2-Butanone peroxide

Methyl ethyl ketone peroxide (MEKP) is an organic peroxide, a high explosive similar to acetone peroxide. MEKP is a colorless, oily liquid whereas acetone peroxide is a white powder at STP; MEKP is slightly less sensitive to shock and temperature, and more stable in storage. Depending on the experimental conditions, several different adducts of methyl ethyl ketone and hydrogen peroxide are known. The first to be reported was a cyclic dimer, C8H16O4, in 1906. Later studies found that a linear dimer is the most prevalent in the mixture of products typically obtained, and this is the form that is typically quoted in the commercially available material from chemical supply companies.
Dilute solutions of 30 to 60% MEKP are used in industry and by hobbyists as the catalyst which initiates the crosslinking of unsaturated polyester resins used in glass-reinforced plastic, and casting. For this application, MEKP is dissolved in dimethyl phthalate, cyclohexane peroxide, or diallyl phthalate to reduce sensitivity to shock. Benzoyl peroxide can be used for the same purpose.
MEKP is a severe skin irritant and can cause progressive corrosive damage or blindness.
MEKP, acetone peroxide and HMTD have all been reported to be the explosives used in the alleged 2006 transatlantic aircraft plot.