In the manufacture of phenol, cumene (isopropylbenzene, C6H5CH(CH3)2) is oxidised by air to cumene hydroperoxide, which is then treated with dilute acid. What mass of acetone is obtained from 24 g of cumene, assuming complete conversion? (Atomic masses: H = 1, C = 12, O = 16)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 11.6 g
In the cumene process, one molecule of cumene gives one molecule of cumene hydroperoxide, and dilute acid splits this into one molecule of phenol and one molecule of acetone:
\( \displaystyle \ce{C6H5CH(CH3)2 + O2 -> C6H5C(CH3)2OOH} \)
\( \displaystyle \ce{C6H5C(CH3)2OOH} \xrightarrow{\ce{H+}/\ce{H2O}} \ce{C6H5OH + CH3COCH3} \)
So the moles of acetone formed are equal to the moles of cumene taken.
\( \displaystyle M(\ce{C9H12}) = 9 \times 12 + 12 \times 1 = 120\ \mathrm{g\ mol^{-1}} \)
\( \displaystyle n(\text{cumene}) = \frac{24\ \mathrm{g}}{120\ \mathrm{g\ mol^{-1}}} = 0.200\ \mathrm{mol} = n(\text{acetone}) \)
\( \displaystyle m(\ce{CH3COCH3}) = 0.200\ \mathrm{mol} \times 58\ \mathrm{g\ mol^{-1}} = 11.6\ \mathrm{g} \)