ROUTERA

Chapter 11 Alcohols, Phenols and Ethers

Class 12th Chemistry Chapter Hots

1. Explain the mechanism of dehydration of alcohols to alkenes with the help of an example. Discuss the factors affecting the rate of dehydration.

Answer: The dehydration of alcohols to form alkenes is a typical example of an elimination reaction, specifically an E1 or E2 mechanism depending on the conditions.

  • E1 Mechanism: In an E1 mechanism, the reaction proceeds in two steps:
    1. The alcohol undergoes protonation and forms a good leaving group (water), resulting in the formation of a carbocation.
    2. The carbocation then undergoes a loss of a proton from an adjacent carbon, leading to the formation of an alkene.

Example: When 2-methylpropan-2-ol undergoes dehydration, the mechanism follows the E1 pathway:

(CH3)3COH→(CH3)2C++H2O→(CH3)2C=CH2(CH_3)_3COH \rightarrow (CH_3)_2C^+ + H_2O \rightarrow (CH_3)_2C = CH_2
  • E2 Mechanism: The E2 mechanism is a single-step process where the base abstracts a proton from the β-carbon while the leaving group (water) leaves simultaneously.

Factors Affecting Rate of Dehydration:

  1. Temperature: Higher temperature favors dehydration as it provides sufficient energy to break the bonds.
  2. Concentration of Acid: The presence of concentrated sulfuric acid speeds up the formation of the carbocation.
  3. Nature of Alcohol: Tertiary alcohols undergo dehydration more easily than primary alcohols due to the stability of the tertiary carbocation.
  4. Solvent: Protic solvents like water or alcohols favor the E1 mechanism, while aprotic solvents promote the E2 mechanism.

2. Discuss the effect of steric hindrance on the nucleophilic substitution reaction of alcohols.

Answer: The nucleophilic substitution of alcohols involves the replacement of the hydroxyl group (-OH) with a nucleophile. This reaction can occur via two mechanisms:

  • SN1 Mechanism: Involves the formation of a carbocation intermediate.
  • SN2 Mechanism: Involves a direct displacement of the leaving group by the nucleophile.

Steric Hindrance affects the mechanism and rate of reaction in the following ways:

  • In SN1 reactions, the formation of the carbocation intermediate is critical. Therefore, the steric hindrance at the carbon attached to the hydroxyl group affects the rate. Tertiary alcohols are more likely to undergo SN1 reactions due to the stability of the tertiary carbocation, while primary alcohols undergo SN2 reactions.
  • In SN2 reactions, steric hindrance plays a significant role. The nucleophile attacks the carbon atom directly, so bulky groups around the carbon will hinder the approach of the nucleophile, thus slowing the reaction. Secondary alcohols tend to undergo SN2 reactions more readily compared to primary alcohols because of the increased steric hindrance from surrounding groups.

3. Explain the difference in acidic strength between alcohols and phenols with suitable examples.

Answer: Alcohols and phenols differ significantly in their acidity. This difference is due to the availability of lone pairs on oxygen and the ability to stabilize the negative charge on the conjugate base after deprotonation.

  • Alcohols: Alcohols have the general formula R-OH. The oxygen in alcohols can form hydrogen bonds with water, but the negative charge on the oxygen after deprotonation is not stabilized. Therefore, alcohols are weak acids. For example, ethanol (C₂H₅OH) has a pKₐ around 16.
  • Phenols: Phenols have the general formula C₆H₅OH. The negative charge on the oxygen after deprotonation is stabilized through resonance, as the negative charge can delocalize into the aromatic ring. This makes phenols significantly stronger acids than alcohols. For example, phenol (C₆H₅OH) has a pKₐ around 9.

Example: In the reaction of phenol and alcohol with sodium, phenol reacts more readily because it dissociates more easily into phenoxide ions (C₆H₅O⁻), while alcohols are much weaker acids.

