Oxidation of Olefins by Palladium(II). 12. Product Distributions and Kinetics of the Oxidation of 3-Buten-2-ol and 2-Buten-1-ol by PdCl42- in Aqueous Solution

Article abstract of DOI:10.1021/jo00293a031

The rate expression for oxidation of both allyl alcohols was determined to be rate = k2->/+>->², an expression identical in form with that found previously for the oxidation of ethene, allyl alcohol, and other acyclic olefins, indicating similar mechanisms.Contrary to previous reports, the product distribution from 3-buten-2-ol (6) was completely different from that for 2-buten-1-ol (7), indicating that fast isomerization into an equilibrium mixture before oxidation was not occuring.A short study of the rate of isomerization using deuteriated 6 and 7 confirmed that isomerization was slow under the oxidation conditions.The distributions gave considerable information on the effects of steric and electronic factors on the modes of hydroxypalladation.While allyl alcohol gave a 3/1 preference for addition of the Pd(II) to the center carbon due to the directing influence of the hydroxyl group, 6 gave 4/1 preference for addition of Pd(II) to the end carbon.The steric effect of the methyl is thus appreciable.With 7 the double bond is internal so steric factors are not important and the directing influence of the hydroxyl will be the important effect.The ratio of Pd(II) addition next to the carbon containing the hydroxyl group to addition to the other side of the double bond is 34/1, indicating considerable directing influence of the hydroxyl.The preference for secondary over primary hydride shift is 1.25, a value which indicates almost no carbonium ion character and considerable Pd(II)-H character.Using a specifically deuterated 7, the value of the deuterium isotope effect, k_H/k_D, can be determined by internal competitive hydride transfer by taking into account the positional preferance for secondary hydride shift.This value of 2.2 is close to values previously determined for ethene and allyl alcohol.