3733. ---------------. [WITTKA, F.] Synthetic Aliphatic Acids. Soap Sanit. Chemicals, vol. 16, 1940, No. 8, pp. 28-32, 73; No. 9, pp. 34-37, 73; Chem. Abs., vol. 34, 1940, pp. 7636-7637.
Raw materials used in the German process are synthetic paraffins prepared from water gas by the Fischer-Tropsch process, yielding up to 50%. The paraffins are distilled, and those having a b.p. above 350° are used. They are mixed with 0.1% of powdered KMnO4 and heated to 150° for 10 min. By adding catalysts and blowing air through porous plates made of sintered metal, the temperature can be reduced to 100° and the time of oxidation shortened to about 20 hr. Various salts of Mn including KMnO4, Mn stearate, and Mn soaps of unsaturated acids are used in quantities from 0.5-1%, depending on the quality of the soaps. The products of oxidation are gaseous, as well as volatile and nonvolatile liquids. The gases formed are H2O and low aliphatic acids of all kinds. Acetic acid is the main constituent of the soluble acids. The insoluble low-aliphatic acids make up 10-12% of the original weight of the paraffins and have an acid value of about 272 and a saponification number of about 370. The acids of low molecular weight have little value and are used in small amounts only industrially. The nonvolatile liquid products of the oxidation are used for making soaps after being separated from the large quantities of unsaponifiable substances with which they are mixed. If light-colored acids are desired, the oxidation is stopped when only 30-40% of the paraffins have been oxidized. Naphtha is used as the solvent in the continuous process for the removal of the unsaponified materials, and the soap solutions are first mixed with Et or isopropyl alcohol to prevent the formation of emulsions. Two solvent-extraction plants are described, both processes requiring 2 treatments for producing usable acids. Another process, the high-temperature and pressure method, consists in heating the soap solution at high temperature under pressure and dispersing the hot soap solution without a drop in temperature. The oxidized acids are dehydrated to form unsaturated acids, and the acid products are changed into neutral ones. The soap remains as a yellow liquid, which when cooled over rollers gives an odorless yellow powder. Approximately 0.1% of unsaponifiable remains in the soap. Aliphatic acids made from the Fischer-Gatsch paraffins have the following constants: Acid value, 261.8; I number, 7.0; oxidized acids, 0.2%; average molecular weight, 214. Separation of the acids in this mixture shows that virtually all from C7 to C22 are present. For soap making all under C10 and over C20 are eliminated by fractional distillation. The fraction that can be used for soaps has the following properties: Solidification point, 26.2°-30°; acid value, 244.2-239; saponification number, 247.2; average molecular weight, 229.8=C13H27COOH; I number, 4.9; hydroxyl value, 3.7; unsaponifiable, 0.29%. Through esterification, the lower acids can be converted into a form that can be used in the perfume industry, but no use has been found for the higher acids, which are sent back to the oxidation tower.