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A Friedel-Crafts Alkyla

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A Friedel-Crafts Alkyla

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tionIntroduction:In order to produce an alkyl arene, aromatic rings usually undergo the Friedel-Crafts alkylation. This is usually done in the presence of an alkyl halide with a Lewis acid catalyst. As limitations for this reaction to take place, the arene should be unsubstituted or should have an activating group attached. Such activating groups include: -OH, -OCH3, and -CH3 which provide extra resonance stabilization. Deactivating groups are electron withdrawing groups such as NO2. These withdrawing groups fail most of the time to carry out this type of reaction due to the lack of resonance stabilization.

In this reaction the arene p-xylene is the starting aromatic compound. In this case the p-xylene is more reactive than the starting material, n-propyl chloride and aluminum chloride, so multiple substitutions can take place. The p-xylene is present in excess to prevent multiple alkylations of the reaction to take place.

Rearrangements such as carbocation rearrangements and methyl/hydride shifts can result in different alkyl arenes as products. The alkyl halides, with an exception to methyl and ethyl, undergo these rearrangements. Usually, under the Friedel-Crafts alkylation conditions, primary alkyl halides rearrange to either secondary or tertiary carbocations that are much more stable. The reactant in this experiment is n-propyl chloride. The products in this experiment from the p-xylene are the unrearranged n-propyl group attached to the p-xylene (1,4-Dimethyl-2-n-propylbenzene) and the rearranged isopropyl group attached to the p-xylene (1,4-Dimethyl-2-isopropylbenzene). The aluminum chloride is the Lewis acid catalyst in the reaction and combines with the chloride ion of the n-propyl chloride to form the Friedel-Crafts complex.

Gas chromatography will be used to decide the quantitative product distribution of the resulting compounds.

The purpose of this experiment is to carry out the Friedel-Crafts alkylation of p-xylene. Also the...