Electrochemical　synthesis　of　o-benzoquinone　derivatives　and　their　in　situ　transformation　are　one　of　the　versatile　approaches　for　the　synthesis　of　derivatized　catechols.　In　the　present　work,　electrochemical　oxidation　of　catechols　1a-1d　in　the　presence　of　a　unique　nucleophile,　4-amino-3-methyl-5-mercapto-1,2,4-triazole　3,　bearing　two　nucleophilic　groups　(-NH(2)　and　-SH),　have　been　studied　in　phosphate　buffer　solutions　using　cyclic　voltammetry　and　control　led-potential　electrolysis　(CPE)　methods.　The　results　show　that　only　the　mercapto　group　participated　selectively　in　the　Michael　addition　reaction　and　led　to　the　formation　of　catechol　Substituted　products　of　types　4　and　5,　bearing　a　free　amino　group,　potentially　useful　for　further　chemical　modifications,　e.g.　of　interest　in　biomedical　applications.　Various　electrolytic　conditions,　such　as　the　nature　of　anode　material,　amount　of　passed　charge,　pH　of　the　electrolytic　solution　and　cell　configuration　(divided　or　undivided　cell),　were　also　investigated　to　optimize　the　yields　of　corresponding　products.　(C)　2008　Published　by　Elsevier　B.V.