What Is Methyl Ethyl Ketone (MEK)?
Methyl ethyl ketone, abbreviated MEK and also known under its IUPAC name 2-butanone, is a colourless, highly flammable liquid with a sharp sweet or acetone-like odour. Its molecular formula is C4H8O, its relative molecular mass is 72.11, and its CAS number is 78-93-3. Because the carbonyl group sits between a methyl and an ethyl group, the molecule is small, only moderately polar and completely miscible with water, alcohols, esters, ketones and aromatic hydrocarbons.
That combination of a low boiling point, a fast evaporation rate and broad solubility is the key to its industrial role. MEK is not a slow, film-forming solvent like an aromatic naphtha; it is a fast, aggressive solvent used where rapid drying, strong solvency for polar resins and easy removal are the priorities. It is an excellent solvent for nitrocellulose, vinyl, acrylic, epoxy, polyurethane and polyester systems.
Typical Properties and Specification Data
| Property | Typical value |
|---|---|
| Chemical name | 2-butanone (methyl ethyl ketone) |
| CAS number | 78-93-3 |
| Molecular formula | C4H8O |
| Relative molecular mass | 72.11 |
| Appearance | colourless clear liquid |
| Odour | sharp, sweet, acetone-like |
| Boiling point at 101.3 kPa | about 79.6 degrees C |
| Flash point, closed cup | about minus 6 degrees C |
| Auto-ignition temperature | about 404 degrees C |
| Explosive limits in air | about 1.4 to 11.4 percent by volume |
| Relative density at 20 degrees C | about 0.805 |
| Vapour pressure at 20 degrees C | about 105 hPa |
| Solubility in water | fully miscible |
| Assay, industrial grade | 99.5 percent minimum by gas chromatography |
Industrial material is supplied in tank cars, ISO tanks, 200 litre drums and smaller repackaged units, with acidity, water content, colour and non-volatile residue specified alongside assay. Values in the table are typical published figures and each delivery is governed by its certificate of analysis.
Solvency and Coating Applications
MEK dissolves resins, rubbers and cellulose derivatives that aliphatic hydrocarbons cannot, and it does so while evaporating quickly enough to leave a tack-free film in minutes. In coatings and paints it gives the wet film good flow, drying speed and gloss, and it is widely used in furniture, automotive refinish, marine and industrial coating lines where throughput matters.
Formulators rarely use MEK alone. It is blended with slower solvents such as xylene, aromatic naphtha or glycol ethers to balance evaporation, and with alcohols or esters to adjust polarity and reduce the risk of blushing on humid days. In cellulose nitrate lacquers and vinyl copolymer coatings, MEK is often the active or true solvent that keeps the resin in solution, while the co-solvents control flow and open time.
Adhesives, Inks and Electronics Cleaning
Adhesives. MEK dissolves the polymer base of solvent-borne adhesives, adjusts viscosity and open time, and improves wetting so the adhesive grips wood, leather, plastic, metal and rubber surfaces. It is common in contact adhesives, in laminating and shoe adhesives, and in cements for PVC and other polar plastics.
Printing inks. As a fast solvent it carries resins and colourants, sets the drying speed of flexographic and gravure inks, and keeps the ink transferring cleanly at high press speeds without drying on the rollers.
Electronics. Electronics and printed circuit board manufacturing use MEK to remove flux residues, oils and particulate contamination from components and boards. It evaporates without leaving a residue and does not attack most substrate materials, which supports the performance and reliability of the finished assembly.
Surface preparation. In metal and plastic fabrication it is used as a wipe solvent to remove mould release agents, cutting oils and marking inks before bonding, coating or welding.
Organic Synthesis and Process Uses
MEK is an important organic synthesis intermediate. Catalytic hydrogenation or condensation converts it into methyl isobutyl ketone, a widely used medium-boiling solvent for coatings and extraction. It is also a starting material for MEK peroxide, used as a curing initiator for unsaturated polyester and vinyl ester resins, for antioxidants, and for a range of flavour and fragrance compounds where the butanone skeleton is retained.
In pharmaceutical and fine chemical manufacturing it serves as a reaction solvent, a crystallisation solvent and a work-up solvent, valued because it is water-miscible, easy to strip and available in high-purity grades with a controlled water content.
In refining, MEK is the ketone component of the MEK-toluene dewaxing process, where it precipitates wax from lubricating oil stocks, lowers the pour point and improves low-temperature fluidity of the finished lubricant. In textiles it acts as a carrier and solvent in dyeing and printing, helping dyes penetrate and fix to the fabric. In plastics processing it is used as a solvent, cleaning agent and processing aid to improve handling and surface quality.
Handling, Storage and Safety
MEK is a highly flammable liquid and its vapour forms explosive mixtures with air over a wide range, so it must be handled in bonded and earthed equipment with no ignition sources, hot surfaces or non-explosion-proof electrical fittings nearby. Vapour is heavier than air and can travel to a remote ignition point. Local exhaust ventilation is required wherever the liquid is open, and respiratory protection is needed if the exposure limit cannot be met by engineering controls.
The liquid defats skin and irritates eyes, so nitrile gloves, chemical goggles and protective clothing are standard. Store in closed steel containers or dedicated tanks, out of direct sunlight and away from oxidising agents, strong acids and strong bases, at temperatures below 30 degrees C. Drums should be kept dry, since water pick-up degrades solvent performance in moisture-sensitive applications.
Frequently Asked Questions
Q: What is MEK methyl ethyl ketone used for?
It is used as a fast-drying solvent in coatings, printing inks, adhesives and electronics cleaning, as a synthesis intermediate for methyl isobutyl ketone and MEK peroxide, and as a dewaxing solvent in lubricant refining.
Q: Is MEK the same as acetone?
No. Both are ketones and both are fast solvents, but MEK is 2-butanone with CAS 78-93-3 and boils near 79.6 degrees C, while acetone has a lower boiling point and different solubility behaviour.
Q: What is the CAS number and formula of MEK?
The CAS number is 78-93-3, the molecular formula is C4H8O, and the relative molecular mass is 72.11.
Q: Is MEK miscible with water?
Yes, MEK is fully miscible with water, which is why it is easy to clean equipment with and also why it is a common reaction and crystallisation solvent.
Q: How flammable is MEK?
It is a highly flammable liquid with a closed-cup flash point near minus 6 degrees C and an explosive range of roughly 1.4 to 11.4 percent by volume in air.
Q: What purity is used for industrial applications?
Standard industrial grade is 99.5 percent minimum by gas chromatography, with acidity, water content and colour controlled because trace water affects moisture-sensitive systems.