Reagents for High Temperature Aqueous Chemistry: Trifluoromethanesulfonic Acid and its Salts

Abstract

The rate of decomposition of trifluoromethanesulfonic acid (HTFMS) in water is first order with respect to each of H+ and TFMS−. The bimolecular rate coefficient kH can be represented by[Formula: see text]at ionic strength 1.0 mol kg−1 over the temperature range 571 < T < 593 K, although the decomposition occurs by two pathways of comparable importance, one leading to C(II) and S(VI) and the other to C(IV) and S(IV). In alkaline solution, the rate of decomposition of TFMS− is first order in each of TFMS− and OH−, and the bimolecular rate coefficients kOH at ionic strength 2.3 are given by[Formula: see text]This represents a single reaction pathway leading initially to C(II) and S(VI) and ultimately to CO32−, SO42−, F−, and H2, since C(II) (as formate) reduces aqueous alkali to H2 under the reaction conditions. No decomposition of NaTFMS could be detected after 24 h at 620 K in neutral aqueous solution. HTFMS reduces certain aqueous species at significant rates at moderate temperatures (e.g., Fe(III) to Fe(II) at 470 K), and metals which depend on oxide films for their corrosion resistance are attacked by HTFMS even at 294 K (e.g., Ti dissolves giving Ti(H2O)63+). Otherwise, HTFMS and its salts have good potentialities as inert electrolytes for aqueous studies at high temperatures.