Alcohols Phenols And Ethers Class 12 Chemistry Chapter 7 Notes

Alcohols Phenols and Ethers Class 12 Chemistry Chapter 7 Notes

Alcohols Phenols and Ethers

Alcohols, phenols, and ethers are important classes of organic compounds with diverse applications in various aspects of our daily lives and industry. Let’s briefly explore each of these classes:

1. Alcohols

Definition: Alcohols are organic compounds characterized by the presence of one or more hydroxyl (-OH) groups directly attached to carbon atoms in aliphatic hydrocarbon chains.
Applications:
- Ethanol (ethyl alcohol) is widely used as a solvent, antiseptic, disinfectant, and as an ingredient in alcoholic beverages.
- Methanol is used as an industrial solvent and as a fuel.
- Higher alcohols find applications in the production of perfumes, flavors, and cosmetics.
- Alcohols are also used as intermediates in the synthesis of various organic compounds, including pharmaceuticals and plastics.

2. Phenols

Definition: Phenols are aromatic compounds characterized by the presence of one or more hydroxyl (-OH) groups directly attached to carbon atoms in an aromatic ring, typically a benzene ring.
Applications:
- Phenol itself is used in the production of various chemicals, including plastics (e.g., Bakelite) and pharmaceuticals.
- Cresols, a type of phenol, are used in disinfectants and as intermediates in chemical synthesis.
- Phenolic resins are used as adhesives and in the manufacturing of composites and laminates.

3. Ethers

Definition: Ethers are organic compounds characterized by the presence of an oxygen atom (-O-) bonded to two alkyl or aryl groups (R-O-R’ or Ar-O-R’).
Applications:
- Dimethyl ether (DME) is used as a propellant in aerosol sprays, a refrigerant, and as a fuel in some applications.
- Diethyl ether, commonly known as “ether,” was historically used as a general anesthetic but has been largely replaced by safer anesthetics.
- Ethers can also serve as solvents in chemical reactions and extractions.

These classes of compounds have diverse chemical properties and reactivities, making them valuable in various industrial processes, pharmaceuticals, and everyday products. Understanding their chemistry is essential for the development of new materials and the improvement of existing ones.

Classification of Alcohols Phenols and Ethers

1. Alcohols – Mono, Di, Tri or Polyhydric Alcohols

The classification of alcohols based on the number of hydroxyl (-OH) groups and the hybridization of the carbon atom to which the hydroxyl group is attached is as follows:

Mono, Di, Tri, or Polyhydric Alcohols:

Monohydric Alcohols: Alcohols that contain one hydroxyl (-OH) group in their structure. Monohydric alcohols can be further classified based on the hybridization of the carbon atom to which the hydroxyl group is attached.a. Compounds containing C-OH – sp³ bond: In this class, the -OH group is attached to an sp³ hybridized carbon atom of an alkyl group. These are further categorized as:
- Primary Alcohols: When the -OH group is attached to a primary (1°) carbon atom, which is directly bonded to only one other carbon atom.
- Secondary Alcohols: When the -OH group is attached to a secondary (2°) carbon atom, which is directly bonded to two other carbon atoms.
- Tertiary Alcohols: When the -OH group is attached to a tertiary (3°) carbon atom, which is directly bonded to three other carbon atoms.
b. Allylic Alcohols: In these alcohols, the -OH group is attached to an sp³ hybridized carbon atom adjacent to a carbon-carbon double bond, known as an allylic carbon.c. Benzylic Alcohols: In these alcohols, the -OH group is attached to an sp³ hybridized carbon atom next to an aromatic ring, such as a benzene ring.
Dihydric Alcohols: Alcohols that contain two hydroxyl (-OH) groups in their structure.
Trihydric Alcohols: Alcohols that contain three hydroxyl (-OH) groups in their structure.
Polyhydric Alcohols: Alcohols that contain multiple (-OH) groups in their structure. Examples include glycols like ethylene glycol and glycerol.

Compounds containing C-OH – sp bond: These alcohols have the -OH group attached to a carbon-carbon double bond. They can be further classified based on the specific structure:

Vinylic Alcohol: This refers to an alcohol where the -OH group is attached to a vinylic carbon atom in a carbon-carbon double bond. The general structure is CH₂=CH-OH.

2. Phenols – Mono, Di or Trihydric Phenols

Phenols, which are aromatic compounds containing one or more hydroxyl (-OH) groups, can be classified as mono-, di-, or trihydric phenols based on the number of hydroxyl groups they contain:

Monohydric Phenols: These phenols contain a single hydroxyl (-OH) group in their structure. Monohydric phenols are also referred to as simple phenols. Examples of monohydric phenols include:
- Phenol (C₆H₅OH): The simplest monohydric phenol, commonly known as phenol, where one -OH group is attached to the benzene ring.
Dihydric Phenols: These phenols contain two hydroxyl (-OH) groups in their structure. They are also known as diphenols. Examples of dihydric phenols include:
- Resorcinol (C₆H₄(OH)₂): A dihydric phenol where two -OH groups are attached to adjacent carbon atoms on the benzene ring.
- Catechol (C₆H₄(OH)₂): Another dihydric phenol with two -OH groups, but the -OH groups are attached to non-adjacent carbon atoms on the benzene ring.
Trihydric Phenols: These phenols contain three hydroxyl (-OH) groups in their structure. They are also known as triphenols. An example of a trihydric phenol is:
- Phloroglucinol (C₆H₃(OH)₃): A trihydric phenol with three -OH groups attached to non-adjacent carbon atoms on the benzene ring.

