134 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



the acid and acetic anhydride on an oil bath for 4 to 7 hours. ^''^ The re- 

 flux method is also applicable to the shorter chain acids, *^^ and has been 

 demonstrated to be satisfactory*^^ in the case of the even acids from €» to 

 Ci8. The reaction can be carried out to advantage*^'' under CO2 with the 

 highly unsaturated acids such as linoleic. 



In addition to acetic anhydride, other dehydrating agents may be used. 

 Phosphorus pentoxide gives a yield of approximately 78-79% with pal- 

 mitic and stearic acids, when ketones are present as impurities.^^^ Acetyl 

 chloride has a satisfactory dehydrating action on caproic acid*^^ or on the 

 higher fatty acids in ether solution. *^^ 



A second method, which is applicable for the preparation of both simple 

 and mixed anhydrides, involves the reaction between the sodium salt of the 

 fatty acid and the acid chloride''^* according to the following reaction: 



RC-ONa+CI -CR-^RC-0-C-R + NaCI 



Na salt Acid Acid Sodium 



of fatty chloride anhydride chloride 

 acid 



When the sodium salt and acid chloride are derived from the same acid, a 

 simple anhydride results. ^^^'**^ By varying these two components, any 

 desired mixed anhydride can be obtained. When the sodium salts are 

 heated with acetic anhydride under pressure, the anhydrides are also 

 formed. ''^^ 



A third procedure originally suggested by HentscheP^^ involves the treat- 

 ment of tlie sodium soaps with phosgene; in addition to the anhydride, 

 CO2 and 2 molecules of sodium chloride result. Phosgene has been em- 

 ployed on benzene suspensions of the fatty acids of tall oil for synthesis of 

 the anhydrides. ■'^^ The pyrosulfates as such,**" or those formed from the 

 action of SO2 on concentrated sulfuric acid,**^ react with the anhydrous 

 sodium soaps to produce the anhydrides. 



^" D. Ilolde, J. Ripper, and F. Zadek, Ber., B57, 103-104 (1924). 



^" W. Autenrieth, Ber., 34, 168-187 (1901). 



^7" D. Holde and R. Centner, Ber., B58, 1418-1424 (1925). 



^s" D. Holde and R. Centner, Ber., B58, 1067-1071 (1925). 



«• C. Rankov, Ann. univ. Sofia II, Faculte phys.-math. [2], 33, 221-227 (1937); 

 Chern. AbsL, 32, 3335 (1938). 



^«2 H. Fournier, Bull. soc. chim. [4], 5, 920-926 (1909). 



«3 J. Gsell, Chem.-Ztg., 31, 99-100 (1907); Chem. AbsL, 1, 1066 (1907). 



«^ C. Cerhardt, Ann., 87, 57-84 (1853). 



<85 A. Villier, Ber., 9, 1932-1933 (1876). 



«6 F. Krafft and W. Rosiny, Ber., 33, 3576-3579 (1900). 



«T A. Michael, Ber., 34, 918-930 (1901). 



^88 W. Hentschel, Ber., 17, 1284-1289 (1884). 



«9 D. Holde and K. Schmidt, Z. angew. Chem., 35, 502-503 (1922). 



^90 H. Dreyfus, French Patent No. 478,951 (Jan. 26, 1916); Chem. AhsL, 10, 2278 

 (1916); cited by A. W. Ralston, Fatty Acids and Their Derivatives, Wiley, New York, 

 1948, p. 797. 



«i H. Dreyfus, French Patent No. 20,261 (June 1, 1917); Chem. Abst., 12, 1195 (1918). 



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