What Are the Physical and Chemical Properties of Phenol and Why Is Phenol Acidic
Phenols are a type of organic compounds that contain a benzene ring which is bonded to a hydroxyl group. They are also called carbolic acids. They exhibit unique physical and chemical properties when compared to alcohol. These physical and chemical properties of phenol are mainly because of the presence of the hydroxyl group in them. Phenols are much similar to alcohols but form much stronger hydrogen bonds than the alcohols. Hence, they are more soluble in water than alcohols and have a higher boiling point. Phenols occur in either the form of colourless liquids or white solids at room temperature and can be highly toxic and caustic in nature. In this article, we will learn about the properties of phenol in detail and include both the physical properties of phenol and the chemical properties of phenol.
Properties of Phenol in Detail
1. Boiling Point of Phenol
Phenols usually have a higher boiling point when compared to the other hydrocarbons that have equal molecular masses. This is because of the presence of the intermolecular hydrogen bonding between the hydroxyl groups of the phenol molecules. In general, the boiling point of phenol increases when there is an increase in the number of carbon atoms.
2. Solubility of Phenol
The solubility of phenol in water is generally decided by the hydroxyl group that is present.
The hydroxyl group in phenol is involved to form the intermolecular hydrogen bonding.
Therefore, these hydrogen bonds are formed between water and phenol molecules that make phenol soluble in water.
However, the aryl group that is attached to the hydroxyl group is hydrophobic.
Hence, the solubility of phenol tends to decrease with an increase in the size of the aryl group present.
3. Acidity of Phenols
Phenols react with active metals like sodium, potassium, etc. and form the corresponding phenoxide. These reactions of phenols say about them that they are acidic in nature. In phenol, the sp2 hybridized carbon in the benzene ring which is attached directly to the hydroxyl group acts as the electron-withdrawing group. Therefore, it tends to decrease the electron density of oxygen.
Because of the delocalization of the negative charge in the benzene ring, the phenoxide ions are generally more stable than the alkoxide ions. Phenols, as a result, are more acidic in nature than alcohols. In the case of the substituted phenols, the acidity decreases if there is an electron-donating group which is attached to the ring when the acidity increases in case of the electron-withdrawing group.
4. Chirality of Phenols
Phenols exhibit the property of chirality within their molecules, for example, in catechin. This chirality is because of the absence of a planar and axial symmetry in the molecule of phenol.
The Application of Phenol in Day to Day Life
Phenol is an organic compound that is used in various fields, laboratory experiments and medical procedures. Even though it is a toxic organic substance, It is still contained in small amounts in mouth washed and in other day-to-day products.
Phenol is Used as an Injection
Phenol is used as an injection to treat muscle spasms. During severe cases of muscle stiffness, The person loses the ability to walk, phenol is used as it helps relax and limit the signals sent to the brain.
It is also used in the treatment of severe cases of an ingrown toenail. However, the news reports have said that hydrogen peroxide has fewer complications than phenol.
Phenol Used a Preservative
The vaccination doses for polio, smallpox, typhoid, meningitis and pneumonia are all stored in phenol for preservation.
Phenol Used in Chemical Peel
The compounds derived by the phenol are used in chemical peels as they let go of old and damaged skin from the surface. Although not very safe, The derived compounds might be highly mild when used on the skin. The phenol of trichloroacetic acid is used for this case. It can infiltrate deep into the skin.
Phenol is Used in Cosmetic and Food Preservation
Phenol is also used for food as well as cosmetic preservations. The safety is assured as it is FDA approved. Although, now the use of phenol derived BHT(butylated hydroxytoluene) is stopped as public awareness regarding its toxicity has come to the light.
Phenol and Health
Even though the toxicity of phenol is widely known, it is still used in the field of medicine. There are some rare benefits of phenol as well.
Did you know that flavonoids contained in teas, fruits, vegetables and wines are actually a derivative compound of phenol!
Apart from this, the resveratrol found in certain fruits, red wines as well nuts is also a phenol derivative.
Strangely, phenol derived compounds might have the properties to prevent cancer.
The Risk Involved in Using Phenol in our Day-To-Day Lives
If a human being is exposed to phenol for an extended period of time, it may lead to the risk of heart disease.
If phenol or the related compounds carrying any amount of phenol is physically ingested by a human being, it will severely damage the digestive parts of the body such as the esophagus, the stomach, the intestines as well as other body parts that are in contact with it.
When phenol comes in contact with the skin, it will immensely irritate and damage the skin. This will lead to severe skin conditions such as corrosion, blisters etc. Phenol is absorbed by the skin leading to other unidentified dangers to the human body.
Inhaling the fumes of phenol for a long time will lead to difficulty breathing and other lung-related conditions. It is also known to cause a lot of damage to the muscles.
