One major problem with the Friedel-Crafts alkylation is that the product formed

Question

One major problem with the Friedel-Crafts alkylation is that the product formed is often more active than the starting material, this causes the product react faster than the starting material leading to multiple alkylated products. What is one way we could control this in the reaction we performed this week and get only the mono-substituted product?

(The reaction we performed was between 1,4-dimethoxybenzene and tert-butyl alcohol, which was transformed into a tert-butyl carbocation so that we could perform Friedel-Craft alkylation with it.)

a. Run the reaction at high temperatures

Use a large excess of 1,4-dimethoxybenzene

c. Slowly add the 1,4-dimethoxybenzene to a solution containing sulfuric acid and tert-butanol

Use only 1 equivalent of the tert-butanol

a. Run the reaction at high temperatures

Use a large excess of 1,4-dimethoxybenzene

c. Slowly add the 1,4-dimethoxybenzene to a solution containing sulfuric acid and tert-butanol

Use only 1 equivalent of the tert-butanol

Explanation / Answer

The polyalkylation is a limitation in friedel-Crafts reaction.

The reaction between 1,4-dimethoxybenzene and tert-butanol in H2SO4 catalyst is controlled by,

b. Use a large excess of 1,4-dimethoxybenzene

With aromatic substrate in excess, all of tert-butanol would react to form 1 monoalkylated product only.

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