| Research Abstract |
The Synthetic method to obtain ultra-pure higher n-alkanes (abbr. C_n, n: the number of carbon atoms in chain) was ketene dimarization from carboxylic acid, the starting materials which had been purified by preparative liquid chromatography for the odd n-alkanes. We confirmed that for the even n-alkanes , Wurtz condensation of monoiodoalkane (abbr. C_nI) was the most suitable method up to C102. But little progress has been made with the synthesis of C120 , C160 through Wurtz condensation from C60I and C80I respectively, as the depression in reaction activity with the chain length of C_nI become long. It is necessary to investigate the condition of this reaction.
In order to obtain more higher n-alkanes in the region that chain folding is found, Wurtz condensation of alpha,omega-diiodotetracontane was performed. That resulted in the mixture of H[(CH_2)_<40>]nH=1,2,3,4. The mixture of n-alkanes was first fractionated by adsorption column method, and was separated almost step-wise according to molecular weight up to C160. They were, furthermore purified by GPC on repeated runs.
The purity of the sample was examined by a Shimadzu capillary gas chromatogragh, GC-14AHF_<sc> equipped with data analyzer of C-R6A. The homologous impurity was proved to be quantitatively determined by the chromatography at a programmed-temperature operation up to 450ﾟC for C102,98.8%, C80 was 99.3%. Analysis of C160 couldn't done.
DSC measurements were done on C80,C102,C120 and C160 which were melt crystallized samples (chain extended crystals). Melting point of them were 109.6ﾟC, 115.7ﾟC, 119.7ﾟC and 125.0ﾟC, respectively. On the DSC thermogram of solution crystallized C160 was shown that melting of once-folded chain crystals was immediately followed by recrystallization (exotherm) in the extended chain form, which melted at a somewhat higher temperature. That the thickness of C160 crystals was about 10nm from observation by TEM, shows the formation of once-folded crystals.
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