Precautions to be Taken When Using Phenol
As a protective measure when using phenol, one must always wear long fitting trousers, shoes covering the toe, and protective eyewear. Also, a lab coat is recommended. Fully covering gloves is a must. The chloroprene gloves are not recommended, wear thicker gloves instead.
Classification of Phenols
Although there are various ways in which a phenol can be classified, It is generally done based on the number of phenol units present. The compound in which only one phenol unit is present is called a parent compound, and other compounds in which more than one unit of phenol are present are called polyphenols.
Phenol is used in chemical synthesis and as a disinfectant, it is a parent compound.
BHT- Butylated hydroxytoluene is a food additive.
Picric acid is trinitro-phenol and is a kind of explosive material. It is also known to be used as a dye.
Xylenol is also used in disinfectants and antiseptics.
Phenolphthalein has used an indicator of pH
Orthophenylphenol is used in waxing fruits and is a form of fungicide.
Phenolic Acid and Human Diet
Phenolic acid is composed of an organic carboxylic acid and a phenolic ring. It belongs to the group of aromatic compounds and is widely found in plant kingdoms.
Generally, it is also referred to as polyphenol and is a kind of phytochemical.
Phenolic acid is considered to be a crucial dietary supplement. It contains rich antioxidants and is known to improve human health. Flavonoid is a type of phenolic acid. For more information on phenolic acids, visit Vedantu.
Appearance of Phenol
In appearance, the phenol resembles a solid crystalline, is light pink coloured and has a sweet acrid odour to it.
FAQs on Properties of Phenol and Its Chemical Behavior
1. What are the physical properties of phenol?
The physical properties of phenol (C6H5OH) include its crystalline nature, characteristic odor, and moderate solubility in water due to hydrogen bonding.
- It is a white crystalline solid at room temperature.
- Melting point: about 40–43°C.
- Boiling point: about 181–182°C.
- Slightly soluble in cold water but more soluble in hot water.
- Has a characteristic medicinal (carbolic) smell.
2. What are the chemical properties of phenol?
The chemical properties of phenol include weak acidity, electrophilic substitution reactions, and reactions with metals and bases.
- Acts as a weak acid and forms phenoxide ion (C6H5O−).
- Reacts with sodium metal: 2C6H5OH + 2Na → 2C6H5ONa + H2(g).
- Undergoes electrophilic aromatic substitution such as nitration, halogenation, and sulfonation.
- Forms colored complexes with FeCl3 (violet coloration test).
3. Why is phenol acidic in nature?
Phenol is acidic because it forms a resonance-stabilized phenoxide ion (C6H5O−) after losing a proton.
- The –OH group releases H+ in aqueous solution.
- The negative charge on oxygen is delocalized over the aromatic ring through resonance.
- This stabilization makes phenol more acidic than alcohols.
4. Is phenol more acidic than alcohol?
Yes, phenol is more acidic than alcohols because its conjugate base is resonance-stabilized.
- Alcohols form alkoxide ions (RO−) that are not resonance-stabilized.
- Phenol forms phenoxide ion (C6H5O−), where the negative charge is delocalized.
- The pKa of phenol is about 10, while typical alcohols have pKa around 16–18.
5. How does phenol react with sodium hydroxide?
Phenol reacts with sodium hydroxide to form sodium phenoxide (C6H5ONa) and water. The balanced equation is:
- C6H5OH(aq) + NaOH(aq) → C6H5ONa(aq) + H2O(l)
6. How does phenol react with bromine water?
Phenol reacts with bromine water to form 2,4,6-tribromophenol as a white precipitate. The balanced reaction is:
- C6H5OH(aq) + 3Br2(aq) → C6H2Br3OH(s) + 3HBr(aq)
7. What happens when phenol reacts with nitric acid?
When phenol reacts with nitric acid, it undergoes nitration to form nitrophenols or picric acid depending on conditions.
- With dilute HNO3: forms a mixture of o-nitrophenol and p-nitrophenol.
- With concentrated HNO3: forms 2,4,6-trinitrophenol (picric acid).
8. Why does phenol give a violet color with ferric chloride?
Phenol gives a violet color with ferric chloride because it forms a colored complex with Fe3+ ions.
- Phenol reacts with neutral FeCl3 solution.
- A violet or purple complex is formed.
- This reaction is used as a qualitative test for phenols.
9. What is the effect of the –OH group on the benzene ring in phenol?
The –OH group in phenol is an activating, ortho-para directing group in electrophilic aromatic substitution.
- It donates electron density to the ring by resonance (+R effect).
- Increases reactivity compared to benzene.
- Directs incoming electrophiles to the ortho and para positions.
10. What are the uses of phenol based on its properties?
Phenol is used in industry and laboratories due to its antiseptic properties and chemical reactivity.
- Used in the manufacture of phenolic resins (Bakelite).
- Preparation of drugs such as aspirin.
- Used as a disinfectant and antiseptic (carbolic acid).
- Intermediate in the production of dyes, plastics, and explosives (picric acid).
