The adsorption of 4-cyanopyridine on a Au(111) electrode is studied by cyclic voltammetry, FTIR and Sum Frequency Generation (SFG). This subject needs insight because potential-dependent irreversible reactions occur on the electrode. The present study is the continuation of a previous one which dealt with the potential-dependent orientation of 4-cyanopyridine (4-CP) on Au(111) electrodes. In this paper we are considering the hydrolysis of 4-CP into isonicotinamide occurring competitively to the reorientation of the 4-CP molecule. This results in the dissociation of the CN group into CONH, We show that in a perchlorate supporting test electrolyte, the adsorbed cyanopyridine adlayer is progressively hydrolyzed when the electrode potential is successively swept negatively then positively between - 0.8 and + 0.6 V (Ag I AgCl). The product and the mechanism of the hydrolysis reaction are identified thanks to the use of in situ FTIR. SFG spectroscopy is used in the 850-1100 cm(-1) range to address the question of the very slow kinetics of the reaction.