Question

The following compound used in perfumery has a violet-like scent. Propose a synthesis of this compound from benzene. CC(=O)c1ccc(C(C)C)cc1 4-Isopropylacetophenone

Short answer

Question: Outline the step-by-step synthesis of 4-isopropylacetophenone starting from benzene. Answer: The synthesis of 4-isopropylacetophenone from benzene involves the following steps: 1. Friedel-Crafts acylation of benzene with acetyl chloride to obtain acetophenone. 2. Conversion of acetophenone to its corresponding enolate ion using a strong base like sodium hydride (NaH). 3. Alkylation of the acetophenone enolate using isopropyl bromide to introduce the isopropyl group, forming the final product, 4-isopropylacetophenone.

Step-by-step solution

Acylation of Benzene

To synthesize the target molecule from benzene, we first need to introduce the acetophenone group. We can achieve this through Friedel-Crafts acylation of benzene with acetyl chloride in the presence of a Lewis acid catalyst, such as AlCl3. This reaction will yield acetophenone. Reaction: \(\text{C}_6\text{H}_6 + \text{CH}_3\text{COCl} \xrightarrow{\text{AlCl}_3} \text{C}_6\text{H}_5\text{C(O)CH}_3\)

Conversion of Acetophenone to Acetophenone Enolate

The next step is to convert acetophenone to its corresponding enolate ion. This can be achieved by treating the ketone with a strong base, such as sodium hydride (NaH) in an aprotic solvent, e.g., THF. The base will abstract the alpha-proton from acetophenone, forming acetophenone enolate. Reaction: \(\text{C}_6\text{H}_5\text{C(O)CH}_3 + \text{NaH} \to \text{C}_6\text{H}_5\text{C(O)CH}_2^− + \text{Na}^+ + \text{H}_2\)

Alkylation of Acetophenone Enolate with Isopropyl Bromide

The next step is to introduce the isopropyl group to the para position of the benzene ring using an alkylation reaction. For this, we can use isopropyl bromide as an alkylating agent. The acetophenone enolate will undergo an SN2 reaction with isopropyl bromide, leading to the formation of the final product, 4-isopropylacetophenone. Reaction: \(\text{C}_6\text{H}_5\text{C(O)CH}_2^- + \text{(CH}_3\text{)}_2\text{CHBr} \to \text{C}_6\text{H}_5\text{C(O)CH(CH}_3\text{)}_2 + \text{Br}^-\) In summary, the sequence of reactions to synthesize 4-isopropylacetophenone from benzene involves the following steps: 1. Friedel-Crafts acylation of benzene to obtain acetophenone. 2. Conversion of acetophenone to its enolate form. 3. Alkylation of the enolate ion with isopropyl bromide to introduce an isopropyl group, ultimately forming 4-isopropylacetophenone.