Friedel Crafts Alkylation Reaction

Friedel-Crafts Alkylation Reaction

Friedel-Crafts Alkylation Reaction

Preparation of 1, 4-Di-t-butyl-2, 5-dimethoxybenzene

Microscale Experiment

Leah Monroe

April 8, 2003

Organic Chemistry Lab II

Experiment performed on March 20 and 25, 2003

Lab Partners (NMR only): Shannon Land and Jamie Yeadon

Abstract:

In this experiment, 1,4-dimethoxybenzene reacted with t-butyl alcohol to form 1, 4-Di-t-butyl-2, 5 - dimethoxybenzene via a Friedel-Crafts Alkylation mechanism. A small amount of 1,4-dimethoxybenzene was dissolved in acetic acid and t-butyl alcohol, along with H2SO4. The reaction was then allowed to go to completion at room temperature, and the crystals were washed with water and methanol. The percent yield of the product was 57.48%. This was lower due to the fact that many of the crystals were stuck in the reaction tube and could not be removed for weighing. Also, when a Pasteur pipet was used to remove the solvent from the reaction tube, many crystals were lost. The observed melting point of the product was 96 - 98oC, which is considerably lower than the literature value of 104 - 105oC. This may be due to impurities in the product or the sample may still have been wet. An NMR spectrum of the sample indicated that the sample was 1, 4-Di-t-butyl-2, 5 - dimethoxybenzene and that the reaction was successful.

Friedel-Crafts Alkylation Reaction

Introduction: The purpose of this experiment is to synthesize 1, 4-Di-t-butyl-2, 5 - dimethoxybenzene by reacting 1, 4 - dimethoxybenzene with tertiary-butyl alcohol in the presence of sulfuric acid as a Lewis acid catalyst. The reaction will occur via the Friedel-Crafts alkylation mechanism, and involves the attack of the aryl group at the electrophilic trimethylcarbocation. The resulting product will be recrystallized using methanol and characterized using IR spectroscopy and melting point analysis.

Materials Used:

1 beaker, 400-mL sand bath

ice for ice bath Erlenmeyer flask, 25-mL

several Pasteur pipets, 1.0-mL 10 x 100 mm reaction tube

glass stirring rod rubber bulb

Substances

Formula

Weight, g/mol

Amount Used

Moles

Used

Mole

Ratio

Melting

Point

oC

Boiling

Point

oC

Density

g/mL

1, 4-dimethoxybenzene

138.16

0.120 g

8.69 x 10-4

1 to 1

58 - 60

N/A

1.053

Acetic acid

60

0.4 mL

N/A

N/A

N/A

118

1.049

t-butyl alcohol

74.12

200 мL

0.00213

2 to 1

N/A

83

0.7856

Concentrated H2SO4

98.06

2.0 mL

N/A

N/A

N/A

327

1.84

Methanol

32.0

1.0 mL

N/A

N/A

N/A

64.7

0.7914

Water

18.0

2.5 mL

N/A

N/A

N/A

212

1.0

1, 4-Di-t-butyl-2, 5 - dimethoxybenzene

250.17

product

product

1 to 1

104 - 105

N/A

N/A

Reaction and its Mechanism:

The limiting reagent for this reaction is 1, 4 - dimethoxybenzene. See calculations section for explanation.

Overall Reaction: C8H10O2 + 2C4H10O �� C16H26O2 + 2H2O

1,4-di-t-butyl-2,5-dimethoxybenzene H2SO4 1, 4-dimethoxybenzene OCH3 OCH3 + OH CH3 CH3 CH3 Tert-butyl alcohol OCH3 OCH3 H2O +

Mechanism:

H H H O SO3H Sulfuric Acid OH CH3 CH3 CH3 O CH3 CH3 CH3 + + CH3 CH3 CH3 C

Friedel-Crafts Alkylation Reaction

Mechanism (con't) + CH3 CH3 CH3 C OCH3 OCH3 + OCH3 OCH3 H + OCH3 OCH3 H + OCH3 OCH3 H -OSO3H OCH3 OCH3 + H OCH3 OCH3 + + CH3 CH3 CH3 C OCH3 OCH3 -OSO3H H OCH3 OCH3 + H OCH3 OCH3 OCH3 OCH3 H2SO4 + 1,4-di-t-butyl-2,5-dimethoxybenzene

Procedure:

Dissolve 120 mg 1,4-dimethoxybenzene in a 10 x 100 mm reaction tube with 0.4 mL acetic acid. Add to it 0.2 mL t-butyl alcohol and heat gently until the mixture