Phase Transitions and Solid Polymorphis of Cholesteryl Acetate

Abstract

The thermal behavior of cholesteryl acetate has been studied by means of thermal analytic microscopy (microscopy synchronized with thermal analysis) and X-ray powder diffraction. The main results of teh work are as follows:

Thermal Analytic Microscopy: 1, Cholesteryl acetate (99.7 mol%) purified with 1-pentanol exhibits a solid-solid transition on first run, similarly to the case of cholesteryl acetate purified with ethanol; 2. The sample displays the cholesteric phase only when special thermal treatment is performed; 3. Once, melted, recrystallized samples are classified into four solid state of SI, SII, SIII, and SIV; 4. Thermal data for the transition have been estimated.

X-ray Powder Diffraction:1. Three patterns have been obtained and denoated as A, B, and C. The crystal deposited from teh I-pentanol solution displays. “A”, the same pattern as that of the crystal deposited from the ethanol solution. “B” is obtained from solid SIII. “C” is obtained from SI, SIV, and teh crystal after the first run transition; 2. It has been found that “B” and “C” revert to “A” with the passage of time. The rate of reversion is less at a higher temperature, a longer time of sample treatment, and a lower cooling rate. Impurities delay the reversion.

SIV forms special, colorful figures similar to annual rings of a tree on the course of transition to “A”.