Adsorption of 3‐phenyl‐1‐propanol on Gold Electrode from Perchloric Acid Solutions

Abstract

Adsorption parameters of 3-phenyl-l-propanol and some other co-phenyl alkanols were calculated after the isotherm of 0/(1 -O)" = Kad~' Xorg. The adsorption peaks appeared at 0.70 and 0.35V (vs. SCE) for the adsorbate. The peak near 0.70V seems to be due to ~r-electron interaction of the benzene ring and another peak at 0.35V to the alcohol group as side chain. The peak height of coverage-potential curve at 0.35V became larger depending upon the number of carbon atoms in the aliphatic alcohol group on the benzene ring. The differential capacity was measured by a rapid rectangular single-pulse technique, and the voltage-time curve was memorized electrically set by a "Wave Memory." Then, the reproducibility of the_capacity measurement became approximately within -+6%. The values of n and the standard free energy of adsorption (AG ~ of the adsorbate at 0.70V were calculated as 2.8 and -7.4 kcal/mol, respectively.In the adsorption of benzene compounds on electrode surface, the ~-electron interaction between the adsorbed molecule and the electrode surface plays a dominant role (1). As reported in a previous paper (2), the adsorption peak of benzoic acid appears at 0.60V (vs. SCE), and the peak seems to be due to adsorption of benzene ring by its ;~-electron interaction on the gold electrode. In this report, adsorption of 3-phenyl-l-propanol (PPA) on gold electrode was studied. The adsorption peak was found at 0.70V. However, we found out that the new peak appeared at 0.35V. Peak height of the coverage-potential curve became larger depending upon the number of carbon atoms in the aliphatic alcohol group on the benzene ring from the coverage data of benzyl alcohol, 2-phenyl ethanol, and 3-phenyl-l-propanol. Kinetic parameters were calculated after the concept of competitive adsorption by Bockris and Swinkels (3, 4), Dahms and Green (5), and Conway and Dhar (6). They assumed that one molecule of an organic substance took the place of n molecules of water on the electrode surface. Lawrence and Parsons (7) calculated the n value from the geometrical ratio of the area occupied by the organic molecule to the one by water molecule. Dahms and Green (5) calculated the value for adsorption of aromatic hydrocarbons on gold electrode with radiotracer technique. ExperimentalGold electrode.--The gold electrode which was used as the working electrode which was made from polycrystalline pure gold (99.99%, Tokuriki Manufacturing Company Limited) and was sheathed in a Teflon rod (2). The electrode surface was polished before each series of electrochemical works with very fine emery papers and then polished with dilute suspension of 600 mesh dichromium trioxide polishing powder. The electrode surface was reduced by setting the potential near --0.20V for 20 min or more. The surface condition of the reducing process was observed by drawing a cyclic voltammetric curve of the gold electrode. The apparent surface area of the electrode was 0.049 cm 2, and the roughness factor as calculated with the method of Brummer and Makrides (8) wa...