遷移金属カルボニルの触媒作用 (第1報)

鉄ペンタカルボニルによる綿実油の水素添加反応の選択性と副反応について

抄録

Authors investigated the catalytic behavior of iron pentacarbonyl in the hydrogenation of C-C double bond. Each 30 g of cotton seed oil was reacted with 1.2 or 2.4 g of iron-pentacarbonyl in the following reaction conditions ; initial hydrogen pressure : 25 or 50 kg/cm², temperature : 180 or 200°C and time : 2 or 4 hr.
From the statistical consideration of the relations between reaction conditions and the composition of reaction products authors recognized the selectivity of hydrogenation between linoleic acid and oleic acid, namely, higher temperature and smaller quantity of catalyst were favourable to the selective formation of oleic acid, on the other hand higher temperature, higher hydrogen pressure and increase in amount of catalyst accelerated the stearic acid formation. As the side reactions the formation of high boiling substance and an iron-carbonyl complex compound were also detected. The former is considered as dimer of linoleic acid, and was preponderately produced in the case of lower temperature and more catalyst. The latter was revealed to be conjugated linoleic acid iron-tricarbonyl.
Experimental results suggest the following reaction mechanism : -A certain labile complex compound such as monoene-iron-tetracarbonyl is formed at first from linoleic acid. If iron-pentacarbonyl is present in a larger amount, such intermediate is also formed from oleic acid. In the next step of hydrogencracking, oleic acid or stearic acid is formed from each of their respective intermediates. The intermediate, formed from linoleic acid, is simultaneously converted into comparatively stable type of diene iron-tricarbonyl, which can be also produced directly through the conjugation reaction of linoleic acid followed by complex formation reaction. In the excess thermal treatment this compound is decomposed and converted into dimer, on this occasion the iron-carbonyl residue of transition state may also act as the catalyst for dimerization.