[janru]

searching 4 a proper system 2 detect sec. amines (and some amides) with tlc

NH2 is located at an aromatic ring/system (in all samples I use)

does anyone know an adequate setup/system?????

[Alexey]

actually, if you have Ar it should be UV active.

Have you tried Ninhydrin?

Detection of Primary Amines (sec as well but not always good)
Ninhydrin
For detection of amino acids, amines, amino sugars.
Spray with a solution of 0.2g ninhydrin in 100ml ethanol and heat to 110 C (drying oven) until spots appear.
Results: reddish spots appear

be careful, it's carcinogenic if touches skin.

another possibility
Hydroxylamine / iron (III) chloride
For detection of amides, lactones, carboxylic acid esters and anhydrides
Solution 1) Mix 1 vol part of 7g hydroxylammonium chloride in 100ml methanol w 1 vol part of a solution of 7.2 g
potassium hydroxide in 100ml methanol. Filter from precipitated potassium chloride.
Solution 2) 2% solution of iron (III) chloride in 1% aqueous hydrochloride acid
Spray air dried plate first with solution 1, then with solution 2

took from (http://www.emdchemicals.com/analytics/literature/TLC_Visualization_Reagents.pdf)

another possibility:
"you'll get far better sensitivity for secondary amines with this ninhydrin recipie:

-0.75g ninhydrin
-250 mL 95% EtOH
-2.5 mL glacial AcOH

Mix it up, it stores well on the bench sealed. dip your plate in, gently heat. voila! secondary amines appear as orange spots. i used this routinely to analyse reductive amination reactions, and it worked for me." (took from http://orgprepdaily.wordpress.com/2006/09/27/tlc-staining-solutions/feed/)
additionally I would try a chamber with I2.
or Cerium system


"2.5 g phosphomolybdic acid
1 g Ce(SO4)2
6 mL conc H2SO4
94 ml H2O
The addition of Ce salts to standard phosphomolybdic acid gives a really nice royal blue color, and it is "magic" because nearly everything stains." Dip it and then heat with a heat gun.

I remember using extremely unhealthy but powerfull detection system 2 decades ago: tert-Bu-hypochlorite in CCl4 first spray, dry with cold hair-dryer until no more stink of hypochlorite is palpable by sniffing the TLC, then spray with a solution of m,m'-dimethoxybenzidine (anisidine??). Amides and amines which have a free NH give intense black spots on white background (or black background if one forgets to dry the hypochlorite first spray). Very general.(took from http://orgprepdaily.wordpress.com/2006/09/27/tlc-staining-solutions/feed/)

[Guest]

Ninhydrin Stain Recipe from Curly Arrow:

"100 ml container
0.2 g Ninhydrin
0.5 ml Acetic acid
100 ml n-Butanol
4.5 ml Water"

It works even for Boc-protected amines (heat and AcOH cleave BOC on TLC).

"After treatment with a heat gun Ninhydrin Stain tends to give brightly coloured pink to purple spots as shown above. The spots can fade rather fast so record the result immediately. In the past I have been using a Ninhydrin Stain that didn't contain water, however adding a bit of water seems to improve the result a fair bit."

Comments by milkshake:

"You can spray your TLC with a solution of a copper or cadmium salt after developing it with ninhydrin - the colors will get a bit stronger and more stable. Cadmium is unhealthy though."

"For a very sensitive detection of all NH bonds (promary secondary amines,amides and carbamates, the TLC can be sprayed with a diluted solution of tBuOCl in CCl4, dried with a hair drier without heating, until you can no longer sniff the tBu hypochlorite, and the produced N-chlorinated spots are then developed by a tolidine spray at room temp, as black spots on white. Tolidine is a methylated analog of benzidine, hence it is very unhealthy also. But the detection works like a charm."

Quoted from http://curlyarrow.blogspot.com/2008/08/lets-talk-about-tlcs-part-4-ninhydrin.html
See also for other comments in this reference.