# Reaction of amines with diethyl oxalate (Hofmann amine separation method)

Why does only one molecule of secondary amine react with diethyl oxalate and two molecules of primary amine react with diethyl oxalate?

I feel secondary amine also should have reacted similar to primary amine.

From JEE-Main 2015:

### Reaction with diethyl oxalate

1°, 2°, and 3° amines can be distinguished by their reactions with diethyl oxalate. Primary (1°) amines react with diethyl oxalate forming N,N-oxamide, which is a solid.

Secondary (2°) amines react with diethyl oxalate forming oxamic ester, which is a liquid.

Tertiary (3°) amines do not react with diethyl oxalate.

• Probably a steric issue. Seems reasonable.
– Zhe
Jan 10, 2018 at 3:47
• You may want to look at the Hinsberg test for distinguishing between amines. Jul 21, 2018 at 21:51
• @Zhe: From this site, I looked at structutr of oxamic ester, which was different from the one given in this post. As, the -OR and -NR2 groups are on opposite sides, hence I think steric reason aren't reasonable. Jul 21, 2020 at 3:59
• The second reaction has a typo: it should be $\ce{CONR2}$. Jul 22, 2020 at 16:26
• Tetra-substituted oxamide or N,N,N',N'-tetraalkyloxamide can be prepared by the action of oxalyl chloride on secondary amines.(see here) Jul 23, 2020 at 5:39