8.2 Carboxylic acids and their derivative — Chemistry STD 12 Science — Question

$\begin{array}{*{20}{c}}
  \,\,\,{{C_2}{H_5}} \\ 
  {|\,\,\,\,\,\,\,} \\ 
  {C{H_3} - C - COOH} \\ 
  {|\,\,\,\,\,\,} \\ 
  \,\,\,{{C_3}{H_7}} 
\end{array}\xrightarrow{{{N_3}H/Conc.\,{H_2}S{O_4}}}\begin{array}{*{20}{c}}
 \,\,\,\,\,\,\,\,\,{{C_2}{H_5}} \\ 
  | \\ 
  {C{H_3} - C - N{H_2}} \\ 
  | \\ 
  \,\,\,\,\,\,\,\,\,{{C_3}{H_7}} 
\end{array}$

is called :