Guanidine is the compound with the formula HNC(NH₂)₂. It is a colourless solid that dissolves in

polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...

solvents. It is a

strong base In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rou ...

that is used in the production of

plastics Plastics are a wide range of synthetic polymers, synthetic or semi-synthetic materials that use polymers as a main ingredient. Their Plasticity (physics), plasticity makes it possible for plastics to be Injection moulding, moulded, Extrusion, e ...

and

explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...

. It is found in urine predominantly in patients experiencing renal failure. A guanidine moiety also appears in larger organic molecules, including on the side chain of

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the am ...

Structure

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

Production

Guanidine can be obtained from natural sources, being first isolated by Adolph Strecker via the degradation of guanine. It was first synthesized in 1861 by the oxidative degradation of an aromatic natural product, guanine, isolated from Peruvian

guano Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...

. A laboratory method of producing guanidine is gentle (180-190 °C) thermal decomposition of dry ammonium thiocyanate in anhydrous conditions: :3 NH4SCN -> 2 CH5N3 + H2S + CS2 The commercial route involves a two step process starting with the reaction of dicyandiamide with

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

salts. Via the intermediacy of biguanidine, this ammonolysis step affords salts of the guanidinium cation (see below). In the second step, the salt is treated with base, such as sodium methoxide.

Chemistry

Guanidinium cation

With a p''K''_b of 0.4, guanidine is a strong base. Most guanidine derivatives are in fact salts containing the conjugate acid. The conjugate acid is called the guanidinium

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

, (). This planar, symmetric ion consists of three amino groups each bonded to the central carbon atom with a covalent bond of

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

4/3. It is a highly stable +1 cation in aqueous solution due to the efficient resonance stabilization of the charge and efficient solvation by water molecules. As a result, its p''K''_aH is 13.6 meaning that guanidine is a very strong base in water; in neutral water, it exists almost exclusively as guanidinium. Image:Guanidinium-ion-3D-balls.png, Image:Guanidinium-ion-2D-skeletal.png, Image:Guanidinium-ion-canonical-forms-2D-skeletal.png,

Testing for guanidine

Guanidine can be selectively detected using sodium 1,2-naphthoquinone-4-sulfonic acid (

Folin's reagent Folin's reagent or sodium 1,2-naphthoquinone-4-sulfonate is a chemical reagent used as a derivatizing agent to measure levels of amines and amino acids. The reagent reacts with them in alkaline solution to produce a fluorescent material that can ...

) and acidified urea.

Uses

Industry

The main salt of commercial interest is the nitrate ()₃ It is used as a propellant, for example in

air bag An airbag is a vehicle occupant-restraint system using a bag designed to inflate extremely quickly, then quickly deflate during a Traffic collision, collision. It consists of the airbag cushion, a flexible fabric bag, an inflation module, and a ...

Medicine

Since the Middle Ages in Europe, guanidine has been used to treat diabetes as the active antihyperglycemic ingredient in

French lilac French lilac is a common name for several plants and may refer to: *''Syringa vulgaris'' of the family Oleaceae *''Galega officinalis ''Galega officinalis'', commonly known as galega or goat's-rue, is an herbaceous plant in the subfamily Faboid ...

. Due to its long-term hepatotoxicity, further research for blood sugar control was suspended at first after the discovery of insulin. Later development of nontoxic, safe biguanides led to the long-used first-line diabetes control medicine metformin, introduced to Europe in the 1950s & United States in 1995 and now prescribed to over 17 million patients per year in the US. Guanidinium chloride is a now-controversial adjuant in treatment of botulism. Recent studies have shown some significant subsets of patients who see no improvement after the administration of this drug.

Biochemistry

Guanidine exists protonated, as guanidinium, in solution at physiological pH. Guanidinium chloride (also known as guanidine hydrochloride) has chaotropic properties and is used to denature proteins. Guanidinium chloride is known to denature proteins with a linear relationship between concentration and free energy of unfolding. In aqueous solutions containing 6 M guanidinium chloride, almost all

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

lose their entire

secondary structure Protein secondary structure is the three dimensional conformational isomerism, form of ''local segments'' of proteins. The two most common Protein structure#Secondary structure, secondary structural elements are alpha helix, alpha helices and beta ...

and become randomly coiled peptide chains. Guanidinium thiocyanate is also used for its denaturing effect on various biological samples. Recent studies suggest that guanidinium is produced by bacteria as a toxic byproduct. To alleviate the toxicity of guanidinium, bacteria have developed a class of transporters known as guanidinium exporters or Gdx proteins to expel the extra amounts of this ion to the outside of the cell. Gdx proteins, are highly selective for guanidinium and mono-substituted guanidinyl compounds and share an overlapping set of non-canonical substrates with drug exporter EmrE.

Other

Guanidinium hydroxide is the active ingredient in some non-lye hair relaxers.

Guanidine derivatives

Guanidines are a group of organic compounds sharing a common functional group with the general structure . 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

, triazabicyclodecene, saxitoxin, and creatine.

Galegine Galegine is a toxic chemical compound that has been isolated from Goat's rue (''Galega officinalis''). It has also been found to be the principal cause of the toxicity of poison sedge (''Schoenus asperocarpus''). Galegine was used in the 1920s ...

is an

isoamylene 2-Methyl-2-butene, 2m2b, 2-methylbut-2-ene, also beta-isoamylene is an alkene hydrocarbon with the molecular formula C5H10. Used as a free radical scavenger in Chloroform, trichloromethane (chloroform) and dichloromethane (methylene chloride). J ...

guanidine.

References

{{Authority control Guanidines Bases (chemistry)