4. What is the mechanism of reaction of alcohols with sodium? Discuss the formation of alkoxide ions.

Answer: The reaction of alcohols with sodium is a typical redox reaction where sodium metal reacts with alcohol to produce hydrogen gas and alkoxide ions. The mechanism involves the following steps:

  • Step 1: Sodium (Na) donates an electron to the oxygen atom of the alcohol, which leads to the breaking of the O-H bond. This results in the formation of an alkoxide ion (R-O⁻) and hydrogen gas (H₂).
  • Step 2: The alkoxide ion formed is a strong base and can participate in various nucleophilic reactions.

Example: When ethanol (C₂H₅OH) reacts with sodium, the reaction proceeds as:

2C2H5OH+2Na→2C2H5O−+H22C_2H_5OH + 2Na \rightarrow 2C_2H_5O^- + H_2

The sodium metal donates electrons, breaking the O-H bond in ethanol, leading to the formation of ethanol alkoxide (C₂H₅O⁻) and hydrogen gas.

Critical Thinking: The reactivity of alcohols with sodium varies with the structure of the alcohol. Primary alcohols react more readily compared to tertiary alcohols because of the steric effects that hinder the approach of sodium to the hydroxyl group in tertiary alcohols.

5. Discuss the method of preparation of ethers from alcohols. Explain the mechanism involved in the reaction of alcohols with an acid catalyst.

Answer: Ethers are prepared from alcohols through two main methods:

  • Williamson Synthesis: This method involves the reaction of an alkoxide ion with a primary alkyl halide.
  • Acid-Catalyzed Dehydration of Alcohols: This method involves the dehydration of alcohols in the presence of an acid catalyst, usually sulfuric acid.

Mechanism of Dehydration of Alcohols: The mechanism follows a two-step process:

  • Step 1: The alcohol is protonated by the acid catalyst, forming an oxonium ion (R-OH₂⁺). This makes the oxygen a better leaving group.
  • Step 2: A second alcohol molecule attacks the carbon center of the oxonium ion via an SN2 mechanism, leading to the formation of an ether.

Example: When ethanol reacts with sulfuric acid at high temperatures, it forms diethyl ether:

C2H5OH→H2SO4,ΔC2H5−O−C2H5+H2OC_2H_5OH \xrightarrow{H_2SO_4, \Delta} C_2H_5-O-C_2H_5 + H_2O

Critical Thinking: The reaction temperature is crucial for this process. At lower temperatures (140°C), an ether is formed, but at higher temperatures (180°C), the reaction may proceed to give alkenes due to further dehydration of the alcohol.

6. Explain the reaction of phenols with bromine water. How does the substitution pattern differ for phenols and alcohols?

Answer: When phenols react with bromine water, they undergo an electrophilic aromatic substitution reaction. The hydroxyl group on phenol is an activating group, which makes the aromatic ring more reactive towards electrophiles like Br₂.

Reaction of Phenol with Bromine:

  • The hydroxyl group (-OH) on the phenol donates electron density to the aromatic ring, increasing its electron density and making it more susceptible to attack by electrophiles.
  • The reaction with bromine water leads to the substitution of bromine at the ortho and para positions relative to the hydroxyl group. This results in the formation of 2,4,6-tribromophenol (white precipitate).
C6H5OH+Br2→C6H2Br3OHC_6H_5OH + Br_2 \rightarrow C_6H_2Br_3OH

Substitution Pattern: The substitution pattern in phenols is mainly ortho-para due to the resonance donation of electron density from the hydroxyl group to the ring, activating the ortho and para positions.

In contrast, alcohols generally do not undergo such substitution reactions with bromine, as the hydroxyl group is less activating and does not stabilize the intermediate carbocation formed during electrophilic substitution.

7. Describe the reaction of phenol with an alkali. What is the reason behind the difference in the acidity of phenol and alcohol?

Answer: Phenol reacts with sodium hydroxide (NaOH) to form phenoxide ions (C₆H₅O⁻) and sodium phenoxide (C₆H₅O-Na⁺). The reaction can be represented as:

C6H5OH+NaOH→C6H5O−Na++H2OC_6H_5OH + NaOH \rightarrow C_6H_5O^-Na^+ + H_2O

The phenoxide ion is a resonance-stabilized structure, making phenol more acidic than alcohols.

