AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM7
Fluorinated Carboxylic Acids Deprotonation on the Cu(100) Surface

Tuesday, November 4, 2003, 10:20 am, Room 327

Session: Catalysis II: Hydrocarbons at Metal Surfaces
Presenter: P. Ye, Carnegie Mellon University
Authors: B. Immaraporn, Fritz-Haber Institute, Germany
P. Ye, Carnegie Mellon University
A.J. Gellman, Carnegie Mellon University
Correspondent: Click to Email
The kinetics of acid deprotonation on the Cu(100) surface have been studied using four different fluorinated carboxylic acids (CF@sub 2@HCO@sub 2@H, CF@sub 3@CO@sub 2@H, C@sub 2@F@sub 2@HCF@sub 2@CO@sub 2@H, and CF@sub 3@CF@sub 2@CO@sub 2@H). All four acids adsorb molecularly on Cu(100) at 90 K and then undergo deprotonation to form carboxylates during heating below 300 K. Temperature programmed reaction spectroscopy and x-ray photoemission spectroscopy were used to verify that the acids deprotonate on the Cu(100) surface. Work function measurements were used to study the deprotonation kinetics during heating and estimate the activation energy barriers (@DELTA@E@super ‡@@sub OH@) to deprotonation. The nature of the transition state to acid deprotonation on Cu(100) was probed by analysis of linear free energy relationships (LFER) or correlations of with @sigma@@sub F@. The field reaction constant, @rho@@sub F@, or the slope of the LFER was found to be @rho@@sub F@ = 57 ± 9 kJ/mol in the limit of zero coverage and @rho@@sub F@ = 22 ± 2 kJ/mol at 0.5 ML coverage. These values of @rho@@sub F@ can be compared to the values of @rho@@sub F@ = 104 kJ/mol for acid deprotonation in the gas phase. This comparison suggests that the transition state for acid deprotonation on Cu(100) must be anionic with respect to the reactant (RCO@sub 2@H@sub (ad)@@super ↔@[RCO@sub 2@@super delta@@super -@@super …@H@super delta@@super +@]@super ‡@.