Each of these classes of phenols has unique properties and chemical reactivity, making them important compounds in various applications, including pharmaceuticals, cosmetics, and industrial processes. The number and positions of hydroxyl groups on the benzene ring influence their properties and uses.

3. Ethers

Ethers, a class of organic compounds, can be classified as simple (symmetrical) or mixed (unsymmetrical) based on the nature of the alkyl or aryl groups attached to the oxygen atom:

Simple Ethers (Symmetrical Ethers): In simple ethers, both alkyl or aryl groups attached to the oxygen atom are the same. These ethers have a symmetric structure. An example of a simple ether is:
- Dimethyl Ether (CH₃OCH₃): In this compound, both alkyl groups are methyl (-CH₃) groups. It is a symmetrical ether.
Mixed Ethers (Unsymmetrical Ethers): Mixed ethers have different alkyl or aryl groups attached to the oxygen atom. These ethers have an unsymmetrical structure. Examples of mixed ethers include:
- Ethyl Methyl Ether (CH₃OC₂H₅): In this compound, one alkyl group is ethyl (-C₂H₅), and the other is methyl (-CH₃). It is an unsymmetrical ether.
- Ethyl Phenyl Ether (C₆H₅OC₂H₅): In this compound, one group is an ethyl (-C₂H₅), and the other is a phenyl (-C₆H₅) group. It is also an unsymmetrical ether.

Ethers are known for their unique chemical properties and are commonly used as solvents in various applications, including laboratory work, pharmaceuticals, and chemical synthesis. The classification of ethers into simple and mixed categories helps describe their structural diversity and chemical reactivity.

Nomenclature Of Alcohols

Alcohols are a class of organic compounds containing the hydroxyl (-OH) functional group attached to a hydrocarbon chain. They can be named using both common names and IUPAC (International Union of Pure and Applied Chemistry) systematic names. Here’s how to name alcohols:

Common Names: Common names of alcohols are based on the alkyl group attached to the hydroxyl group, followed by the word “alcohol.” Here are some examples:

CH₃OH: Common name – Methyl alcohol
C₂H₅OH: Common name – Ethyl alcohol
(CH₃)₂CHOH: Common name – Isopropyl alcohol

IUPAC Systematic Names: For systematic IUPAC names of alcohols, follow these rules:

Identify the Longest Carbon Chain (Parent Chain): Determine the longest continuous chain of carbon atoms that contains the hydroxyl group (-OH). This is your parent chain.
Number the Chain: Start numbering the carbon chain from the end closest to the hydroxyl group. The carbon atom where the -OH group is attached is given the lowest possible number.
Suffix for Alcohols: Replace the “-e” ending of the alkane name with “-ol.” This indicates that you are dealing with an alcohol. The position of the -OH group is indicated by the number.
Locants for Substituents: If there are other substituents on the carbon chain, assign numbers to them based on their positions. Use hyphens to separate numbers and commas to separate multiple substituents.
Use Multiplicative Prefixes: If the alcohol contains more than one hydroxyl group (-OH), use multiplicative prefixes such as “di” for two, “tri” for three, and so on, before the “-ol” suffix. Include the positions of each -OH group.
Cyclic Alcohols: If the alcohol is cyclic, use the prefix “cyclo” and number the carbons in the ring, starting with the carbon bearing the -OH group.

Here are some examples of IUPAC names for alcohols:

CH₃OH: IUPAC name – Methanol (It’s the simplest alcohol)
C₂H₅OH: IUPAC name – Ethanol
CH₃CH₂CH₂OH: IUPAC name – 1-Propanol (The -OH group is on carbon 1)
CH₃CH(OH)CH₃: IUPAC name – 2-Propanol (The -OH group is on carbon 2)
HOCH₂CH₂CH₂OH: IUPAC name – Ethane-1,2-diol (Diol indicates two -OH groups)
(CH₃)₂C(OH)CH₂CH₃: IUPAC name – 2-Methylpentan-2-ol (A branched chain alcohol)

These rules apply to both mono- and polyhydric alcohols. When naming alcohols systematically, prioritize indicating the positions of substituents and the hydroxyl group accurately.

