoxyacetophenone did you actually obtain? o 1.062 g Calculate the percent yield for your experiment. o (1.062 g of 4-methoxyacetophenone / .77 moles of 4methoxyacetophenone) x 100 = 138% yield o (1.062 g / .77 g) x 100 = 138% yield 2. The following infrared absorption bands are observed in the spectrum of 4methoxyacetophenone. Assign each band to the structural feature of the compound that produces that band. a. 1668cm^-1 is carbonyl peaks b. 1022 cm^-1 is the C-O bonding c. 835 cm^-1 is the bending of the benzene ring 3. Account for the fact that the aromatic region of the proton NMR spectrum of 4methoxyacetophenone consists of two doublets, at 7.9 and 6.9. There are two type of protons present in the ring each with a multiplicity that equals two. 4. Nitration of the aromatic ring of 4-methoxyacetophenone yields only one product. Identify that product and account for its formation. Because the methoxy group is electron donating and ortho-para directing and the acyl group is electron withdrawing and meta direction the nitro group will be position on the products positions that are ortho to methoxy and meta to the ketone. It is the same position thus it is the same product.

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Mia Ruiz CHEM 2125.04 Dr. Macossay

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Mia Ruiz CHEM 2125.04 Dr. Macossay CITATIONS:

"Limiting Reagents And Percent Yield". Khan Academy, 2019, https://www.khanacademy.org/science/chemistry/chemical-reactions-stoichiome/limitingreagent-stoichiometry/a/limiting-reagents-and-percent-yield. Accessed 18 Sept 2019. Beran, Jo Allen. Laboratory Manual For Principles Of General Chemistry. 9th ed., Wiley, 2010. Hunt, Ian. "Ch12: Friedel-Crafts Acylation". Chem.Ucalgary.Ca, 2019, http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch12/ch12-7.html. Accessed 18 Sept 2019.

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