Pw. Park et al., KINETIC EVALUATION OF 3-BETA-HYDROXYCHOLEST-5-EN-7-ONE (7-KETOCHOLESTEROL) STABILITY DURING SAPONIFICATION, Journal of the American Oil Chemists' Society, 73(5), 1996, pp. 623-629
To clarify conflicting information regarding 7-ketocholesterol (7-KC)
recovery from saponification, we evaluated the stability of 7-KC in me
thanolic alkaline medium. We added 1 N alcoholic KOH to 7-KC or lard s
piked with 7-KC and held the mixtures at 45, 55, 65, and 75 degrees C
for different times to simulate various saponification conditions. Gas
-chromatographic determination of residual 7-KC with 5 alpha-cholestan
e as the internal standard (IS) showed that the higher the saponificat
ion temperature, the greater the 7-KC degradation. Hot saponification
at 75 degrees C for 30 min caused extensive destruction and left only
31% 7-KC. 7-KC loss during saponification could be described by pseudo
first-order kinetics, and the dependence of degradation rate on tempe
rature (T, K) by k (h(-1)) = (2.6 x 10(17)) exp (-1.36 x 10(4)/T). As
predicted by the kinetic equation, 7-KC loss during room-temperature s
aponification (21 degrees C) was practically negligible; following the
exposure of 7-KC or lard spiked with 7-KC to 1 N alcoholic KOH for 18
h, about 97% 7-KC was recovered. 6-Ketocholestanol, when used as an I
S, should be looked at carefully because of potential tautomerization,
leading to the formation of two enol isomers when in extended contact
with trimethylsilyl derivatization reagents.