Acetone

Acetone, with the chemical formula C₃H₆O or (CH₃)₂CO, is a simple organic compound that occupies a central role in both industrial chemistry and daily life. Known chemically as propanone, it is the simplest member of the ketone family. Acetone is a colourless, volatile, and flammable liquid with a distinctive sweet, pungent odour. It is widely used as a solvent, intermediate, and cleaning agent, and also occurs naturally in the environment and in the human body. Because of its wide applicability, low toxicity at small doses, and chemical reactivity, acetone has become one of the most significant compounds in organic chemistry and industry.

Historical Background and Discovery

Acetone has been known since the early days of organic chemistry. Its discovery is credited to the French chemist Jean-Baptiste Dumas and the German chemist Justus von Liebig in 1832, who described it as a distinct compound produced through the dry distillation of acetates, particularly calcium acetate. The word “acetone” originates from the Latin word acetum, meaning vinegar, reflecting its early association with acetic acid derivatives.
During the 19th and early 20th centuries, acetone was produced primarily through dry distillation of wood and acetic acid salts. Its importance grew significantly during the First World War, when it was used as a solvent in the manufacture of cordite, a smokeless gunpowder. The shortage of natural sources prompted the development of a biological fermentation method by Chaim Weizmann in 1916, using Clostridium acetobutylicum to produce acetone from starch. This “Weizmann process” marked one of the earliest industrial-scale applications of biotechnology.
With industrial advancement, acetone production shifted to chemical synthesis, especially from petroleum and natural gas derivatives, leading to large-scale, cost-effective manufacturing that continues today.

Physical and Chemical Properties

Acetone is a highly volatile and miscible organic solvent that mixes with water, ethanol, ether, and most organic liquids. Its molecular structure consists of a central carbonyl group (C=O) bonded to two methyl groups, giving it the molecular formula CH₃COCH₃ and a molecular weight of 58.08 g mol⁻¹.
Key physical properties:

• Appearance: Colourless liquid with a sweet odour
• Boiling point: 56.05 °C
• Melting point: –94.7 °C
• Density: 0.791 g cm⁻³ at 20 °C
• Solubility: Completely miscible with water and most organic solvents
• Flash point: –20 °C (highly flammable)
• Vapour pressure: 24.6 kPa at 25 °C

Acetone’s high volatility and low boiling point make it an excellent solvent for substances that require rapid evaporation during drying or processing.
Chemically, acetone is a polar aprotic solvent, meaning it dissolves polar and non-polar compounds without forming hydrogen bonds with solutes. The carbonyl group imparts reactivity typical of ketones—susceptibility to nucleophilic addition and oxidation.

Production and Manufacturing Processes

Modern acetone production is predominantly based on the cumene process, which simultaneously yields phenol and acetone. In this process, benzene reacts with propylene to form cumene (isopropylbenzene), which is then oxidised to cumene hydroperoxide. This intermediate is acid-cleaved to produce phenol and acetone:
C₆H₅CH(CH₃)₂ + O₂ → C₆H₅C(CH₃)₂OOH → C₆H₅OH + (CH₃)₂CO
This method accounts for over 90% of global acetone production, ensuring a consistent supply for industrial applications.
Alternative methods include:

• Isopropanol dehydrogenation:CH₃CHOHCH₃ → CH₃COCH₃ + H₂
• Catalytic oxidation of isopropyl alcohol using copper or zinc catalysts.
• Fermentation processes, once again gaining attention as part of sustainable “green chemistry” initiatives, particularly for bio-based acetone derived from renewable feedstocks.

Chemical Behaviour and Reactions

Acetone’s central carbonyl group defines its chemical reactivity. The C=O bond creates a partially positive carbon atom, making acetone susceptible to nucleophilic attack.
Key reactions include:

1. Oxidation – Acetone can be oxidised to acetic acid or carbon dioxide using strong oxidising agents such as potassium permanganate.
2. Reduction – Reduction by hydrogen or metal hydrides (e.g., LiAlH₄) converts acetone into isopropanol.
3. Aldol condensation – Under basic or acidic conditions, acetone undergoes self-condensation to form diacetone alcohol and further dehydration to mesityl oxide and phorone.
4. Formation of hydrazones and oximes – Reaction with hydrazine or hydroxylamine derivatives forms acetone hydrazone and acetone oxime, respectively.
5. Halogenation – Acetone reacts with halogens in the presence of acids to produce haloacetones.

These reactions make acetone a crucial starting material and intermediate in organic synthesis and industrial chemistry.

