Alcohol 12

What is an alcohol?

• An organic compound formed when a hydrogen atom of an alkane is replaced by a **hydroxyl (-OH)** group.<br>• General formula: **R-OH**

What is the functional group of an alcohol?

• **Hydroxyl group (-OH)**

Classify alcohols based on the number of -OH groups.

• **Monohydric:** One -OH group<br> - Example: Ethanol<br>• **Dihydric:** Two -OH groups<br> - Example: Ethylene glycol<br>• **Trihydric:** Three -OH groups<br> - Example: Glycerol<br>• **Polyhydric:** More than three -OH groups

What is a primary (1°) alcohol?

• -OH group attached to a **primary carbon**<br>• Primary carbon = carbon bonded to only one other carbon<br> - Example: **CH₃CH₂OH**

What is a secondary (2°) alcohol?

• -OH group attached to a **secondary carbon**<br>• Secondary carbon = carbon bonded to two other carbons<br> - Example: **CH₃CH(OH)CH₃**

What is a tertiary (3°) alcohol?

• -OH group attached to a **tertiary carbon**<br>• Tertiary carbon = carbon bonded to three other carbons<br> - Example: **(CH₃)₃COH**

IUPAC name of CH₃OH?

• IUPAC: **Methanol**<br>• Common: **Methyl alcohol**

IUPAC name of CH₃CH₂OH?

• IUPAC: **Ethanol**<br>• Common: **Ethyl alcohol**

IUPAC name of CH₃CH₂CH₂OH?

• IUPAC: **Propan-1-ol**<br>• Common: **n-Propyl alcohol**

IUPAC name of CH₃CH₂CH₂CH₂OH?

• IUPAC: **Butan-1-ol**<br>• Common: **n-Butyl alcohol**

What are the IUPAC rules for naming alcohols?

• Select the **longest carbon chain** containing the -OH group<br>• Number the chain to give -OH the **lowest possible number**<br>• Replace the '-e' of the alkane name with **'-ol'**<br>• Name substituents **alphabetically**

What types of structural isomerism do alcohols exhibit?

• **Chain isomerism**<br>• **Positional isomerism**<br>• **Functional isomerism**

Give an example of chain isomerism in alcohols.

• **Butan-1-ol** and **2-methylpropan-1-ol**<br>• Both have the formula **C₄H₁₀O**

Give an example of positional isomerism in alcohols.

• **Propan-1-ol** and **Propan-2-ol**<br>• Both have the formula **C₃H₈O**

Alcohols are functional isomers of which class of compounds?

• **Ethers**<br>• They share the general formula **CₙH₂ₙ₊₂O**

Preparation of alcohol from a haloalkane.

• Reaction: **R-X + aq. KOH/NaOH → R-OH + KX**<br>• Type: **Nucleophilic substitution**

Preparation of alcohol from a primary amine.

• Reaction: **R-NH₂ + HNO₂ (cold) → R-OH + N₂ + H₂O**

Preparation of alcohol by ester hydrolysis.

• Reaction: **RCOOR' + H₂O (H⁺) ⇌ RCOOH + R'OH**

What is fermentation?

• A biochemical process where sugar is converted into **ethanol and CO₂** by yeast<br>• Enzyme: **zymase**<br> - Equation: **C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂**

What is the oxo process for alcohol preparation?

• Alkene + CO + H₂ → **aldehyde** → **alcohol**<br>• Catalyst: **dicobalt octacarbonyl**

How is ethanol prepared industrially from molasses?

• Molasses contains **sugar**<br>• Fermentation with **yeast** gives ethanol and CO₂

What is the hydration of an alkene?

• **CH₂=CH₂ + H₂O → CH₃CH₂OH**<br>• Conditions: **H₃PO₄/H₂SO₄, heat**

Define Absolute alcohol.

• Ethanol containing **not more than 1% water**<br>• Approximately **99.5% ethanol**

Define Power alcohol.

• Mixture of **absolute ethanol + petrol/gasoline**<br>• Used as a **fuel**

Define Denatured alcohol (Methylated spirit).

• Ethanol made **unfit for drinking**<br>• Added substances: **methanol, pyridine, dyes**

Define Rectified spirit.

• Constant-boiling mixture of **95.6% ethanol** and **4.4% water**

Define Alcoholic beverage.

• Any drink containing **ethanol**<br>• Produced by **fermentation of sugars**

Physical state of lower and higher alcohols.

• C₁–C₄: **colourless liquids**<br>• Higher alcohols: **waxy solids**

Why do alcohols have higher boiling points than alkanes/ethers?

• Due to **intermolecular hydrogen bonding** through the -OH group

Solubility of alcohols in water.

