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Alcohols and phenols are both classes of organic compounds containing a hydroxyl (-OH) functional group. However, while they both feature hydroxyl groups, they differ fundamentally from each other. Alcohols have hydroxyl groups attached to alkyl carbon atoms, whereas phenols have the hydroxyl group directly attached to an aromatic benzene ring.
The difference between alcohol and phenol is very important from the perspective of class 11 and 12 students, especially for those preparing for the NEET exam. In this article, we will explore the differences between alcohol and phenol, including their definitions, properties, types, and many other important terms.
What are Alcohols is Chemistry?
Alcohol is a common organic compound that consists one or more hydroxyl (OH) groups. The general formula of alcohol is R-OH, where R represents the alkyl group. The molecules of alcohol attached to the carbon atom of alkyl groups or hydrocarbon chain. Most of the alcohols are colorless liquid. Based on the bonding of carbon atoms to the hydroxyl groups, alcohol can be classified in three types namely – primary, secondary and tertiary. Alcohol is widely used in industries for manufacturing beverages and preparing perfumes.
Types of Alcohols
Alcohol can be classified based on the hydroxyl group attached as primary, secondary, and tertiary. Let’s discuss these types in detail as follows.
Primary alcohols can be defined as the carbon atom that contains -OH group is attached only to an alkyl group. The examples of primary alcohols are Methanol (propanol), ethanol, butanol etc.
Secondary alcohols can be defined as a hydroxyl group attached to carbon atom which is connected to two alkyl groups. The examples of secondary alcohols are propan-2, butan-2-ol etc.
Tertiary alcohols can be defined as the carbon atom that carries -OH group, is attached directly to three alkyl groups. The groups may be same or different. The examples of tertiary alcohols are 2-methypropan-2-ol, 2-methylbutan-2-ol etc.
What are Phenols?
Phenols are a class of organic compounds characterized by a hydroxyl (OH) group attached directly to an aromatic benzene ring. Chemically, they are aromatic compounds with a hydroxyl group bonded to one of the carbon atoms in the benzene ring. Phenols are often referred to as derivatives of benzene with one or more hydroxyl (-OH) groups attached.
Some examples of phenols include: Phenol (C6H5OH), Cresols, Bisphenol A(BPA), Resorcinol (1,3-dihydroxybenzene), Gallic Acid( trihydroxybenzoic acid), Flavonoids, Quinones and Stilbenes.
Phenol as Special Type of Alcohol
Phenol has -OH group that is attached to two carbon atoms like a secondary alcohol. So sometimes phenol is called as a secondary alcohol. But for some reasons it is not considered as an alcohol. Phenol consists -0H group similar to alcohol, but the -OH group of phenol is attached to a benzene ring. In addition to, phenol is more acidic nature than alcohol.
Physical Properties Comparison
Comparison table outlining some key physical properties of alcohols and phenols is given as:
| Property |
Alcohols |
Phenols |
| Molecular Structure |
R-OH |
Ar-OH |
| Hydrogen Bonding |
Form hydrogen bonds with water and themselves |
Form hydrogen bonds with water and themselves |
| Solubility in Water |
Soluble in water, with shorter chains being more soluble |
Soluble in water, but less so than alcohols due to the presence of the aromatic ring |
| Boiling Point |
Generally lower boiling points compared to phenols |
Generally higher boiling points compared to alcohols due to stronger intermolecular hydrogen bonding |
| Odor |
Typically have a characteristic odor, often described as “alcoholic” |
Less odor compared to alcohols, often described as “sweet” |
| Acidity |
Less acidic compared to phenols |
More acidic compared to alcohols due to the resonance stabilization of the phenoxide ion |
| Reactivity |
Undergo reactions such as oxidation, dehydration, and esterification |
Reactivity influenced by the aromatic ring, undergo reactions such as electrophilic aromatic substitution and oxidation |
| Toxicity |
Generally less toxic compared to phenols |
Phenols can be toxic, especially in higher concentrations |
Chemical Properties Comparison
Comparision of different chemical propertes such as oxidation, esterification, reaction with metlas, etc. are given in the following table:
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Chemical properties
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Alcohol
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Phenol
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Oxidation
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R-OH + HO-NO2→ R-O-NO2
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Phenols get easily oxidized to para-benzoquinone. This when reduced forms quinones.
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Esterification
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When the alcohol reacts with acid, it forms an ester and water.
