What is Phenol?
Phenol which is also referred to as carbolic acid has a molecular formula C6H5OH and is an aromatic organic compound. It is volatile in nature and appears in the form of a white crystalline solid. It has a phenolic group which is (C6H5) and is attached to the hydroxyl group which is (OH). It is very mildly acidic in nature and requires very careful handling because it may cause chemical burns if split.
Phenol was first extracted from the coal tar but these days it is produced on a huge scale from the derivatives of the petroleum feedstock. It is a very important commodity for the industries and is the chemical element that participates in the chemical reactions in order to develop many other materials and compounds. It is commonly used to develop plastics and many other related compounds. The phenols and their derivatives are very useful in developing polycarbonates, epoxies, Bakelite, nylon, detergents, herbicides such as phenoxy herbicides, and numerous pharmaceutical drugs.
Properties of Phenol
Some of the basic physical and chemical properties of phenol are listed below in a tabular manner:
Some of the chemical properties of the phenols are listed below:
Acidity of Phenols: In order to form the corresponding phenoxide, phenols react with active metals such as sodium, potassium, etc. The acidic nature of the phenol is indicated by all these reactions. The carbon that has SP2 hybridization is attached to the benzene ring and is also attached directly to the hydroxyl group which acts as an electron-withdrawing group. Hence, it helps in decreasing the electron density of the oxygen.
Phenoxide ions are more stable than alkoxide ions because of the de-localization of the negative charge in the benzene ring. This is the reason why phenols show a more acidic nature than alcohol. If the electron-donating group is attached to the ring in case of substituted phenol, its acidity diseases but if the electron-withdrawing group is attached to the ring, the acidity increases.
Hydrogen Bonding: In carbon tetrachloride and alkyne solvents, there is a wide range of Lewis bases such as pyridine, diethyl ether, and diethyl sulfide which form a hydrogen bond with the phenol. Phenol is compatible with the C/E ratio of the EWC model as it is classified as hard acid where EA = 2.27 and CA = 1.07. The CB plot is used for illustration of the relative acceptor strength of phenol towards a series of bases versus other Lewis acids.
Phenoxide Anion: The phenoxide anion is one of the strong nucleophiles where its nucleophilicity e is comparable to one of the carbanions or tertiary amines. It acts as an important nucleophile that reacts at both its carbon and oxygen sites. Generally, when the oxygen attacks the phenoxide anions, it is kinetically favored whereas when the carbon attacks the phenoxide anion, it is thermodynamically preferred. When the reaction rate reaches the diffusion control, a mix of oxygen or carbon attack results in a loss of selectivity.
Chirality of Phenols: Phenols are seen to be exhibiting chirality within their molecules for example catechin. This chirality arises due to the absence of planar and axial symmetry in the phenol molecules.
Reactions of Phenols: Phenols are very highly reactive towards electrophilic aromatic substitution. It is because the enhanced nucleophilicity results in a donation of Pi electron density from oxygen into the ring. There is a possibility of many groups getting attached to the rain by halogenation, acylation, sulphonation, and many other related processes. As we know aqua solutions of phenol are weak acids and it turns blue litmus likely to red. Phenols are also neutralized by sodium hydroxide that results in the formation of sodium phenate or phenolate. But it cannot be neutralized by sodium bicarbonate or sodium carbonate to liberate carbon dioxide as it is weaker than carbonic acid.
C6H5OH + NaOH → C6H5ONa + H2O
When in the presence of a dilute sodium hydroxide solution, the mixture of phenol and benzoyl chloride is shaken, as a result, phenyl benzoate forms. This reaction is often known as Schouten–Baumann reaction:
C6H5COCl + HOC6H5 → C6H5CO2C6H5 + HCl
When phenol is distilled with zinc dust or when its vapour is passed over granules of zinc at 400°C, it gets reduced to benzene.