Nomenclature Of Phenols

Phenols are a class of organic compounds containing a hydroxyl (-OH) group attached to a benzene ring. They can be named using both common names and IUPAC (International Union of Pure and Applied Chemistry) systematic names. Here’s how to name phenols:

Common Names: Common names of phenols are often based on their substituted benzene ring, with the positions of substituents indicated using the terms ortho (1,2-disubstituted), meta (1,3-disubstituted), and para (1,4-disubstituted). Here are some examples:

C₆H₅OH: Common name – Phenol (Simplest phenol)
C₆H₄(CH₃)OH: Common name – o-Cresol (Ortho-cresol)
C₆H₄(CH₃)OH: Common name – m-Cresol (Meta-cresol)
C₆H₄(CH₃)OH: Common name – p-Cresol (Para-cresol)

IUPAC Systematic Names: For systematic IUPAC names of phenols, follow these rules:

Identify the Benzene Ring: Locate the benzene ring in the structure.
Number the Ring: Start numbering the carbon atoms in the benzene ring, assigning the carbon bearing the hydroxyl group (-OH) as carbon 1.
Use Appropriate Substituent Prefixes: If there are substituents on the benzene ring, use the appropriate prefixes such as “methyl” or “chloro” to indicate them. Place these prefixes before the name of the benzene ring.
Indicate the Position of the -OH Group: Use the position number of the carbon to which the -OH group is attached as part of the name. If there are multiple substituents, number them accordingly.

Here are some examples of IUPAC names for phenols:

C₆H₅OH: IUPAC name – Phenol
C₆H₄(CH₃)OH: IUPAC name – 2-Methylphenol (Ortho-substituted)
C₆H₄(CH₃)OH: IUPAC name – 3-Methylphenol (Meta-substituted)
C₆H₄(CH₃)OH: IUPAC name – 4-Methylphenol (Para-substituted)

When naming phenols systematically, accurately indicate the positions of substituents and the hydroxyl group.

Nomenclature Of Ethers

Ethers are a class of organic compounds containing an oxygen atom bonded to two alkyl or aryl groups. They can be named using both common names and IUPAC (International Union of Pure and Applied Chemistry) systematic names. Here’s how to name ethers:

Common Names: Common names of ethers are based on the names of the alkyl or aryl groups bonded to the oxygen atom, with the word “ether” added at the end. If both alkyl groups are the same, the prefix “di” is added before the alkyl group. Here are some examples:

CH₃OC₂H₅: Common name – Methyl ethyl ether
C₂H₅OC₂H₅: Common name – Diethyl ether (when both alkyl groups are the same)

IUPAC Systematic Names: For systematic IUPAC names of ethers, follow these rules:

Identify the Alkyl/Aryl Groups: Determine the two alkyl or aryl groups bonded to the oxygen atom.
Choose the Parent Hydrocarbon: Select the larger of the two alkyl or aryl groups as the parent hydrocarbon.
Name the Parent Hydrocarbon: Name the parent hydrocarbon using standard IUPAC rules for naming alkanes or arenes, depending on whether it’s an alkyl or aryl group.
Use Appropriate Prefixes: Use prefixes such as “methyl,” “ethyl,” “propyl,” or “phenyl” to indicate the alkyl or aryl groups.
Indicate the Oxygen Atom: Use the word “oxy” to indicate the oxygen atom.
Combine the Names: Combine the names of the parent hydrocarbon and the alkyl or aryl group(s) bonded to the oxygen atom. Place the alkyl or aryl group(s) in alphabetical order.

Here are some examples of IUPAC names for ethers:

CH₃OC₂H₅: IUPAC name – Ethyl methyl ether
C₂H₅OC₂H₅: IUPAC name – Diethyl ether (when both alkyl groups are the same)
C₆H₅OCH₃: IUPAC name – Methoxybenzene (An aryl group is present)
C₆H₅OC₆H₅: IUPAC name – Diphenyl ether (Two aryl groups are present)

When naming ethers systematically, accurately indicate the alkyl or aryl groups and the position of the oxygen atom.

Structures of Functional Groups

The structural aspects of functional groups in alcohols, phenols, and ethers are as follows:

Alcohols: In alcohols, the oxygen of the -OH group is attached to carbon by a sigma (σ) bond formed by the overlap of a sp3 hybridized orbital of carbon with a sp3 hybridized orbital of oxygen. The bond angle in alcohols is slightly less than the tetrahedral angle (109°-28°). This deviation from the ideal tetrahedral angle is due to the repulsion between the unshared electron pairs of oxygen.

Phenols: In phenols, the -OH group is attached to sp2 hybridized carbon of an aromatic ring. The carbon-oxygen (C-O) bond length in phenol is shorter (about 136 pm) than that in alcohols. This shorter bond length is attributed to two factors:

Partial Double Bond Character: Phenol exhibits partial double bond character because of the conjugation of the unshared electron pair of oxygen with the aromatic ring.
sp2 Hybridization: The carbon to which oxygen is attached in phenol is sp2 hybridized, which results in shorter bond lengths compared to sp3 hybridization.

Ethers: In ethers, the oxygen atom is bonded to two alkyl or aryl groups. The four electron pairs around oxygen, including the two bond pairs and two lone pairs, are arranged approximately in a tetrahedral arrangement. The bond angle in ethers is slightly greater than the ideal tetrahedral angle due to repulsive interactions between the two bulky (-R) groups attached to oxygen.

