What is the action of hydrogen gas on cyanogen?

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

1 Answer
May 20, 2016

Given that a nitrile ("C"-="N") like cyanogen is similar to a comparable imine (which has "C"="N" bonds instead), "H"_2 should behave similarly to how it behaves with imines.

It reduces imines into amines, so it should reduce nitriles ("C"-="N") into imines ("C"="NH"), and then amines ("C"-"NH"_2), as it indeed shows here.

This parallels the reduction of alkynes ("C"-="C") into alkenes ("C"="C"), and then alkanes ("C"-"C").


These types of hydrogenation reactions require a catalyst to cleave the "H"_2 bond such that it can add cis to the substrate compound (in this case, the nitrile). Here is an example:

http://www.masterorganicchemistry.com/http://www.masterorganicchemistry.com/

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.

"N"-="C"-"C"-="N" stackrel("H"_2" "" ")(->) "N"-="C"-"CH"="NH"
color(white)(ssaaaaaaaaaaaa)""^("Pd/C")

"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.