Acetone reaches the world through two broad channels: chemical factories that churn out millions of tonnes per year, and living organisms that produce it as a natural byproduct of metabolism. The dominant industrial route, called the cumene process, generates acetone as a co-product alongside phenol and accounts for the vast majority of global supply. But acetone also forms inside your body when you burn fat for fuel, inside soil bacteria that ferment sugars, and even in the open ocean where microbes release it as metabolic waste. The story of how this single molecule gets made spans petrochemistry, wartime history, human physiology, and marine ecology.
The Cumene Process
Nearly all acetone produced industrially today comes from the cumene process, sometimes called the Hock process after its inventor. The chemistry starts with two common petroleum-derived chemicals: benzene and propylene. These react together over an acid catalyst to form cumene (isopropylbenzene). Cumene is then oxidized with air to form cumene hydroperoxide, a relatively unstable intermediate. In the final step, the hydroperoxide is cleaved with an acid catalyst to yield two commercially valuable products at once: phenol and acetone, in roughly equal molar amounts.
The acid-catalyzed cleavage step is where the acetone molecule actually emerges, and it has been the subject of ongoing catalyst research. Traditionally, dilute sulfuric acid has been used, but zeolite catalysts can achieve comparable efficiency. High-silica zeolites, for instance, readily decompose cumene hydroperoxide into phenol and acetone with good selectivity, performing on par with sulfuric acid while avoiding the corrosion and waste-disposal problems of a mineral acid.
1Applied Catalysis A: General. Efficient cleavage of cumene hydroperoxide over HUSY zeolites: The role of Brønsted acidityAn interesting quirk of this process is that acetone is technically a co-product, not the primary target. Phenol is the higher-value chemical, used in everything from plastics to pharmaceuticals. Acetone comes along for the ride. This means the global supply of acetone is partly tied to demand for phenol. When phenol demand is high, more acetone floods the market, sometimes driving its price down. When phenol demand softens, acetone can get tight. This linked production is one reason alternative acetone routes have periodically attracted interest.
Before Cumene Took Over
The cumene process only became dominant in the mid-twentieth century. Before that, acetone was made by quite different methods. The oldest industrial route was the dry distillation of calcium acetate, itself a byproduct of wood distilling.2Chemical & Engineering News Archive. ACETONE: Tonnage By-Product Heating calcium acetate drives off water and carbon dioxide, leaving behind acetone vapor that can be condensed and collected. This was the standard method through the nineteenth century and into the early twentieth, but it was slow and produced relatively small quantities.
A related reaction, ketonization, converts two molecules of acetic acid into one molecule of acetone plus carbon dioxide and water. This chemistry once served as an industrial acetone route and is now attracting renewed interest for upgrading bio-oils derived from plant biomass.3ACS Catalysis. Ketonization of Carboxylic Acids: Mechanisms, Catalysts, and Implications for Biomass Conversion The idea of turning agricultural waste into acetone via ketonization of bio-derived acetic acid is one pathway researchers are exploring to reduce the chemical industry’s dependence on petroleum feedstocks. Several metal oxide catalysts, including those based on titanium, zirconium, and cerium oxides, can drive this reaction at moderate temperatures.4Applied Catalysis A: General. Ketonisation of acetic acid on metal oxides: Catalyst activity, stability and mechanistic insights
Other Chemical Routes That Never Dominated
Beyond the cumene process and ketonization, several other chemical routes to acetone exist. Each has found niche use or has been explored as an alternative, though none has displaced cumene in large-scale production.
