2-Pentanone CAS 107-87-9: Properties, Solvent Uses and Handling

What 2-Pentanone Is

2-Pentanone, also known as methyl propyl ketone, MPK or pentan-2-one, is a straight-chain aliphatic ketone with the molecular formula C5H10O and a molecular weight of 86.13. Its CAS number is 107-87-9. The molecule consists of a five-carbon chain with the carbonyl group on the second carbon, which gives it a polarity and solvent strength that sit between acetone and the higher dialkyl ketones while retaining a comparatively low boiling point of about 101-102 degrees C at atmospheric pressure.

At room temperature 2-pentanone is a colourless, mobile liquid with a characteristic sweet, fruity and somewhat ketonic odour. It is sparingly soluble in water and freely miscible with ethanol, diethyl ether, acetone, esters and most aromatic and aliphatic hydrocarbons. That combination of moderate polarity, low viscosity and moderate evaporation rate is what makes the substance useful as a solvent and as a synthetic intermediate.

It is important to distinguish 2-pentanone from its close relatives, because confusion in purchasing documents is a common source of rejected deliveries. 3-Pentanone, also called diethyl ketone, is CAS 96-22-0 and is a symmetrical ketone with a different boiling point and reactivity profile. Pentanal, also called valeraldehyde, is CAS 110-62-3 and is an aldehyde with markedly different hazards and odour. 4-Methyl-2-pentanone, CAS 108-10-1, is a branched homologue that behaves as a slower-evaporating solvent. Each has its own specification and must be ordered by CAS number and by full chemical name rather than by the generic term pentanone.

Physical and Chemical Properties

The technical data below are the parameters that appear on typical commercial certificates of analysis and material safety documentation. They should be read together with the supplier specification, which remains the binding document for a specific delivery.

Two derived points deserve attention. First, because the vapour is roughly three times as dense as air, any release in a confined or low-lying area will accumulate near the floor, in pits and in sumps, where it can reach a flammable concentration well below the level at which an operator would notice the odour. Second, because the flash point is close to ordinary ambient temperature in a temperate climate, the liquid itself is not the only hazard: an open tray of 2-pentanone at room temperature can generate a flammable atmosphere above its surface, so flameproof electrical equipment, bonding and grounding and local exhaust ventilation are design requirements rather than optional refinements.

Chemical Reactivity

The reactivity of 2-pentanone is that of a simple methyl ketone. The carbonyl carbon is electrophilic, so the substance undergoes nucleophilic addition with a wide range of reagents, forming alcohols on reduction and cyanohydrins with hydrogen cyanide; it condenses with hydroxylamine, hydrazine derivatives and semicarbazide to give the corresponding oxime, hydrazone and semicarbazone, which are classical derivatives used for identification and purification. The hydrogen atoms on the carbon adjacent to the carbonyl group are acidic enough to be removed by strong base, which allows aldol additions and condensations and, under the right conditions, alkylation at that position.

Oxidation of 2-pentanone under vigorous conditions cleaves the carbon chain and yields a mixture of carboxylic acids, while careful oxidation with reagents such as peroxy acids can give esters by the Baeyer-Villiger route. All of these reactions belong to the standard repertoire of organic synthesis and are the reason the ketone is traded as an intermediate as well as a solvent.

From a stability standpoint 2-pentanone is a comparatively well-behaved material. It does not readily autoxidise to peroxides in the way that ethers do, and it does not polymerise spontaneously. Good practice nevertheless requires storage away from strong oxidising agents, strong bases and strong acids, because these can trigger vigorous or hazardous reactions. The substance hydrolyses slowly in the presence of acid or base, and its water content is controlled in storage to keep the acidity value within specification and to avoid the corrosion of carbon steel drums.

Manufacture and Supply Chain Position

Industrially the dominant route to 2-pentanone is the catalytic dehydrogenation of 2-pentanol, which is itself produced from C5 streams derived from naphtha cracking or from the hydration of pentenes. Catalytic dehydrogenation over metal-based catalysts converts the secondary alcohol to the ketone with hydrogen as the by-product, and the crude ketone is purified by distillation to the required assay. A secondary route is the recovery of 2-pentanone as a co-product from the oxidation of hydrocarbon fractions, where it appears alongside other ketones and alcohols and must be separated by fractional distillation.

The practical implication for buyers is that supply of 2-pentanone is linked to the availability and price of C5 feedstock and to the operating rates of upstream crackers and refinery units. Material sold into regulated applications is usually produced from dedicated synthetic streams rather than from recovered co-product, because the impurity profile of a recovered stream can vary with the feedstock. A certificate of analysis should therefore identify the assay by gas chromatography, the principal impurities, the water content and the acidity value, and should be supported by a change-control statement if the product is used in a regulated formulation.