C6H5OH + Zn → C6H6 + ZnO
Uses and Structural Formula of Phenol
Phenol is a member of a class of organic compounds with the same name, Phenols. It is the most commonly studied member of its family. Generally, phenols refer to any chemical compound which contains an –OH group attached directly to an aromatic ring system. Phenol is a common name of the first discovered and the simplest member of this family, monohydroxy benzene, which just contains an –OH group attached directly to a benzene ring.
Its structural formula is C6H5OH and is also sometimes referred to as benzenol or carbolic acid. Its structure may be represented in the following manner:
(Image will be uploaded soon)
(Image will be uploaded soon)
Phenol is widely used in a lot of industries for varied purposes. A complete list of the uses of phenols is given below:
Phenol is the most commonly used disinfectant since ancient times. It has got amazing antiseptic properties too. It was one of the most common chemicals used to clean household materials, especially washrooms and floor tiles.
Phenol is proven to be an effective anti-bacterial, anti-fungi, and anti-viral agent. A lot of studies have been conducted to find the mechanism of action behind these properties. It has been hypothesized by some studies that it hinders the protein and RNA synthesis in microorganisms, thereby leading to their death. Besides, some studies claim that it damages the cytoplasmic membranes of the microorganisms.
Phenol, although in very minor quantity, is also used in the manufacturing of mouthwashes for effective cleansing of the mouth and removal of mouth bacteria.
Phenol is also sometimes used as an oral analgesic and mild anesthetic. This is because of the numbing sensation it provides due to its astringent properties since it is an alcohol. However, precautions should be taken while using it orally because the concentrated solution of phenol can be toxic to human skin and may cause damage to the mucosal membrane.
Phenol was one of the ingredients used by Hitler in the Second World War for executing the Nazi community due to its toxic effects when used in concentrated volume.
Phenol is used as one of the starting materials for the synthesis of many chemicals such as picric acid, pharmaceutical drugs, explosive materials, and plastic polymers.
Phenols are one of the starting materials for the formation of azo dyes in the coloring industry.
Phenol is produced as an intermediate in a lot of industries to be further utilized for the manufacture or production of various substances in different industries.
Phenol is also used as a preservative in the wood industry to keep wood safe from the attack of microorganisms like bacteria or fungi.
Phenol is used in the cosmetics and skincare products manufacturing industries for the production of various skincare and cosmetics products such as skin lightening creams and lotions, sunscreens, and hair colors and dyes’ solutions.
Phenol is used in the extraction of biomolecules for study and research purposes. In Molecular biology laboratories, phenol is widely used for the extraction of nucleic acids from DNA structures of the tissue samples of various sources for research studies and investigations.
Phenol is used for its polymerization reaction with formaldehyde. This reaction is commercially used in the polymer industry for the preparation of phenolic resins. The polymeric resin which is formed in this reaction is named as phenol-formaldehyde resin, which is also known commonly by its commercial name, Bakelite. This phenol-formaldehyde resin is used in electrical appliances such as switches. It is also used in the automobile industry to provide lubrication to certain small and sensitive parts of the engine of any vehicle. This resin finds its applicability in so many industries due to its amazing property to withstand highly extreme conditions in terms of electrical resistance and heat or corrosion from other chemical agents.
Another intermediate resin-like substance is formed during the polymerization reaction between phenol and formaldehyde, named novolac. This resin has very good adhesive properties and hence is used as a binding material in many industries. It is also used as a protective coating over substances that are easily degraded in the presence of moisture.
One of the widest and most extensive uses of phenol is in the plastic industry where it is used as a starting material to carry out the polymerization reactions which result in the production of various types of plastics. Life in today’s world seems impossible without plastics. They form an immensely important part of our routine life. We use so many materials made up of plastic daily. Phenol is made to react with acetone which leads to the formation of bisphenol A. This product is further utilized to produce a wide range of polymers used for the synthesis of epoxide resins and polycarbonates which are the basic skeletal structure of various plastics.
