P-NITROPHENOL: CHARACTERISTICS, USES AND TOXICITY - BIOLOGY - 2024

The p-nitrophenol or 4-nitrophenol is an organic phenolic compound, since it has a benzene ring attached to a hydroxyl group. The letter "p" means "for", and indicates that its radicals are located in positions 1 and 4 of the benzene ring.

The groups present are hydroxyl at position 1 and nitro group at position 4. The chemical formula of p-nitrophenol is C ₆ H ₅ NO ₃. P-nitrophenol is a pH indicator that is colorless at pH below 5.4 and is yellow in color above 7.5.

Chemical structure of p-nitrophenol at acidic and alkaline pH. Source: Dannybalanta /pxhere.com/pexels.com. Edited image

On the other hand, this compound is used for the synthesis of various substances of importance to health, such as paracetamol (also known as acetaminophen), which is a recognized analgesic and antipyretic.

Likewise, it serves as a precursor to synthesize phenethidine, which is an anticonvulsant, and acetophenethidine, which serves as an analgesic. Other substances that can be derived from p-nitrophenol are various raw materials necessary for the manufacture of certain fungicides and pesticides.

Apart from this it is also a raw material for the production of dyes, used to darken leather.

However, despite its benefits, p-nitrophenol is a substance that must be handled with great care, as it poses a high risk to health. It has slight flammability and moderate reactivity, as indicated by the NFPA (National Fire Protection Association).

characteristics

P-Nitrophenol is a synthetic chemical, meaning it is not produced from natural sources.

It is characterized by being a yellowish-white or light yellow crystalline powder. P-nitrophenol has a molecular mass of 139.11 g / mol, a boiling point of 279 ° C, a melting point of 110-115 ° C, and an autoignition temperature of 268 ° C. This substance does not evaporate at room temperature.

The solubility in water at room temperature is 16 g / L. It is soluble in ethanol, chloroform and in diethyl ether.

P-nitrophenol is a complex compound, since its solid state (crystals) is made up of a mixture of two molecular forms: one called alpha and the other beta.

In the alpha form (4-nitrophenol) it is colorless, shows instability at room temperature and does not show changes in the face of sunlight (stable).

While the beta form (4-nitrophenolate or phenoxide) appears as yellow crystals and behaves in the opposite way; that is, it is stable at room temperature, but in the face of sunlight it gradually turns red.

This substance has its isosbestic point at 348 nm for the alpha and beta forms.

Applications

PH indicator

Although this compound has a pH indicator function, it is not widely used for this purpose. Regarding the color changes according to pH, it has a lot of similarity with other pH indicators such as thymophthalein and phenolphthalein. They have in common that they are colorless at low pH.

Precursor in the synthesis of compounds

P-nitrophenol is a compound used in the pharmaceutical industry to synthesize substances with beneficial effects on health.

For example, acetaminophen or paracetamol can be synthesized from p-nitrophenol, which is one of the drugs with analgesic and antipyretic action most used by the community in general.

Phenethidine, an anticonvulsant used in cases of CNS disorders, is also derived from it. As well as, acetophenethidine with analgesic action.

Formation of p-nitrophenol from the action of certain enzymes on specific substrates

4-Nitrophenyl phosphate is a synthetic substrate used for the determination of alkaline phosphatase. When the enzyme acts on this substrate, it forms p-nitrophenol (colorless substance).

Later, 4-nitrophenol loses protons to become 4-nitrophenolate, which is yellow in color. The reaction must occur at alkaline pH> 9.0 to promote conversion to the beta (4-nitrophenolate) form.

The generated color is measured spectrophotometrically at 405 nm, and thus this enzyme can be quantified.

The same is true for other enzymes on other substrates. Among them we can mention the action of the carbonic anhydrase enzyme on 4-nitrophenyl acetate and the glycosidases on 4-nitrophenyl-β-D-glucopyranoside.

Toxicity

According to the NFPA (National Fire Protection Association), p-nitrophenol is classified as a substance with a grade 3 health risk. This means that the damage it causes to health is severe.

On the other hand, it has a flammability risk of 1, which means that the risk of it producing fire is slight. Finally, it has a reactivity risk grade 2 (moderate risk). This means that under certain conditions this substance is capable of emitting energy.

Health effects

Among the most prominent effects of this substance on health are those that we will mention below.

At the skin level it produces irritation, inflammation and burns. In addition, contact with the skin represents a route of absorption of the product. An exaggerated exposure to p-nitrophenol can affect the Central Nervous System (CNS).

On the ocular mucosa it can cause a severe burn, with severe eye damage. At the respiratory level, inflammation, coughing, and suffocation. In case of accidental ingestion, it causes vomiting with severe abdominal pain, mental confusion, rapid heartbeat, fever and weakness.

If it is absorbed in large amounts, it can cause a disease called methemoglobinemia, characterized by an increase in the amount of methemoglobin in the blood.

This disease significantly affects oxygen transport, and therefore generates a symptomatology characterized by headache, fatigue, dizziness, cyanosis, and respiratory distress. In severe cases it can also cause death.

People exposed to small amounts will pass the product through urine. Finally, despite all the harmful effects described, it has not been proven to have a carcinogenic effect.

First aid

If you have come into contact with the product, it is necessary to remove contaminated clothing and wash the affected area (skin or mucous membranes) with plenty of water. In case of inhalation, take the victim to a well-ventilated place. In case the patient is not breathing, apply assisted respiration.

After this, it is necessary to transfer the victim to a medical care center as soon as possible.

Biosecurity measures

- You must work under a fume hood, or otherwise wear respirators. Wear suitable clothing (gown, gloves, safety glasses, closed shoes and hat).

- Immediately wash clothes contaminated with the product.

- Do not take contaminated work implements home.

- The workplace must be equipped with eyewash and emergency showers.

- While handling this substance, do not wear contact lenses.

- Do not smoke, eat or drink inside the facilities where this substance is handled.

- Bear in mind that p-nitrophenol is incompatible with certain substances, and therefore must be stored separately from strong alkalis, such as sodium hydroxide or potassium hydroxide. It is also incompatible with peroxides, perchlorate, permanganates, chlorine, nitrates, chlorates, bromine and fluorine, among other oxidants.

- Bear in mind that in case of fire the containers containing this substance may explode.

References

1. New Jersey Department of Health and Senior Services. Fact Sheet on Hazardous Substances. 4-nitrophenol. 2004. Available at: nj.gov/health.
2. "4-nitrophenol." Wikipedia, The Free Encyclopedia. 22 Feb 2019, 13:58 UTC. 29 May 2019, 03:59 wikipedia.org.
3. Rojas H, Cubillos J, Guerrero D. Hydrogenation of p-nitrophenol through the use of Ir, Ni and Ir-Ni catalysts supported on TiO2. Faculty of Engineering Magazine, UPTC; 2012, 21 (3): 63-72
4. Agencies for toxic substances and disease registry. Public health summaries. Nitrophenols. Available at: atsdr.cdc.gov
5. National Institute of Safety and Hygiene at Work. International Chemical Safety Cards. 4-nitrophenol. Spain. Available at: insht.es/InshtWeb