212 III. CHEMISTRY OF NEUTRAL FATS 



containing one or more unsaturated fatty acid residues. When potassium 

 permanganate is used for oxidation, the unsaturated acid residues are oxi- 

 dized at the double bonds, without hydrolysis of the ester linkage with 

 glycerol, to water-soluble azelaoglycerides. Thus, from the three types of 

 glycerides containing unsaturated acids, the following products will result on 

 oxidation : 



/(O- CO -8)2 

 //. Monoazelaoglyceride, C3H3<^ 



\(0-CO-(CH2)7COOH) 



/(0-CO-S) 

 ///. Diazelaoglyceride, C3H5<^ 



\(0-CO-(CH.,);COOH), 



IV. Triazelaoglyceride, C3H5(0-CO-(CH2)7COOH)3 



According to the Hilditch and Lea technic, the neutralized fat mixture, 

 dissolved in dry acetone, is treated with an excess of finely powdered potas- 

 sium permanganate after the solution has been brought to the boiling point. 

 Permanganate is added to the extent of about 4 times the weight of the fat 

 sample used. After the permanganate has been gradually added to the 

 acetone solution of the fat, the mixture is refluxed for several hours, after 

 which the acetone is distilled off and the final traces are removed under 

 suction. The dried residue is then mixed with sodium bisulfite in an 

 amount 1.25 times the weight of permanganate employed (5 times the 

 weight of the fat used), and the mixture is gradually and cautiously added 

 to water. It is allowed to remain until the reaction has been completed. 

 This is then acidified with 30% sulfuric acid until acid to Congo red paper, 

 and the contents are heated until the sulfur dioxide set free by the reaction 

 is completely removed and all the manganic oxides have been dissolved. 

 After cooling of the aqueous solution, the organic compounds are removed 

 by extraction with diethyl ether (Extract 1). 



If a large portion of saturated triglycerides is present, the following proce- 

 dure is adopted: The solid layer of saturated triglycerides and other or- 

 ganic material is removed and washed free from traces of mineral acids and 

 salts by heating with water several times. The solid fat is then dissolved in 

 about 10 volumes of diethyl ether and allowed to stand for several hours at 

 O^^C. The fully saturated glycerides which precipitate are filtered and 

 washed with cold ether, dried by heating at 100°C. under a vacuum, and 

 weighed. 



Additional traces of fully saturated triglycerides may be obtained by an 

 ether extraction of the original aqueous extract (Extract la). This ether 

 extract (1 or la) is washed to remove acidic products. It is advisable 

 to treat the extract first with 10% potassium bicarbonate (KHCO3) solu- 

 tion 2 or 3 times to remove nonanoic or hexanoic acid originating from the 