The C-O bond length in ethers is about 141 pm, which is almost the same as in alcohols.

These structural aspects contribute to the chemical properties and reactivity of alcohols, phenols, and ethers in various chemical reactions.

Preparation of Alcohols

The preparation of alcohols can be achieved through various methods. Here are some common methods for preparing alcohols:

1. From Alkenes:

Acid-Catalyzed Hydration: Alkenes can react with water in the presence of an acid catalyst to form alcohols. The addition of water follows Markovnikov’s rule, where the hydrogen atom is added to the carbon atom with more hydrogen substituents.
Hydroboration-Oxidation: Alkenes react with diborane (BH3) followed by oxidation with hydrogen peroxide (H2O2) in the presence of aqueous sodium hydroxide (NaOH) to produce alcohols. Unlike acid-catalyzed hydration, this method follows an anti-Markovnikov addition, resulting in the formation of alcohols with the hydrogen atom attached to the carbon atom carrying fewer hydrogen substituents.

2. From Carbonyl Compounds:

Reduction of Aldehydes and Ketones: Aldehydes and ketones can be reduced to the corresponding alcohols by the addition of hydrogen gas (H2) in the presence of catalysts such as platinum, palladium, or nickel. Alternatively, they can be reduced using reducing agents like sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4). Aldehydes yield primary alcohols, while ketones yield secondary alcohols.
Reduction of Carboxylic Acids and Esters: Carboxylic acids can be reduced to primary alcohols using a strong reducing agent like lithium aluminum hydride (LiAlH4). Commercially, carboxylic acids are first converted into esters and then reduced to alcohols using hydrogen gas and a catalyst (catalytic hydrogenation).

3. From Grignard Reagents:

Alcohols can be produced by reacting Grignard reagents with aldehydes and ketones. The reaction involves the nucleophilic addition of the Grignard reagent to the carbonyl group, followed by hydrolysis to yield the alcohol.

The choice of method depends on the starting materials and the desired type of alcohol (primary, secondary, or tertiary). Each method has its advantages and is used in specific chemical syntheses.

Preparation of Phenols

Preparation of Phenols:

From Haloarenes:
- Chlorobenzene is heated with NaOH at 623K and 320 atmospheric pressure.
- Phenol is obtained by acidifying the sodium phenoxide formed.
From Benzenesulphonic Acid:
- Benzene is sulphonated with oleum (fuming sulfuric acid) to produce benzenesulphonic acid.
- This benzenesulphonic acid is then converted to sodium phenoxide by heating with molten sodium hydroxide.
- Phenol is obtained by acidifying the sodium salt.
From Diazonium Salts:
- A diazonium salt is formed by treating an aromatic primary amine with nitrous acid (NaNO2 + HCl) at 273-278 K.
- Diazonium salts are hydrolyzed to phenols by warming with water or by treating with dilute acids.
From Cumene:
- Phenol is manufactured from cumene (isopropylbenzene).
- Cumene is oxidized in the presence of air to form cumene hydroperoxide.
- Cumene hydroperoxide is then converted to phenol and acetone by treatment with dilute acid.
- Acetone is also obtained as a by-product.

Physical Properties

The properties of alcohols and phenols are primarily influenced by the hydroxyl (-OH) group they contain.

1. Boiling Points

The boiling points of alcohols and phenols are influenced by several factors, including molecular size, branching, and the presence of hydrogen bonding. Here’s a summary of how these factors affect boiling points:

1. Molecular Size: Generally, as the number of carbon atoms in the molecule increases, the boiling point also increases. This is because larger molecules have more electrons, leading to stronger van der Waals forces (London dispersion forces) between them. Alcohols and phenols follow this trend.

2. Branching: In alcohols, as the carbon chain becomes more branched, the boiling point decreases. This is because branching reduces the surface area for intermolecular interactions, resulting in weaker van der Waals forces. Consequently, less energy is required to overcome these forces, leading to a lower boiling point.

3. Hydrogen Bonding: Both alcohols and phenols can form hydrogen bonds due to the presence of the hydroxyl (-OH) group. Hydrogen bonds are stronger than van der Waals forces and require more energy to break. Therefore, compounds capable of forming hydrogen bonds tend to have higher boiling points.

4. Comparison to Other Compounds: Alcohols and phenols generally have higher boiling points than hydrocarbons (alkanes, alkenes, and alkynes), ethers, haloalkanes, and haloarenes of similar molecular masses. This is primarily due to the presence of hydrogen bonding in alcohols and phenols, which is absent or weaker in the other classes of compounds.

For example, ethanol (an alcohol) and propane (a hydrocarbon) have similar molecular masses, but ethanol has a higher boiling point due to the presence of hydrogen bonding in ethanol molecules.

