SYNTHESIS OF POTENTIAL LIQUID CRYSTALS WITH CHOLESTEROL FRAGMENT BY WITTIG REACTION

Abstract

Liquid crystals are substances that owing to  the  features  of  their  structure  and  physical  properties are of interest not only as objects for theoretical  research, but also significantly important practically due to the possibilities of their effective application in various brunches of industry, medicine, in household   etc.  Among  the  known  classes  of  liquid  crystals,  substances  known  as  cholesterics  are an important group. Cholesteric liquid crystals demonstrate very high optical activity, that significantly exceeds the optical activity of most other known classes of organic compounds. Their ability for appreciable change of color at change of the temperature and environment composition is also practically important. Among all compounds belonging to the class of cholesterics an important place possess cholesterol derivatives, especially cholesterol esters. Therefore, the elaboration of new methods of their synthesis and the introduction of new functional groups into their molecules are an urgent tasks indeed. This work is devoted  to  the  investigation  of  the  possibility  of  synthesis  of  new cholesterol derivatives, namely cholesteryl esters of unsaturated acids by the Wittig reaction - the interaction of various classes  of  aldehydes  with  phosphonium  salts,  with  the  intermediate  formation  of phosphorus ylides - alkylidene phosphoranes. We found that  the  Wittig  reaction  is  a convenient method for the synthesis of cholesteryl esters of unsaturated carboxylic acids. We have developed methods for the synthesis of potential cholesteric liquid crystals by the Wittig reaction, which use a phosphonium salt containing a cholesterol fragment and  corresponding  aldehydes.  The  process proceed without the release of an  intermediate compound –  alkylidene phosphorane,  which  reduces the labor intensity of the method. The application of various aldehydes enables the easily obtaining of cholesteryl esters of unsaturated acids containing various aliphatic, aromatic and heterocyclic fragments in the acid radical. The reaction takes place in mild conditions, without using of high temperatures or aggressive environments. The resulting esters show signs of mesophase formation, which is a confirmation of their liquid crystalline properties.