Abstrato

Kinetics of acid-catalyzed breakdown of -bonds and formation of carbonium ions for heptene in wide-ranging concentrations of H2SO4

Lev G.Helfman, Vladimir V.Gridin, Israel Schechter*

UV-absorption of heptene was studied for variable concentrations, CA, of sulfuric acid. The kinetic analysis of the experimental results involves thermodynamic considerations of acidity function (H0) and activities of acid solutions. The -bond originated band nearby 200 nm is blue shifted for CA < 40%. The corresponding extinction coefficient of this band, 200, sharply drops by a factor of 4 on passing from the aqueous solution of heptene (200 =1300) to about 200 = 350 for the CA = 2% case. Moreover, kinetic analysis of the data indicates a monotonic increase of 200 to about 3000 nearbyCA = 60%.Asudden drop to zero is observed for 200 in the concentration range between 60% and 80%. This is accompanied by the appearance of an absorption band nearby 300 nm. The corresponding extinction coefficient, 300, shows a gradual rise to about 2500 at the highest CA studied (= 96%). A similar monotonic rise of 200 to about 4000 was also observed for this range of acid concentrations. The order of kinetic processes abruptly changes from 1 (for CA < 60%) to 2 (for CA> 80%). These new results are discussed in relation to the well-known formation of carbonium ions and the breakdown of -bonds.