2. Solubility

Solubility of alcohols and phenols in water is primarily attributed to their ability to form hydrogen bonds with water molecules. The presence of the hydroxyl (-OH) group in alcohols and phenols allows for hydrogen bonding interactions with water, which is a polar solvent. These hydrogen bonds significantly enhance the solubility of alcohols and phenols in water.

Here’s how solubility in water is affected by various factors:

Hydroxyl Group: The hydroxyl group (-OH) is polar and capable of forming hydrogen bonds with water molecules. This interaction promotes the solubility of alcohols and phenols in water.
Size of Alkyl/Aryl Groups: The size of the alkyl or aryl groups attached to the hydroxyl group can influence solubility. Smaller alkyl groups or aryl groups enhance solubility because they have less steric hindrance and allow for better interactions with water molecules. As the size of these groups increases, solubility decreases due to the hydrophobic (“water-fearing”) effect, which outweighs the hydrophilic (“water-loving”) effect of the hydroxyl group.
Hydrogen Bonding Capacity: Alcohols are more soluble in water than phenols because phenols have a hydrogen atom bonded to the benzene ring (the phenolic hydrogen), which can participate in intramolecular hydrogen bonding. This reduces the availability of the phenolic hydrogen for intermolecular hydrogen bonding with water, making phenols less soluble than alcohols of similar size.
Molecular Size: In general, lower molecular weight alcohols and phenols are more soluble in water than higher molecular weight ones. For example, methanol and ethanol are completely miscible with water because they are small molecules with strong hydrogen bonding capability.
Hydrogen Bonding with Water: The ability of alcohols and phenols to donate hydrogen bonds to water molecules and accept hydrogen bonds from water contributes to their solubility. This makes them particularly effective solvents for polar and ionic compounds.

As a result of these factors, lower molecular weight alcohols (e.g., methanol, ethanol) are highly soluble in water and can be mixed in all proportions. However, as the size of the alkyl or aryl groups increases or if phenolic hydrogen bonding is reduced (in phenols), solubility in water decreases.

3. State at Room Temperature

At room temperature (around 25°C or 77°F):

Lower-Molecular-Weight Alcohols: Lower-molecular-weight alcohols, such as methanol (CH3OH) and ethanol (C2H5OH), are typically colorless liquids. They have relatively low boiling points and are volatile, meaning they can easily evaporate into the air.
Higher-Molecular-Weight Alcohols: As the molecular weight of alcohols increases, they become less volatile and may exist as either liquids with higher viscosities or solids at room temperature. For example, n-butanol (C4H9OH) is a liquid at room temperature, while n-octanol (C8H17OH) is a higher-molecular-weight alcohol that is also a liquid. Alcohols with even higher molecular weights may be waxy solids at room temperature.
Phenols: Phenols, due to their aromatic nature, are often solids at room temperature. Phenol itself (C6H5OH) is a white crystalline solid at room temperature and has a distinctive odor. The aromatic ring structure contributes to the solid-state nature of phenols at room temperature.

It’s important to note that the physical state of alcohols and phenols at room temperature can vary depending on their molecular weight and structure. Lower-molecular-weight alcohols tend to be liquid, while higher-molecular-weight alcohols and phenols can be solids or more viscous liquids.

4. Odour

Alcohols: Alcohols, especially lower-molecular-weight ones, often have a characteristic “sweet” or “fruity” odor. For example, ethanol (the alcohol found in alcoholic beverages) has a slightly sweet odor. This odor can vary depending on the specific type of alcohol.
Phenols: Phenols are known for their distinct and often strong medicinal or disinfectant-like odor. Phenol itself has a pungent and somewhat medicinal smell. This characteristic odor can be attributed to the aromatic ring structure in phenols.

The odour of these compounds can be quite noticeable, and it’s often used as a distinguishing feature in various applications, including perfumery and the production of disinfectants and cleaning agents.

5. Color

Alcohols: Many alcohols, especially the lower-molecular-weight ones like methanol and ethanol, are typically colorless liquids. However, as the size and complexity of the alcohol molecule increase, they may become slightly colored or have a faint coloration.
Phenols: Phenols can vary in color. Some phenols are colorless, while others may have a faint coloration. The presence or absence of color in phenols can depend on the specific compound and its chemical structure.

So, color in these compounds can indeed vary, but many alcohols are indeed colorless, and phenols may exhibit a range of colors or be colorless depending on their individual characteristics.

6. Density

The density of alcohols and phenols can vary depending on the specific compound, but in general, they are close to the density of water, which is approximately 1 gram per milliliter (g/mL) at room temperature and standard pressure. Alcohols and phenols, being similar in molecular structure to water with the presence of polar hydroxyl (OH) groups, often have densities close to or slightly higher than that of water. However, the exact density can vary depending on factors such as the size and molecular weight of the molecule and any additional functional groups present.

7. Refractive Index

Both alcohols and phenols typically have refractive indices higher than that of water, which makes them useful in various optical applications. The refractive index is a measure of how much a substance can bend or refract light. Due to the presence of polar functional groups like the hydroxyl (OH) group in alcohols and phenols, these compounds interact differently with light compared to water, leading to higher refractive indices. This property is often exploited in industries like optics and cosmetics where these compounds are used in the formulation of various products.