Reason for Difference in Acidity:

  • Phenol: The negative charge on the conjugate base (phenoxide ion) is delocalized onto the aromatic ring through resonance, stabilizing the phenoxide ion and making phenol a stronger acid.
  • Alcohol: In alcohols, the negative charge on the oxygen after deprotonation is localized on the oxygen atom, making the conjugate base less stable and alcohols weaker acids than phenol.

8. Discuss the properties of ethers, particularly their solubility in water, and compare them with alcohols.

Answer: Ethers have the general formula R-O-R’. They are polar molecules due to the presence of an oxygen atom, but they do not have the ability to form hydrogen bonds with each other like alcohols.

  • Solubility in Water: Ethers can form hydrogen bonds with water molecules, but not with each other. They are slightly soluble in water, especially when the alkyl groups are small. For example, dimethyl ether (CH₃-O-CH₃) is moderately soluble in water, while larger ethers like diethyl ether are less soluble.
  • Comparison with Alcohols: Alcohols, on the other hand, can form hydrogen bonds both with themselves and with water, making them much more soluble in water compared to ethers. For example, ethanol (C₂H₅OH) is highly soluble in water, while diethyl ether (C₂H₅-O-C₂H₅) is less soluble.

Critical Thinking: The higher solubility of alcohols is due to their ability to both donate and accept hydrogen bonds, whereas ethers can only accept hydrogen bonds, making them less soluble in water.

9. How does the reaction of alcohols with hydrogen halides differ for primary, secondary, and tertiary alcohols?

Answer: The reaction of alcohols with hydrogen halides (HX, where X = Cl, Br, or I) involves the nucleophilic substitution of the hydroxyl group (-OH) with the halide ion (X⁻), forming alkyl halides. The mechanism differs based on the type of alcohol.

  • Primary Alcohols: Primary alcohols react slowly with hydrogen halides due to the formation of a less stable primary carbocation. The reaction typically follows the SN2 mechanism.
  • Secondary Alcohols: Secondary alcohols form a more stable carbocation than primary alcohols, making the reaction faster and allowing it to follow either the SN1 or SN2 mechanism.
  • Tertiary Alcohols: Tertiary alcohols form the most stable carbocations and react the fastest with hydrogen halides. The reaction typically follows the SN1 mechanism, where the leaving group departs first, and then the halide ion attacks the carbocation.

10. What is the significance of the Lucas test in distinguishing between alcohols? Explain the mechanism involved.

Answer: The Lucas test is a qualitative test used to distinguish between primary, secondary, and tertiary alcohols. The test involves the reaction of alcohols with Lucas reagent (a mixture of concentrated hydrochloric acid and zinc chloride) and observing the rate of reaction.

  • Primary Alcohols: React very slowly or not at all, as they form a primary carbocation that is unstable.
  • Secondary Alcohols: React moderately, forming a more stable secondary carbocation.
  • Tertiary Alcohols: React almost instantly, as they form the most stable tertiary carbocation.

Mechanism:

  • The alcohol is protonated in the presence of HCl, making the hydroxyl group a better leaving group.
  • The alcohol then undergoes either an SN1 or SN2 mechanism, depending on its structure.

11. Explain the concept of alkoxide formation and its significance in organic reactions. How does it affect the reactivity of alcohols?

Answer: An alkoxide ion (R-O⁻) is formed when an alcohol (R-OH) reacts with a strong base (such as sodium or potassium metal) or another base like sodium hydroxide. The reaction proceeds as follows:

R−OH+Na→R−O−+Na++H2R-OH + Na \rightarrow R-O^- + Na^+ + H_2

Significance: Alkoxide ions are highly reactive because they are strong bases. They can:

  1. Participate in nucleophilic substitution reactions.
  2. Attack electrophilic centers, leading to the formation of new carbon-carbon or carbon-heteroatom bonds.

