Synthesis of 1, 4-Di-t-butyl-2, 5-dimethoxybenzene in terms of Friedel-Crafts Alkylation

Friedel- Craft alkylation response is a type of electrophilic aromatic substitution (EAS) response that involves carbonation of the aromatic ring. The technique requires polyalkylation using an excess of carbocationic intermediate such as an alkyl or acyl team prepared through protonation of an alkene the usage of hydrogen fluoride, treating it with alcohol, dehydrating using boron trifluoride or concentrated sulfuric acid. A integral application of Friedel-Craft alkylation is during the practise of 1, 4-di-tert-butyl-2, 5-dimethoxybenzene from 1, 4- dimethoxybenzene and t-butyl. In this reaction, the carbocation generated by dehydrating a tertiary alcohol with a high acid such as sulfuric acid acts as the electrophile. This electrophile assaults the benzene ring twice at ortho-para positions since alkylation increases the nucleophilicity of the benzene ring and also the methoxy group is an active activating ortho-para director. However, hydrogen in the other two remaining positions cannot be replaced since the positions are sterically hindered from further reactions. However, application of these results in organic synthesis is limited due to the natural formation of many unwanted side reactions (Carey 83).

Aim of the experiment

This experiment purposed to prepare 1, 4-di-t-butyl-2-5-dimethoxybenzene by reacting 1, 4-dimethoxybenzene and t-butyl.

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Procedure of experiment

1. 0.30g of 1,4-dimethoxybenzene and 0.5 mL of t-butyl alcohol and 1.0 mL of glacial acetic acid were placed in an 18×150 mm test tube. The test tube was swirled to dissolve the 1, 4-dimethoxybenzene and after that placed in an ice-water bath.
2. 2.0 mL of concentrated sulfuric acid was added to another test tube and put in the ice-water bath.
3. The temperatures of the two solutions in the separate test tubes were allowed to cool to between 00C and 50C. After that, a disposable pipette was used to add the sulfuric acid dropwise to the mixture, and test tube swirled. Occasional stirring of this mix was also done using a glass rod.
4. The mixture was removed from the ice-water bath after adding all the sulfuric acid. Stirring of the mixture using the glass rod continued and its temperature allowed to rise to 250C. The mixture was then stirred for further 5 min.
5. Chips of ice were added to the mixture and stirred, followed by addition of water to almost the brim of the test tube. The mixture was vacuum filtered using Hirsch funnel, and the filtrate washed with 10 mL of water. The white solid was allowed to dry for a further 5 min while still on the suction.
6. The filtrate was transferred to a 25 mL conical flask and recrystallized using 5 mL of ethanol. Its melting point and percentage yield were recorded after the drying process.

Results and Calculations

Total weight of the product after purification: 0.7872 grams
The melting point of the product obtained: 96.40C-99.50C.

Responses to Questions

1. Acetic acid is used as a solvent in this reaction. Concentrated sulfuric acid is the dehydrating agent for the tertiary alcohol to obtain the carbocation as well as the catalyst for the Friedel-Craft reaction.
2. a. 2, 4-t-butyl-1-methoxybenzene
b. 2, 4- (1, 1, 2-trimethylpropyl)-anisole and bis alkylation product.
c. 1, 4-di-t-butyl-2, 5-dimethoxybenzene
d. 2, 5-(1, 3-dimethylbutyl)-1, 4-dimethoxybenzene
3. There are three singlets in the 1H NMR spectra with peak spectra at 7.26 ppm and a solvent impurity at 2.2 ppm.
4. In Friedel-Crafts alkylation, the reactor is an alkyl halide (R-X), and AlCl3 catalyst is required while in Friedel-Crafts acylation, the reactor is an organic acid group (R-COOH).
5. a. Ortho and para acetyl products.
b. Ortho products and a small para product.
c. Meta product.

Discussion

Friedel-Crafts reactions are used when attaching an alkyl or acyl group to an aromatic ring. During the reaction process, a strong electrophilic carbocation (R+) or acylium ion (RC=O+) used for the process is formed by dehydrating an alkyl or acyl group using concentrated sulfuric acid respectively. Ions formed are then used during the electrophilic substitution reaction on the benzene ring (Olah 114).

The total yield was not one hundred percent since there was a loss of some crystals during the transfer process. Some of the crystals stuck in the test tube and couldn't be removed for weighing. The boiling point of the product was also lower because the product obtained could be containing some impurities.

Conclusion

The purpose of the experiment was achieved since 1, 4-di-t-butyl-2-5-dimethoxybenzene was obtained as the end product. Great care was required when handling sulfuric acid since it is incredibly corrosive as well as when handling ethanol because it is a flammable liquid. Sources of errors during the reaction could arise due to an inaccurate following of the procedure provided as well as the use of contaminated reactants.

Works Cited

Carey, F.A. Organic Chemistry. 3rd ed. New York: McGraw-Hill, 1996.
Olah, G.A. Friedel-Crafts Chemistry. New York: John Wiley, 1973.