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ARMY NIGHT VISION LAB FORT BELVOIR VA
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A homologous series of S-cholesteryl alkanethioates was prepared by reaction of 3beta-mercaptocholest-5-ene with the imidazolides of alkanoic acids. The mesomorphic properties of 20 members, S-cholesteryl thioformate through eicosanethioate were determined. All alkanethioates are monotropic cholesteric except the cholesteryl thioformate. Cholesteryl thioheptanoate and all higher homologues in this series also exhibit a monotropic smectic mesophase. A comparison with the corresponding cholesteryl alkanoates shows that the replacement of the ester group by the thiol ester group leads to an increase in both the smectic-cholesteric and the cholesteric-isotropic transition temperatures.
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