Effect on Reactivity: The formation of alkoxides increases the reactivity of alcohols in organic reactions. Alkoxides are more nucleophilic than alcohols because the negative charge on the oxygen is localized, making it easier for the alkoxide to attack electrophiles.

12. Explain how ethers are classified based on their structure and provide examples.

Answer: Ethers are classified based on the structure of their alkyl groups:

  • Simple Ethers: Both alkyl groups attached to the oxygen atom are the same. Example: Dimethyl ether (CH₃-O-CH₃).
  • Mixed Ethers: The alkyl groups attached to the oxygen atom are different. Example: Ethyl methyl ether (C₂H₅-O-CH₃).
  • Cyclic Ethers: Ethers that form part of a ring structure. Example: Tetrahydrofuran (THF), where the oxygen atom is part of a four-membered ring.

Critical Thinking: The classification of ethers is significant as it determines their physical and chemical properties, such as boiling points, solubility, and reactivity. Simple ethers typically have lower boiling points than alcohols of comparable molecular weight due to the absence of hydrogen bonding.

13. Explain the mechanism of dehydration of alcohols to form alkenes.

Answer: The dehydration of alcohols to form alkenes typically occurs in the presence of an acid, such as concentrated sulfuric acid (H₂SO₄) or phosphoric acid (H₃PO₄), under heat. The mechanism follows the E1 or E2 pathway, depending on the type of alcohol.

  • Primary Alcohols: These usually follow the E2 mechanism, where the proton is abstracted from the β-carbon (the carbon adjacent to the one bearing the hydroxyl group) and the leaving group (OH⁻) departs simultaneously, leading to the formation of the alkene.
  • Secondary and Tertiary Alcohols: These alcohols typically undergo the E1 mechanism. The reaction starts with the protonation of the alcohol, forming a good leaving group (water). After the departure of water, a carbocation is formed, which is then dehydrogenated to form the alkene.

Example: For ethanol (CH₃CH₂OH), when treated with concentrated H₂SO₄ and heated, it undergoes dehydration to form ethene (CH₂=CH₂):

CH3CH2OH→H2SO4,ΔCH2=CH2+H2OCH₃CH₂OH \xrightarrow{H_2SO_4, \Delta} CH₂=CH₂ + H₂O

14. Describe the reaction of alcohols with carboxylic acids to form esters.

Answer: The reaction of alcohols with carboxylic acids is known as esterification. It is a nucleophilic acyl substitution reaction where the hydroxyl group (-OH) of the carboxylic acid is replaced by the alkoxy group (-OR) of the alcohol.

The general reaction is:

R−OH+R′COOH→acid catalystR′COOR+H2OR-OH + R'COOH \xrightarrow{\text{acid catalyst}} R'COOR + H₂O

In this reaction, an ester (R'COOR) and water (H₂O) are formed.

Mechanism:

  • The carboxyl group (-COOH) is protonated in the presence of an acid catalyst, increasing its electrophilicity.
  • The alcohol (R-OH) acts as a nucleophile and attacks the carbonyl carbon of the carboxylic acid, forming a tetrahedral intermediate.
  • The intermediate collapses, releasing water and forming the ester.

Example: The reaction between ethanol (CH₃CH₂OH) and acetic acid (CH₃COOH) in the presence of a catalyst (such as sulfuric acid) forms ethyl acetate (CH₃COOCH₂CH₃) and water.

15. Discuss the oxidative reactions of alcohols and the products formed.

Answer: Alcohols undergo oxidation to form aldehydes, ketones, or carboxylic acids, depending on the type of alcohol and the conditions.

  • Primary Alcohols: Upon oxidation, primary alcohols first form aldehydes and can be further oxidized to carboxylic acids.

    R-CH₂OH→[O]R-CHO→[O]R-COOH\text{R-CH₂OH} \xrightarrow{[O]} \text{R-CHO} \xrightarrow{[O]} \text{R-COOH}

    Example: Ethanol (CH₃CH₂OH) is oxidized to acetaldehyde (CH₃CHO), which can further oxidize to acetic acid (CH₃COOH).