Chemical Reactions

Alcohols and phenols indeed exhibit a wide range of chemical reactions due to the versatility of their functional groups. Here’s a brief overview of their reactivity:

Alcohols as Nucleophiles:

Substitution Reactions: Alcohols can undergo substitution reactions where the hydroxyl group (-OH) is replaced by another group. For example, they can react with hydrogen halides (HX) to form alkyl halides.
Reaction with Active Metals: Alkali metals like sodium (Na) can react with alcohols to produce hydrogen gas and alkoxide ions. This is often referred to as the “alcohol-metal reaction.”
Esterification: Alcohols can react with carboxylic acids in the presence of an acid catalyst to form esters and water in a reaction known as esterification.

Protonated Alcohols as Electrophiles: When alcohols are protonated (i.e., the oxygen atom is protonated, forming H2O as a leaving group), they can act as electrophiles. These protonated alcohols can react with nucleophiles to form new compounds.

Alcohols and Phenols Reactions Based on Cleavage of O–H and C–O Bonds: The chemical reactions of alcohols and phenols can be categorized based on whether the O–H or C–O bond is cleaved:

Reactions Involving Cleavage of O–H Bonds: These reactions typically lead to the formation of new compounds by breaking the O–H bond. Examples include the formation of alkyl halides (via substitution reactions) and esters (via esterification).
Reactions Involving Cleavage of C–O Bonds: In these reactions, the C–O bond within the alcohol or phenol molecule is broken. Protonated alcohols can act as electrophiles and react with nucleophiles, leading to the cleavage of the C–O bond.

(a) Reactions involving cleavage of O–H bond

The acidity of alcohols and phenols is a fundamental characteristic that arises from their ability to donate a proton (H+) to a base. Here’s a summary of their acidity:

Acidity of Alcohols:

Reaction with Metals: Alcohols react with active metals like sodium, potassium, and aluminum to form alkoxides and release hydrogen gas.Example: R-OH + Na → R-O^-Na^+ + 1/2 H₂
Comparison to Water: Alcohols are weaker acids than water. Water can donate a proton more readily than alcohols, as shown by the reaction of water with an alkoxide ion.Example: H₂O + RO^-Na^+ → ROH + NaOH
Influence of Substituents: The acidic strength of alcohols depends on the nature of the alkyl group attached. Electron-releasing groups (-CH₃, -C₂H₅) increase electron density on oxygen, decreasing the polarity of the O-H bond and reducing acidity. The order of acidity is usually:Methanol > Primary Alcohols > Secondary Alcohols > Tertiary Alcohols

Acidity of Phenols:

Stronger than Alcohols: Phenols are generally stronger acids than alcohols and water. They exhibit acidity due to the presence of the hydroxyl group directly attached to the sp² hybridized carbon of the benzene ring.
Effect of Resonance: Phenol’s acidity is enhanced by resonance structures that delocalize the negative charge. Phenoxide ion, the conjugate base of phenol, is stabilized by charge delocalization, making phenols more acidic.
Substituent Effects: The presence of electron-withdrawing groups (e.g., nitro group) at ortho and para positions increases the acidic strength of phenols by enhancing charge delocalization. Conversely, electron-releasing groups (e.g., alkyl groups) tend to decrease the acidity of phenols.

(b) Reactions involving cleavage of carbon – oxygen (C–O) bond in alcohols

Reactions involving the cleavage of the carbon-oxygen (C-O) bond in alcohols are essential chemical transformations. Here are the key reactions involving the cleavage of the C-O bond in alcohols:

1. Reaction with Hydrogen Halides:

Alcohols react with hydrogen halides (HCl, HBr, HI) to form alkyl halides and water.
The reactivity order among alcohols is based on the type of alcohol:
- Tertiary alcohols react fastest.
- Secondary alcohols react moderately.
- Primary alcohols react the slowest.

2. Reaction with Phosphorus Trihalides:

Alcohols can be converted to alkyl bromides by reacting with phosphorus tribromide (PBr₃).

3. Dehydration:

Alcohols undergo dehydration, a removal of a water molecule, to form alkenes.
Dehydration can be achieved using concentrated sulfuric acid (H₂SO₄), concentrated phosphoric acid (H₃PO₄), or catalysts like anhydrous zinc chloride or alumina.
The relative ease of dehydration follows this order: Tertiary > Secondary > Primary.

4. Oxidation:

Oxidation of alcohols leads to the formation of a carbon-oxygen double bond (C=O) and involves cleavage of the O-H and C-H bonds.
Depending on the oxidizing agent used, primary alcohols can be oxidized to aldehydes (which can further be oxidized to carboxylic acids) or directly to carboxylic acids.
Secondary alcohols are oxidized to ketones.
Tertiary alcohols generally do not undergo oxidation reactions.

