Iodine catalysed disproportionation reactions between abietic acid and linolic acid have been studied.
When the mixture of equimolecular amounts of abietic acid and linolic acid was treated with iodine (2mol% of abietic acid used) at 220°C, hydrogens were transferred from abietic acid to linolic acid to give dehydroabietic acid and octadecenoic acid mainly. The mixture of equimolecular amounts of abietic acid and conjugated linolic acid also gave the same products as well as the former in better yield.
The ratios of homo-molecular reaction to hetero-molecular reaction were evaluated by the amounts of product in each reaction to give 1 : 4 in the former and 1 : 10 in the latter.
Further dehydrogenation of abietic acid and hydrogenaton of linolic acid were investigated in detail. When equimolecular amount of iodine was added to abietic acid in the presence of water, the abietic acid changed into dehydroabietic acids in 89% by mole and the iodine was recovered as hydrogen iodide in 90% by mole.
It was suggested that iodine catalysed disproportionation reaction between abietic acid and linolic acid consisted of the conjugation of linolic acid, the dehydrogenation of abietic acid, and the hydrogenation of conjugated linolic acid with hydrogen iodide formed in the reaction.
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