# What is the action of hydrogen gas on cyanogen?

## Complete the following reactions: (CN)_2 + H_2 -> ? (CN)_2 + 4H_2 -> ?

May 20, 2016

Given that a nitrile ($\text{C"-="N}$) like cyanogen is similar to a comparable imine (which has $\text{C"="N}$ bonds instead), ${\text{H}}_{2}$ should behave similarly to how it behaves with imines.

It reduces imines into amines, so it should reduce nitriles ($\text{C"-="N}$) into imines ($\text{C"="NH}$), and then amines (${\text{C"-"NH}}_{2}$), as it indeed shows here.

This parallels the reduction of alkynes ($\text{C"-="C}$) into alkenes ($\text{C"="C}$), and then alkanes ($\text{C"-"C}$).

These types of hydrogenation reactions require a catalyst to cleave the ${\text{H}}_{2}$ bond such that it can add cis to the substrate compound (in this case, the nitrile). Here is an example:

It likely depends on the catalyst whether or not a single $\pi$ bond will be removed, or all of them.

I will assume a palladium catalyst over carbon (as you would traditionally use on alkenes and alkynes for full reduction), and that the catalyst promotes reduction of one $\pi$ bond at a time without reducing all the way in one go.

$\text{N"-="C"-"C"-="N" stackrel("H"_2" "" ")(->) "N"-="C"-"CH"="NH}$
color(white)(ssaaaaaaaaaaaa)""^("Pd/C")

${\text{N"-="C"-"C"-="N" stackrel(4"H"_2" "" ")(->) "H"_2"N"-("CH"_2)_2-"NH}}_{2}$
color(white)(ssaaaaaaaaaaaa)""^("Pd/C")

Either way, it accomplishes the same result at each step, just multiple times where applicable.

For the reduction of nitriles, elevated temperatures and pressures promote the reduction.