C₃H₇OH — Propanol

Propanol (C₃H₇OH) is a primary alcohol containing three carbon atoms and one hydroxyl (–OH) group. It exists as two structural isomers—1-propanol (n-propyl alcohol) and 2-propanol (isopropyl alcohol). Both isomers are colorless, volatile liquids with similar chemical properties but different physical and industrial characteristics. Propanol is widely used as a solvent, disinfectant, fuel additive, and precursor to other organic compounds.

1-Propanol is a primary alcohol where the hydroxyl group is attached to the terminal carbon atom, while 2-propanol (commonly called isopropanol or isopropyl alcohol) is a secondary alcohol with the hydroxyl group attached to the middle carbon atom. Both forms are polar due to the –OH group and form hydrogen bonds with water, making them completely miscible in water.

The molecular formula of propanol is \(C_3H_7OH\). It can be represented structurally as:

• 1-Propanol: \(CH_3CH_2CH_2OH\)
• 2-Propanol: \((CH_3)_2CHOH\)

In both forms, each carbon atom is sp³ hybridized, forming four sigma bonds with other atoms. The presence of the polar hydroxyl group allows hydrogen bonding, leading to relatively high boiling points and solubility in water.

The geometry around the hydroxyl carbon is tetrahedral, and the O–H bond is polar due to the higher electronegativity of oxygen compared to hydrogen. This polarity contributes to its characteristic solvent properties.

Propanol can be synthesized through various industrial and laboratory methods, including:

1. Hydrogenation of Propionaldehyde

In this process, propionaldehyde is reduced in the presence of a catalyst to produce 1-propanol:

2. Hydration of Propene

2-Propanol is produced by the direct hydration of propene using an acid catalyst:

This is a major industrial route for manufacturing isopropyl alcohol.

3. Fermentation of Biomass

Some bacteria such as Clostridium species can produce propanol as a by-product of fermentation. However, this route is less common compared to petrochemical methods.

• Appearance: Colorless liquid with a characteristic alcoholic odor.
• Solubility: Completely miscible with water due to hydrogen bonding between –OH groups and water molecules.
• Boiling and Melting Points: 1-propanol boils at about 97°C, whereas 2-propanol boils at 82.6°C. The difference arises from molecular branching, which reduces intermolecular forces in isopropanol.
• Flammability: Both isomers are highly flammable and burn with a clean blue flame:

\(2C_3H_7OH + 9O_2 \rightarrow 6CO_2 + 8H_2O\)

• Acid-Base Nature: Propanol is neutral but can act as a weak acid by donating a proton from its hydroxyl group to strong bases.
• Reaction with Sodium: Reacts slowly with sodium metal to form sodium propoxide and hydrogen gas:

\(2C_3H_7OH + 2Na \rightarrow 2C_3H_7ONa + H_2\uparrow\)

• Oxidation: 1-propanol oxidizes to propanal and further to propanoic acid; 2-propanol oxidizes to acetone:

\(CH_3CH_2CH_2OH + [O] \rightarrow CH_3CH_2CHO + H_2O\)

\((CH_3)_2CHOH + [O] \rightarrow (CH_3)_2CO + H_2O\)

• 1. Solvent: Propanol is an excellent solvent for fats, oils, resins, and cellulose derivatives. It is widely used in the pharmaceutical and cosmetic industries.
• 2. Disinfectant: 2-Propanol (isopropyl alcohol) is a common disinfectant and antiseptic used in hospitals and homes as rubbing alcohol due to its ability to kill bacteria and viruses by protein denaturation.
• 3. Fuel Additive: Used as a fuel or blended with gasoline to improve combustion efficiency and reduce emissions.
• 4. Chemical Intermediate: Employed in the production of acetone, propyl acetate, and other esters.
• 5. Laboratory Use: Used as a drying agent and solvent for organic reactions due to its miscibility with both polar and non-polar solvents.
• 6. Cosmetic and Personal Care: Acts as an antiseptic and solvent in lotions, perfumes, and deodorants.

Propanol is relatively less toxic compared to methanol but more toxic than ethanol. Ingestion can cause dizziness, headache, and central nervous system depression. Prolonged inhalation of vapors may lead to irritation of the respiratory tract.

Environmentally, propanol is biodegradable and breaks down rapidly under aerobic conditions. It has low potential for bioaccumulation and does not persist in the environment, making it environmentally safe when handled properly.

• Highly flammable—keep away from heat, sparks, and open flames.
• Use in a well-ventilated area to avoid inhalation of vapors.
• Avoid skin and eye contact; wear protective gloves and goggles.
• Store in tightly closed containers, away from oxidizing agents.
• In case of ingestion, do not induce vomiting and seek medical attention immediately.

Proper handling and storage ensure safe use in industrial and laboratory environments.