Investigations on pyrazine derivatives. V. A more detailed investigation on the catalytic hydrogenation of esters of pyrazine carboxylic acids

In the first publication in this series it was shown that only partial reduction of the pyrazine ring occurs in the catalytic hydrogenation of tetra‐carbethoxypyrazine. The remaining double bonds in the resultant reaction product are apparently stabilised. In agreement with the hypotheses put forward to explain this result, esters of other pyrazine carboxylic acids also are only partially reducible with palladium on carbon at room temperatures. The conclusion must be drawn that a carbalkoxy group attached to a pyrazine ring protects an adjacent double bond in the ring against catalytic hydrogenation. The partially hydrogenated products from the esters of some pyrazine carboxylic acids are extraordinarily labile. Dehydrogenation by dismutation or reoxidation, which occurs to some extent, can be followed from the spectra. Similar phenomena have been encountered in the pyridine series, which may be put forward as supporting the conclusions reached.