Apart from bisphenol A, the reaction of phenol and hydroxylamine in acidic media is also used in the production of caprolactam. In this reaction, phenol is first reduced to acetophenone which then reacts with hydroxylamine to result in the production of an intermediate named cyclohexanone oxime which is formed as a result of Beckmann Rearrangement between the reactants acetophenone and hydroxylamine. The intermediate (cyclohexanone oxime) is then heated with a 20% solution of oleum to convert it finally into caprolactam, which is a basic unit used in the polymerization reaction involved in the production of the polymer Nylon-6 (polycaprolactam).
Phenol is an active ingredient of various pharmaceutical lotions, ointments, and ear drops used to prevent bacterial or fungal infections.
Phenol is also used in the sclerotherapy of varicose veins as it is a sclerosing agent. Due to its alcoholic nature, it forms an irritant solution which when injected into the blood vessels, it causes inflammation in the inner lining of the blood vessels, which leads to its collapse. As soon as the two opposite walls of the blood vessels collapse over each other, it gets stuck leading the blood to clot in that area. This is done to stop the blood flow through the affected veins instead of forcing it to direct itself through the healthy veins. It is a very destructive form of treatment and phenol is generally not recommended unless all other viable options such as hypertonic saline solution, polidocanol, sodium tetradecyl sulfate solution, or chromated glycerin solution cannot be used.
Phenol is used as an active agent for the “Nail Matrix Phenolization Method” which is used in the treatment of ingrown nails. This treatment method is the only alternative cure for this condition apart from the surgical option. In this method, the toenail is partially pulled or torn away from its lateral edge followed by chemical treatment with a solution of concentrated (80–88%) phenol. Although destructive to the skin, it is the only medicinal option available apart from surgery.
Phenol is used for another destructive type of treatment. It acts as a neurolytic agent and it helps in getting relief from chronic nerve pain of muscle spasms. Since it is well known that nerves are a medium of pain sensation carriers, blocking of nerve signals is sometimes the only option remaining when normal analgesics do not work to cure this type of nerve pain. Although this method is not recommended due to its destructive nature, it sometimes remains as the last terminal option for patients suffering immense nerve pains.
Due to its astringent properties, phenol is also used as an ingredient in the chemical face peeling masks manufactured by the dermatological industry. Although it is a harsh treatment, it is considered an effective remedial treatment for patients with severe skin burns on their face, hands, or feet. Apart from this, the phenol chemical peel-off masks can also be used for treating rough wrinkle lines, scars, and in some cases even premature tumor outgrowths. However, this phenol peel mask should only be used under the supervision of your dermatologist as it can cause severe harm to certain skin areas and does not suit all skin types, and may result in severe swelling, redness, and itching in some people.
Phenol is sometimes also used as a chemical sterilizing agent for hospital rooms and medical equipment.
An injection of phenol can treat muscle spasms in patients of Parkinson’s disease, brain trauma or cerebral palsy. It works in the same manner as described earlier for the treatment of varicose veins or chronic nerve pain. It disrupts any kinds of signals (including pain or spasms) from the brain to nerves, muscles, or blood vessels.
Phenol is used as a preservative in many vaccines such as Pneumovax 23 (used for the prevention of Pneumonia and Meningitis), Typhim Vi (used for the prevention of Typhoid fever), ACAM2000 (used for the prevention of Smallpox), and Ipol (used for the prevention of Polio).
Phenol is a very dilute concentration that can relieve a sore throat.
FAQs on Uses of Phenol
1. What is phenol and what is its chemical formula?
Phenol is an aromatic organic compound with the chemical formula C₆H₅OH. It is also known as carbolic acid. Structurally, it consists of a hydroxyl group (–OH) directly attached to a benzene ring. This structure gives it unique properties that distinguish it from aliphatic alcohols.
