Question

Hydrocarbons do not dissolve in concentrated H2SO4 but methyl benzoate does. Explain this difference and give a reaction equation showing the ions formed when methyl benzoate dissolves in H2SO4.

Based on the protonated methyl benzoate ions formed in the first question, explain why nitration occurs at the meta position and not at ortho or para.

Answer 1

1) Hydrocarbons are completely nonpolar molecules and hence do not soluble in polar solvent H2SO4 while methyl benzoate an ester get soluble in water due to protonation of oxygen

Sulfuric acid can protonate the carboxyl group of the methyl benzoate, which produces an ionic species which is soluble in the polar sulfuric acid.
H2SO4 ---> HSO4- + H+
H+ + C6H5COOCH3 -----> [C6H5C(HO)OCH3]+
Now that the methyl benzoate has a positive charge it will be able to dissolve in polar sulfuric acid

2) From the resonance structures of protonated methyl benzoate it is clear that the electron density is not available at ortho and para positions to attack an electrophile and hence nitration occurs at meta positon due to availability of electron density