Guanidine

• Iminoharnstoff
• Aminomethanamidin
• Carbamidin

Colorless, hygroscopic crystals

Fixed

50 ° C.

Slightly soluble in ethanol, easily soluble in water protonation to guanidinium

500 mg · kg -1 ( LD50, rabbit, oral)

-56.0 KJ / mol

Template: Infobox chemical / molecular formula search available

Guanidine is a chemical compound on the border between inorganic and organic chemistry. Guanidine can be considered as a nitrogen analog of the carbon dioxide, similar to the corresponding carbamic acid, and urea intermediates.

Guanidine was already synthesized in the mid-19th century for the first time, but the crystal structure was solved in 2009. It has been suggested that so much time had to pass since guanidine is one of the strongest organic bases ( in obvious contrast to carbonic acid) and reacts spontaneously with air humidity and carbon dioxide to guanidinium carbonate.

Guanidine was investigated in various quantum- chemical calculations, especially in relation to the concept of Y- aromaticity. Furthermore guanidine provides an important substructure in many biological molecules such as guanine, arginine or guanosine dar.

History

Guanidine was first synthesized in 1861 by the oxidative degradation of guanine. Radiographic data structure of adducts of guanidine were obtained in 2007, but managed to complete elucidation of the guanidine -type crystal structure in spite of the simple molecular structure until 148 years after the first synthesis. Finally, the position of the hydrogen atoms by neutron diffraction on single crystal guanidine was 2013 determined very accurately.

Occurrence

Many natural products are guanidine derivatives, including such important as the proteinogenic amino acid arginine, creatine and creatinine. The guanidine and arginine argininosuccinate play an important role in the urea cycle and thus in the detoxification of ammonia formed by metabolic processes.

Chemical Properties

Guanidine in water is an extremely strong base with a pK value of 0.30 and is thus comparable basic as an alkali metal hydroxide. Before the discovery of proton sponges guanidine was regarded as the strongest organic base. Therefore forms immediately on contact with moisture, such as humidity, the guanidinium cation [C (NH2 ) 3] . The reactivity is sufficient to prevent carbon dioxide from the air in the guanidinium carbonate. The basicity in the gas phase, however, was significantly less than predicted.

This high reactivity of guanidine and the very high stability of the guanidinium cation was trying to explain with different concepts. A simple proposal was the greater resonance stabilization of the Guanidiniumions against the free base. This led to the concept of Y- aromaticity; Although the guanidinium is not cyclic, but has six π - electrons, which are delocalized over the molecule. This should lead to stabilization. Other studies, however, were the predominant stabilization in the numerous hydrogen bonds between guanidinium and water molecules.

Guanidine can be understood as structurally related to the carbonic acid, the hydroxyl groups are replaced by amino groups and the carbonyl group by an imino group. Accordingly, carbamic acid, and urea intermediates of these nitrogen - and oxygen analogs.

Carbamic

Urea

Guanidine

Production and representation

Adolph Strecker synthesized from guanidine guanidinium sulfate, which he won by oxidative degradation of guanine. To this end, he put the salt of the sulfuric acid with baryta water ( a solution of barium hydroxide ) and evaporated the solvent under vacuum. Due to the high hygroscopicity of the guanidine but he could not study the free base.

Another synthetic procedure used a metathesis reaction in order to obtain guanidine. For potassium hydroxide was reacted with Guanidiniumperchlorat stoichiometrically in ethanol. The resulting Guanidiniumhydroxid was dried over phosphorus pentoxide in vacuo to cleave water. An IR spectrum of the as-synthesized guanidine yielded first evidence of the molecular structure.

To crystallize guanidine, guanidinium chloride was dissolved in THF and treated with a solution of sodium methoxide also in THF under exclusion of air. To the solution was allowed to diffuse slowly acetonitrile. In this case, crystals of the adduct of guanidine and 3 -Amino-5 ,6-dimethyl- [1,2,4] triazine made ​​, the latter by reaction of acetonitrile with guanidine in the presence of alkoxide. So guanidine could be examined as a molecule for the first time by X-ray.

With a similar metathesis reaction, the pure free base guanidine could be synthesized. Guanidinium chloride to sodium ethoxide in ethanol was - reacted with sodium chloride precipitated (see reaction equation) - under an inert gas atmosphere. The solution was filtered, the solvent was allowed to evaporate slowly. On cooling, crystals fell out.

A sufficiently large for neutron diffraction crystal was grown by a guanidine solution in ethanol could crystallize about half a year.

Derivatives

• Guanidine formed with acids guanidinium salts such as guanidinium chloride, guanidinium thiocyanate, guanidinium nitrate and Guanindiniumcarbonat
• Guanidine derivatives are used for the preparation of flame retardants and resin. Cocospropylendiaminguanidiniumacetat for disinfectants.

• Guanidine, a number of explosives derives, such as: guanidine nitrate
• Nitroguanidine
• Aminonitroguanidine
• Amino-, diamino-, and triaminoguanidine salts thereof
• Dinitroguanidin and its salts
• Tetrazene

• As drugs, the biguanide metformin is in the treatment of type 2 diabetes using

• A number of derivatives of guanidine has an extremely sweet taste, up to 200,000 times the sweetening power of sucrose. They represent one of the sweetest compounds known to date.