Potassium phthalimide is heated with bromoethane to give A, and A is heated with aqueous $\mathrm{NaOH}$ to give B and disodium phthalate. B is

In the Gabriel synthesis the N-alkylphthalimide (A, N-ethylphthalimide) is hydrolysed to the primary amine $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{NH}{}_2$ (B) and the phthalate. Only the primary amine is formed, since the nitrogen is blocked from further alkylation.