RATE CONSTANTS FOR THE REACTION OF THE HYDROGEN-ATOM WITH ALIPHATIC-KETONES IN WATER

Arrhenius parameters for the reaction of hydrogen atoms with 3-methyl- 2-butanone, 3-pentanone, cyclopentanone, 4-methyl-2-pentanone, and 2-b utanone in aqueous solution have been directly calculated from electro n paramagnetic resonance free induction decay (FID) attenuation measur ements. For these compounds, absolute scavenging rate constants at 25. 0 degrees C of (8.84 +/- 0.26) x 10(7), (4.20 +/- 0.15) x 10(7), (4.91 +/- 0.28) x 10(7), (3.25 +/- 0.27) x 10(7), and (2.20 +/- 0.32) x 10( 7) dm(3) mol(-1) s(-1), with corresponding activation energies of 17.4 3 +/- 0.29, 20.69 +/- 0.31, 18.73 +/- 0.35, 22.24 +/- 0.80, and 22.30 +/- 1.04 kJ mol(-1) were determined, respectively. Competition kinetic measurements based on total H-2 yields have established that for all of these ketones the dominant hydrogen atom reaction path is by H-. at om abstraction. The new activation energy for 2-butanone is much lower than the previously reported value of 40.1 +/- 0.7 kJ mol(-1) with th is difference attributed to interfering reactions from the added bromi de previously used as a hydroxyl radical scavenger.