Question

Amongst the following Kjeldahl’s method can’t be used for.
(I) $PhNO _{2}$
(II) $Ph - N = N - Ph$
(III) $PhNHCOPh$


(VII) $PhNH _{2}$
(VIII) Acetone
(IX) Ethane nitrile
(X) Urea

Answer 1

This method is not applicable to compounds containing $N$ in nitro and azo groups, and $N$ present in the ring (e.g., pyridine) as $N$ of these compounds does not change to $\left( NH _{4}\right)_{2} SO _{4}$ (ammonium sulphate) under these reaction conditions.
This method is not applicable to compounds containing $N$ atom in nitro $\left(- NO _{2}\right)$, azo compounds $(- N = N -)$, and $N$ atom present in ring.
I, II, IV, V, VI, VIII (It is a keto compound which does not have $N$ atom). Compounds are not used for the quantitative estimation of $N$ in Kjeldahl's method.