Isolation and Purification of Cholesterol from Egg Yolk

The purpose of this experiment was to isolate and purify cholesterol from egg yolks.

Two hard boiled egg yolks were twice extracted with diethyl ether and methanol, with the filtrate collected via vacuum filtration. Potassium hydroxide pellets were added to the filtrate, the ether was distilled off, and the mixture was saponified by reflux. The crude cholesterol was isolated through a series of ether extractions and aqueous washes; then the ether was dried with MgSO4 and removed by rotary evaporation. The melting point of the yellow, sticky crude product was 91-119 oC. This crude product was then recrystallized from methanol, yielding 0.128g of pale yellow crystals with a melting point of 131-135 oC. This represents 0.33% of the original mass of the two yolks. The cholesterol was then dissolved in ether and further purified by bromination with a bromine/acetic acid reagent and debromination with zinc powder, a series of aqueous washes, and a final recrystallization from methanol. Here, a yield of 28% was recovered from an initial mass of