320 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



(3) From Tissues. 



The tissue is dried by spreading out in thin layers on plates, by mixing 

 with alcohol and evaporating, or by mixing with an absorbent material, such 

 as sand or siliceous earth. The dry mass is extracted with ether in a Soxhlet 

 extractor. The ethereal extract is mixed with excess of alcoholic potassium 

 hydroxide to saponify the fats and esters, any soap which is formed is filtered 

 off and the ethereal solution distilled to remove ether. The residue is dis- 

 solved in water and extracted with ether. The ethereal solution containing 

 the cholesterol is evaporated and the cholesterol recrystallisep!. 



Properties. 



Cholesterol forms a white crystalline solid melting at 147. It 

 crystallises in needles from ether, benzene, etc. ; in characteristic four- 

 sided plates with a notched angle and 

 containing I molecule of water of 

 crystallisation (Fig. 5 2) from aqueous 

 alcohol. It is insoluble in water 

 and soluble with difficulty in cold 

 alcohol. In hot alcohol, ether, ace- 

 tone, chloroform and other organic 

 solvents it is readily soluble. 



The unsaturated character of 

 cholesterol is shown by the forma- 

 tion of addition compounds with the 

 halogens and halogen acids. 



As an alcohol, cholesterol forms 

 esters. The acetate and benzoate 

 are very characteristic and i serve to distinguish cholesterol from phy- 

 tosterols (p. 322). 



Cholesteryl Acetate. A small quantity of dry cholesterol is boiled 

 with 2 or 3 c.c. of acetic anhydride for I or 2 minutes. The acetic 

 anhydride is evaporated, or the solution is poured into watei. The 

 residue, or precipitate, is crystallised from dilute alcohol. It melts 

 at 114. 



Cholesteryl Benzoate. Cholesterol is boiled with benzoyl 

 chloride for a few minutes and the solution poured into alcohol. The 

 precipitate of cholesteryl benzoate is recrystallised from hot alcohol. 

 This compound melts at 145 to a turbid liquid, which becomes clear 

 at 178-180; on cooling it exhibits a play of colours, of which blue 

 is the most marked. 



Esters of cholesterol with palmitic, oleic and other acids have also 

 been prepared. 



FIG. 52. Cholesterol. (After Furl e.) 



