Radiation Chemical Production and Lifetimes of Trialkoxymethyl Carbocations in Aqueous Solution

Article abstract of DOI:10.1021/ja00271a004

Trialkoxymethyl radicals were produced in aqueous solution by H abstraction from trialkoxymethanes by OH and H.The radicals were then oxidized by one-electron transfer to give trialkoxymethyl carbocations.The reactions of the cations with water and with OH^- were studied by using time-resolved conductance techniques. (CH3O)3C⁺ hydrolyzes with a rate constant of (1.4 +/- 0.2)E3 s^1- and it reacts with OH^- with k = (7 +/- 1)E7 M^1-s^1-.The activation parameters for the reaction with water are E_A = 7.6 kcal/mol and ΔS(excit.) = -20.2 eu.Replacement of methoxy in the cation by ethoxy and isopropoxy leads to a pronounced decrease in the rate constants for these processes: the Taft ρ^* values for the reaction of (RO)3C⁺ with H2O and OH^- are 5.7 and 3.7, respectively.With cyclic trialkoxymethyl cations that from the six-membered 1,3-dioxane system is more stable than that from 1,3-dioxolane, the five-atom counterpart.Trialkoxymethyl cations are also produced by a β-fragmentation reaction from α-(β-trialkoxy)methoxyalkyl cations.