Cumene hydroperoxide explosion
Manuel A. Francisco
Chemical & Engineering News (31 May 1993) Vol. 71, No. 22, pp. 4.
An explosion occurred in our laboratory during the purification of 100 mL of cumene hydroperoxide. The explosion was violent enough to completely shatter the ceramic top of a magnetic stir plate. Modifications of the published procedure ("Purification of Laboratory Chemicals," D. D. Perrin, W. L. F. Armarego, and D. R. Perrin, 2nd Ed.) were used and involved washing the sodium salt of the hydroperoxide with toluene rather than benzene and drying the hexane extracts of the cumene hydroperoxide over anhydrous magnesium sulfate. The magnesium sulfate had been removed by filtration, and the hexane was evaporated under vacuum at ambient temperature when the flask exploded. Most of the hexane appeared to have been removed because the residue in the flask was quite viscous. The cumene hydroperoxide was probably present in very high concentration, with little hexane remaining just before the explosion. All other aspects of the procedure were identical to those published in the book cited.
The exact cause of the explosion is not known. The only modification of the procedure that could possibly be connected to the explosion is the use of magnesium sulfate. It does not seem likely that substituting toluene for benzene would have any effect. This modified procedure has been used many times by several researchers in our laboratories with no problems; however, the incident serves as a poignant reminder of the sensitive nature of hydroperoxides, even those hydroperoxides known to be thermally quite stable, such as cumene hydroperoxide.
Cumene hydroperoxide at 0.2M concentration in benzene is thermally stable with a half-life of 29 hours at 145 C. The material, as it is purchased, is often listed as 80% cumene hydroperoxide. We know from analysis that the impurities are decomposition products of cumene hydroperoxide (alpha methyl styrene, acetophenone, and cumyl alcohol). Many vendors warn that in the concentrated state, as purchased, cumene hydroperoxide should be stored at temperatures below 80 C. The thermal data on hydroperoxides can be misleading and lull one into a false sense of security. The literature is full of examples showing that cumene, as well as other hydroperoxides, can undergo rapid decomposition at room temperature with a wide range of compounds, even when these compounds are present in trace or catalytic concentrations (acids and metal are examples). If one happens to be purifying a relatively large quantity of the hydroperoxide in a neat or concentrated state, the potential for an uncontrolled reaction and explosion is high.
During a purification procedure, there are many opportunities to inadvertently introduce small amounts of materials that may prove to be active catalysts for hydroperoxide decomposition. This can occur even when using well-established purification procedures. We recommend staying with the published procedures and not using active drying agents such as magnesium sulfate. The drying agent could contain traces of unidentified materials that may catalyze decomposition of the hydroperoxide.
We also recommend purifying small quantities of cumene hydroperoxide
(< 5 g) and using it immediately. One should also take advantage of
all available protective measures. Such measures include keeping the
hood clear of any other flammable or potentially dangerous materials
during purification. This precaution helps to avoid the possibility
of secondary accidents being initiated by the uncontrolled reaction
of the hydroperoxide during purification. Safety visor, apron, and
heavy gloves should also be worn and explosion-proof shields used.
page last revised December 7, 1998