J no II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



tion. For example, periodic acid, HsIOe, prepared by the interaction of 

 sulfuric acid and barium or potassium periodate, brings about fission of 9- 

 keto-10-hydroxystearic and 9-hydroxy-lO-ketostearic acids between car- 

 bons 9 and 10^^^; this also occurs with dihydroxystearic acid.*^- Lead 

 tetraacetate, a reagent developed by Criegee^''^"^^^ for the cleavage of gly- 

 cols of the form: 



H H 



R— C C— R 



I I 



OH OH 



acts in a highly specific manner to cause fission between the carbons con- 

 taining the two hydroxyl groups. 9,10-Dihydroxystearic acid is decom- 

 posed by lead tetraacetate to n-nonanal (CH3(CH2)7CHO) and azelaic 

 semialdehyde (CHO(CH2)7COOH).''44 The rate at which polyhydroxy- 

 acids are oxidized by Criegee's reagent is quite variable. The two low- 

 melting forms of 9,10,12,13-tetrahydroxystearic acids are more rapidly 

 oxidized than the high-melting forms, while the same variation is noted for 

 the low-melting (m.p., 95 °C.) and high-melting (m.p., 132 °C.) forms of 

 9,10-dihydroxystearic acid.^^^ 



d. Other Reactions of Aliphatic Chain of Fatty Acids. Hydrohalogena- 

 tion, i. e., the addition of a halogen halide, HX, to an unsaturated carbon- 

 to-carbon linkage, is a common reaction. This occurs with the acids of 

 the four halogens. The reaction proceeds most readily with hydrogen 

 iodide, is somewhat slower with hydrogen bromide, and may require 

 several days for completion with hydrogen chloride. ^"■''^^ The relation- 

 ship of hydrogen fluoride is less clear. The hydrohalogenation can occur 

 in the presence or absence of solvents. Two isomers are possible with a 

 monoethenoid acid in w^hich the positions of the hydrogen and halide atoms 

 are reversed. 



The position taken by the halide is influenced by several factors. It usu- 

 ally adds to the carbon having the fewer hydrogens. ^^^ The position of 

 the double bond in relation to the carboxyl has some effect; in a- or (3- 

 imsaturated acids, the halide adds to the carbon more remote from the 

 carboxyl, while with the 7-unsaturated acid the relationship is re- 



692 G. King, /. Chem. Soc, 1942, 387-391. 

 6" R. Criegee, Ber., 64, 260-266 (1931). 

 «94 R. Criegee, Ann., 481, 263-302 (1930). 



695 R. Criegee, L. Kraft, and B. Rank, Ann., 507, 159-197 (1933). 



696 T. P. Hilditch and H. Jasperson, Nature, 147, 327 (1941). 

 69' S. Piotrowski, Ber., 23, 2531-2,533 (1890). 



698 A. Albitskil, /. Rms. Phys. Chem. Soc, 31, 100-103 (1899); cited by A. W. Ralston, 

 Fatty Acids and Their Derivatives, Wiley, New York, 1948, p. 444. 



699 W. MarkownikofT, Ann., 153, 228-259 (1870). 