One straightforward approach is the dehydrogenation of isopropanol (rubbing alcohol). Passing isopropanol vapor over a metal catalyst at a few hundred degrees strips off hydrogen and converts it to acetone. Recent catalyst work has pushed this reaction’s selectivity above 92%, with conversion rates over 90%.5PubMed. A Lewis acid-base paired InBO(3) catalyst: synthesis and high selectivity for isopropanol dehydrogenation Oxidative dehydrogenation, where a small amount of oxygen participates, has also been studied on metal-zeolite catalysts.6Azerbaijan Chemical Journal. MATHEMATICAL DESCRIPTION FOR THE OXIDATIVE DEHYDROGENATION OF ISOPROPANOL TO ACETONE In practice, this route is circular for most producers because much of the world’s isopropanol is itself made from acetone by hydrogenation, so the economics only work where cheap isopropanol is independently available.
Another route adapts the Wacker process, originally developed to oxidize ethylene to acetaldehyde, by extending it to propylene. Direct oxidation of propylene with a palladium catalyst and a heteropoly acid co-catalyst can produce acetone with very high selectivity, above 99%.7Applied Catalysis A: General. Homogeneous catalytic oxidation of propene to acetone and butene-1 to butanone in the presence of palladium and molybdovanadophosphoric heteropoly acid This Wacker-type oxidation was reported as early as the 1960s.8Chemical & Engineering News. Wacker Process Can Make Acetone, MEK It remains a viable laboratory-scale option and has been commercialized in limited settings, but palladium costs and process complexity have kept it from competing head-to-head with the cumene process.
A more unusual route starts from acetylene. In the presence of specialized catalysts containing iron, zinc, and nickel oxides, acetylene can be hydrated to form acetone rather than the usual product, acetaldehyde. One study reported an acetone yield of about 82% and selectivity near 86% at 450 °C.9E3S Web of Conferences. Production of acetone by catalytic hydration of acetylene This approach is a curiosity more than a commercial contender, but it illustrates how many different carbon feedstocks can, in principle, be channeled into the same simple three-carbon ketone.
The ABE Fermentation
Long before petrochemistry existed, microbes were making acetone. The bacterium Clostridium acetobutylicum naturally produces acetone alongside butanol and ethanol in what is known as ABE (acetone-butanol-ethanol) fermentation. This process was scaled up to industrial levels during World War I, when demand for acetone as a solvent for manufacturing the explosive propellant cordite outstripped what the old calcium-acetate method could supply. The Weizmann process, named after chemist Chaim Weizmann, used C. acetobutylicum to ferment starchy feedstocks like maize and produce acetone at military scale.
The biology is a two-phase affair. In the first phase, the bacteria ferment sugars into organic acids, mainly acetic acid and butyric acid, causing the pH to drop. When the acidity reaches a critical threshold, the cells switch gears and begin re-absorbing those acids and converting them into solvents: acetone, butanol, and ethanol.10PubMed. Role of extracellular cues to trigger the metabolic phase shifting from acidogenesis to solventogenesis in Clostridium acetobutylicum The shift from acid production to solvent production is triggered by a combination of low pH, high intracellular acid concentrations, and shifts in the cell’s energy balance. Researchers have tracked the transition closely and found that the intracellular acid concentration can spike to around 440 mM before the switch flips, and that the cell’s ATP reserves dip to a minimum right before solvent production kicks in.11PubMed Central. Physiological Events in Clostridium acetobutylicum during the Shift from Acidogenesis to Solventogenesis in Continuous Culture and Presentation of a Model for Shift Induction
The key enzyme for acetone formation in this pathway is acetoacetate decarboxylase, which strips a carbon dioxide molecule off acetoacetate to yield acetone.12PubMed Central. Purification of acetoacetate decarboxylase from Clostridium acetobutylicum ATCC 824 and cloning of the acetoacetate decarboxylase gene in Escherichia coli This enzyme is essential for the bacterium’s solvent-producing lifestyle, and its gene has been cloned and transferred into other organisms for engineering purposes, as we’ll see below.
ABE fermentation fell out of favor after World War II as cheap petroleum made the cumene process far more economical. But it has never fully disappeared. Interest in biobutanol as a fuel has periodically revived work on Clostridium fermentation, and acetone comes along as an unavoidable co-product, just as it does in the cumene process, albeit from a completely different starting material.
