Explosion in preparation of 5-bromo-4(3H)-pyrimidinone

Thomas J. Dietsche; Bruce Powers
Agricultural Chemicals Process Research
Thermal & Reactive Chemicals
Dow Chemical Co.

Chemical & Engineering News (10 Jul 1995) Vol. 73, No. 28, pp. 4.

Powers We would like to report a serious experience we had using a literature preparation of 5-bromo-4(3H)-pyrimidinone [J. Org. Chem. 50, 3073 (1985)]. Two moles (20-fold increase over literature preparation) of 5-bromopyrimidine was dissolved in about 1,800 mL of acetone. Over a four-hour period, a mixture of 1 L of peracetic acid and 115 mL of concentrated sulfuric acid was added dropwise while keeping the reaction below 20 C. On four earlier runs, the white solid product was filtered, washed with ether, and allowed to air dry for two to four hours. This run was filtered late on a Friday evening and allowed to air dry over the weekend. On Monday morning, the powder-dry product was being scraped from a sintered glass funnel to complete the neutralization of the hemiacid salt when an explosion occurred.

Subsequent testing determined that the peroxide dimer of acetone was the most likely cause of the explosion. This material is reported to be both shock and friction sensitive and known to sublime at room temperature. This reaction had been run numerous times in these and other laboratories without any suggestion of the hazards. We had scaled the reaction up from the literature preparation through several intermediate levels before deciding to proceed in our preparation of several kilograms of the desired pyrimidinone on the 2-molar scale.

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