2. What are some of the most important industrial uses of phenol?
The primary industrial importance of phenol lies in its use as a precursor for synthesising other chemicals and materials. Some major applications include:
- Production of Phenolic Resins: It is used to manufacture Bakelite (phenol-formaldehyde resin), which is used in electrical switches and automobile parts.
- Synthesis of Plastics: Phenol is a key ingredient in making bisphenol A, which is then used to produce polycarbonates and epoxy resins.
- Manufacturing Nylon: It is used in the production of caprolactam, a precursor to Nylon-6.
- Chemical Synthesis: It serves as a starting material for a wide range of products, including detergents, herbicides, and numerous pharmaceutical drugs.
3. How is phenol used in the medical and pharmaceutical fields?
In medicine and pharmacy, phenol is valued for its antiseptic and disinfectant properties. It is used in:
- Antiseptics and Disinfectants: Dilute solutions of phenol are used to sanitise medical equipment and as a component in antiseptic lotions and ointments.
- Oral Analgesics: It is found in some mouthwashes and sore throat lozenges for its mild anaesthetic (numbing) effect.
- Vaccine Preservatives: A very small amount of phenol is used as a preservative in some vaccines, such as Pneumovax 23, to prevent bacterial growth.
- Chemical Synthesis: It is a starting material for synthesising important drugs like aspirin and phenacetin.
4. What is the role of phenol in the synthesis of polymers like Bakelite?
Phenol plays a crucial role in the production of Bakelite through a process called condensation polymerisation. Phenol reacts with formaldehyde in the presence of an acid or base catalyst. This reaction forms a cross-linked polymer known as phenol-formaldehyde resin, or Bakelite. This polymer is a thermosetting plastic, meaning it is strong, heat-resistant, and an excellent electrical insulator, making it ideal for products like electrical switches and kitchenware handles.
5. Why is phenol considered an acid but not an alcohol, despite having an -OH group?
Although phenol has a hydroxyl (–OH) group like alcohols, its chemical behaviour is distinctly acidic. This is because the –OH group is attached to an sp² hybridised carbon of the aromatic benzene ring. The ring acts as an electron-withdrawing group, and the lone pair of electrons on the oxygen atom gets delocalised into the ring. This delocalisation stabilises the resulting phenoxide ion (C₆H₅O⁻) after the proton (H⁺) is released, making phenol more likely to donate a proton and thus behave as a weak acid. Alcohols lack this resonance stabilisation, making them much less acidic.
6. If phenol is used in skincare and medicine, why is it also considered toxic and require careful handling?
The effects of phenol are highly dependent on its concentration. In highly diluted solutions, it acts as an effective antiseptic and anaesthetic, which is useful in medical products. However, in its concentrated form, phenol is corrosive and toxic. It can cause severe chemical burns upon contact with the skin because it rapidly denatures proteins. Ingesting or absorbing significant amounts can lead to systemic poisoning. Therefore, its use in consumer products is strictly regulated to very low, safe concentrations.
7. What makes the benzene ring in phenol highly reactive towards electrophilic aromatic substitution?
The benzene ring in phenol is highly activated towards electrophilic aromatic substitution due to the strong activating effect of the hydroxyl (–OH) group. The oxygen atom has lone pairs of electrons that are donated to the benzene ring through resonance. This increases the electron density on the ring, particularly at the ortho and para positions. As a result, the ring becomes much more attractive to electron-deficient species (electrophiles), making reactions like halogenation, nitration, and sulfonation occur more readily than with benzene itself.
8. What is the importance of phenol as an 'intermediate' in the chemical industry?
The importance of phenol as a chemical intermediate means its primary value is not just as a final product, but as a fundamental building block for creating other, more complex and valuable substances. Industries purchase phenol not necessarily to sell it directly, but to use it as a starting material in multi-step chemical reactions. For example, the plastics industry uses phenol to create bisphenol A, which is the actual monomer for polycarbonate plastics. This role as a precursor makes phenol a high-volume industrial chemical essential for many manufacturing chains.
