The protective properties of dodecanethiol layers against copper corrosion in a Borax buffer containing chloride anions are investigated by using electrochemical techniques complemented with scanning tunneling microscopy. Results show that copper is protected against corrosion provided that the copper electrode does not reach the potential region of Cu(II) oxide formation and the concentration of chloride ions in the environment remains low. These findings should be taken into account for the use of alkanethiol layers for the corrosion protection of copper.