  • Secondary Alcohols: Secondary alcohols are oxidized to ketones, which cannot be further oxidized under mild conditions.

    R-CHOH-R’→[O]R-CO-R’\text{R-CHOH-R'} \xrightarrow{[O]} \text{R-CO-R'}

    Example: Isopropyl alcohol (CH₃CH(OH)CH₃) is oxidized to acetone (CH₃COCH₃).

  • Tertiary Alcohols: Tertiary alcohols do not undergo oxidation under normal conditions because they lack a hydrogen atom attached to the carbon bearing the hydroxyl group.

16. Explain the formation and properties of phenols. How do phenols react with bases?

Answer: Phenols are a class of compounds in which a hydroxyl group (-OH) is directly attached to an aromatic ring. The simplest phenol is hydroxybenzene (C₆H₅OH), also known as phenol.

Properties:

  • Acidity: Phenols are more acidic than alcohols because the negative charge on the phenoxide ion (C₆H₅O⁻) is stabilized by resonance with the aromatic ring.
  • Solubility: Phenols are moderately soluble in water due to hydrogen bonding with water molecules, but less soluble than alcohols.

Reaction with Bases: Phenols react with strong bases like sodium hydroxide (NaOH) to form phenoxide ions (C₆H₅O⁻) and water:

C6H5OH+NaOH→C6H5O−Na++H2OC₆H₅OH + NaOH \rightarrow C₆H₅O⁻Na⁺ + H₂O

The phenoxide ion is resonance-stabilized, which makes phenol a stronger acid than alcohols.

17. Discuss the properties and applications of alcohols in the pharmaceutical and industrial fields.

Answer: Alcohols have a wide range of properties that make them useful in pharmaceuticals and industrial applications.

  • Pharmaceutical Applications:

    1. Disinfectants and Antiseptics: Ethanol and isopropyl alcohol are commonly used as disinfectants and antiseptics due to their ability to kill bacteria, viruses, and fungi.
    2. Solvents: Alcohols are used as solvents for extracting medicinal compounds, preparing tinctures, and making liquid medications.
    3. Preservatives: Alcohols are used in some pharmaceutical preparations to preserve drugs and prevent microbial growth.

  • Industrial Applications:

    1. Solvents: Alcohols, particularly ethanol, are used as solvents in the production of paints, varnishes, and coatings.
    2. Fuel: Ethanol is used as a renewable fuel source and is blended with gasoline to reduce dependence on fossil fuels.
    3. Polymer Production: Alcohols are used in the synthesis of plastics, resins, and other polymer materials.

Critical Thinking: The versatility of alcohols in both industrial and pharmaceutical sectors is due to their solubility in water, ability to form hydrogen bonds, and the ease with which they can undergo various chemical reactions.

18. What are the environmental impacts of alcohols, especially ethanol, as a biofuel?

Answer: The use of ethanol as a biofuel has both positive and negative environmental impacts:

Positive Impacts:

  • Renewable Source: Ethanol is produced from biomass such as corn, sugarcane, or agricultural waste, making it a renewable energy source.
  • Reduced Greenhouse Gas Emissions: When ethanol is burned as a fuel, it produces fewer greenhouse gases (GHGs) compared to gasoline. It also absorbs CO₂ during its production, which can help offset some of the emissions.
  • Energy Independence: The production of ethanol can help reduce reliance on imported oil, contributing to energy security.

Negative Impacts:

  • Land Use: Large-scale ethanol production requires significant agricultural land, which may compete with food production, leading to higher food prices and land-use changes.
  • Water Consumption: The production of ethanol is water-intensive, which can strain water resources in areas where water scarcity is a concern.
  • Energy Efficiency: The energy required to produce ethanol (including farming, processing, and transportation) can sometimes exceed the energy it provides, reducing its overall environmental benefit.