Because 2-pentanone is a flammable liquid of packing group II, logistics are more demanding than for a non-hazardous fine chemical. Road tankers, ISO tanks and drums must meet the applicable dangerous goods requirements, drivers and loading staff must be trained, and unloading points need bonding and grounding provisions. The shipping description on the transport document must state the correct proper shipping name together with the UN number, class and packing group, in line with the applicable modal regulations for road, sea and air transport.

Solvency and Industrial Applications

The largest volume use of 2-pentanone is as a solvent. Its blend of moderate polarity and moderate evaporation rate makes it effective for cellulose esters, vinyl resins, acrylic resins and many natural resins, and it is formulated into coatings, printing inks, adhesives and leather finishing products. In a coating or ink, the solvent is chosen for its evaporation profile as much as for its dissolving power: a solvent that is too volatile causes blushing and premature drying at the surface, while one that is too slow leaves residual solvent in the film and can cause blocking. 2-Pentanone sits in the useful middle of that spectrum, which is why it is often used as a component of a solvent blend rather than as the sole solvent.

In adhesives and sealants the ketone acts as a carrier that keeps the polymer in solution during application and then evaporates to leave a coherent film. Here again the evaporation rate governs open time and initial tack, and the solvent must be compatible with the tackifying resins and plasticisers in the formulation. In the printing industry, 2-pentanone is used in gravure and flexographic ink systems where a controlled drying rate is needed across a range of press speeds.

Beyond coatings, the substance is used as an extraction and process solvent in organic synthesis and as a cleaning and degreasing component in industrial formulations, where its ability to dissolve both polar and non-polar residues reduces the number of separate cleaning steps. In all of these uses the flammability of the material drives the engineering design: closed vessels, inert gas blanketing where practicable, explosion-proof motors and lighting, adequate ventilation at floor level, and elimination of ignition sources within the classified zone.

Flavour, Fragrance and Fine Chemical Uses

2-Pentanone occurs naturally in a range of foods and is widely recognised as a flavour-active substance with a sweet, fruity, slightly ethereal character. It appears among the synthetic flavouring substances permitted for use in food under the food additive regulations of the United States, within 21 CFR Part 172, and it is used in flavour compositions where a light fruity or dairy-type note is wanted. As with all flavour ingredients, the use level is set by the formulator against sensory evaluation and by the applicable national food law rather than by the technical limits of the chemical itself.

In the fragrance industry the ketone is used as a top-note modifier and as an intermediate for the synthesis of more complex odorants. Its relatively high volatility means that it contributes to the opening impression of a composition and does not persist on the substrate, which is useful when a light, fresh effect is desired and undesirable when substantivity is required.

As a fine chemical intermediate, 2-pentanone is a starting point for oximes and hydrazones, for the synthesis of substituted pyridines and other heterocycles through condensation chemistry, and for building blocks used in pharmaceutical and agrochemical development. In the pharmaceutical and crop protection supply chains the ketone is normally supplied against a tighter specification than the solvent grade, with defined limits on water, acidity, colour and related ketones, because those parameters can affect both reaction yield and the impurity profile of the final active substance. Purchasers in these channels should confirm the impurity limits that matter for their own process and place them in the specification rather than relying on a generic solvent-grade certificate.

Quality Control and Specification Parameters

A workable specification for 2-pentanone is short but precise. Identity is confirmed by infrared spectroscopy against a reference spectrum and, for a liquid of this kind, by measurement of relative density and refractive index against a retained reference sample. Assay is determined by gas chromatography with flame ionisation detection and an external standard, with the principal related substances reported individually rather than grouped, since the level of 3-pentanone and of lower alcohols or aldehydes can affect downstream reactions.

Water content is measured by Karl Fischer titration, for which GB/T 6283 describes the general method accepted in Chinese chemical trade, and is typically limited to a low value because water both promotes hydrolysis and contributes to corrosion of mild steel containers. Acidity, expressed as acetic acid or as an acid value in mg KOH per gram, is determined by titration with standard volumetric solutions prepared in accordance with GB/T 601; an increase in acidity during storage is the earliest warning that a drum has absorbed moisture or has been contaminated. Colour is measured on the platinum-cobalt scale, and the value is meaningful because colour development accompanies the formation of higher-molecular-weight condensation products.

Because 2-pentanone is a flammable liquid, sampling must be carried out with bonding and grounding and with non-sparking tools. Representative sampling of drums and tanks should follow a documented procedure such as GB/T 6678 so that the sample submitted to the laboratory actually represents the bulk. Packaging marks should follow GB/T 191 for handling pictograms, and the safety data sheet should be prepared in the recognised structure described by ISO 11014 and include the classification and labelling information required by the destination market.