5. Dehydrogenation:

When the vapors of a primary or secondary alcohol are passed over heated copper (Cu) at 573 K, dehydrogenation takes place.
This leads to the formation of an aldehyde or a ketone.

These reactions provide a range of products depending on the type of alcohol and the conditions used. They are fundamental transformations in organic chemistry and have various applications in synthesis and industry.

(c) Reactions of phenols

The chemical reactions of phenols, particularly in the aromatic ring, are primarily electrophilic substitution reactions due to the presence of the -OH group on the benzene ring. This -OH group activates the ring towards electrophilic substitution and directs incoming groups to the ortho and para positions through resonance effects. Here are some common electrophilic aromatic substitution reactions involving phenols:

1. Nitration:

Phenol reacts with dilute nitric acid at low temperature (298 K) to yield a mixture of ortho and para nitrophenols.
Concentrated nitric acid can convert phenol to 2,4,6-trinitrophenol, commonly known as picric acid.

2. Halogenation:

Phenol can undergo halogenation to form monobromophenols under certain conditions. The presence of the -OH group makes this reaction more favorable.
When phenol is treated with bromine water, it forms 2,4,6-tribromophenol as a white precipitate.

3. Kolbe’s Reaction:

Phenoxide ion, generated by treating phenol with sodium hydroxide, is highly reactive towards electrophilic aromatic substitution. It reacts with carbon dioxide to produce ortho-hydroxybenzoic acid.

4. Reimer-Tiemann Reaction:

Phenol treated with chloroform in the presence of sodium hydroxide undergoes the Reimer-Tiemann reaction, introducing a -CHO group at the ortho position of the benzene ring, leading to the formation of salicylaldehyde.

5. Reaction with Zinc Dust:

Phenol can be converted to benzene by heating it with zinc dust.

6. Oxidation:

Oxidation of phenol with chromic acid yields benzoquinone, a conjugated diketone.
In the presence of air, phenols are slowly oxidized to form dark-colored mixtures containing quinones.

These reactions demonstrate the versatility of phenols in electrophilic aromatic substitution reactions and their susceptibility to various chemical transformations, making them valuable compounds in organic synthesis.

Some Commercially Important Alcohols

Methanol and ethanol are two commercially important alcohols. Here’s some information about them:

1. Methanol (CH3OH):

Methanol is commonly known as ‘wood spirit.’
Historically, it was produced by the destructive distillation of wood.
Today, most methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature in the presence of a ZnO – Cr2O3 catalyst.
Methanol is a colorless liquid with a boiling point of 337 K.
It is highly poisonous and even small quantities of ingested methanol can lead to blindness, while larger quantities can be fatal.
Methanol is used as a solvent in paints and varnishes and is primarily used in the production of formaldehyde.

2. Ethanol (C2H5OH):

Ethanol is obtained commercially by fermentation, which is the oldest method for its production. It is derived from sugars.
Sugars in sources like molasses, sugarcane, or fruits are converted to glucose and fructose with the help of the enzyme invertase.
Glucose and fructose are then fermented in the presence of the enzyme zymase, which is found in yeast.
Ethanol fermentation is used in processes like wine-making, where grapes are the source of sugars.
Fermentation takes place in anaerobic conditions (without air), and carbon dioxide is released during the process.
The action of zymase is inhibited when the alcohol content exceeds 14 percent. If air gets into the fermentation mixture, oxygen from the air can oxidize ethanol to ethanoic acid, which negatively affects the taste of alcoholic drinks.
Ethanol is a colorless liquid with a boiling point of 351 K.
It is used as a solvent in the paint industry and in the preparation of various carbon compounds.
Commercial alcohol is often denatured to make it unfit for drinking. This is done by adding substances like copper sulfate (to give it color) and pyridine (a foul-smelling liquid) to discourage consumption.
Nowadays, large quantities of ethanol are obtained by the hydration of ethene.

Both methanol and ethanol serve important industrial and commercial purposes, but it’s essential to handle them with care, especially due to the toxic nature of methanol and the potential health risks associated with ethanol consumption.

Preparation of Ethers

The preparation of ethers can be achieved through various methods, including:

1. Dehydration of Alcohols:

Alcohols can undergo dehydration in the presence of protic acids such as H2SO4 or H3PO4.
The formation of either an alkene or an ether depends on the reaction conditions. For example, ethanol can be dehydrated to form either ethene or ethoxyethane.
The formation of an ether in this process involves a nucleophilic bimolecular reaction (SN2), where the alcohol molecule attacks a protonated alcohol. This can be represented as follows:

R-OH + R’-OH → R-O-R’ + H2O

This method is suitable for the preparation of ethers with primary alkyl groups, and the alkyl group should be unhindered. Lower temperatures are favored to prevent the formation of alkenes.
Dehydration of secondary and tertiary alcohols to form ethers is generally unsuccessful because elimination reactions (formation of alkenes) often compete with substitution reactions.

