Diphenylamine: Formula, Chemical Structure, Uses, Preparation and Properties

The diphenylamine is an organic compound whose chemical formula is (C ₆ H ₅ ) ₂ NH Its name indicates that it is an amine, as well as its formula (-NH ₂ ). On the other hand, the term"diphenyl"refers to the presence of two aromatic rings bonded to nitrogen. Accordingly, diphenylamine is an aromatic amine.

Within the world of organic compounds, the aromatic word is not necessarily related to the existence of its odors, but with characteristics that define its chemical behaviors against certain species.

In the case of diphenylamine, its aromaticity and the fact that its solid present a distinctive aroma coincide. However, the foundation or the mechanisms that govern their chemical reactions can be explained by their aromatic character, but not by their pleasant aroma.

Its chemical structure, basicity, aromaticity and intermolecular interactions are the variables responsible for its properties: from the color of its crystals to its applicability as an antioxidant agent.

Chemical structure

In the upper images are represented the chemical structures of diphenylamine. The black spheres correspond to the carbon atoms, the white spheres correspond to the hydrogen atoms and the blue spheres correspond to the nitrogen atom.

The difference between both images is the model of how they represent the molecule graphically. In the lower one, the aromaticity of the rings with the black dotted lines stands out and, likewise, the flat geometry of these rings is evident.

Neither of the two images shows the solitary pair of electrons not shared on the nitrogen atom. These electrons"walk"through the conjugated π system of the double bonds in the rings. This system forms a kind of circulating cloud that allows intermolecular interactions; that is, with other rings of another molecule.

This means that the non-shared pair of nitrogen goes through both rings, distributing their electron density equally, and then return to nitrogen, to repeat the cycle again.

In this process the availability of these electrons decreases, bringing as a consequence a decrease in the basicity of diphenylamine (its tendency to donate electrons as a Lewis base).

Applications

Diphenylamine is an oxidizing agent capable of fulfilling a series of functions, and among them are the following:

- During storage, apples and pears undergo a physiological process called scald, related to the production of conjugated trienes, which leads to damage to the skin of fruits. The action of diphenylamine allows to increase the period of storage, reducing the damage of fruits to 10% of what was observed in their absence.

- When combating oxidation, diphenylamine and its derivatives lengthen the operation of the engines by preventing the thickening of used oil.

- Diphenylamine is used to limit the action of ozone in rubber manufacturing.

- Diphenylamine is used in analytical chemistry for the detection of nitrates (NO ₃ ^- ), chlorates (ClO) ₃ ^- ) and other oxidizing agents.

- It is an indicator used in the detection tests of nitrate poisoning.

- When RNA is hydrolyzed for one hour, it reacts with diphenylamine; this allows its quantification.

- In veterinary medicine diphenylamine is used topically in the prevention and treatment of screwworm manifestations in breeding animals.

- Some of the diphenylamine derivatives belong to the category of non-steroidal anti-inflammatory drugs. Likewise, they may have pharmacological and therapeutic effects such as antimicrobial, analgesic, anticonvulsant and anticancer activity.

Preparation

Naturally, diphenylamine is produced in onions, corianders, green and black tea leaves, and citrus fruit peels. Synthetically, there are many routes that lead to this compound, such as:

Thermal deamination of aniline

It is prepared by thermal deamination of the aniline (C ₆ H ₅ NH ₂ ) in the presence of oxidizing catalysts.

If the aniline in this reaction does not incorporate an oxygen atom into its structure, why is it oxidized? Because the aromatic ring is an electron-withdrawing group, unlike the H atom, which donates its low electron density to nitrogen in the molecule.

2 C ₆ H ₅ NH ₂ => (C ₅ H ₅ ) ₂ NH + NH ₃

Also, aniline can react with the aniline hydrochloride salt (C ₆ H ₅ NH ₃ ⁺ Cl ^- ) under a 230 ° C heating for twenty hours.

C ₆ H ₅ NH ₂ + C ₆ H ₅ NH ₃ ⁺ Cl ^- => (C ₅ H ₅ ) ₂ NH

Reaction with phenothiazine

Diphenylamine causes several derivatives when combined with different reagents. One of these is phenothiazine, which when synthesized with sulfur is a precursor of derivatives with pharmaceutical action.

(C ₆ H ₅ ) ₂ NH + 2S => S (C ₆ H ₄ ) NH + H ₂ S

Properties

Diphenylamine is a white crystalline solid that, depending on its impurities, can acquire bronze, amber or yellow tones. It has a pleasant aroma to flowers, has a molecular weight of 169.23 g / mol and a density of 1.2 g / mL.

The molecules of these solids interact by Van der Waals forces, among which are the hydrogen bonds formed by the nitrogen atoms (NH-NH) and the stacking of the aromatic rings, resting their"electronic clouds"one on top of the other .

As the aromatic rings take up a lot of space, they hinder the hydrogen bonds, without considering also the rotations of the N-ring bonds. This causes that the solid does not have a very high melting point (53 ºC).

However, in liquid state the molecules are more separated and the efficiency of the hydrogen bridges improves. Likewise, diphenylamine is relatively heavy, requiring a lot of heat to pass to the gas phase (302 ° C, its boiling point). This is also due in part to the weight and interactions of the aromatic rings.

Solubility and basicity

It is very insoluble in water (0.03 g / 100 g of water) due to the hydrophobic character of its aromatic rings. On the other hand, it is very soluble in organic solvents such as benzene, carbon tetrachloride (CCl) ₄ ), acetone, ethanol, pyridine, acetic acid, etc.

Its acidity constant (pKa) is 0.79, which refers to the acidity of its conjugate acid (C ₆ H ₅ NH ₃ ⁺ ). The proton added to the nitrogen has a tendency to detach, because the pair of electrons with which it is bound can walk through the aromatic rings. Thus, the high instability C ₆ H ₅ NH ₃ ⁺ reflects the low basicity of diphenylamine.

References

1. Gabriela Calvo (April 16, 2009). How does diphenylamine affect the quality of the fruit? Retrieved on April 10, 2018, from: todoagro.com
2. The Lubrizol Corporation. (2018). Diphenylamine Antioxidants. Retrieved on April 10, 2018, from: lubrizol.com
3. Arun Kumar Mishra, Arvind Kumar. (2017). Pharmacological Applications of Diphenylamine and Its Derivative as Potent Bioactive Compound: A Review. Current Bioactive Compounds, volume 13.
4. PrepChem. (2015-2016). Preparation of diphenylamine. Retrieved on April 10, 2018, from: prepchem.com
5. PubChem. (2018). Diphenylamine. Retrieved on April 10, 2018, from: pubchem.ncbi.nlm.nih.gov.
6. Wikipedia. (2018). Diphenylamine. Retrieved on April 10, 2018, from: en.wikipedia.org