A primary amine, `RNH_(2)` can be reacted with `CH_(3)-X` to get secondary amine, `R-NHCH(3)`, but the only disadvantage is that `3^(@)` amine and quaternary ammonium salts are also obtained as side products. Can your suggest a method where `RNH_(2)` forms only `2^(@)` amine?

Explanation

`underset("Primary amine")(RNH_(2)) underset("Carbylamine reaction Alkyl to iso cyanide")overset(KOH//CHCl_(3))to underset("Alkyl iso cyanide")(RNC) overset(H_(2)//Pd)to underset("Secondary amine")(RNHCH_(3))`
Primary amines show carbylamine reaction in which two H-atoms attached to N-atoms of `NH_(2)` are replaced by one C-atom. On catalystic reduction, isocyanide (formed) produces secondary amine and not tetiary or quaternary salts.