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Q.a) How is phenol manufactured by Cumene process?

(3)
b) Explain Kolbe's reaction with equation. (2)
Karnataka PUCKarnataka II PUC Board 2022Subjective· 5mImportance★★★★★
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Phenol is made industrially by air-oxidising cumene (from benzene + propene) to cumene hydroperoxide, then acid-cleaving it to phenol + acetone; Kolbe's reaction converts sodium phenoxide + CO₂ into salicylic acid.

a) Manufacture of phenol by the Cumene process

  1. Benzene is alkylated with propene in the presence of an acid catalyst to give cumene (isopropylbenzene):

C6H6+CH3–CH=CH2→H+C6H5–CH(CH3)2\text{C}_6\text{H}_6 + \text{CH}_3\text{–CH=CH}_2 \xrightarrow{\text{H}^+} \text{C}_6\text{H}_5\text{–CH(CH}_3)_2

  1. Cumene is oxidised by air (atmospheric oxygen) to cumene hydroperoxide:

C6H5CH(CH3)2+O2→C6H5C(CH3)2–O–O–H\text{C}_6\text{H}_5\text{CH(CH}_3)_2 + \text{O}_2 \rightarrow \text{C}_6\text{H}_5\text{C(CH}_3)_2\text{–O–O–H}

  1. The hydroperoxide is treated with dilute acid, which cleaves it into phenol and acetone:

C6H5C(CH3)2OOH→H3O+C6H5OH+CH3COCH3\text{C}_6\text{H}_5\text{C(CH}_3)_2\text{OOH} \xrightarrow{\text{H}_3\text{O}^+} \text{C}_6\text{H}_5\text{OH} + \text{CH}_3\text{COCH}_3

Acetone is obtained as a valuable by-product.

b) Kolbe's reaction …

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