• Lower alcohols: **highly soluble** (H-bonding with water)<br>• Solubility **decreases** as alkyl group size increases

Density of alcohols.

• Generally **less dense than water**<br>• Density **increases** with molecular mass

Smell and taste of lower alcohols.

• **Characteristic smell**<br>• **Burning taste**

Reaction of alcohol with sodium (Na).

• **2R-OH + 2Na → 2R-ONa + H₂**<br>• Shows the **acidic nature** of alcohols

Reaction of alcohol with hydrogen halides (HX).

• **R-OH + HX → R-X + H₂O**<br>• Reactivity: **3° > 2° > 1°**

Reaction of alcohol with PCl₅.

• **R-OH + PCl₅ → R-Cl + POCl₃ + HCl**

Reaction of alcohol with SOCl₂.

• **R-OH + SOCl₂ → R-Cl + SO₂ + HCl**

Dehydration of alcohol.

• **R-CH₂-CH₂OH → R-CH=CH₂ + H₂O**<br>• Condition: **conc. H₂SO₄, heat**

Oxidation of a primary (1°) alcohol.

• 1° alcohol → **aldehyde** → **carboxylic acid**<br> - Example: **CH₃CH₂OH → CH₃CHO → CH₃COOH**

Oxidation of a secondary (2°) alcohol.

• 2° alcohol → **ketone**<br> - Example: **CH₃CH(OH)CH₃ → CH₃COCH₃**

Oxidation of a tertiary (3°) alcohol.

• **Resistant to oxidation** under normal conditions

Catalytic dehydrogenation of 1° and 2° alcohols.

• 1° → **aldehyde + H₂**<br>• 2° → **ketone + H₂**<br>• 3° → undergoes **dehydration** instead

Esterification reaction.

• **R-OH + R'COOH ⇌ R'COOR + H₂O**<br>• Catalyst: **conc. H₂SO₄**

Combustion of ethanol.

• **C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat**

What is Victor Meyer's method used for?

• To **distinguish** between **primary, secondary, and tertiary alcohols**

What are the steps of Victor Meyer's method?

• Alcohol + PI₃ → **iodoalkane**<br>• + AgNO₂ → **nitroalkane**<br>• + HNO₂ then alkali → **observe colour**

What are the colours in Victor Meyer's test?

• 1° = **Blood red**<br>• 2° = **Blue**<br>• 3° = **Colourless**

What is the Lucas test?

• Reagent: **conc. HCl + anhydrous ZnCl₂**<br>• 3° → **immediate turbidity**<br>• 2° → **turbidity on heating**<br>• 1° → **no reaction at room temp**

How is the oxidation method used to distinguish alcohols?

• 1° → **aldehyde/acid**<br>• 2° → **ketone**<br>• 3° → **no reaction**

Iodoform test for ethanol.

• Ethanol gives a **yellow precipitate** of **CHI₃ (iodoform)** with I₂/NaOH

Uses of Methanol.

• **Solvent**<br>• **Antifreeze**<br>• Production of **formaldehyde**<br>• **Fuel**

Uses of Ethanol.

• **Alcoholic beverages**<br>• **Antiseptic**<br>• **Solvent**<br>• **Power alcohol**

Uses of Glycol (Ethylene glycol).

• **Antifreeze** in automobile radiators<br>• **Polyester** production

Uses of Glycerol.

• **Cosmetics**<br>• **Pharmaceuticals**<br>• **Humectant**<br>• **Nitroglycerine**

Which alcohol resists oxidation?

• **Tertiary alcohol**

Which alcohol gives a blood-red colour in Victor Meyer's test?

• **Primary alcohol**

Condition for dehydration of ethanol to ethene.

• **Conc. H₂SO₄, about 170°C**

Why do alcohols have higher boiling points than alkanes?

• **Intermolecular hydrogen bonding**

Solubility trend of alcohols in water.

• **Decreases** with increase in alkyl group size

Are alcohols more acidic or less acidic than water?

• **Less acidic than water**<br>• They react with Na but **not with NaOH**

What is the composition of power alcohol?

• **Absolute ethanol + petrol/gasoline**<br>• Usually **20–25% ethanol**

How is absolute alcohol obtained from rectified spirit?

• Treat rectified spirit with **quicklime (CaO)** and distill

Why is the boiling point of ethanol higher than methoxyethane?

• Ethanol has **intermolecular hydrogen bonding** through -OH<br>• Ethers **cannot form hydrogen bonds** (no H attached to O)

Write the structural formula of alcohols with molecular formula C₄H₁₀O and arrange them in decreasing order of boiling point.

• Isomers: Butan-1-ol, Butan-2-ol, 2-Methylpropan-1-ol, 2-Methylpropan-2-ol<br>• Boiling point order: **Butan-1-ol > Butan-2-ol > 2-Methylpropan-1-ol > 2-Methylpropan-2-ol**

Why is methanol more acidic than ethanol?

