Registration Dossier

Data platform availability banner - registered substances factsheets

Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Dissociation constant

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Guanidine carbonate gets dissolved in the Guanidinium kation and the Carbonate. While the equilibrium of the Carbonate species will in the environmental range strongly depend on the actual pH, the Guanidine equilibrium will be about 100 % on the side of the Guanidinium kation according to the guanidine pKa value given below.

Key value for chemical safety assessment

pKa at 20°C:

Additional information

The dissociation constant of the submission item Guanidine carbonate was determined according to the OECD TG 112 protocol by titration (Reuse 2009). 2.5 g of Guanidine carbonate were dissolved in 200 g of distillate water. Hydrochloric acid (CAS 7647-01-0) 1M was added continuously under stirring and the pH-value was measured. It was possible to distinguish two contributions of Guanidine carbonate to the pH-curve. The inflexion point is reached for pH-values of 6.1 and 2.5. The report concludes therefore on dissociation constants pKb1 = 7.9 and pKb2 = 11.5. The author did not draw any conclusion on the assignment of these values to dissociated species. The applied titration method suffers from possible Carbon dioxide (CAS 124-38-9) formation and release. The addition of Hydrochloric acid effects simultaneous protonation of Guanidine (CAS 113-00-8), Carbonate (CAS 3812-32-6) and Hydrogen carbonate (CAS 71-52-3). In consequence the measured values are of little relevance for the chemical safety assessment.

According to Holleman & Wiberg (2007) the pKa values for the carbonic acid are 6.35 for the formation of Hydrogen carbonate from Carbon dioxide (plus two water molecules) and 10.33 for the formation of Carbonate from Hydrogen carbonate (plus one water molecule). It seems that the results of Reuse (2009) are significantly influenced by carbonate, which is deemed not relevant for the chemical safety assessment of Guanidine carbonate.

As the relevant part of the solute Guanidine carbonate is considered to be Guanidine, its pKa of ca. 12.5 (Budaravi 1996) should be reported here. This value indicates that under environmental conditions and in body fluids Guanidine is present solely in the form of the Guanidinium kation. The dissociation behaviour of this species expressed by the pKa ca. 12.5 is thus the key value for assessment.

In summary the submission item Guanidine carbonate gets dissolved in the Guanidinium kation and the Carbonate. Both moieties equilibrate then according to the given pKa values. While the equilibrium of the carbonate species will in the environmental pH range (5-9 according to page 69 of ECHA 2012 or 4-9 according to page 1 of OECD TG 111) strongly depend on the actual pH, the guanidine equilibrium will be on the side of the Guanidinium kation, which represents 100 % at pH 4, 99.97 % at pH 9 and 99.75 % at pH 10.

  • Budaravi S ed (1996). The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals, 12th edition. ISBN 0911910-12-3 New York, NJ, U.S.A., Merck
  • ECHA European Chemicals Agency (2012).Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance, FIRST DRAFT FOR PEG, 2nd March 2012, Guidance for the implementation of REACH. Self-published. 167 p
  • Holleman AF, Wiberg N (2007). Lehrbuch der Anorganischen Chemie. 102. Auflage, de Gruyter, Berlin, Germany. ISBN 978-3-11-017770-1
  • OECD Organisation for Economic Co-operation and Development (2004). Hydrolysis as function of pH. Self-published (OECD Publishing). ISSN 2074-5753 (online) ISBN 9789264069701 (PDF) doi: 10.1787/9789264069701-en OECD Guideline for the Testing of Chemicals, Section 1, Test No. 111, adopted 13th April 2004.15 p