Conclusion: While ethanol offers a cleaner alternative to fossil fuels in terms of emissions, it is not without environmental challenges. Careful management of its production processes is necessary to maximize its benefits and minimize its drawbacks.

19. How can ethers be synthesized using alcohols? Describe the mechanism.

Answer: Ethers can be synthesized from alcohols through a reaction known as the Williamson Ether Synthesis. This reaction involves the nucleophilic substitution of an alkoxide ion (RO⁻) on an alkyl halide (R'X) to form an ether (R-O-R').

The general reaction is:

R−OH+R′X→BaseR−O−R′+HXR-OH + R'X \xrightarrow{\text{Base}} R-O-R' + HX

The mechanism proceeds through the following steps:

  1. Deprotonation: The alcohol (R-OH) is first deprotonated by a strong base like NaH or NaOEt to form an alkoxide ion (RO⁻).
  2. Nucleophilic Attack: The alkoxide ion (RO⁻) then attacks the alkyl halide (R'X) in a nucleophilic substitution reaction (SN2 mechanism) to form the ether and release HX.

Example: The reaction between ethanol (CH₃CH₂OH) and sodium (Na) will form sodium ethoxide (CH₃CH₂O⁻) and hydrogen gas. When this sodium ethoxide is treated with methyl iodide (CH₃I), it forms methyl ethyl ether (CH₃OCH₂CH₃).

20. What is the difference between the structure and reactivity of alcohols and phenols?

Answer: Alcohols and phenols are both compounds containing hydroxyl groups (-OH), but they differ significantly in structure and reactivity:

  • Structure:

    • Alcohols: Alcohols contain a hydroxyl group (-OH) attached to a saturated carbon atom (sp³ hybridized carbon).
    • Phenols: In phenols, the hydroxyl group (-OH) is attached to a benzene ring (an unsaturated sp² hybridized carbon).

  • Reactivity:

    • Alcohols: Alcohols are generally less reactive due to the electron-donating effect of the alkyl group, which stabilizes the alcohol. Alcohols can undergo reactions like oxidation, esterification, and dehydration.
    • Phenols: Phenols are more reactive than alcohols due to the electron-withdrawing nature of the aromatic ring, which makes the hydroxyl group more acidic. Phenols can easily undergo electrophilic substitution reactions (like halogenation, nitration, and sulfonation), and they are more acidic than alcohols.

Conclusion: The difference in structure, especially the attachment of the hydroxyl group, influences the reactivity of alcohols and phenols, making phenols generally more reactive and acidic than alcohols.

21. What is the significance of the Lucas test for alcohols?

Answer: The Lucas test is used to differentiate between primary, secondary, and tertiary alcohols based on their reactivity with Lucas reagent, a solution of anhydrous zinc chloride (ZnCl₂) in concentrated hydrochloric acid (HCl).

The test relies on the fact that tertiary alcohols react very quickly with the Lucas reagent, while primary alcohols react very slowly or not at all. Secondary alcohols show an intermediate rate of reaction.

  • Tertiary alcohols (e.g., tert-butyl alcohol) react almost immediately, forming a cloudy solution or a layer of alkyl chloride.
  • Secondary alcohols (e.g., isopropyl alcohol) react in a few minutes.
  • Primary alcohols (e.g., ethanol) react slowly or not at all.

Mechanism:

  1. The alcohol is protonated by HCl, forming a good leaving group (water).
  2. The resulting carbocation intermediate undergoes nucleophilic substitution with chloride ions (Cl⁻) to form the alkyl chloride.

The Lucas test is primarily used to differentiate alcohols based on their structure and is an effective method to determine the classification of alcohols.

22. Explain the concept of the acidity of phenols. How does it compare with alcohols?

Answer: The acidity of phenols is due to the ability of the phenoxide ion (C₆H₅O⁻) to stabilize the negative charge on the oxygen atom through resonance with the benzene ring. This resonance delocalizes the negative charge, making phenols more acidic than alcohols, where no such resonance stabilization occurs.

