C₃H₆O — Acetone

Acetone (C₃H₆O) is the simplest and most important ketone, consisting of a carbonyl group bonded to two methyl groups. It is a colorless, highly volatile, and flammable liquid with a distinctive sweet odor. Acetone occurs naturally in plants, trees, volcanic gases, and even as a byproduct of metabolic processes in the human body (during ketosis).

It is one of the most widely used organic solvents in both laboratories and industries. Due to its excellent solubility, acetone serves as a universal cleaning agent, solvent for plastics, paints, and varnishes, and as a starting material in the synthesis of many organic compounds like methyl methacrylate and bisphenol A.

Acetone’s molecular formula is \(C_3H_6O\) and its structural formula is \(CH_3COCH_3\). The molecule contains a central carbon atom double-bonded to an oxygen atom (the carbonyl group) and single-bonded to two methyl groups.

The carbon atom in the carbonyl group is sp² hybridized, and the oxygen atom has two lone pairs of electrons. The C=O bond is polar, giving acetone significant dipole moment and strong intermolecular forces such as dipole–dipole interactions. This polarity is the reason behind its excellent solvent properties, allowing it to dissolve both polar and nonpolar substances.

Acetone is produced both naturally and synthetically. Industrial production is primarily through oxidation and dehydrogenation of isopropanol or as a byproduct of other chemical processes.

1. From Isopropanol (Dehydrogenation Method)

In this common industrial method, isopropanol (isopropyl alcohol) is passed over a heated copper catalyst at about 400°C:

This method is efficient and economical since it produces hydrogen as a valuable byproduct.

2. From Cumene Process

In the cumene process for phenol production, acetone is obtained as a co-product. Cumene (isopropylbenzene) is oxidized to cumene hydroperoxide and then acidified to yield phenol and acetone:

3. From Acetic Acid (Dry Distillation)

Calcium acetate, when heated strongly, decomposes to give acetone and calcium carbonate:

4. Fermentation Method

Acetone can also be obtained through acetone–butanol fermentation using certain bacterial strains such as Clostridium acetobutylicum.

Physical Properties:

• Colorless and volatile liquid with a sweet odor.
• Boiling point: 56.05°C; Melting point: -94.7°C.
• Miscible with water, alcohol, and ether due to hydrogen bonding with polar molecules.
• Highly flammable with a flash point of -20°C.

Chemical Properties:

• 1. Reduction: Acetone can be reduced to isopropanol by catalytic hydrogenation:

\((CH_3)_2CO + H_2 \xrightarrow{Ni} (CH_3)_2CHOH\)

• 2. Oxidation: Oxidation of acetone with strong oxidizing agents such as potassium dichromate yields acetic acid and formic acid:

\((CH_3)_2CO + O_2 \rightarrow CH_3COOH + HCOOH\)

• 3. Iodoform Reaction: Acetone gives a positive iodoform test due to the presence of the methyl ketone group:

\((CH_3)_2CO + 3I_2 + 4NaOH \rightarrow CHI_3 + CH_3COONa + 3NaI + 3H_2O\)

• 4. Reaction with Hydrogen Cyanide (HCN): Acetone reacts with hydrogen cyanide to form acetone cyanohydrin:

\((CH_3)_2CO + HCN \rightarrow (CH_3)_2C(OH)CN\)

• 5. Aldol Condensation: In the presence of a base, acetone undergoes self-condensation to form diacetone alcohol, which can dehydrate to mesityl oxide:

\(2(CH_3)_2CO \xrightarrow{NaOH} CH_3COCH_2C(OH)(CH_3)_2 \xrightarrow{heat} CH_3COCH=C(CH_3)_2 + H_2O\)

• 1. Solvent: Widely used as a solvent in paints, varnishes, adhesives, and nail polish removers due to its ability to dissolve many organic compounds.
• 2. Chemical Intermediate: Used as a precursor in the production of methyl methacrylate, bisphenol A, and acetic anhydride.
• 3. Laboratory Reagent: Used for cleaning glassware and as a solvent in chromatography.
• 4. Cosmetic Industry: Found in nail polish removers and certain skin-cleaning formulations.
• 5. Pharmaceutical Industry: Used as a solvent for certain active ingredients in drug manufacturing.
• 6. Plastics and Fibers: Essential in the synthesis of polycarbonates, acrylic plastics, and synthetic fibers.

Acetone is generally considered to have low toxicity but can cause irritation and health issues with prolonged or concentrated exposure. Inhalation of acetone vapors can lead to dizziness, nausea, and headaches. Prolonged skin contact can cause dryness and irritation due to its solvent properties.

Safety Measures:

• Use acetone in well-ventilated areas.
• Store away from heat, sparks, and open flames since it is highly flammable.
• Wear gloves, goggles, and protective clothing when handling acetone in the laboratory.
• Dispose of waste acetone according to environmental safety regulations.