Regarding ethyl methyl ether:

The bimolecular dehydration method may not be appropriate for the preparation of ethyl methyl ether because the reaction would involve the attack of a methyl alcohol molecule on a protonated methyl alcohol. This leads to the same molecule, which means no new compound (ether) would be formed.

2. Williamson Synthesis:

Williamson synthesis is a laboratory method used for the preparation of both symmetrical and unsymmetrical ethers.
In this method, an alkyl halide reacts with a sodium alkoxide (RONa).
The reaction is represented as follows: R–X + NaR’–O → R–O–R’ + NaX
It is suitable for the preparation of ethers containing primary alkyl groups, and it can also be used for secondary and tertiary alkyl halides, but in those cases, elimination reactions may compete with substitution reactions.
If a tertiary alkyl halide is used, it will exclusively form an alkene as the product.
Phenols can also be converted to ethers using this method, where phenol is used as the phenoxide moiety.

Physical Properties Of Ether

Ethers possess some distinctive physical properties due to the presence of polar C-O bonds, although they are less polar than alcohols. Here are some key physical properties of ethers:

Polarity and Dipole Moment: Ethers have polar C-O bonds, which result in a net dipole moment for the molecule. However, this dipole moment is generally weaker than in alcohols due to the lower electronegativity of carbon compared to oxygen.
Boiling Points: Ethers have boiling points that are comparable to those of alkanes with similar molecular masses. However, they have significantly lower boiling points compared to alcohols with similar molecular masses. This is because the relatively weaker dipole-dipole interactions in ethers do not significantly affect their boiling points, whereas alcohols have higher boiling points due to the presence of hydrogen bonding.
Comparison with Alkanes and Alcohols: For example, consider the boiling points of n-pentane (alkane), ethoxyethane (ether), and butan-1-ol (alcohol):
- n-Pentane: 309.1 K
- Ethoxyethane: 307.6 K
- Butan-1-ol: 390 K
The large difference in boiling points between butan-1-ol and ethoxyethane is primarily due to the presence of hydrogen bonding in butan-1-ol, which significantly raises its boiling point compared to the non-hydrogen bonding ether, ethoxyethane.
Miscibility with Water: Ethers exhibit miscibility with water similar to alcohols of the same molecular mass. Both ethoxyethane and butan-1-ol are miscible with water to a significant extent. This is because, like alcohols, the oxygen atom in ethers can form hydrogen bonds with water molecules. The ability to form hydrogen bonds allows ethers to mix well with water.

Regarding the observation that pentane is essentially immiscible with water, it’s because alkanes like pentane lack the polar oxygen atom and, therefore, cannot form hydrogen bonds with water. As a result, alkanes are generally immiscible or have limited miscibility with water.

Chemical Reactions Of Ether

Ethers are relatively unreactive compared to other functional groups. Their chemical reactions primarily involve the cleavage of the C-O bond in ethers under harsh conditions or electrophilic substitution reactions in the aromatic ring of aryl alkyl ethers (phenylalkyl ethers). Here are some important chemical reactions of ethers:

1. Cleavage of C-O Bond in Ethers:

Ethers can undergo cleavage of the C-O bond, but this typically requires drastic conditions and an excess of hydrogen halides (HCl, HBr, or HI).
When a dialkyl ether reacts with a hydrogen halide (H-X), it yields two alkyl halide molecules. The reaction is more favorable with concentrated HI or HBr at high temperatures.
Alkyl aryl ethers are cleaved at the alkyl-oxygen bond due to the stability of the aryl-oxygen bond. This reaction results in the formation of phenol and an alkyl halide.
Ethers with two different alkyl groups can also undergo cleavage in a similar manner.

The order of reactivity of hydrogen halides for cleaving ethers is HI > HBr > HCl. Tertiary ethers can yield tertiary halides because the reaction proceeds through the SN1 mechanism when a tertiary group is present.

2. Electrophilic Substitution Reactions in Aryl Alkyl Ethers:

Aryl alkyl ethers, also known as phenylalkyl ethers, can undergo electrophilic substitution reactions in the aromatic ring due to the activating and ortho/para directing nature of the alkoxy (-OR) group.
These reactions include halogenation, Friedel-Crafts reactions, and nitration:
- Halogenation: Phenylalkyl ethers can undergo halogenation in the benzene ring. For example, anisole can undergo bromination with bromine in ethanoic acid, even in the absence of an iron (III) bromide catalyst. This is because the methoxy group activates the benzene ring, and the para isomer is obtained in high yield.
- Friedel-Crafts Reaction: Anisole and similar compounds can undergo Friedel-Crafts reactions. These reactions introduce alkyl or acyl groups at the ortho and para positions of the benzene ring. Anhydrous aluminum chloride (a Lewis acid) is often used as a catalyst.
- Nitration: Anisole can react with a mixture of concentrated sulfuric and nitric acids to yield a mixture of ortho and para nitroanisole.

These reactions demonstrate the ortho and para directing nature of the alkoxy group (-OR) in phenylalkyl ethers, making them susceptible to electrophilic substitution in the benzene ring.