The benzoin or benzoe It is a white crystalline solid with a camphor odor that consists of an organic compound. It is an acetone, specifically, an acetophenone with adjacent hydroxy and phenyl carbons. It is produced by the catalytic condensation of benzaldehyde, with potassium cyanide as a catalyst.
It was first reported in 1828 by Julius Von Liebig and Friedrich Woehler, during their investigations of a bitter almond oil, which consisted of benzaldehyde, and hydrocyanic acid. The catalytic synthesis of benzoin was later improved by Nikolai Zinin.
Benzoin is practically insoluble in water, but it is soluble in hot alcohol and other organic solvents, such as carbon disulfide and acetone..
This name is also used to refer to benzoin resin, obtained from the tree Styrax benzoin. The resin contains benzoic acid, phenylpropionic acid, benzaldehyde, cinnamic acid, benzyl benzoate and vanillin, which gives it a vanilla smell..
This essential oil should not be confused with the compound benzoin, which has a different composition and origin..
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In the image above, the molecular structure of benzoin was shown with a spheres and rods model. It can be appreciated that it has two aromatic rings separated by two oxygen-bearing carbons; from left to right, CHOH, and CO. Also note that the rings have different orientations in space..
The hydrophobic part predominates in its structure, while oxygens contribute slightly to its dipole moment; since both aromatic rings attract electron density towards them, dispersing the charge more homogeneously.
The result is that the benzoin molecule is not too polar; which justifies that it is poorly soluble in water.
By focusing on both oxygen atoms, it will be seen that the OH group could form an intramolecular hydrogen bond with the adjacent carbonyl group; that is, they would not bind two benzoin molecules, but rather a specific spatial conformation would be reinforced, preventing the H (OH) C-CO bond from rotating too much.
Although benzoin is not considered a high polarity molecule, its molecular mass gives it sufficient cohesion force to define a monoclinic white crystal, which melts around 138ºC; depending on the level of impurities it can be at a lower or higher temperature.
Some of its many additional names are:
- 2-hydroxy-1,2-diphenylethanone.
- benzoylphenylcarbanol.
- 2-hydroxy-2-phenylacetophenone.
- 2-hydroxy-1,2-diphenyl-ethane-1-one.
C14H12ORtwo or C6H5COCH (OH) C6H5.
212.248 g / mol.
Benzoin is a white to off-white crystalline solid with a camphor odor. When broken, fresh surfaces are milky white. It can also appear as a dry powder or white or yellow crystals.
Not described. Slightly acrid.
344 ºC.
137 ºC.
181 ºC.
Practically insoluble.
Soluble in hot alcohol and carbon disulfide.
In alcoholic solution it is acidic, being determined by litmus paper.
In stable. It is a combustible compound and incompatible with strong oxidizing agents.
Reduce Fehling's solution.
The lower image shows the condensation reaction of benzaldehyde to give rise to benzoin. This reaction is favored in the presence of potassium cyanide in ethyl alcohol solution..
Two benzaldehyde molecules are covalently linked by releasing a water molecule.
How does this happen? Through the mechanism illustrated above. CN anion- it acts as a nucleophile by attacking the carbon of the carbonyl group of benzaldehyde. In doing so, and with the participation of water, C = O becomes C = N; but now the H is replaced by an OH, and the benzaldehyde becomes nitrile enolate (second row of the image).
The negative charge of nitrogen is delocalized between it and carbon -C-CN; this carbon is then said to be nucleophilic (it looks for positive charges). So much so, that it attacks the carbonyl group of another benzaldehyde molecule.
Again, a water molecule intervenes to produce an OH- and deprotonate an OH group; which later forms a double bond with carbon to give rise to a C = O group, while the CN group migrates as a cyanide anion. Thus, the CN- catalyzes the reaction without being consumed.
Benzoin is involved in the synthesis of organic compounds through catalytic polymerization. It is an intermediate for the synthesis of α-benzoin oxime, an analytical reagent for metals. It is a precursor agent for benzyl, which acts as a photoinitiator.
The synthesis of benzyl proceeds by organic oxidation using copper (III), nitric acid or ozone. Benzoin is used in the preparation of pharmaceutical drugs such as oxaprozin, ditazole and phenytoin.
Benzoin is used as a food flavoring agent.
In veterinary medicine it is used as an antiseptic for topical application, used in the treatment of skin ulcerations to produce their healing..
It is also used in medicine in formulations for the manufacture of inhalants for the treatment of bronchitis and expectorants for oral use..
Benzoin is used in the manufacture of deodorants.
This essential oil has been known to stimulate circulation. A beneficial action on the nervous system has also been reported, manifested by a relief of anxiety and stress. Likewise, it has been indicated that it has an antiseptic action on open wounds..
Some compounds present in benzoin essential oil, such as benzaldehyde, benzoic acid and benzyl benzoate, are bactericidal and fungicidal substances that prevent a situation of sepsis..
It has been indicated that it has antiflatulent and carminative action, an effect attributed to its relaxing action on the abdominal muscles. Likewise, it is attributed a diuretic action that contributes to the elimination of toxic substances for the body.
This essential oil is used as an expectorant that relieves congestion in the respiratory tract. Likewise, they have been used in the relief of arthritis, through topical application that allows the absorption of medicinal components through the skin..
Benzoin on contact causes redness and irritation of the skin and eyes. On inhalation of the compound dust, irritation of the respiratory tract occurs, manifested by coughing. However, in general it is not a very toxic compound..
To the tincture of benzoin, an alcoholic extract of the tree's resin Stirax benzoin, A set of toxic actions have been pointed out to him. Perhaps because the tincture is a mixture of compounds; including benzoic acid, benzaldehyde, etc..
Contact with the skin does not cause significant irritation. But, contact with the eyes can cause irritation, manifested by redness, pain, tearing and blurred vision..
Inhaling the vapors of benzoin tincture can cause irritation of the respiratory tract, coughing, sneezing, runny nose, hoarseness and sore throat..
Finally, ingestion of the tincture can cause gastrointestinal irritation, manifested by abdominal pain, nausea, vomiting and diarrhea..
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