I have a molecule that is the solubility is very low in the solvent. From proton NMR, I cannot see the peak from NH2, so I am wondering if this amine is still safe in the molecule. Does anyone know if there are quick ways to prove the existence of NH2 in my molecule? The structure of my molecule is attached.
Hello Juan,
how about infrared spectroscopy? Primary amines have clear characteristic bands (double band at 3300 - 3400 cm-1). See attached link: http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/3/anc/ir_spek/n_s_verbindungen.vlu/Page/vsc/de/ch/3/anc/ir_spek/schwspek/spektreninterpretation/ir_13_4_8_1/amine.vscml.html
Regards Markus
Hi Juan,
If you want to skip the IR, take a 15N NMR. You can confirm the presence of primary aromatic nitrogen from the chemical shift.
Thanks
A chemical way of doing this might be to use reactive dyes e.g. vinyl sulphone or triazine types which will react with the amine at alkaline pH.
Then simple paper chromatography to look for additional dye spots.
Dear Juan Yang , Your amine is a very sterically hindered amine. You can try one of the following to confirm the presence of amine:
i) Method-I: Classical Dye test: take little of the finely powered sample (say ~50 mg) , suspend it in 4-5 ml of 1:1 aq. HCl shake vigorously for few minutes, cool in ice to 5-10 oC. Now to this solution or suspension add dropwisely a dilute solution of cold aq. NaNO2 solution with shaking until the diazotization is completed (may be verified by physical observation of evolution of brown fumes or chemically with starch-iodide paper. A drop of reaction mixture turns a filter paper soaked with starch + potassium iodide violet when the diazotization is completed). Now add this diazotized solution (filter if it is suspension and use the filtrate) dropwise with shaking to a well cooled (in ice) solution 2-naphthol in aqueous NaOH. If amine is present then immediately a red/dark red or orange dye will appear.
ii) In method II: Treat the amine(~50-100 mg) with acetic anhydride (~ 1-2 ml) in acetic acid (~3-5 ml) solution or suspension of the sample, Heat it at 100 oC for 15-30 minutes protecting from moisture. Pour the reaction mixture in excess ice water and scratch well with a glass rod. The solid anilide derivative separated as ppt should be filtered and recrystallised from suitable solvent. Now in 1H-NMR the NH protons will go to a much down field (~7-9 delta ppm) and the previous signals of NH2 which appeared at relatively much high field will vanish.
iii) Method -Iii: I am doubtful whether it will work in this system or not as the sample is of high molecular weight and also the amine is sterically very crowded by two methyl group at 2,6 position (hence unreactive). In addition the imide functionality itself can get hydrolyzed to produce amine under the reaction condition. But even the you can take an attempt.
Take little (~50-100 mg) sample + EtOH (2-4 ml)+ CHCl3 10-15 drops + aqueous alcoholic NaOH or KOH (very conc solution) + heat. An obnoxious smell of carbylamine derivative (toxic !!) confirms presence of primary amine (to verify the smell of carbylamine, the test can be done as a practice with 1-2 drops of aniline)
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