Engineering Microbes to Make Acetone on Demand
Modern metabolic engineering has taken the acetone-producing machinery from Clostridium and transplanted it into more tractable organisms, especially Escherichia coli. Researchers have assembled synthetic operons combining genes from multiple bacterial species to create custom acetone pathways inside E. coli. In one approach, a modified pathway used genes from C. acetobutylicum for two enzymes (thiolase and acetoacetate decarboxylase) plus a thioesterase gene from Bacillus subtilis or Haemophilus influenzae. The resulting pathway produced up to 122 mM acetone in fed-batch cultures, and it operated independently of acetate, unlike the native Clostridium route which requires a CoA transferase step that consumes acetate.13PubMed. A modified pathway for the production of acetone in Escherichia coli
Other engineered E. coli strains have been designed to consume acetate as a feedstock and convert it directly to acetone. One study found that the choice of CoA-transferase enzyme made a large difference: a strain carrying a transferase with higher acetate affinity produced about 6.5 times more acetone than the weakest performer in the same comparison.14PubMed Central. Metabolic engineering of Escherichia coli carrying the hybrid acetone-biosynthesis pathway for efficient acetone biosynthesis from acetate The appeal of acetate-fed pathways is that acetate is cheap and abundant, a common waste product in industrial fermentation.
Perhaps the most striking bioengineering effort involved an engineered Clostridium strain that ferments synthesis gas (a mixture of carbon monoxide and hydrogen, often derived from waste gasification). The engineered strain, Clostridium sp. MAceT113, was redirected so that it stopped producing ethanol and acetate entirely and channeled its carbon flow into acetone, reaching 1.8 mol per liter in continuous fermentation.15PubMed. Selective production of acetone during continuous synthesis gas fermentation by engineered biocatalyst Clostridium sp. MAceT113 Using syngas as a feedstock is attractive because syngas can be produced from municipal waste, agricultural residues, or even industrial off-gases, decoupling acetone production from both petroleum and food-grade sugars.
Acetone Your Body Makes
You don’t need a chemical plant or a bacterial culture to produce acetone. Your liver makes it every day as part of normal fat metabolism. When your body breaks down fatty acids for energy, the liver converts some of the resulting acetyl-CoA into molecules called ketone bodies. There are three main ketone bodies: beta-hydroxybutyrate, acetoacetate, and acetone. Acetone forms when acetoacetate spontaneously loses a carbon dioxide molecule, the same decarboxylation reaction that Clostridium uses an enzyme to catalyze. The acetone enters your bloodstream and is partly exhaled through your lungs.
Under normal conditions, ketone body production is low and the acetone on your breath is barely detectable. But during fasting, very-low-carbohydrate diets, or uncontrolled diabetes, ketone production ramps up dramatically. In people with type 1 diabetes experiencing ketoacidosis, breath acetone can range from less than 1 part per million to nearly 500 parts per million.16PubMed. The correlation between breath acetone and blood betahydroxybutyrate in individuals with type 1 diabetes That is an enormous range, and it tracks closely with blood ketone levels. Across multiple studies, the correlation between breath acetone and blood beta-hydroxybutyrate averages around 0.77 on a squared scale, strong enough that researchers have proposed breath acetone tests as a simple, non-invasive substitute for finger-prick ketone measurements.17PubMed Central. Measuring breath acetone for monitoring fat loss: Review
In people with type 2 diabetes, the picture is similar. Breath acetone correlates strongly with blood acetoacetate (R = 0.89) and with beta-hydroxybutyrate (R = 0.82), confirming that the breath signal reflects what is happening in the blood.18PubMed Central. Blood Ketone Bodies and Breath Acetone Analysis and Their Correlations in Type 2 Diabetes Mellitus The practical upshot is that breath acetone sensors could eventually replace blood tests for routine ketone monitoring, making life easier for people managing diabetes or tracking nutritional ketosis.
