[nlieb]

So I'm doing this total synth and one step involves a nucleophilic substitution of a chlorine for an amine group with ammonia as the nucleophile. I want to be able to test to make sure this step of the reaction is successfull. Are there any tests for amine groups which will not turn up a false positive in the presence of ammonia?

[nlieb]

So I'm doing this total synth and one step involves a nucleophilic substitution of a chlorine for an amine group with ammonia as the nucleophile. I want to be able to test to make sure this step of the reaction is successfull. Are there any tests for amine groups which will not turn up a false positive in the presence of ammonia?

Also, since it makes a difference, the amine group would be in a primary position. I know how to distinguish ammonia from secondary amines.

[fledarmus]

Are you using a particularly volatile substrate? Usually you just evaporate the ammonia away.

[nlieb]

No, but that doesn't help me, because the excess ammonia will evaporate off whether or not a reaction has taken place. I want to make sure that a reaction has taken place before moving on to the next step in my synth, to avoid wasting materials.

[Dan]

Can't you just monitor the reaction by the usual chromatographic methods? For example, you should get a sizeable shift in R_f on silica TLC sheets if you have replaced Cl with NH₂.

[discodermolide]

So I'm doing this total synth and one step involves a nucleophilic substitution of a chlorine for an amine group with ammonia as the nucleophile. I want to be able to test to make sure this step of the reaction is successfull. Are there any tests for amine groups which will not turn up a false positive in the presence of ammonia?

Use TLC. Blow the plate dry before running it in the solvent, blow it dry again and spray with ninhydrin and heat.

[nlieb]

So I'm doing this total synth and one step involves a nucleophilic substitution of a chlorine for an amine group with ammonia as the nucleophile. I want to be able to test to make sure this step of the reaction is successfull. Are there any tests for amine groups which will not turn up a false positive in the presence of ammonia?

Use TLC. Blow the plate dry before running it in the solvent, blow it dry again and spray with ninhydrin and heat.

\


Ninhydrin doesn't distinguish primary amines and ammonia, only secondary amines from primary amines/ammonia.

[nlieb]

Never mind, I see what you mean.

[fledarmus]

No, but that doesn't help me, because the excess ammonia will evaporate off whether or not a reaction has taken place. I want to make sure that a reaction has taken place before moving on to the next step in my synth, to avoid wasting materials.

Exactly - so if you get an amine response after evaporating the ammonia, you will know that it is a primary amine and not ammonia.

Oh - looks like you figured it out! sorry...

[mpv]

I don't understand exactly what you want. But if you want to find out if the reaction had taken place you can try adding some HNO2 and see if there is a release of N2 ( only if you have a primary amine). You can also try the Hinsberg. Just add ArSO2Cl and if its a primary amine it should be soluble in base, if it's a secondary it shouldn't dissolve in base, and if its tertiary the reaction won't take place. Zerevitinov should work only if you don't have any other group that will react with a Grignard(add MeMgCl and CH4 should be released. This way you can recover the wasted material just by adding water). Hope it helps.

[408]

14N NMR.  Somewhere -350 or so is NH4+  , ammonia is -300 I think, and amines are between -100 and -300.

Do do 14N of compound and precursor.

If you see a peak in the desired range, dope the tube with a mix of NH4X and NH3(aq)   to make sure the observed peak is not ammonia or ammonium.

Or mass spec.