Flammability, Safe Handling, Storage and Transport

2-Pentanone is classified as a flammable liquid, and its flash point close to ambient temperature places it in the more restrictive flammable classes used in the GHS and CLP systems for liquids with a low flash point and a boiling point above 35 degrees C. It also carries hazard statements for eye and respiratory irritation. Any risk assessment should therefore address three separate exposure routes: inhalation of vapour, skin contact with the liquid, and eye contact from splashes or from handling saturated vapour in a confined space.

Engineering controls come first. Local exhaust ventilation at the point of use, general ventilation designed to remove vapour at floor level, closed transfer systems, and flameproof or intrinsically safe electrical equipment within the classified area are the standard measures. Where exposure cannot be controlled by engineering means, respiratory protection appropriate to organic vapours is used within the framework of a written programme that includes fit testing and exposure monitoring. Personal protective equipment includes chemical splash goggles or a face shield, gloves resistant to ketones, and antistatic clothing and footwear where a flammable atmosphere could be present.

For storage, the material should be kept in tightly closed containers in a cool, dry, well-ventilated area away from heat, direct sunlight, oxidising agents, strong acids and strong bases, and separated from other hazard classes in accordance with local fire codes. Drums should be stored in bunded areas with secondary containment sized to hold the contents of the largest container, and earthing straps should be used when decanting. Because the vapour is denser than air, storage areas should not have open drains, pits or basements into which vapour can sink and collect.

First aid measures follow the expected pattern for a solvent of this type: move the affected person to fresh air, remove contaminated clothing, irrigate eyes with water for at least fifteen minutes, and obtain medical attention where symptoms persist. Spills should be absorbed with inert material, the area ventilated, and the absorbed waste disposed of as a flammable solvent waste under the applicable local regulations. Fire fighting should use foam, dry chemical or carbon dioxide; a water jet is unsuitable because it can spread the burning liquid, although water spray may be used to cool unopened containers.

For transport, the material is shipped under UN 1249 with the proper shipping name for methyl propyl ketone, hazard class 3 and packing group II, in packaging that meets the applicable construction and testing requirements. The same description is used across road, sea and air modes with the appropriate documentation, and quantities are limited according to the mode and to whether the shipment is a full load or a limited quantity consignment.

FAQ

Q: What is the CAS number and molecular formula of 2-pentanone?
2-Pentanone is CAS 107-87-9, with the molecular formula C5H10O and a molecular weight of 86.13. It is an aliphatic methyl ketone, also known as methyl propyl ketone or pentan-2-one.

Q: How does 2-pentanone differ from 3-pentanone and from 4-methyl-2-pentanone?
They are distinct substances with different CAS numbers and properties. 3-Pentanone is the symmetrical diethyl ketone, CAS 96-22-0, with a different boiling point and reactivity pattern, while 4-methyl-2-pentanone is CAS 108-10-1, a branched ketone with a higher boiling point and a slower evaporation rate. Orders and specifications should always quote the full chemical name together with the CAS number.

Q: What are the main industrial uses of 2-pentanone?
Its largest use is as a solvent in coatings, printing inks, adhesives and industrial cleaning and degreasing formulations, where its moderate evaporation rate and broad solubility are valuable. It is also used as a flavouring substance, as a fragrance ingredient and as an intermediate in organic synthesis, including the manufacture of oximes, heterocycles and pharmaceutical or agrochemical building blocks.

Q: Is 2-pentanone dangerous to transport and store?
Yes, it is a flammable liquid shipped under UN 1249, hazard class 3, packing group II. Storage requires closed containers in a cool, ventilated area away from ignition sources, oxidising agents and strong acids or bases, with secondary containment and earthing provisions for transfers. Because the vapour is about three times as dense as air, it can travel along the floor to a distant ignition source.

Q: How is 2-pentanone normally assayed and specified?
Assay is measured by gas chromatography, identity by infrared spectroscopy together with relative density and refractive index checks, water by Karl Fischer titration in line with GB/T 6283, and acidity by titration with standard volumetric solutions prepared according to GB/T 601. Colour on the platinum-cobalt scale and a listing of principal related substances complete a typical specification.

Q: How should 2-pentanone be stored for a long shelf life?
Keep containers tightly closed in a cool, dry, well-ventilated store away from heat, sunlight, oxidants, strong acids and strong bases, with bonding and grounding used during decanting. Unlike ethers, the ketone does not readily form peroxides, but moisture uptake raises the acidity value and free acid promotes corrosion of mild steel, so drums should be resealed promptly and the water content and acidity checked at retest.