SYNTHESIS OF 1,4-BUTANEDIOL BY CATALYTIC REDUCTION OF 2-BROMOETHANOL AND 2-IODOETHANOL WITH HOMOGENEOUS-PHASE NICKEL(I) SALEN ELECTROGENERATED AT CARBON AND MERCURY CATHODES

Cyclic voltammetry reveals that, at a glassy carbon or hanging mercury drop cathode in dimethylformamide or acetonitrile containing a tetraa lkylammonium salt, nickel(II) salen undergoes a reversible one-electro n reduction to the corresponding nickel(I) species. When 2-bromo- or 2 -iodoethanol is added to the nickel(II) salen solution, the cyclic vol tammogram shows an enhancement in the cathodic current and a disappear ance of the anodic current, which are attributed to the catalytic redu ction of the 2-haloethanol at a potential more positive than those req uired for direct reduction of these species. Controlled-potential cata lytic reduction of 2-bromo- or 2-iodoethanol with nickel(I) salen elec trogenerated at a reticulated vitreous carbon cathode gives rise to th e formation of 1,4-butanediol in as much as 41% yield, along with Etha nol (11 to 31%), and ethylene (13 to 55%); when a proton donor (1,1,1, 3,3,3-hexafluoro-2 propanol or acetic acid) is introduced into the sys tem, ethane in yields as high as 30% (as well as the preceding three c ompounds) is obtained. If a mercury pool electrode is used and no prot on donor is added, the products of the catalytic reduction of 2-bromoe thanol are 1,4-butanediol (8 to 26%), ethanol (14 to 51%), and ethylen e (33 to 62%).