• Methyl group has a **+I effect**<br>• It destabilizes the **methoxide ion** less than the ethyl group destabilizes the **ethoxide ion**

Give the oxidation product of Propan-1-ol and Propan-2-ol.

• Propan-1-ol → **Propanal → Propanoic acid**<br>• Propan-2-ol → **Propanone**

Which structural isomer of C₄H₁₀O cannot be dehydrogenated by copper at 300°C? Give its dehydration reaction.

• **2-Methylpropan-2-ol** (tertiary alcohol)<br>• Dehydration: **(CH₃)₃COH → (conc. H₂SO₄, heat) → (CH₃)₂C=CH₂ + H₂O**

What happens when ethanol is treated with conc. H₂SO₄ at 443K and 413K?

• At **443K** → **Ethene** (dehydration)<br>• At **413K** → **Diethyl ether** (dehydration)

What is the reaction of alcohol with acetyl chloride in pyridine?

• **R-OH + CH₃COCl → R-O-COCH₃ + HCl**<br>• Type: **Esterification**

Why can sodium metal be used for drying diethyl ether but not ethanol?

• Sodium reacts with ethanol (acidic -OH) to **liberate hydrogen gas**<br>• Sodium does **not react** with diethyl ether

Explain why alcohols show both acidic and basic properties.

• **Acidic:** -OH group can donate a proton (reacts with Na)<br>• **Basic:** Oxygen has lone pairs and can accept a proton (reacts with HX)

What is meant by the acidic nature of alcohols?

• Alcohols react with **active metals like Na** to form **alkoxides** and **hydrogen gas**<br>• They are **weakly acidic**

What is the reaction of ethanol with sodium?

• **2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂**

What is the reaction of ethanol with HCl and ZnCl₂ (Lucas reagent)?

• **C₂H₅OH + HCl → C₂H₅Cl + H₂O**<br>• Catalyst: **ZnCl₂**

What is the reaction of ethanol with acetic acid?

• **C₂H₅OH + CH₃COOH ⇌ CH₃COOC₂H₅ + H₂O**<br>• Type: **Esterification**

What is the reaction of propan-2-ol with P + I₂?

• Propan-2-ol + P + I₂ → **2-Iodopropane (A)**<br>• A + alc. KOH → **Propene (B)**

What is the action of Cu on methanol?

• **2CH₃OH + O₂ (Cu, 300°C) → 2HCHO + 2H₂O**<br>• Product: **Formaldehyde**

What is the reaction of ethanol with SOCl₂?

• **C₂H₅OH + SOCl₂ → C₂H₅Cl + SO₂ + HCl**

Convert propan-1-ol to propan-2-ol.

• Propan-1-ol → (P + I₂) → **1-iodopropane**<br>• → (alc. KOH) → **propene**<br>• → (H₂O/H⁺) → **propan-2-ol**

Convert propan-2-ol to propan-1-ol.

• Propan-2-ol → (P + I₂) → **2-iodopropane**<br>• → (alc. KOH) → **propene**<br>• → (HBr/peroxide) → **1-bromopropane**<br>• → (aq. KOH) → **propan-1-ol**

Convert ethene to propan-1-ol.

• Ethene → (HBr) → **bromoethane**<br>• → (Mg/dry ether) → **ethyl magnesium bromide**<br>• → (HCHO) → **propan-1-ol**

Convert ethanol to nitrolic acid (Victor Meyer test product).

• Ethanol → (P + I₂) → **iodoethane**<br>• → (AgNO₂) → **nitroethane**<br>• → (HNO₂) → **nitrolic acid (blood red colour)**

Convert propan-2-ol to pseudonitrol.

• Propan-2-ol → (P + I₂) → **2-iodopropane**<br>• → (AgNO₂) → **2-nitropropane**<br>• → (HNO₂) → **pseudonitrol (blue colour)**

Identify the product: CH₃CH₂OH → (P + I₂) → A → (alc. KOH) → B.

• A = **iodoethane (C₂H₅I)**<br>• B = **ethene (CH₂=CH₂)**

Identify the product: CH₂=CH₂ + CO + H₂ → (dicobalt octacarbonyl, heat/pressure) → A → (H₂/Ni, heat) → B.

• A = **propanal (CH₃CH₂CHO)**<br>• B = **propan-1-ol (CH₃CH₂CH₂OH)**

Primary alcohol is more acidic than secondary alcohol. Why?

• **+I effect** of alkyl groups destabilizes the **alkoxide ion**<br>• Primary alcohol has **fewer alkyl groups** attached to the carbon bearing -OH<br>• So its alkoxide is **more stable** → more acidic