3298.     STOSSEL, E.  Oxidation of Paraffins.  Oil Gas Jour., vol. 44, 1945, No. 11, pp. 130, 132, 134, 137, 139; No. 15, pp. 145, 147, 148, 151; No. 17, pp. 69, 70, 73, 74, 77.

        Major steps in the oxidation of paraffin waxes to form fatty acids and other oxygenated products are presented together with the various theories of the sequence of steps in the oxidation process.  Also discussed are the possibilities of synthetic fatty acids produced by oxidation of paraffin in the light of the cheap raw materials made available in the slack wax from the Fischer-Tropsch synthesis.  Consideration also is given to the closely related products and intermediates of the paraffin oxidation reaction, for example, alcohols, aldehydes, ketones, and wax esters.  The mechanism of the oxidation is still a matter of discussion, the simplest reaction being as follows:

        (1)  R·CH2·CH2·CH3+O2→R·CH2·CH2·CH2OH+→

                                    H

                                  /

              R·CH2·CH2·C          +O2→R·CH2·CH2·COOH;

                                  \

                                    O

        (2)  R·CH2·CH2·CH3+O2→R·CH2·CHOH·CH3+O2→

               R·CH2·CO·CH3+O2→R·CH2·CO·COOH.

It is not as simple as this, however, since H2O, formic acid, and peroxides are always formed.  One theory postulates that our C-H bond is split and unsaturated compounds are formed, which subsequently oxidize; another proposes the free radical mechanism whereby the attack takes place through rupture of a C-C bond; by the peroxidation mechanism, peroxides are always formed at the start and reach a maximum after 2-3 hr., after which they decrease rapidly and acid formation takes place; by the hydroxylation theory, alcohols are formed as the 1st step in the sequence:  Hydrocarbon-alcohol-glycol-aldehyde-acid-carbon dioxide, the process repeating itself until the final degradation products are CO2 and H2O.  Below 100° C., oxidation proceeds slowly, but, by preheating the hydrocarbons with alkali manganates to 100°-200° for several hr., oxidation proceeds well at 80°-100°.  The longer the straight chan of C atoms contained in organic molecules, the less difficulty is encountered in their oxidation.  Oxidation also is preceded by an induction period, after which the reaction is more rapid.  The use of catalysts shortens the oxidation period by eliminating the induction period, destroying anti-oxygens or inhibitors present in the original material, and producing prooxidants, which direct the course of the oxidation.  Catalytic material from a few thousandths up to 3% by weight of the initial material is generally used.  Suitable catalysts are carboxylic acid salts, especially those of higher fatty acids, and oxides of the metals of groups 5 and 6.  There is an optimum temperature range, which varies with the materials used and the results desired.  For maximum yields of alcohols or high-molecular weight fatty acids the oxidation temperature is kept 110°-140° at a pressure of 60-150 p.s.i.  A typical analysis of a Fischer-Tropsch slack wax used for oxidation is:

                    C16H34 to C19H40 27.4%; C23H48 to C25H52 23.6%;

                    C20H42 to C22H46 31%; C26H54 to C28H58 13.3%.

Bibliography of 145 refs.