C₂H₅OH — Ethanol

Ethanol (C₂H₅OH) is a simple alcohol with two carbon atoms and one hydroxyl (–OH) functional group. It is one of the most important organic compounds due to its wide range of uses in industrial, medical, and domestic applications. Ethanol occurs naturally through the fermentation of sugars by yeast and is also synthesized industrially from petrochemical feedstocks such as ethylene.

It is a volatile, flammable, colorless liquid with a characteristic odor. Ethanol acts as a psychoactive substance in alcoholic beverages, as a fuel additive, and as a solvent in pharmaceuticals, cosmetics, and perfumes. It also has disinfectant and antiseptic properties, making it a common ingredient in hand sanitizers and medical cleaning solutions.

Ethanol consists of two carbon atoms, six hydrogen atoms, and one hydroxyl group (–OH). The molecular structure can be written as \(CH_3CH_2OH\) or simply \(C_2H_5OH\). It is a polar molecule due to the electronegative oxygen atom in the hydroxyl group, which can form hydrogen bonds with other molecules.

The structure of ethanol can be represented as:

The carbon atoms are sp³ hybridized, forming tetrahedral geometry. The presence of hydrogen bonding significantly affects ethanol’s physical properties, such as its high boiling point and solubility in water.

Hydrogen bonding: The –OH group allows ethanol molecules to form intermolecular hydrogen bonds, which makes ethanol miscible with water in all proportions and gives it a relatively high boiling point compared to other compounds of similar molecular mass.

Ethanol can be prepared by two major methods — biological (fermentation) and chemical synthesis from petroleum derivatives.

1. Fermentation of Carbohydrates

Fermentation is the natural process by which sugars such as glucose, sucrose, or starch are converted into ethanol and carbon dioxide using yeast enzymes.

This method is the basis of alcohol production in beverages and bioethanol fuel. The process requires an anaerobic environment (absence of oxygen) and temperatures around 30°C.

2. Hydration of Ethylene

Industrially, ethanol is produced by the catalytic hydration of ethylene:

This method is widely used due to its efficiency and lower cost compared to fermentation. The ethanol produced is later purified by distillation to remove water and other impurities.

• Appearance: Ethanol is a colorless, volatile liquid with a characteristic odor.
• Solubility: Completely miscible with water due to hydrogen bonding between ethanol and water molecules.
• Boiling and Melting Points: Boiling point at 78.37°C and melting point at -114.1°C due to strong intermolecular hydrogen bonding.
• Flammability: Highly flammable and burns with a blue, non-sooty flame:

\(C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O\)

• Acidity and Basicity: Ethanol is a very weak acid that can lose a proton from its hydroxyl group in reaction with active metals:

\(2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2\uparrow\)

• Oxidation: Ethanol can be oxidized to acetaldehyde and further to acetic acid by suitable oxidizing agents:

\(C_2H_5OH + [O] \xrightarrow{K_2Cr_2O_7/H_2SO_4} CH_3CHO + H_2O\)

Further oxidation:

\(CH_3CHO + [O] \rightarrow CH_3COOH\)

• Reaction with Carboxylic Acids: It reacts with carboxylic acids in the presence of acid catalysts to form esters (esterification):

\(C_2H_5OH + CH_3COOH \xrightarrow{H_2SO_4} CH_3COOC_2H_5 + H_2O\)

• 1. As a Solvent: Ethanol dissolves a wide range of organic and inorganic substances and is used in paints, perfumes, and pharmaceuticals.
• 2. Fuel and Biofuel: Ethanol is blended with gasoline to produce gasohol (commonly E10 or E85). It enhances octane rating and reduces carbon monoxide emissions.
• 3. Disinfectant and Antiseptic: Ethanol has antimicrobial properties, making it a key ingredient in sanitizers, wipes, and medical disinfectants.
• 4. Beverage Alcohol: Ethanol is the active component of alcoholic drinks such as beer, wine, and spirits. It acts as a depressant of the central nervous system.
• 5. Chemical Feedstock: Used to manufacture various organic compounds like ethyl acetate, acetic acid, and diethyl ether.
• 6. Preservation: Used in laboratories and museums as a preservative for biological specimens.

In small quantities, ethanol is metabolized by the liver to produce energy. However, excessive consumption can lead to intoxication, liver damage, and addiction. Industrial exposure to ethanol vapors may cause irritation to the eyes and respiratory tract.

Environmentally, ethanol is considered an eco-friendly fuel because it burns cleanly and reduces greenhouse gas emissions compared to fossil fuels. It is biodegradable and does not persist in the environment.

Due to its flammability and volatility, ethanol should be stored and handled with care. Containers should be tightly closed and kept away from heat sources and open flames. Use in well-ventilated areas to avoid inhaling vapors. In laboratory use, proper personal protective equipment such as gloves and safety goggles should be worn.

First Aid: In case of skin contact, wash with water; in case of ingestion, seek medical help immediately. Avoid inhaling ethanol vapors for extended periods.