Hinsberg Test ($$1^\circ$$ vs. $$2^\circ$$ vs. $$3^\circ$$)

Reaction Notation & Equations by Amine Class

• Primary Amine ($$1^\circ$$ Amine):

$$\text{R--NH}_2 + \text{C}_6\text{H}_5\text{SO}_2\text{Cl} \xrightarrow{-\text{HCl}} \text{C}_6\text{H}_5\text{SO}_2\text{--NH--R} \quad (\text{N-Alkylbenzenesulfonamide})$$
$$\text{C}_6\text{H}_5\text{SO}_2\text{--NH--R} + \text{NaOH} \to [\text{C}_6\text{H}_5\text{SO}_2\text{--N--R}]^-\text{Na}^+ + \text{H}_2\text{O} \quad (\text{Soluble Sodium Salt})$$
Notation: Dissolves in aqueous NaOH due to acidic hydrogen on N: reprecipitates upon acidification with HCl

• Secondary Amine ($$2^\circ$$ Amine):

$$\text{R}_2\text{NH} + \text{C}_6\text{H}_5\text{SO}_2\text{Cl} \xrightarrow{-\text{HCl}} \text{C}_6\text{H}_5\text{SO}_2\text{--NR}_2 \quad (\text{N,N-Dialkylbenzenesulfonamide})$$
$$\text{C}_6\text{H}_5\text{SO}_2\text{--NR}_2 + \text{NaOH} \to \text{No Reaction} \quad (\text{Insoluble in aqueous } \text{NaOH})$$
Notation: Precipitate remains insoluble in alkali due to absence of acidic hydrogen on N

• Tertiary Amine ($$3^\circ$$ Amine):

$$\text{R}_3\text{N} + \text{C}_6\text{H}_5\text{SO}_2\text{Cl} \to \text{No Reaction under alkaline conditions}$$
Notation: Insoluble in NaOH but dissolves in dilute HCl due to salt formation: $$R_3\text{NH}]^+\text{Cl}^-$$