When polyunsaturated fatty acids are heated, cyclization occurs as well as decomposition and polymerization. J.A. MacDonald, R.B. Hutchson and J.C. Alexander
et al. have reported that cyclic monomers from heated linseed oil contain cyclohexadiene compounds. N. Matsuo informed the presence of cyclohexadiene compounds as main components and ortho-substituted aromatic compounds in heated ethyl β-eleostearate.
One double bond in polyunsaturated straight chain monomer disappears in intramolecular cyclization as a matter of course. But it is very interesting that aromatic compounds are present in the heated trienoic acid.
In this paper, cyclic monomers were prepared from linseed oil under the condition of 295°C, 15min. in stainless autoclave with alkaline catalyst. Heated linseed oil fatty acid sodium salt was acidified and methyl esterified by the usual method, thus cyclic monomers were obtained by urea adduct separation. Nextly, the cyclic monomers were heated in 25ml ampoules under various conditions. These samples were analyzed by GLC, IR, and colorimetry of cyclohexadiene ring, etc.
As a result, cyclohexadiene compounds gradually decreased, with inverse increase in the aromatic and cyclohexene compounds. The mechanism of formation of aromatic compounds in the cyclic monomers was explained by disproportionation reaction.
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