Facile conversion of cis into trans oxane as liquid crystals.

Trans-oxanes are important liquid crystals. The commonly used techniques for the synthesis were to react 2-substituted propylene glycols with substituted formaldehydes. Such process produces toxic cis-oxanes, which are harmful to the environment. The cis to trans isomerization of wasted cis-oxanes was studied in the presence of p-toluenesulfonic acid as catalyst. The yield of cis to trans conversion was over 70%, which was much higher than 42-69% when traditional methods were employed. The total yield of the new method was increased to 90%. Further investigation of effects of catalysts, reaction times, temperatures on the cis-trans conversion was carried out. Proposed mechanism of this process for the conversion was discussed.