C₄H₉OH — Butanol

Butanol (C₄H₉OH) is a simple aliphatic alcohol that contains four carbon atoms and a single hydroxyl group. It exists as four structural isomers: n-butanol (1-butanol), sec-butanol (2-butanol), isobutanol (2-methyl-1-propanol), and tert-butanol (2-methyl-2-propanol). Each isomer has distinct physical properties and industrial uses but shares similar chemical reactivity typical of alcohols.

Butanol is an important industrial chemical used as a solvent, intermediate, and biofuel. It is also naturally produced by the anaerobic fermentation of carbohydrates by bacteria such as Clostridium acetobutylicum. Due to its favorable energy content and lower volatility, butanol is gaining attention as a potential alternative to gasoline in sustainable energy solutions.

The molecular formula of butanol is \(C_4H_9OH\), indicating the presence of four carbon atoms, ten hydrogen atoms, and one oxygen atom. The hydroxyl group can attach to different carbon atoms in the chain, giving rise to four isomers:

• 1-Butanol (n-butanol): \(CH_3CH_2CH_2CH_2OH\)
• 2-Butanol (sec-butanol): \(CH_3CH_2CHOHCH_3\)
• Isobutanol (2-methyl-1-propanol): \((CH_3)_2CHCH_2OH\)
• Tert-butanol (2-methyl-2-propanol): \((CH_3)_3COH\)

The isomers differ in structure and the type of carbon atom bonded to the hydroxyl group (primary, secondary, or tertiary). This structural difference affects boiling points, solubility, and reactivity. For example, 1-butanol is a primary alcohol, whereas tert-butanol is a tertiary alcohol with greater steric hindrance and lower boiling point.

Butanol can be synthesized through various industrial methods:

1. Fermentation (ABE Process)

Biological fermentation of carbohydrates (starch, molasses, or sugar) by Clostridium acetobutylicum yields acetone, butanol, and ethanol. This process is known as the ABE (Acetone–Butanol–Ethanol) fermentation:

This eco-friendly route is regaining industrial importance due to the need for bio-based fuels.

2. Oxo Process (Hydroformylation)

The industrial synthesis of butanol involves the hydroformylation of propylene with carbon monoxide and hydrogen in the presence of a catalyst:

3. Reduction of Butanal

Butanal (butyraldehyde) can be reduced using hydrogen or a metal hydride (like NaBH₄) to produce butanol:

• Appearance: Colorless liquid with a strong alcoholic odor.
• Solubility: Slightly soluble in water but miscible with organic solvents such as ether, acetone, and chloroform.
• Boiling Point: Ranges between 82°C to 118°C depending on isomeric form.
• Flammability: Highly flammable; burns with a blue flame producing carbon dioxide and water:

\(C_4H_9OH + 6O_2 \rightarrow 4CO_2 + 5H_2O\)

• Reaction with Sodium: Produces sodium butoxide and hydrogen gas:

\(2C_4H_9OH + 2Na \rightarrow 2C_4H_9ONa + H_2\uparrow\)

• Oxidation: 1-butanol oxidizes to butanal and further to butanoic acid (butyric acid):

\(CH_3CH_2CH_2CH_2OH + [O] \rightarrow CH_3CH_2CH_2CHO + H_2O\)

\(CH_3CH_2CH_2CHO + [O] \rightarrow CH_3CH_2CH_2COOH\)

• Esterification: Reacts with carboxylic acids to form butyl esters used in perfumes and solvents:

\(C_4H_9OH + CH_3COOH \xrightarrow{H_2SO_4} CH_3COOC_4H_9 + H_2O\)

• 1. Solvent: Used in paints, varnishes, coatings, and plastics due to its moderate polarity and volatility.
• 2. Fuel and Biofuel: Butanol is an alternative biofuel with higher energy content than ethanol and compatibility with gasoline engines without modification.
• 3. Chemical Intermediate: Used in manufacturing butyl acetate, glycol ethers, and plasticizers.
• 4. Pharmaceuticals and Cosmetics: Acts as a solvent in perfumes, lotions, and other personal care products.
• 5. Laboratory Use: Used as a solvent and reagent in organic synthesis.
• 6. Cleaning and Coating Industry: Its slow evaporation rate makes it ideal for coatings and polishes.

Butanol is relatively less toxic than methanol but can cause irritation of the eyes, nose, and throat at high concentrations. Ingestion or prolonged exposure can lead to central nervous system depression. Safety guidelines recommend good ventilation and personal protective equipment when handling butanol.

Environmentally, butanol is biodegradable and considered a sustainable biofuel. It has lower volatility than ethanol, reducing evaporation losses and air pollution. However, spills should be contained as it can contaminate water sources.

Butanol should be handled in well-ventilated areas away from open flames and sparks. It should be stored in sealed containers made of non-reactive material. Proper personal protective equipment, such as gloves and goggles, should be worn. In case of skin contact, wash thoroughly with water and soap. For ingestion, seek immediate medical attention.

First Aid Tips: Inhalation—move to fresh air; Skin contact—wash with water; Eye contact—rinse thoroughly; Ingestion—do not induce vomiting, seek medical care.