# Reaction of urea and thiourea with nitrous acid

I was told that urea on reaction with nitrous acid gives nitrogen gas, carbon dioxide and water. While on the other hand, thiourea on reaction with nitrous acid gives $$\ce{H+}$$, thiocyanate ion and water.

I tried looking for the mechanism and thought that this would be related:

I carried out the above procedure on both the nitrogens of urea and was able to obtain the products of the first reaction enlisted above. Now, my questions are:

• Isn't the nucleophilicity of the lone pairs of urea's nitrogens negligible, and any reaction should proceed via attack by oxygen's lone pairs? (I thought that this was similar to amidines and amides)

• Why are the products of the reactions with urea and thiourea different, as the carbonyl oxygen, or sulphur doesn't seem involved in the reaction according to me

• More importantly, is this even the correct mechanism?

• It is similar as in amidines and amides and it doesn't matter. Any attacks on O are unproductive, so effect of conjugation is rather kinetical. – Mithoron Jan 12 at 19:17