- R-OH + R’-COOH + H+ ↔ R’-COOR
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Phenyl esters (RCOOAr) do not form directly from RCOOH, but for this acid chlorides or anhydrides react with ArOH in the presence of a strong base.
- (CH3CO)2O + C6H5OH + NaOH → CH3COOC6H5 + CH3COONa + H2O
- C6H5COCl + C6H5OH + NaOH → C6H5COOC6H5 + Na+Cl– + H2O
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Reaction with metals
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Alcohol (ethanol) reacts with sodium metal and produced hydrogen gas and sodium ethoxide.
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Generally phenol does not react with most of the metals. In some cases it reacts with sodium, potassium, and magnesium. Phenol reacts with sodium or potassium to form phenoxide ions and hydrogen gas.
- 2C6H5OH + 2Na = 2C6H5O– (phenoxide ion) + H + 2Na+
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Reaction with halogen group elements
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When the halogen group elements ( chlorine, bromine) react with alcohol, the chlorine, bromine replace the -OH group in alcohol.
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Phenol can react with halogens (fluorine, chlorine, bromine, iodine) to form halogenated phenols.
- C6H5OH + Cl2 = C6H5Cl2 + HCl + H+
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Difference between Alcohol and Phenol
The key differences between Alcohol and Phenol are listed in the following table:
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Parameter
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Alcohol
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Phenol
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Functional Group
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hydroxyl (OH) groups
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hydroxyl ( -OH) group attached to a benzene ring
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Formula/Chemical Name
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R-OH
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C6H5OH
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Number of -OH group
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Alcohol consisting one or more -OH groups.
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Phenols consisting a -OH group attached to aromatic benzene group.
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Aromaticity
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Alcohol does not contain aromatic ring.
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Phenol contains aromatic benzene ring.
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Nature of compound
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Alcohols are aliphatic compounds.
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Phenols are aromatic compounds.
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Acidity
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Alcohols are less acidic than phenols.
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Phenols are more acidic than alcohols.
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State at Room Temperature
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generally colorless and liquid
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Typically solid at room temperature due to stronger intermolecular forces.
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Solubility in Water
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More Soluble in water.
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Less Soluble in water.
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Boiling point
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Alcohols have less boiling point than phenols.
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Phenols have higher boiling point than alcohols.
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Reactivity with Metals
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Reacts with active metals to produce hydrogen gas.
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Phenols do not react with metals.
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Reaction on Litmus
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As alcohols are neutral type, they do not show any reaction in an undergoing test.
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Due to acidic nature, phenol can change the litmus paper into red color.
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Reaction with NaOH
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Alcohols do not react with NaOH.
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Phenols react with NaOH to form phenoxides.
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Example
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Ethanol (C2H5OH), Methanol (CH3OH).
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Phenol (C6H5OH).
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Usage
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Used as the main component of alcoholic beverages. It is also used in pharma company, industries, to prepare perfume and ink.
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It is mainly used in pharma company to manufacture medical products.
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Conclusion
In conclusion, while both alcohols and phenols contain hydroxyl (-OH) groups, they exhibit distinct chemical properties due to differences in molecular structure. Alcohols feature the hydroxyl group attached to a saturated carbon atom in an alkyl chain, while phenols have the hydroxyl group directly bonded to an aromatic benzene ring.
These structural disparities result in variations in physical properties such as solubility, boiling points, and acidity. Additionally, the aromatic nature of phenols imparts unique reactivity and potential toxicity compared to alcohols.
FAQs on Alcohol and Phenol
What are alcohols and phenols?
Alcohols and phenols are classes of organic compounds containing a hydroxyl (-OH) functional group.
What are the main differences between alcohols and phenols?
Alcohols have the hydroxyl group attached to a saturated carbon atom in a hydrocarbon chain, while phenols have the hydroxyl group directly bonded to an aromatic benzene ring.
What are some common examples of alcohols?
Common examples of alcohols include ethanol (found in alcoholic beverages), methanol (used as a solvent and fuel), isopropyl alcohol (used as a disinfectant), and glycerol (found in skincare products and as a solvent).
What are some common examples of phenols?
Common examples of phenols include phenol (carbolic acid), cresols, bisphenol A (BPA), resorcinol, and gallic acid.
Are alcohols and phenols toxic?
While alcohols are generally less toxic, phenols can be toxic, especially in higher concentrations. Some phenolic compounds, such as cresols and BPA, have been associated with health concerns and are regulated in certain products.
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