Industrial and Commercial Applications

Solvent Applications

Acetone is among the most widely used industrial solvents due to its ability to dissolve a wide range of organic substances such as resins, plastics, oils, fats, and waxes. Its rapid evaporation makes it ideal for applications where quick drying is necessary. Major uses include:

• Paints and coatings: As a thinning and cleaning solvent.
• Adhesives: For bonding plastics and rubbers.
• Printing inks: For achieving fast-drying finishes.
• Laboratory cleaning: For degreasing glassware and instruments.

Chemical Intermediate

Acetone serves as a precursor for manufacturing several key organic compounds, including:

• Methyl methacrylate (MMA) – used in acrylic plastics and resins.
• Bisphenol A (BPA) – a critical component of polycarbonate plastics and epoxy resins.
• Acetone cyanohydrin – a precursor to methyl methacrylate and other fine chemicals.

Pharmaceutical and Cosmetic Uses

In pharmaceuticals, acetone functions as a solvent for active ingredients and an intermediate in the synthesis of various medicines. It is also employed in chemical peeling agents and nail polish removers, where its solvent power effectively dissolves lacquer films.
In cosmetics, acetone is used to clean equipment and as a volatile carrier for certain formulations. It is approved in small quantities in regulated cosmetic products, though its drying effect limits its direct use on the skin.

Domestic and Cleaning Applications

Household-grade acetone is widely used as a paint remover, stain cleaner, and degreaser. It removes ink, glue, and oil residues effectively, making it a valuable component in cleaning agents. Due to its volatility, acetone evaporates rapidly, leaving minimal residue.

Laboratory and Analytical Uses

In laboratories, acetone is employed as:

• A solvent for recrystallisation and sample preparation.
• A rinse solvent for glassware and chromatography.
• A coolant in low-temperature baths when mixed with dry ice (forming mixtures reaching –78 °C).

Environmental and Biochemical Presence

Acetone naturally occurs in the environment as part of atmospheric and biological processes. It is formed in small quantities by the photochemical oxidation of hydrocarbons in the atmosphere and by plants and animals as a metabolic by-product.
In humans, acetone is one of the ketone bodies produced during fat metabolism, especially in conditions of fasting, prolonged exercise, or uncontrolled diabetes mellitus. Elevated acetone levels in breath, known as acetone breath, are a diagnostic sign of diabetic ketoacidosis.

Safety, Hazards, and Handling

While acetone is generally regarded as a low-toxicity compound, it requires careful handling due to its high flammability and volatility.
Health hazards:

• Inhalation of concentrated vapour can cause irritation, dizziness, and headaches.
• Prolonged skin contact may lead to dryness and irritation due to its degreasing effect.
• Eye contact produces irritation and watering.
• At very high exposure levels, acetone may depress the central nervous system, though this is rare in occupational settings.

Fire and explosion risks:

• Acetone vapour forms explosive mixtures with air.
• Flash point: –20 °C; auto-ignition temperature: ~465 °C.
• Proper ventilation, spark-proof equipment, and grounding are essential during industrial handling.

Environmental aspects: Acetone is readily biodegradable, and its release to the environment poses minimal long-term risk. It does not bioaccumulate and breaks down rapidly through photochemical reactions in air and microbial degradation in water and soil. Consequently, acetone is often regarded as an environmentally preferable solvent compared to chlorinated hydrocarbons.

Advantages and Limitations

Advantages:

• Excellent solvent power for a wide variety of compounds
• Fast evaporation and clean drying
• Miscible with water and most organic solvents
• Low toxicity and biodegradability
• Affordable and readily available
• Serves as a versatile chemical intermediate

Limitations:

• Highly flammable and volatile, requiring careful storage
• Can cause skin and eye irritation with prolonged exposure
• Strong odour may limit use in closed environments
• Hygroscopic nature may lead to moisture absorption affecting purity
• Incompatible with strong oxidisers (risk of violent reactions)

Significance and Future Prospects

Acetone continues to be a cornerstone of industrial chemistry, laboratory science, and consumer products. Its essential role as a solvent and intermediate ensures its demand across multiple sectors, from plastics and pharmaceuticals to coatings and electronics.
Future research is focused on green acetone production, emphasising sustainable, bio-based methods that minimise dependence on fossil feedstocks. Advances in biotechnological fermentation, using renewable biomass or waste feedstock, have revived interest in the Weizmann process for large-scale biogenic acetone production.
Additionally, acetone’s potential as a hydrogen carrier and biofuel additive is being explored due to its volatility and clean-burning nature. These developments align with global goals for sustainable manufacturing and reduced environmental impact.