Methyl ethyl ketone
Structure of methyl ethyl ketone.
| IUPAC name
| Preferred IUPAC name
| Other names
|Molar mass||72.11 g/mol|
|Melting point||−86 °C (−123 °F; 187 K)|
|Boiling point||79.64 °C (175.35 °F; 352.79 K)|
|27.5 g/100 ml|
|Vapor pressure||78 mmHg (20 °C)|
|Safety data sheet||Sigma-Aldrich|
|Flash point||−9 °C (16 °F; 264 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (Median dose)
| 2,737 mg/kg (rat, oral)|
4,050 mg/kg (mouse, oral)
LC50 (Median concentration)
| 12,667 ppm (mammal)|
13,333 ppm (mouse, 2 hr)
7,833 ppm (rat, 8 hr)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Butanone, most commonly known as methyl ethyl ketone or simply MEK, is an organic compound commonly used as a polar solvent and lab reagent. This clear liquid is an example of a ketone, and is similar to acetone.
Methyl ethyl ketone is a clear, colorless fluid that is less viscous than water and has a somewhat sharp, sweet odor characteristic of most ketones, with some describing it as similar to butterscotch. Compared to acetone it is much less volatile and is less soluble in water (approximately 27.5 g/100 ml at room temperature). It is a useful solvent for the extraction of gums and oils from plants and for cleaning residues off of metal and glass, hence why it is often found as a cleaner or a component of lacquers.
Methyl ethyl ketone can be purchased at some hardware stores as simply "MEK". It is also a component of some paint thinners and degreasers. Some hobby stores, such as those that carry modelling kits made of polystyrene or acrylic, carry methyl ethyl ketone as a plastic welding solvent, but this is usually more expensive than finding it at a hardware store.
The solvent in certain paint thinner pastes contain a mixture of methyl ethyl ketone and butyl acetate. Due to the large difference between their boiling point (79.64 °C and 126.1 °C respectively), MEK can be extracted through a simple distillation, though better purity can be achieved using fractional distillation.
Butanone is classified as List II drug precursor chemical in most countries, in the US being classified as DEA List II chemical. The sale of concentrated or pure MEK may be monitored or regulated, depending on the country or region.
Butanone is prepared industrially through the oxidative dehydrogenation of 2-butanol, but for use as a reagent or solvent is typically just purchased, this assuming it's readily available in sufficient purity.
Oxidizing 2-butanol with copper(II) permanganate in dichloromethane for 10 minutes is noted to convert virtually all sec-butanol into MEK, with very little side products. Iron(III) nitrate on kieselguhr can also be used instead of permanganate, though the reaction requires heating and takes around 90 minutes to complete, giving a yield of 95%.
Oxidizing n-butane over complex catalysts will also yield MEK and some side products.
A process described by F. Bauer involves the reaction of conc. sulfuric acid with 3-hydroxybutanal at 190 °C yields butanone. As 3-hydroxybutanal can be obtained through the aldol condensation of acetaldehyde in the presence of a base, this reaction is less complex that other processes.
The pyrolysis of anhydrous calcium butyrate with calcium acetate at 400 °C in an oxygen-free environment will yield some butanone. A similar reaction occurs when calcium butyrate is replaced with calcium propionate.
Adding methyl iodide to acetone in the presence of potassium hydroxide yields butanone.
An interesting process involves the oxidation of isobutanol using a ruthenium complex catalyst, more specifically [RuCl(PPh3)(L)2], in the presence of 4-methylmorpholine N-oxide. The reaction takes place in dichloromethane for 3 h, giving an yield of 76%. A less expensive process replaces the ruthenium catalyst with quinolinium fluorochromate (which is made by reacting chromium trioxide with 40% hydrofluoric acid and then reacted with quinoline), which is supported on silica gel. Just like the previous process, the reaction takes place in dichloromethane and produces heat. The reaction runs for 4 hours, giving a yield of 58%. While isobutanol is readily available, the main disadvantage of this route is that they require expensive catalysts.
An interesting process developed involves the electrolytic oxidation of lignin at a lead cathode in a sodium hydroxide solution with a current density of 2 A per 100 cm2. While many lignin sources can be used, the best yield was from butanol lignin from western hemlock. The average yield is 23.3% butanone, with the rest being acetone (15.2%), acetic acid (15.1%), while other compounds are below 10%. While the yields are not great, lignin can be cheaply extracted from plants.
Pyrolysis of cellulose in the presence of air at temperatures between 400 - 600 °C will yield butanone, 2-methylfuran, styrene, toluene. The yields aren't great, but cellulose is cheaply available.
Methyl ethyl ketone is a skin and respiratory irritant. At very high concentrations it poses health problems, may cause birth defects in animals.
MEK is highly flammable and should not be handled near any open flame or strong oxidizing agents.
MEK should be stored in a closed bottle, in a dark place.
MEK can be safely burned.
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