(1) (2) $CH_3CH_2NH_2$
(3) $(CH_3)_2NH$ (4) $\begin{array}{*{20}{c}}
O \\
{|\,|} \\
{C{H_3} - C - N{H_2}}
\end{array}$
image$\xrightarrow{{A{c_2}O}}A\mathop {\xrightarrow{{B{r_2}}}}\limits_{C{H_3}COOH} B\mathop {\xrightarrow{{{H_2}O}}}\limits_{{H^ + }} C$