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Not to be confused with Guanine, Guanosine, or Guanfacine.
Skeletal formula of guanidine
Skeletal formula of guanidine with the implicit carbon shown, and all explicit hydrogens added.
Ball and stick model of guanidine
Spacefill model of guanidine
IUPAC name
113-00-8 YesY
ChEBI CHEBI:42820 YesY
ChemSpider 3400 YesY
DrugBank DB00536 YesY
EC number 204-021-8
Jmol-3D images Image
MeSH Guanidine
PubChem 3520
Molar mass 59.07 g·mol−1
Melting point 50 °C (122 °F; 323 K)
log P −1.251
−57–−55 kJ mol−1
−1.0511–−1.0531 MJ mol−1
7–8 hours
475 mg/kg (oral, rat)[2]
Related compounds
Related compounds
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY verify (what isYesY/N?)
Infobox references

Guanidine is the compound with the formula HNC(NH2)2. It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine as a normal product of protein metabolism. Guanidine is the functional group on the side chain of arginine.


Guanidine can be thought of as a nitrogenous analogue of carbonic acid functional group. That is, the C=O group in carbonic acid is replaced by a C=NH group, and each OH is replaced by a NH2 group.[3] A detailed crystallographic analysis of guanidine was elucidated 148 years after its first synthesis, despite the simplicity of the molecule.[4] In the year 2013, the positions of the hydrogen atoms and their displacement parameters were accurately determined using single-crystal neutron diffraction.[5]


Guanidine can be obtained from natural sources, being formed by the oxidation of guanine.

The molecule was first synthesized in 1861 by the oxidative degradation of an aromatic natural product, guanine, isolated from Peruvian guano.[6] The commercial route involves a two step process starting with the reaction of dicyandiamide with ammonium salts. Via the intermediacy of biguanidine, this ammonolysis step affords salts of the guanidinium cation. In the second step, the salt is treated with base, such as sodium methoxide.[7]

Guanidinium cation[edit]

Guanidine is protonated in physiological conditions. This conjugate acid is called the guanidinium cation, [CH6N3]+. The guanidinium cation has a charge of +1. It is a highly stable cation in aqueous solution due to the efficient resonance stabilization of the charge and efficient solvation by water molecules. As a result, its pKa is 13.6[8] meaning that guanidine is a very strong base in water.

Notable guanidinium salts include guanidinium chloride (GndCl), which has chaotropic properties and is used to denature proteins. Guanidine hydrochloride is known to denature proteins with a linear relationship between concentration and free energy of unfolding. Another such salt is guanidinium thiocyanate; creatine is a derivative of the guanidinium cation.

Guanidine derivatives[edit]

The general structure of a guanidine

Guanidines are a group of organic compounds sharing a common functional group with the general structure (R1R2N)(R3R4N)C=N-R5. The central bond within this group is that of an imine, and the group is related structurally to amidines and ureas. Examples of guanidines are arginine, triazabicyclodecene, and saxitoxin. Another derivative is guanidinium hydroxide, the active ingredient in some non-lye hair relaxers. Guanidinium salts are well known for their denaturing action on proteins; guanidinium chloride is one of the most effective denaturants. In 6 M aqueous GndHCl, almost all proteins lose their ordered "secondary structure" (that results from intramolecular noncovalent interactions) and become "randomly coiled"; that is, their secondary structure interactions are disrupted by the dissolved guanidinium, leaving only the primary covalent structure of their polyamide backbones. Guanidine hydrochloride[9] is used as an adjuvant in treatment of botulism, introduced in 1968,[10] but now its role is considered controversial[11] - because in some patients there was no improvement after this drug administration.

See also[edit]


  1. ^ "Guanidine - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification. Retrieved 29 February 2012. 
  2. ^
  3. ^ M. Goebel, T.M. Klapoetke (2007). "First structural characterization of guanidine". Chem. Commun. 43 (30): 3180–2. doi:10.1039/B705100J. 
  4. ^ T. Yamada, X. Liu, U. Englert, H. Yamane, R. Dronskowski (2009). "Solid-state structure of free base guanidine achieved at last". Chem. Eur. J. 15 (23): 5651–5. doi:10.1002/chem.200900508. PMID 19388036. 
  5. ^ P. K. Sawinski, M. Meven, U. Englert, R. Dronskowski (2013). "Single-Crystal Neutron Diffraction Study on Guanidine, CN3H5". Cryst. Growth Des. 13: 1730–5. doi:10.1021/cg400054k. 
  6. ^ A. Strecker (1861). Liebigs Ann. Chem. 118: 151.  Missing or empty |title= (help)
  7. ^ Thomas Güthner, Bernd Mertschenk and Bernd Schulz "Guanidine and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a12_545.pub2
  8. ^ Perrin, D.D., Dissociation Constants of Organic Bases in Aqueous Solution, Butterworths, London, 1965; Supplement, 1972.
  9. ^ Kaplan, J. E.; Davis, L. E.; Narayan, V; Koster, J; Katzenstein, D (1979). "Botulism, type A, and treatment with guanidine". Annals of Neurology 6 (1): 69–71. doi:10.1002/ana.410060117. PMID 389150.  edit
  10. ^
  11. ^ Pediatric anaerobic infections: diagnosis and management, p.529