Addition of Trifluoroacetic Acid to Substituted Styrenes

Article abstract of DOI:10.1021/jo00143a011

The rate of addition of CF3CO2H to a series of ring-substituted styrenes ArCH=CH2 with 100percent, 50percent, and 20percent solutions of the acid in CCl4 have been measured.The rate of addition of 100percent CF3CO2H to the isomeric 1-phenylpropenes and the rate of cis- to trans-stilbene isomerization by this acid are also reported.The rates are correlated with ?⁺ parameters of the substituents and with aqueous H2SO4-catalyzed hydrations of the same substrates.Deviations from the ?⁺ correlation occur with substituents capable of strong hydrogen bonding to the acidic solvents; these deviations are attributed to a decrease in substituent electron-donating ability caused by this interaction.All of the evidence supports a mechanism of rate-determining protonation on carbon (the Ad_E2 mechanism), with no detectable effects from ? complexation of the acids with the substrates.