THE DETERMINATION OF ACETYL NUMBER.^ 



EDW. B. HOLLAND. 



Introduction. 

 The various hj'droxy compounds that occur in oils, fats and waxes 

 form derivatives on heating with acetic anhydride, the acetyl radical dis- 

 placing the hydrogen of the alcoholic hydroxyl groups. Tliis property 

 serves as the basis of analytical methods for the quantitative determina- 

 tion of these compounds. The proposed acetyl number indicates the 

 milligrams of potassium hydroxide required for the saponification of the 

 acetjd assimilated by one gram of an oil, fat or wax on acetylation.^ On 

 saponifjnng with alcoholic potash the acetyl is hydrolyzed to acetic acid 

 and combines with the alkali to form potassium acetate. The results 

 are expressed in terms of milligrams of potassium hydroxide to conform 

 with the general practice in fat analysis. The compounds involved are 

 monohydroxy and dihydroxy acids and their glycerides, — monoglycer- 

 ides and diglycerides and free alcohols. 



Use of the Test. 

 In the examination of oils and fats a determination of acetyl number is 

 necessary, in most instances, for a thorough understanding of the nature 

 and quality of the product. Some of the hydroxy compounds are natural 

 and others are the result of hydrolysis or of oxidation. Glycerides of 

 hydrox}^ acids are a natural constituent of certain oils and fats, although 

 they do not appear to be very widely distributed in any considerable 

 amount. Castor oil, composed largely of ricinolein, is a notable illus- 

 tration. Hydroxy acids probably occur more frequently as the result of 

 oxidation of unsaturated acids. Oleic acid has been shown repeatedly to 

 be comparatively unstable. By the assimilation of oxygen and water it 

 may be converted into dihydroxystearic acid, a saturated compound. 



C1-H33COOH + H.O +0 = Ci7H33(OH)2COOH. 



Whether the oxidation takes place in the glycerides or in the fatty 

 acids after hydrolysis is uncertain, although the latter appears the more 

 probable supposition. 



]Monoglycerides and diglycerides result from the hydrolysis of tri- 

 glycerides, and free fatty acids condition their presence. The absence of 



' The writer is pleased to acknowledge many suggestions and helpful criticisms by Dr. J. S. 

 Chamberlain. Mr. F. W. Morse, Mr. J. C. Reed and Mr. J. P. Buckley. 

 2 Benedikt and Ulzer, and Lewkowitsch report on the basis of the acetylated product. 



