Reaction of ninhydrin with Tris

[ptulkens]

Does anyone knows why ninhydrin does not react with Tris (even though it has a free aminogroup since it is 2-Amino-1,3-dihydroxy-2-(hydroxymethyl)propane ), but reacts with ethanolamine as well as with aminoacids ?

Regards,

Paul

[nakopf]

I'd investigate two possibilities.
1) steric hinderance - the 1,3 dihyroxy groups and the hyroxymethyl group could get in the way of the formation of a bond of a nucleophile with N.
2) electron withdrawing/donating effects of the neighboring functional groups depreciating the electrophilic properties of N.

[ptulkens]

Thank you.
This seems indeed the reasons. I'll look in these directions.
Kind regards.
paul M. Tulkens

[nakopf]

Nitrogen is a nucleophile