C₄H₈O — Butanone

Butanone (C₄H₈O), commonly known as methyl ethyl ketone (MEK), is an organic compound belonging to the ketone family. It is a colorless, volatile, and flammable liquid with a sweet, sharp odor similar to that of acetone. Butanone is widely used as an industrial solvent in the manufacture of plastics, varnishes, paints, and synthetic fibers. Its strong solvency and quick evaporation rate make it an ideal solvent for various resins and coatings.

Butanone naturally occurs in small quantities in some fruits and vegetables and is also produced by certain bacteria during fermentation. In industrial settings, it is mainly synthesized through oxidation processes involving secondary butanol or 2-butanol. Because of its versatility and efficiency, it is one of the most important low molecular weight ketones used globally in chemical synthesis and manufacturing.

Butanone is a simple aliphatic ketone with the chemical structure:

It contains a carbonyl group (C=O) bonded to two alkyl groups — a methyl (–CH₃) and an ethyl (–CH₂CH₃) group. The central carbon atom of the carbonyl group is sp² hybridized, forming a trigonal planar geometry with bond angles of approximately 120°. The oxygen atom in the carbonyl group has two lone pairs, which contribute to the compound’s polarity and dipole moment.

The presence of the polar C=O bond allows butanone to engage in dipole-dipole interactions and hydrogen bonding with water molecules, explaining its miscibility with water. However, unlike alcohols, butanone cannot form hydrogen bonds between its own molecules since it lacks an –OH group. This structural property influences its physical behavior such as boiling point and volatility, which are intermediate between aldehydes and alcohols of comparable molecular weight.

Butanone can be synthesized through several methods, both in the laboratory and industrially. The most common methods are described below:

• 1. Oxidation of 2-Butanol: The most widely used industrial route involves oxidation of 2-butanol (secondary butanol) in the presence of a catalyst such as copper, zinc, or chromium oxide.

• 2. Dehydrogenation of 2-Butanol: Passing vaporized 2-butanol over heated catalysts results in dehydrogenation, forming butanone and hydrogen gas.

• 3. Oxidation of Butane: In this method, butane undergoes partial oxidation under controlled conditions, though it is less common due to lower selectivity.

Among these, the oxidation of 2-butanol is the most economically viable and environmentally friendly process used in modern industries.

Physical Properties:

• Butanone is a colorless and highly volatile liquid with a pleasant odor resembling acetone.
• It has a boiling point of 79.6°C and a melting point of –86°C.
• It is completely miscible with water and most organic solvents such as ethanol, ether, and benzene.
• Highly flammable and produces explosive vapors in air.

Chemical Properties:

• 1. Reduction: Butanone can be reduced to 2-butanol when treated with reducing agents such as sodium borohydride (NaBH₄) or hydrogen in the presence of nickel.

\( CH_3COCH_2CH_3 + H_2 \xrightarrow{Ni} CH_3CH(OH)CH_2CH_3 \)

• 2. Oxidation: On strong oxidation, butanone breaks down into acetic acid and other smaller carboxylic acids.

\( CH_3COCH_2CH_3 + [O] \rightarrow CH_3COOH + CH_3CH_2COOH \)

• 3. Nucleophilic Addition: The carbonyl carbon in butanone is electrophilic, making it susceptible to attack by nucleophiles like HCN, NH₂OH, and hydrazine, forming derivatives such as oximes and hydrazones.

\( CH_3COCH_2CH_3 + HCN \rightarrow CH_3C(OH)(CN)CH_2CH_3 \)

• 4. Reaction with Hydrazine: Forms hydrazone derivatives used in qualitative organic analysis.

\( CH_3COCH_2CH_3 + N_2H_4 \rightarrow CH_3C=NNH_2CH_2CH_3 + H_2O \)

Butanone (methyl ethyl ketone) serves as a key solvent and chemical intermediate in various industries. Some major uses include:

• 1. Solvent in Coatings and Paints: Used extensively in the paint, lacquer, and varnish industries for dissolving resins, nitrocellulose, and vinyl polymers.
• 2. Adhesives and Sealants: An important solvent in adhesive formulations, particularly in shoe and leather industries.
• 3. Polymer Production: Plays a key role in the production of poly(methyl methacrylate) (PMMA) and other plastic materials.
• 4. Extraction Processes: Used for dewaxing lubricating oils and refining fats and waxes.
• 5. Chemical Intermediate: Acts as a precursor in the synthesis of other organic compounds such as peroxides and catalysts.
• 6. Laboratory Reagent: Utilized in analytical chemistry for preparing standard solutions and extraction processes.

Due to its fast evaporation rate and effective solvency, butanone is also found in printing inks, rubber cements, and cleaning agents.

Butanone is considered moderately toxic and highly flammable. Prolonged or repeated exposure can cause irritation and central nervous system effects.

Health Hazards:

• Inhalation of vapors can cause dizziness, headaches, and nausea.
• Prolonged skin contact may result in dryness or dermatitis.
• Ingestion causes gastrointestinal irritation and vomiting.
• High exposure can affect the liver and kidneys.

Safety Precautions:

• Use in well-ventilated areas or under exhaust hoods.
• Wear gloves, goggles, and protective clothing while handling.
• Keep away from open flames, sparks, and oxidizing agents.
• Store in tightly sealed containers in cool, dry areas.
• Follow local disposal and environmental protection regulations when discarding waste solvents.

Although butanone is less toxic than some chlorinated solvents, strict industrial safety protocols should be followed to minimize health risks and fire hazards.