Alcohols

Alcohols:

Alcohols are a series of compounds with a hydroxyl group (-OH) joined to a carbon atom in a hydrocarbon chain.

General Formula: ( C_n H_{2n + 1}  OH)

Functional Group: (OH)

Note: The above mentioned Alcohols are all in Liquid state at room temperature as their boiling > room temperature. Also moving down the group, the mass and boiling points of Alcohols increases. Alcohols and Carboxylic Acids are not HydroCarbons as they  contain Oxygen atoms in their compounds.

Physical Properties:

• Alcohols are soluble in water(H₂O).
• Alcohols have OH in them but they are not Alkalies.
• Alcohols are more reactive than Alkanes and Alkenes, as they have more electronic density, and presence of hydroxyl (-O-H) and carboxyl group (-C-O) as shown below.

H₃C  –  CH₃       – Ethane

H₂C  –  CH_c      – Ethene

H₃C  –  CH₂ – O – H

Combustion:

Alcohol requires less Oxygen for combustion, as Oxygen is a part of it.

Complete Combustion:

Alcohol + O₂ CO + H₂O

C₂H₅OH + 3O₂ 2CO₂ + 3H₂0

Incomplete Combustion:

Alcohol + O₂  CO + Carbon Soot

This reaction, is highly exothermic, thus alcohols are used as fuels.

Oxidation:

Oxidation is gain of Oxygen and loss of Hydrogen.

Alcohols upon oxidation will form Carboxylic Acids + H₂O

In the presence of acidified Potassium Dichromate (H₂SO₄ K₂Cr₂O₇) an oxidizing agent.

C₂H₅OH     OH   + 2(O)CH₃OOH        H₂O

Hence:

Ethanol will become Ethanoic Acid and Propanol will become Propanoic Acid.

In this oxidation process, we can use either:

• Atmospheric Oxygen
• Acidified Potssium Dichromate , which changes its colour from Orange to Green.
• Purple acidified Potassium Magaate (VII) which is decolourised(K₂Cr₂O₇ MNO₄)

Preperation Of Alcohol:

There are two methods to obtain alcohol:

• Hydration Of Alkene (Lab Method)
• Fermentation (Industrial Method)

Hydration of Alkene  (Lab Method):

In this method, steam is added to Alkene, to convert it to Alcohol.

Conditions:

• Catalyst – Phosphoric Acid (H₃PO₄)
• Temperature – 300 °C

Hydration of Alkene, is actually adding water (H₂O) across the two double bonds Carbon of Alkenes

Fermentation (Industrial Method):

Fermentation is a process whereby an enzyme is used to break down glucose in sugar or starch into ethanol and CO₂ gas.

Fermentation is catalysed by the enzymes present in yeast.

Conditions:

• Temperature – 37°C (25 – 40°C)
• Temperature too high would destroy the yeast and temperature too low would result in yeast becoming dormant.
• Catalyst/ Biological Catalyst – Yeast (enzyme)
• No Oxygen should enter the setup. As Oxygen can react with Alcohol to convert it into Carboxylic Acid.
• CO₂ test (limewater turns milky ) to check the alcohol preparation.
• Alcohol can be separated after the process is completed, through fractional distillation, by using their respective boiling point.

Uses Of Alcohol:

There are different uses of Alcohols such as:

• Alcohol can be used as a constituent of alcohol beverages.
• As a solvent for detergents, perfumes and in medicines.
• As a fuel.