Trichloroacetic acid storage

Leslie Bretherick
Dorset, England

Chemical & Engineering News (26 May 1997) Vol. 75, No. 21, pp. 4.

My recent correspondence with D. J. Mabbott, safety officer, University of Hong Kong, revealed an unexpected reaction hazard in storing aqueous solutions of trichloroacetic acid. A -1/2-L capped bottle containing a 12% weight by volume solution of trichloroacetic acid in water with 30% methanol exploded violently after two years of storage at ambient temperature. The explosion caused several adjacent bottles to break.

In several editions of the Merck Index, but, apparently, not elsewhere, it is stated that trichloroacetic acid is hydrolytically unstable in aqueous solutions less concentrated than 30% by weight. Such solutions are strongly acid (millimolar solutions have a 1.2 pH) and should not be stored. The decomposition products of such solutions include trichloromethane, hydrochloric acid, carbon dioxide, and carbon monoxide.

Assuming complete decomposition of 250 mL of the 12% solution at ambient temperature, the 4.5 L of evolved gases could have pressurized the free space in the bottle toward 19 bar, well above its likely bursting strength.

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