friedel-crafts acylation of toluene

8/13/2019 Friedel-Crafts Acylation of Toluene

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Friedel-Crafts Acylation of Toluene

Objective:The purpose of this experiment is to perform Elecrtophilic Aromatic Substitution reaction (Friedel-Craftsacylation) of toluene. The product will be isolated and analyzed by IR and TLC. The substitution pattern will be

verified. Reaction yield and percent recovery will be discussed.

Chemicals: toluene, anhydrous aluminum chloride, acetyl chloride, methylene chloride, conc. HCl, 5% NaHCO3brine, anhydrous MgSO4or Na2SO4.

Glassware and equipment:50 and 100 mL RBF, air condenser, Claisen adaptor, addition funnel, short stem glassfunnel, 60 and125 mL separatory funnels, 150 mL beaker, 50 mL Erlenmeyer flasks, 10 mL graduated cylinder, lab

jack, crystallizing dish, magnetic stir bar.

Techniques:reflux, extraction, rotary evaporation, IR spectroscopy.

Introduction

CH3

1. AlCl3

2. H3O+, H2O

H3C

O

Cl

CH3O

CH3

CH3

O CH3

+

Electrophilic aromatic substitution reactions (EAS) take place between the nucleophilic a- electrons of an aromatic ring

and an enhanced electrophile. The intermediate carbocation rapidly goes through elimination of proton to restore the

aromatic system. In the case of Friedel-Crafts acylation, the electrophile is an acylium ion, formed by the reaction of an

acyl chloride with aluminum chloride. The mechanism is shown in Fig. 1.

H3C

O

ClAl

Cl

Cl

Cl

Al

Cl

Cl Cl

Cl

++

O

CH3

O

H3C

O

H3C

CH3

-AlCl3/HCl

CH3 O

CH3

CH3

O CH3

+

CH3

O

CH3

H

major minorFig. 1. Reaction mechanism

Experimental Procedure:Caution: anhydrous aluminum chloride is moisture sensitive and will irritate your skin producing HCl. Wear gloves

and handle this chemical carefully. Close the bottle as soon as you obtain the amount needed.

Acetyl chloride is an eye and lung irritant: do not remove from the hood and close tightly after measuring the amount

needed. Wash the glassware after this experiment in the hood with some acetone before moving it to your bench top.


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First Class Period:

1. Assemble apparatus shown below. Weigh carefully anhydrous aluminum chloride (0.0275 mol, MW=133.34g/mol) and add it to the dry 50 mL round bottom flask using glass funnel. Wash the catalyst off the funnel with 8

mL of methylene chloride into the same flask. Equip the RBF with a magnetic stir bar. Place a Claisen adaptor on

top of the RBF and attach a 60 or 125 mL addition funnel and air condenser. Lightly grease the joints.

2. Cool the mixture on an ice bath to 0oC.3. Measure carefully in the hood 0.0275 mol acetyl chloride (MW=78.5 g/mol, d=1.104 g/mL) using a dry graduated

cylinder. Transfer the reagent into a clean addition funnel and add to it 5 mL methylene chloride (use the same

graduated cylinder).

4. Start adding the mixture to the suspension of aluminum chloride in RBF. The addition should be done over 10 minAs you add acyl chloride solution to the mixture in the round bottom flask, the solution should become

homogeneous and turn bright yellow. If you form a cloudy off-white mixture, the chances are your reaction

absorbed moisture and the catalyst was deactivated. Show the setup to your instructor: you might have to start over

5. Once the electrophile is activated, add a solution of 0.025 mol of toluene (MW=92.13 g/mol, d=0.87 g/mL) mixedwith 5 mL methylene chloride into the same addition funnel. Adjust the rate of addition so the solution does not boil

excessively. The solution at this point turns amber color.

6. After the addition is complete, remove the ice bath and let the mixture to come to room temperature. Stir foradditional 15 min at room temperature.

7. Now pour the reaction mixture carefully and slowly with stirring into 25 g of ice and 10 mL of conc. HCl in abeaker. The color will change to off-white. Transfer the mixture into clean 125 mL separatory funnel and extract

the bottom organic layer. Collect the bottom layer in a clean Erlenmeyer flask and extract the aqueous layer one

more time with additional 10 mL methylene chloride. Combine organic layers, wash them with 10 mL deionized

water, 15 mL sodium bicarbonate, 15 mL brine, and dry the organic layer over anhydrous Na 2SO4 in a dry 50mL

Erlenmeyer flask. Cork and parafilm the product; label it and save until next class period.

air condenser: do not cork

Claisen head

125 mLseparatory funnel

50 mL RBF

water-ice bath

Fig. 2.Reaction setup

keck clamps


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Second Class Period:1. Decant the dried solution into a clean, dry pre-weighed 100 mL RBF.2. Rotovap the solution.3. Report actual yield and percent yield.4. Analyze the product by IR (you might have to run a background with methylene chloride to eliminate the

residual peak from the remaining solvent in your product).

5. Run TLC of the product in 20:80 EtOAC/Hexanes mixture.Guidelines for Formal Report: (20 pt)

Note: Attach all spectra and label the important peaks (Draw the structures, label the functional groups or H, C, a

match them with the spectra). Severe point deduction will follow if spectral data is missing.

Abstract (2 pt)

Target molecule and the reactions with mechanisms (2 pt)

Tabulated results:

Product Yields (grams /%) Color/Texture Purity (from TLC)

Rfvalues

Crude product

Purified product

Discussion:

Yield (5 pt): Explain what could affect the yield of reaction. Be specific and refer to your notebook.

TLC (3 pt):compare the TLC of the products and comment on the presence of possible products.

IR and NMR (6 pt):when reporting IR and NMR of the products, please do not just list the chemical shifts and th

wavenumbers on NMR and IR but rather comment on the changes from one compound to another in terms o

reporter peaks.

The NMRs of the starting material and the major possible products are presented below:

Conclusion (2 pt): comment on any disadvantages or failures of this experiment and propose

modifications/improvements for the synthetic procedure. Please be specific and note that general comments such as

use a different solvent, different glassware, etc. are not valid to make your point!


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CH3

012345678

PPM

CH3

0102030405060708090100110120130140150

PPM

H NMR of Toluene:

13C NMR of Toluene:

IR of Toluene:


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CH3

CH3

H NMR of p-product:

13C NMR of p-product:

O CH3

012345678

PPM

O CH3

020406080100120140160180200

PPM

IR of p-product:


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CH3 O

CH3

CH3 O

CH3

H NMR of o-product:

13C NMR of o-product:

PPM

24682PPM

IR of o-product:

friedel-crafts acylation of toluene

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