154 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



which iodine monochloride is employed in glacial acetic acid, and the 

 Hanus method, ^^* which involves the use of iodine monobromide in place 

 of the iodine monochloride. The Hanus solution is more easily prepared 

 than the Wijs reagent, and is more stable, according to Bull.^^* The 

 Wijs reagent lasts about a month while the Hanus solution remains satis- 

 factory for at least a year. Both the Hanus and Wijs procedures are in 

 current use in the United States, but the latter method is employed more 

 in England and Europe. According to BulP*^ the results are 2 to 4% lower 

 with the Hanus than with the Wijs technic, according to Lewkowitsch, 5 

 to 6% lower. ^^^ The Association of Official Agricultural Chemists has 

 adopted the Hanus method as the official one, while the Committee on 

 Analysis of Commercial Fats and Oils of the Division of Industrial Chem- 

 ists and Chemical Engineers of the American Chemical Society has ac- 

 cepted the Wijs procedure as standard.^" A comparison of the three 

 methods mentioned above has been reported by Hunt^^* and by Tolman 

 and Munson.^*^ Excellent chlorinating reagents are sulfur monochloride, 

 (SOCl), thionyl chloride (SOCI2), phosphorus trichloride (PCI3), phosphorus 

 pentachloride (PCIb), hypochlorous acid (HOC!), oxalyl chloride (C0C1-- 

 COCl), phosgene (COCI2), and halogen hydrides. 



(a) Factors Altering the Addition of Halogens. One of the most important 

 factors which control the rate of reaction of the monoethenoid acids is the 

 position of the double bond. Ponzio and Gastaldi^^" were able to intro- 

 duce only 50% of the theoretical amount of iodine into 2-octadecenoic acid, 

 even after 70 hours' reaction, while Eckert and Halla^^" have found iodine 

 values of 9.0, 16.3, and 27.0 for 2-, 3-, and 4-octadecenoic acids, respec- 

 tively, compared with the theoretical value of 89.9. 



In the case of the di- or polyethenoid acids, the rate and completeness of 

 the addition of the halogens depend not only on the position of the un- 

 saturated linkages in the aliphatic chain, but also on their position rela- 

 tive to each other. Most nonconjugated polyethenoid acids add halogens 

 normally. In the case of linoleic acid, bromine adds first to the 12,13- 

 linkage and then to the 9,10-positions,^" but the total amount added is 

 100% of that possible. A stepwise addition of bromine has been noted for 

 linolenic acid, as well, the order being the 15,16-, then the 12,13-, and 



«" J. Hanus, Z. Untersuch Nahr. Genussm., 4, 913-920 (1901). 



«« H. B. Bull, The Biochemistry of the Lipids, Wiley, New York, 1937. 



*^^ J. I. Lewkowitsch, Chemical Technology and Analysis of Oils, Fats and Waxes, 

 6th ed.. Vol. I, Macmillan, London, 1921, p. 409; 1913 ed. p. 408. 



*" Anonymous, "Standard Methods for the Sampling and Analysis of Commercial 

 Fats and Oils," Ind. Eng. Chem., 11, 1161-1168 (1919). 



«« F. W. Hunt, J. Soc. Chem. Ind., 21, 454-456 (1902). 



6« L. M. Tolman and L. S. Munson, /. Am. Chem. Soc, 25, 244-251 (1903). 



650 A. Eckert and O. Halla, Mcmatsh., 34, 1815-1824 (1913). 



«6i Y. Toyama and T. Tsuchiya, /. Soc. Chem. Ind. Japan, 38, suppl., 35-36, 36-38B 

 (1935); Chem. Abst., 29, 2509 (1935). 