Not all the acetone your body produces gets exhaled. Some of it is further metabolized in the liver by an enzyme in the cytochrome P450 family, specifically CYP2E1, which oxidizes acetone into smaller molecules that can be used for energy or excreted.19PubMed. Relationship between cytochrome P450 2E1 and acetone catabolism in rats as studied with diallyl sulfide as an inhibitor This enzymatic breakdown prevents acetone from accumulating to dangerous levels under most circumstances. It is only when ketone production overwhelms the body’s capacity to clear them, as in diabetic ketoacidosis, that acetone builds up enough to become medically significant.
Acetone in the Ocean
Acetone doesn’t just appear in factories and human breath. It is also a surprisingly common molecule in the world’s oceans. Seawater contains measurable concentrations of acetone, and until recently, most researchers assumed the main source was deposition from the atmosphere. A growing body of evidence now points to marine bacteria as significant producers.
A study of natural bacterial communities in coastal seawater found that after the bacteria consumed available glucose, they began producing acetone at a rate of about 84 nanomoles per liter per day, while degrading it at a rate roughly 40 times slower. The resulting turnover time was around 68 days, suggesting that bacteria are a bigger source of oceanic acetone than they are a sink for it.20Journal of Geophysical Research: Biogeosciences. Production of Oxygen‐ and Sulfur‐Containing Volatile Organic Compounds by Marine Bacteria From Coastal Seawater
On the degradation side, the globally abundant marine bacterium Pelagibacter (part of the SAR11 clade, the most common group of bacteria in the ocean) can metabolize acetone at rates similar to those seen in whole seawater communities. Researchers identified genes encoding an acetone-degrading enzyme, an acetone/cyclohexanone monooxygenase, in the Pelagibacter genome and in the genomes of many other abundant marine taxa. These genes were actively transcribed across ocean surface samples worldwide.21PubMed Central. Metabolism of key atmospheric volatile organic compounds by the marine heterotrophic bacterium Pelagibacter HTCC1062 (SAR11) If extrapolated to global SAR11 populations, this consumption could account for a substantial fraction of the total marine acetone budget.
Why does oceanic acetone matter? Acetone is a volatile organic compound that readily escapes to the atmosphere, where it participates in photochemistry and can influence the formation of ozone and other reactive species. Understanding whether the ocean is a net source or a net sink of atmospheric acetone depends on getting the microbial production and consumption rates right. The emerging picture suggests the ocean’s bacterial communities are both making and eating acetone, with the balance varying by location, nutrient conditions, and season. This is an active area of research with direct implications for atmospheric chemistry models that track how organic compounds cycle between the sea surface and the air above it.
Why So Many Paths to the Same Molecule
Acetone’s molecular simplicity is a big part of why it shows up everywhere. Three carbons, one oxygen, six hydrogens. It is one of the smallest possible ketones, sitting at the bottom of a thermodynamic funnel that many different carbon-containing starting materials can roll down into. Acetic acid can be ketonized to it. Isopropanol can be dehydrogenated to it. Propylene can be oxidized to it. Acetoacetate can be decarboxylated to it. Cumene hydroperoxide can be cleaved to it. Each route works because acetone is a low-energy, stable product that many reactions converge on once you have a three-carbon fragment and the right conditions.
This convergence also explains why biology produces it independently in so many organisms. The decarboxylation of acetoacetate is thermodynamically favorable and mechanistically simple, requiring nothing more than removal of carbon dioxide from a beta-keto acid. Your liver does it spontaneously, Clostridium speeds it up with an enzyme, and marine bacteria generate it as a metabolic side product through related chemistry. Evolution did not need to “invent” acetone production; organisms stumbled into it through the basic biochemistry of fatty acid and organic acid metabolism. The molecule’s volatility then ensures it does not linger. In your body, it exits through your lungs. In the ocean, it escapes to the atmosphere. In a fermenter, it can be captured as vapor. Acetone, by its nature, wants to leave the system that created it.