We acquired an 1H spectra of sulfamic acid in DMSO-d6, and it presented one large peak at ~10ppm and a small triplet at ~7ppm (J=52Hz). The triplet at 7 is correlated with nitrogen via HSQC. After 3 days the triplet at 7 increased. Adition of H2O lead to the main peak to shift to ~5ppm.
Looks to me like the sulfamic acid gives the broad peak at 10ppm. The peak at 7ppm is VERY small (try an integration) and is likely impurity and based on an observed coupling to 14N is probably an ammonium salt.
Adding water will cause exchange between H2O protons and those in sulfamic acid giving a single peak.
Looks to me like the sulfamic acid gives the broad peak at 10ppm. The peak at 7ppm is VERY small (try an integration) and is likely impurity and based on an observed coupling to 14N is probably an ammonium salt.
Adding water will cause exchange between H2O protons and those in sulfamic acid giving a single peak.
I think broad peak appear at 10 ppm is due to -OH of sulphamic acid part, further it's broad because of the intermolecular OH exchange, further frequency of the NMR instruments also play significant role on broadness of peak.
Agree with Dr. Stephenson; the triplet at about 7 ppm belongs to protonated ammonia (NH4+), sometimes I see it in my samples as well. It could be the remaining ammonia used in preparation of sulfamic acid, or the product of degradation of the latter.
Thanks, friends. But, why the peak of NH2 (or NH3, considering the resonance structure) of the sulfamic acid did not appeared? If I see the triplet of a such minor impurity, shouldn't I see the H signal and correlation with N of the NH2 from sulfamic acid? And, in case of the triplete being due to an ammonium salt, is a J of 50 Hz expected?
Yes, in literature 14N - 1H coupling constant is given as 52.4 Hz, and it is a triplet with equal intensity of all three peaks since 14N nucleus has spin = 1.
As for the absence of separate NH2 signal in sulfamic acid, it is due to the fast (in NMR time scale) chemical exchange with OH. Therefore, NH2/OH groups give one averaged signal.
Good, Vladimir. I didn't think of a coupling with 14N. Thanks! Couldn't the triplet be due to the small amount of NH2 from sulfamic acid which did not suffer exchange?
The peak at 7ppm only looks significant because the sulfamic acid signal is very broad. It is not usual to see coupling to quadrupolar (spin >1/2) nuclei. The region surrounding the nucleus needs to be very symmetric so you really only have a chance of seeing coupling in ammonium salts. Often if you look closely you can also see coupling to 15N (a doublet) with some isotope shift.
So as was said above the protons in sulfamic acid are exchanging quickly on the NMR timescale so you see one broad peak. Maybe if you cooled the sample you may be able to slow the exchange.
I agree with David Stephenson and Vladimir Khlebnikov : the peak around 7 ppm with 52 Hz splitting is due to ammonium (NH4+); I have often observed it myself. You state that it gives a correlation signal with 15N, so you can use the nitrogen shift to confirm this assignment.
Thanks, Wolfgang Baumann .
I had difficulties to obtain data for 15N resonance.
Dear Gerlon de Almeida Ribeiro Oliveira , I have attached a spectrum of mine where you can see the ammonium triplet (it was taken in a solvent mixture so do not worry about the slightly different chemical shift; the big broad peak is presumably due to ammonia). The nitrogen chemical shifts for NH3 and NH4+ are -358.6 and -361.6 ppm (nitromethane as reference) or 21.7 and18.7 ppm (aq. ammonia as reference). The inset from a textbook shows the relation between the various references...
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