Oxidative dehydrogenation of piperazine to pyrazine with palladium hydroxide in aqueous media

Palladium (II) chloride as a reagent for the mild aromatization of piperidine and cyclohexanone

“…The procedure at initial pH ca. 4, including product identification, has been reported (s) . Using more alkaline conditions (pH 11.6), the reaction between K2PdCI4 (50/amol) and cyclohexanone (110/amol, an excess) was complete in 140 min, as judged by the total deposition of palladium(0).…”

“…Thus at initial pH 10, cyclohexanone for 2 h, whereas 97 h were required at pH 3(s); if oxygen was passed through the reaction medium (initially pH 10) no palladium(0) was detected even after heating for 3 h. Product analyses on the o-cyclohexenylcyclohexanone system showed that partially oxidized and disproportionated intermediates were produced in substantial quantity despite almost complete deposition of palladium(0) -see Experimental section. * Russian workers (4) suggest that the analogous bis-complex dihydroxobis(1,4)-piperazine palladium(ii) is an intermediate in the oxidation to pyrazine. ** Under normal reflux conditions, the oxygen is rapidly removed from the system; no significant difference was detected between such a reaction mixture and one through which nitrogen was continuously bubbled.…”