  • Phenols: The proton from the hydroxyl group is more easily dissociated due to the resonance stabilization of the phenoxide ion (C₆H₅O⁻). As a result, phenols have a lower pKa (~9), indicating higher acidity compared to alcohols.
  • Alcohols: Alcohols, having an alkyl group attached to the oxygen, do not benefit from resonance stabilization, and thus their conjugate base (alkoxide ion, RO⁻) is less stable. Consequently, alcohols are less acidic with a pKa around 16-18.

Comparison:

  • Phenols are significantly more acidic than alcohols due to the resonance stabilization of the phenoxide ion. The electron-donating alkyl group in alcohols further reduces their acidity.

23. Explain the reaction of alcohols with zinc to form alkyl zinc compounds.

Answer: Alcohols react with zinc metal to form alkyl zinc compounds and hydrogen gas. This reaction is typically observed with primary and secondary alcohols.

The general reaction is:

R−OH+Zn→R−Zn+H2R-OH + Zn \rightarrow R-Zn + H_2

The mechanism involves the reduction of alcohol by zinc. Zinc acts as a reducing agent and removes the hydrogen from the hydroxyl group, leading to the formation of an alkyl zinc compound (R-Zn) and the evolution of hydrogen gas.

Example: When ethanol (CH₃CH₂OH) is treated with zinc, ethyl zinc (CH₃CH₂Zn) and hydrogen gas are produced:

CH3CH2OH+Zn→CH3CH2Zn+H2CH₃CH₂OH + Zn \rightarrow CH₃CH₂Zn + H_2

This reaction is an example of a redox reaction, where zinc reduces the alcohol.

24. What are the uses and applications of phenols in the chemical industry?

Answer: Phenols are widely used in the chemical industry due to their ability to undergo a variety of chemical reactions. Some of the major applications of phenols include:

  1. Production of Plastics: Phenol is used as a raw material for the production of phenolic resins (e.g., Bakelite), which are used in the manufacture of electrical insulators, automotive parts, and kitchenware.
  2. Antiseptics and Disinfectants: Phenols like carbolic acid (C₆H₅OH) were historically used as antiseptics. They are still used in some disinfectant products.
  3. Pharmaceuticals: Phenolic compounds are used in the synthesis of various drugs, such as aspirin (acetylsalicylic acid).
  4. Pesticides and Herbicides: Phenol derivatives are used in the production of certain pesticides and herbicides.
  5. Dyes: Phenols are used in the production of dyes and pigments, including some synthetic indigo dyes.

Conclusion: Phenols have a broad range of industrial applications, particularly in the production of polymers, pharmaceuticals, and as disinfectants.

25. Discuss the electrophilic aromatic substitution reactions of phenols and their mechanism.

Answer: Phenols undergo electrophilic aromatic substitution reactions more readily than benzene due to the electron-donating effect of the hydroxyl group (-OH), which increases the electron density on the benzene ring and makes it more reactive towards electrophiles.

Common electrophilic aromatic substitution reactions of phenols include:

  1. Halogenation: When phenol is treated with halogens like bromine (Br₂) or chlorine (Cl₂), the hydroxyl group activates the ring towards substitution, and the reaction typically leads to the formation of halogenated products.
  2. Nitration: Phenol reacts with concentrated nitric acid (HNO₃) to form nitrophenol, primarily at the ortho and para positions relative to the hydroxyl group.
  3. Sulfonation: Phenol reacts with fuming sulfuric acid (H₂SO₄) to form phenolsulfonic acid.

Mechanism:

  1. Activation of the Ring: The lone pair of electrons on the oxygen of the hydroxyl group donates electron density to the aromatic ring, making the ortho and para positions more electron-rich.
  2. Electrophilic Attack: An electrophile (such as Br⁺, NO₂⁺, or SO₃⁺) attacks the electron-rich positions on the ring.
  3. Product Formation: The substitution product is formed after the departure of a proton (H⁺).

Conclusion: The increased electron density on the aromatic ring due to the hydroxyl group makes phenols highly reactive in electrophilic aromatic substitution reactions.