4-tert-Butyltoluene (C11H16) of mass 7.40 g is heated with excess alkaline KMnO4 and then acidified, giving 4-tert-butylbenzoic acid (C11H14O2) as the only aromatic product. The tert-butyl group is untouched. If the isolated yield is 80%, find the mass of the acid in grams (two decimals). Use H = 1, C = 12, O = 16.

JEE Advanced levelNumerical answerDifficulty 3 of 3ro069

4-tert-Butyltoluene ( $C X_{11} H X_{16}$ ) of mass $7.40 g$ is heated with excess alkaline $KMnO X_{4}$ and then acidified, giving 4-tert-butylbenzoic acid ( $C X_{11} H X_{14} O X_{2}$ ) as the only aromatic product. The tert-butyl group is untouched. If the isolated yield is $80%$ , find the mass of the acid in grams (two decimals). Use H = 1, C = 12, O = 16.

Numerical answer type, answer in g, tolerance 0.05.

Only the methyl group has benzylic hydrogens, so it becomes

- COOH

while the tert-butyl group (no benzylic H) stays.

M (C X_{11} H X_{16}) = 148

and

M (C X_{11} H X_{14} O X_{2}) = 178 g/mol

. Moles of substrate

= 7.40/148 = 0.0500

mol, so the theoretical mass is

0.0500 \times 178 = 8.90 g

. At

80%

yield the mass is

8.90 \times 0.80 = 7.12 g