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Environmental fate & pathways

Hydrolysis

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Description of key information

In contact with water ammonium carbamate will hydrolyse rapidly at environmental relevant pH-conditions and concentrations.

Key value for chemical safety assessment

Additional information

When ammonium carbamate is dissolved in water a complex chemical equilibrium is established among the species of carbonate, bicarbonate and carbamate:

H2NCOO-(aq) + H2O(l) ↔ CO32-(aq) + NH4+(aq) ↔ HCO3-(aq) + NH3(aq)

(Ref. Nanping Wen and Murray H. Brooker Ammonium carbonate, ammonium bicarbonate, and ammonium carbamate equilibria: A raman study,J. Phys. Chem.1995, 99,359-368)

In general, carbamates are susceptile to hydrolysis.

The carbamate ion is unstable in acidic medium and decomposes rapidly into ammonium ion and carbon dioxide. Even at weak acidic conditions (buffering system sodium acetate/acetic acid) a complete decomposition occurs in less than a second ( Ref.. C, Faurholt,Dan. Vidensk. Selsk., Mat.-Fys.Medd. 3 (1921) 20 and R. Blakeley et al.,Biochemistry, Vol. 8, No. 5, 1969, 1991-2000).

The rapid hydrolysis of ammonium carbonate under environmental relevant conditionds (pH up to 9.0 - 9.5 and low cincentrations) into carbonate and bicarbonate is also confirmed by the analysis of13C{1H}-NMR spectra obtained dissolving ammonium carbamate in D2O, in which signals referred to the ions carbamate and bicarbonate/carbonate have been observed (BASF SE, analytics report, order number 14Y00397, 2014). The data show that a 1:1 equilibrium between ammonium carbamate and bicarbonate/carbonate establishes after approximately 2 hours without further concentration shifts after that point. In a follow-up experiment,13C{1H}-NMRof a 10% solution of ammonium carbamate in D2O (pH 9-9.5) were recorded (BASF SE, analytics report, order number 14E00249). Two signals at 166.6 ppm (ammonium carbamate) and 163 ppm (ammonium hydrogencarbonate), respectively, were detected after 32 scans (2:16 minutes), the ratio being 1:0.4. After >12 hours, a ratio of 1:1.5 had established. The experiment was repeated with a 1% solution of ammonium carbamate in D2O (pH 9-9.5), which was also the lowest concentration at which NMR signals could be obtained that were distinctive enough for interpretation. Here, the ammonium hydrogencarbonate signal was the only detected signal after 10 minutes, indicating complete decomposition of the carbamate anion. The results above indicate that the hydrolysis rate of ammonium carbamate increases with decreasing concentrations.