Guanidine

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Guanidine
Guanidine base structure.png
Names
IUPAC names
Guanidine
Iminomethanediamine
Other names
Aminomethanamidine
Carbamamidine
Carbamidine
Gdn
Guanidin
Imidourea
Properties
CH5N3
HNC(NH2)2
Molar mass 59.07 g/mol
Appearance Hygroscopic colorless solid
Odor Odorless
Density 1.6 g/cm3
Melting point 50 °C (122 °F; 323 K)
Boiling point Decomposes
0.184 g/100 ml (20 °C)
Solubility Soluble in polar solvents
Vapor pressure 2.2 mmHg at 25 °C
Acidity (pKa) 12.5
Thermochemistry
−57 – −55 kJ/mol
Hazards
Safety data sheet Fluorochem
Lethal dose or concentration (LD, LC):
475 mg/kg (rat, oral)[1]
Related compounds
Related compounds
Ammonia
Hydrazine
Urea
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Guanidine is an organic compound, a base with the formula HNC(NH2)2. Guanidine is sometimes shortened to Gdn.

Properties

Chemical

Guanidine is a strong monobasic Brønsted base, which readily absorbs water and carbon dioxide from air. It can form strongly alkaline solutions with water and alcohols. Aqueous solutions with a concentration of 20% have a pH of 13.5 at 25 °C.

If an aqueous solution of guanidine is heated, guanidine will hydrolyze to urea.[2].

As a base, guanidine will react with acids to form salts. By protanating guanidine, the guanidinium ion is formed.

HNC(NH2)2 + HCl → C(NH2)3+Cl-

Solutions of guanidine in water or other solvents are stable if kept airtight.

Physical

Guanidine is a solid white hygroscopic compound, slightly soluble in water, but more soluble in organic solvents.

Availability

Unlike its salts, free base guanidine is difficult to find. Fluorochem and Oakwood Chemical are one of the few suppliers that sell the free base compound.

Guanidinium salts, of the other hand, can be purchased from many chemical suppliers. To obtain the free base, simply react the salt with a stronger base then extract the resulting guanidine.

Preparation

Free base guanidine can be prepared from guanidinium salts by adding sodium hydroxide to said guanidinium salt, then recrystallizing it from the solvent.

To obtain water-free freebase guanidine, a simple method is to add a guanidinium salt, like guanidinium chloride or sulfate to a methanolic solution of sodium methoxide (which can be easily made by adding sodium metal to dried methanol). The sodium salt will precipitate out of the solution, while the freebase guanidine will remain in solution.

C(NH2)3Cl + CH3ONa → HNC(NH2)2 + CH3OH + NaCl

Heat the MeOH solution to drive off excess solvent, then cool it to obtain the crystallized pure compound.

For the preparation of guanidinium salts, check the page for each compound.

Guanidine can also be obtained from oxidative degradation of guanine, isolated from Peruvian guano (hence its name). Guano fertilizer can be bought from many hardware and gardening stores.

Arginine has a guanidine group, which can be removed via dissociation.

Projects

Handling

Safety

Guanidine and its salts aren't volatile or very toxic and don't require special handling. Freebase guanidine may be irritant, so make sure to wear gloves when handling it. Unfortunately, there isn't much information in literature about its toxicity or prolonged exposure.

Storage

Guanidine free base should be kept in closed bottles, in a dry place.

Disposal

No special disposal is required. Some guanidinium salts are even used as fertilizer.

References

  1. https://www.drugbank.ca/drugs/DB00536
  2. https://onlinelibrary.wiley.com/doi/abs/10.1002/14356007.a12_545.pub2

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