ABSTRACTS 335 



Observations on the Sterol Colour Reactions 



By G. Stafford Whitby 



Presented by Dr. R. F. Ruttan, F.R.S.C. 



(Read May Meeting, 1922) 



Abstract 



Observations made with the object of elucidating the mechanism 

 of the reactions usually used for the detection of sterols indicate that 

 in their general character all or most of these reactions are in essence 

 similar, their common feature being ^he production from the sterol, 

 in an anhydrous medium, of a substance which couples, to give a 

 coloured product, with another substance, derived from the sterol 

 or from a dehydrating agent. In all the reactions some means 

 (sulphuric acid, acetic anhydride, zinc chloride, acetyl chloride, 

 benzoyl peroxide) of rendering the medium anhydrous is employed. 

 The coloured product is very sensitive to traces of moisture. The 

 actual colour obtained depends upon both the thoroughness with 

 which the medium is dehydrated and the nature of the coupling 

 substance. The substance produced initially from the sterol and then 

 undergoing coupling is probably a cholesterilene or cholesteriline 

 produced by the withdrawal of the elements of water from the sterol 

 molecule; or, not improbably, more than one of these hydrocarbons 

 is involved. Some of the coloured products derivable from sterols 

 are insoluble in certain solvents (particularly carbon tetrachloride and 

 ethyl bromide) and can be isolated by carrying out the colour reactions 

 in such solvents. 



It is found that the introduction of formaldehyde to serve as the 

 coupling substance enables colour reactions to be obtained with 

 quantities of sterol smaller than those with which reactions can be 

 obtained in its absence. Two new tests, based on this observation, 

 have been devised. One of them, which may be regarded as an 

 elaboration of the Salkowski reaction, is considerably more sensitive 

 and striking than the latter. The other is more sensitive than any 

 of the reactions hitherto available for the detection of sterols. There 

 is also described a third new reaction, the special interest of which is 

 that it enables cholesterol to be distinguished from phytosterol. The 

 behaviour of amyrin and abeitic acid in these tests, is recorded. 



