Question

Primary nitro compounds when react with \[HN{{O}_{2}}\] from crystalline solids which on reaction with \[NaOH~\] gives
(A) Red solution
(B) Blue solution
(C) White precipitate
(D) Yellow coloration

Answer 1

Hint: Primary nitro compound is one in which the\[N{{O}_{2}}\] group is attached to one carbon which is further bonded with one alkyl chain or an alkyl group such as\[RC{{H}_{2}}N{{O}_{2}}\]. The reaction of this primary nitro compound with nitrous (\[HN{{O}_{2}}\]) results in releases of water molecules to give nitrolic acid. Again nitrolic acid reacts with \[NaOH~\](caustic soda) to release water molecules to give a soluble sodium salt.

Complete Step by Step Solution:
Now let us take a primary nitro alkyl compound, nitro ethane (such as\[C{{H}_{3}}C{{H}_{2}}N{{O}_{2}}\]which on reacting with nitrous reagent (\[HN{{O}_{2}}\]) gives nitrolic acid (double bond between carbon and nitrogen). In this, two hydrogen of first carbon from the nitro group makes the bond with one oxygen of nitrous to release water molecule such as

Now this nitrolic acid reacts with \[NaOH~\](caustic soda) to give soluble sodium salt because after reacting nitrolic acid with \[NaOH~\], the water molecule (H₂O) gets liberated (OH group of \[NaOH~\]and hydrogen atom of NOH attached double boundedly with first carbon of nitrolic acid) and on the place of hydrogen atom (\[OH\]) sodium atom will attach and form sodium salt (\[{{O}^{-}}N{{a}^{+}}\]) such as

The soluble sodium salt formed is red in colour. Thus, the correct option is A.

Note: Primary nitro is one in which the \[N{{O}_{2}}\]group is attached to that carbon which is further attached to only one carbon (alkyl group) or with only one carbon chain (alkyl chain). If \[N{{O}_{2}}\]is attached to a carbon which further bonded with two carbon or with two carbon chains is known as a secondary or \[2{}^\circ \]nitro compound and if carbon is attached to three carbon further, then it is known as \[3{}^\circ \]nitro compound or tertiary nitro compound.